turbopack_ecmascript/analyzer/

graph.rs

use std::{
    iter,
    mem::{replace, take},
    sync::Arc,
};

use anyhow::{Ok, Result};
use rustc_hash::{FxHashMap, FxHashSet};
use swc_core::{
    atoms::Atom,
    base::try_with_handler,
    common::{
        GLOBALS, Mark, SourceMap, Span, Spanned, SyntaxContext, comments::Comments,
        pass::AstNodePath, sync::Lrc,
    },
    ecma::{
        ast::*,
        atoms::atom,
        utils::contains_ident_ref,
        visit::{fields::*, *},
    },
};
use turbo_rcstr::{RcStr, rcstr};
use turbo_tasks::ResolvedVc;
use turbopack_core::source::Source;

use super::{
    ConstantNumber, ConstantValue, ImportMap, JsValue, ObjectPart, WellKnownFunctionKind,
    is_unresolved_id,
};
use crate::{
    AnalyzeMode, SpecifiedModuleType,
    analyzer::{WellKnownObjectKind, is_unresolved},
    references::constant_value::parse_single_expr_lit,
    utils::{AstPathRange, unparen},
};

#[derive(Debug, Clone)]
pub struct EffectsBlock {
    pub effects: Vec<Effect>,
    pub range: AstPathRange,
}

impl EffectsBlock {
    pub fn is_empty(&self) -> bool {
        self.effects.is_empty()
    }
}

#[derive(Debug, Clone)]
pub enum ConditionalKind {
    /// The blocks of an `if` statement without an `else` block.
    If { then: Box<EffectsBlock> },
    /// The blocks of an `if ... else` or `if { ... return ... } ...` statement.
    IfElse {
        then: Box<EffectsBlock>,
        r#else: Box<EffectsBlock>,
    },
    /// The blocks of an `if ... else` statement.
    Else { r#else: Box<EffectsBlock> },
    /// The blocks of an `if { ... return ... } else { ... } ...` or `if { ... }
    /// else { ... return ... } ...` statement.
    IfElseMultiple {
        then: Vec<Box<EffectsBlock>>,
        r#else: Vec<Box<EffectsBlock>>,
    },
    /// The expressions on the right side of the `?:` operator.
    Ternary {
        then: Box<EffectsBlock>,
        r#else: Box<EffectsBlock>,
    },
    /// The expression on the right side of the `&&` operator.
    And { expr: Box<EffectsBlock> },
    /// The expression on the right side of the `||` operator.
    Or { expr: Box<EffectsBlock> },
    /// The expression on the right side of the `??` operator.
    NullishCoalescing { expr: Box<EffectsBlock> },
    /// The expression on the right side of a labeled statement.
    Labeled { body: Box<EffectsBlock> },
}

impl ConditionalKind {
    /// Normalizes all contained values.
    pub fn normalize(&mut self) {
        match self {
            ConditionalKind::If { then: block }
            | ConditionalKind::Else { r#else: block }
            | ConditionalKind::And { expr: block, .. }
            | ConditionalKind::Or { expr: block, .. }
            | ConditionalKind::NullishCoalescing { expr: block, .. } => {
                for effect in &mut block.effects {
                    effect.normalize();
                }
            }
            ConditionalKind::IfElse { then, r#else, .. }
            | ConditionalKind::Ternary { then, r#else, .. } => {
                for effect in &mut then.effects {
                    effect.normalize();
                }
                for effect in &mut r#else.effects {
                    effect.normalize();
                }
            }
            ConditionalKind::IfElseMultiple { then, r#else, .. } => {
                for block in then.iter_mut().chain(r#else.iter_mut()) {
                    for effect in &mut block.effects {
                        effect.normalize();
                    }
                }
            }
            ConditionalKind::Labeled { body } => {
                for effect in &mut body.effects {
                    effect.normalize();
                }
            }
        }
    }
}

#[derive(Debug, Clone)]
pub enum EffectArg {
    Value(JsValue),
    Closure(JsValue, Box<EffectsBlock>),
    Spread,
}

impl EffectArg {
    /// Normalizes all contained values.
    pub fn normalize(&mut self) {
        match self {
            EffectArg::Value(value) => value.normalize(),
            EffectArg::Closure(value, effects) => {
                value.normalize();
                for effect in &mut effects.effects {
                    effect.normalize();
                }
            }
            EffectArg::Spread => {}
        }
    }
}

#[derive(Debug, Clone)]
pub enum Effect {
    /// Some condition which affects which effects might be executed. If the
    /// condition evaluates to some compile-time constant, we can use that
    /// to determine which effects are executed and remove the others.
    Conditional {
        condition: Box<JsValue>,
        kind: Box<ConditionalKind>,
        /// The ast path to the condition.
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    /// A function call or a new call of a function.
    Call {
        func: Box<JsValue>,
        args: Vec<EffectArg>,
        ast_path: Vec<AstParentKind>,
        span: Span,
        in_try: bool,
        new: bool,
    },
    /// A function call or a new call of a property of an object.
    MemberCall {
        obj: Box<JsValue>,
        prop: Box<JsValue>,
        args: Vec<EffectArg>,
        ast_path: Vec<AstParentKind>,
        span: Span,
        in_try: bool,
        new: bool,
    },
    /// A property access.
    Member {
        obj: Box<JsValue>,
        prop: Box<JsValue>,
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    /// A reference to an imported binding.
    ImportedBinding {
        esm_reference_index: usize,
        export: Option<RcStr>,
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    /// A reference to a free var access.
    FreeVar {
        var: Atom,
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    /// A typeof expression
    TypeOf {
        arg: Box<JsValue>,
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    // TODO ImportMeta should be replaced with Member
    /// A reference to `import.meta`.
    ImportMeta {
        ast_path: Vec<AstParentKind>,
        span: Span,
    },
    /// Unreachable code, e.g. after a `return` statement.
    Unreachable { start_ast_path: Vec<AstParentKind> },
}

impl Effect {
    /// Normalizes all contained values.
    pub fn normalize(&mut self) {
        match self {
            Effect::Conditional {
                condition, kind, ..
            } => {
                condition.normalize();
                kind.normalize();
            }
            Effect::Call { func, args, .. } => {
                func.normalize();
                for arg in args.iter_mut() {
                    arg.normalize();
                }
            }
            Effect::MemberCall {
                obj, prop, args, ..
            } => {
                obj.normalize();
                prop.normalize();
                for arg in args.iter_mut() {
                    arg.normalize();
                }
            }
            Effect::Member { obj, prop, .. } => {
                obj.normalize();
                prop.normalize();
            }
            Effect::ImportedBinding { .. } => {}
            Effect::TypeOf { arg, .. } => {
                arg.normalize();
            }
            Effect::FreeVar { .. } => {}
            Effect::ImportMeta { .. } => {}
            Effect::Unreachable { .. } => {}
        }
    }
}

pub enum AssignmentScope {
    ModuleEval,
    Function,
}

#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum AssignmentScopes {
    AllInModuleEvalScope,
    AllInFunctionScopes,
    Mixed,
}
impl AssignmentScopes {
    fn new(initial: AssignmentScope) -> Self {
        match initial {
            AssignmentScope::ModuleEval => AssignmentScopes::AllInModuleEvalScope,
            AssignmentScope::Function => AssignmentScopes::AllInFunctionScopes,
        }
    }

    fn merge(self, other: AssignmentScope) -> Self {
        // If the other assignment kind is the same as the current one, return the current one.
        if self == Self::new(other) {
            self
        } else {
            AssignmentScopes::Mixed
        }
    }
}

#[derive(Debug, Clone)]
pub struct VarMeta {
    pub value: JsValue,
    /// Tracks the locations where this was assigned to:
    /// - [`AssignmentScopes::AllInModuleEvalScope`] if it was assigned only in the root scope
    /// - [`AssignmentScopes::AllInFunctionScopes`] if it was assigned in any set of function
    ///   scopes
    /// - [`AssignmentScopes::Mixed`] if it was assigned in both
    ///
    /// This is used to track the _liveness_ of exports.
    pub assignment_scopes: AssignmentScopes,
}

impl VarMeta {
    pub fn new(value: JsValue, kind: AssignmentScope) -> Self {
        Self {
            value,
            assignment_scopes: AssignmentScopes::new(kind),
        }
    }

    pub fn normalize(&mut self) {
        self.value.normalize();
    }

    fn add_alt(&mut self, value: JsValue, kind: AssignmentScope) {
        self.value.add_alt(value);
        self.assignment_scopes = self.assignment_scopes.merge(kind);
    }
}

#[derive(Debug)]
pub struct VarGraph {
    pub values: FxHashMap<Id, VarMeta>,
    /// Map FreeVar names to their Id to facilitate lookups into [values]
    /// Doesn't necessarily contain every FreeVar, just those who have non trivial values.
    pub free_var_ids: FxHashMap<Atom, Id>,

    pub effects: Vec<Effect>,
}

impl VarGraph {
    pub fn normalize(&mut self) {
        for value in self.values.values_mut() {
            value.normalize();
        }
        for effect in self.effects.iter_mut() {
            effect.normalize();
        }
    }
}

/// You should use same [Mark] for this function and
/// [swc_ecma_transforms_base::resolver::resolver_with_mark]
pub fn create_graph(
    m: &Program,
    eval_context: &EvalContext,
    analyze_mode: AnalyzeMode,
) -> VarGraph {
    let mut graph = VarGraph {
        values: Default::default(),
        free_var_ids: Default::default(),
        effects: Default::default(),
    };

    m.visit_with_ast_path(
        &mut Analyzer {
            analyze_mode,
            data: &mut graph,
            state: analyzer_state::AnalyzerState::new(),
            eval_context,
            effects: Default::default(),
            hoisted_effects: Default::default(),
            early_return_stack: Default::default(),
            var_decl_kind: Default::default(),
        },
        &mut Default::default(),
    );

    graph.normalize();

    graph
}

/// A context used for assembling the evaluation graph.
#[derive(Debug)]
pub struct EvalContext {
    pub(crate) unresolved_mark: Mark,
    pub(crate) top_level_mark: Mark,
    pub(crate) imports: ImportMap,
    pub(crate) force_free_values: Arc<FxHashSet<Id>>,
}

impl EvalContext {
    /// Produce a new [EvalContext] from a [Program]. If you wish to support
    /// webpackIgnore or turbopackIgnore comments, you must pass those in,
    /// since the AST does not include comments by default.
    pub fn new(
        module: Option<&Program>,
        unresolved_mark: Mark,
        top_level_mark: Mark,
        force_free_values: Arc<FxHashSet<Id>>,
        comments: Option<&dyn Comments>,
        source: Option<ResolvedVc<Box<dyn Source>>>,
    ) -> Self {
        Self {
            unresolved_mark,
            top_level_mark,
            imports: module.map_or(ImportMap::default(), |m| {
                ImportMap::analyze(m, source, comments)
            }),
            force_free_values,
        }
    }

    pub fn is_esm(&self, specified_type: SpecifiedModuleType) -> bool {
        self.imports.is_esm(specified_type)
    }

    fn eval_prop_name(&self, prop: &PropName) -> JsValue {
        match prop {
            PropName::Ident(ident) => ident.sym.clone().into(),
            PropName::Str(str) => str.value.clone().into(),
            PropName::Num(num) => num.value.into(),
            PropName::Computed(ComputedPropName { expr, .. }) => self.eval(expr),
            PropName::BigInt(bigint) => (*bigint.value.clone()).into(),
        }
    }

    fn eval_member_prop(&self, prop: &MemberProp) -> Option<JsValue> {
        match prop {
            MemberProp::Ident(ident) => Some(ident.sym.clone().into()),
            MemberProp::Computed(ComputedPropName { expr, .. }) => Some(self.eval(expr)),
            MemberProp::PrivateName(_) => None,
        }
    }

    fn eval_tpl(&self, e: &Tpl, raw: bool) -> JsValue {
        debug_assert!(e.quasis.len() == e.exprs.len() + 1);

        let mut values = vec![];

        for idx in 0..(e.quasis.len() + e.exprs.len()) {
            if idx.is_multiple_of(2) {
                let idx = idx / 2;
                let e = &e.quasis[idx];
                if raw {
                    // Ignore empty strings quasis, happens frequently with e.g. after the
                    // placeholder in `something${v}`.
                    if !e.raw.is_empty() {
                        values.push(JsValue::from(e.raw.clone()));
                    }
                } else {
                    match &e.cooked {
                        Some(v) => {
                            if !v.is_empty() {
                                values.push(JsValue::from(v.clone()));
                            }
                        }
                        // This is actually unreachable
                        None => return JsValue::unknown_empty(true, ""),
                    }
                }
            } else {
                let idx = idx / 2;
                let e = &e.exprs[idx];

                values.push(self.eval(e));
            }
        }

        match values.len() {
            0 => JsValue::Constant(ConstantValue::Str(rcstr!("").into())),
            1 => values.into_iter().next().unwrap(),
            _ => JsValue::concat(values),
        }
    }

    fn eval_ident(&self, i: &Ident) -> JsValue {
        let id = i.to_id();
        if let Some(imported) = self.imports.get_import(&id) {
            return imported;
        }
        if is_unresolved(i, self.unresolved_mark) || self.force_free_values.contains(&id) {
            // These are special globals that we shouldn't consider to be free variables and we can
            // model their values mostly useful for truthy/falsy checks.
            match i.sym.as_str() {
                "undefined" => JsValue::Constant(ConstantValue::Undefined),
                "NaN" => JsValue::Constant(ConstantValue::Num(ConstantNumber(f64::NAN))),
                "Infinity" => JsValue::Constant(ConstantValue::Num(ConstantNumber(f64::INFINITY))),
                _ => JsValue::FreeVar(i.sym.clone()),
            }
        } else {
            JsValue::Variable(id)
        }
    }

    pub fn eval(&self, e: &Expr) -> JsValue {
        debug_assert!(
            GLOBALS.is_set(),
            "Eval requires globals from its parsed result"
        );
        match e {
            Expr::Paren(e) => self.eval(&e.expr),
            Expr::Lit(e) => JsValue::Constant(e.clone().into()),
            Expr::Ident(i) => self.eval_ident(i),

            Expr::Unary(UnaryExpr {
                op: op!("void"),
                // Only treat literals as constant undefined, allowing arbitrary values inside here
                // would mean that they can have sideeffects, and `JsValue::Constant` can't model
                // that.
                arg: box Expr::Lit(_),
                ..
            }) => JsValue::Constant(ConstantValue::Undefined),

            Expr::Unary(UnaryExpr {
                op: op!("!"), arg, ..
            }) => {
                let arg = self.eval(arg);

                JsValue::logical_not(Box::new(arg))
            }

            Expr::Unary(UnaryExpr {
                op: op!("typeof"),
                arg,
                ..
            }) => {
                let arg = self.eval(arg);

                JsValue::type_of(Box::new(arg))
            }

            Expr::Bin(BinExpr {
                op: op!(bin, "+"),
                left,
                right,
                ..
            }) => {
                let l = self.eval(left);
                let r = self.eval(right);

                match (l, r) {
                    (JsValue::Add(c, l), r) => JsValue::Add(
                        c + r.total_nodes(),
                        l.into_iter().chain(iter::once(r)).collect(),
                    ),
                    (l, r) => JsValue::add(vec![l, r]),
                }
            }

            Expr::Bin(BinExpr {
                op: op!("&&"),
                left,
                right,
                ..
            }) => JsValue::logical_and(vec![self.eval(left), self.eval(right)]),

            Expr::Bin(BinExpr {
                op: op!("||"),
                left,
                right,
                ..
            }) => JsValue::logical_or(vec![self.eval(left), self.eval(right)]),

            Expr::Bin(BinExpr {
                op: op!("??"),
                left,
                right,
                ..
            }) => JsValue::nullish_coalescing(vec![self.eval(left), self.eval(right)]),

            Expr::Bin(BinExpr {
                op: op!("=="),
                left,
                right,
                ..
            }) => JsValue::equal(Box::new(self.eval(left)), Box::new(self.eval(right))),

            Expr::Bin(BinExpr {
                op: op!("!="),
                left,
                right,
                ..
            }) => JsValue::not_equal(Box::new(self.eval(left)), Box::new(self.eval(right))),

            Expr::Bin(BinExpr {
                op: op!("==="),
                left,
                right,
                ..
            }) => JsValue::strict_equal(Box::new(self.eval(left)), Box::new(self.eval(right))),

            Expr::Bin(BinExpr {
                op: op!("!=="),
                left,
                right,
                ..
            }) => JsValue::strict_not_equal(Box::new(self.eval(left)), Box::new(self.eval(right))),

            &Expr::Cond(CondExpr {
                box ref cons,
                box ref alt,
                box ref test,
                ..
            }) => {
                let test = self.eval(test);
                if let Some(truthy) = test.is_truthy() {
                    if truthy {
                        self.eval(cons)
                    } else {
                        self.eval(alt)
                    }
                } else {
                    JsValue::tenary(
                        Box::new(test),
                        Box::new(self.eval(cons)),
                        Box::new(self.eval(alt)),
                    )
                }
            }

            Expr::Tpl(e) => self.eval_tpl(e, false),

            Expr::TaggedTpl(TaggedTpl {
                tag:
                    box Expr::Member(MemberExpr {
                        obj: box Expr::Ident(tag_obj),
                        prop: MemberProp::Ident(tag_prop),
                        ..
                    }),
                tpl,
                ..
            }) => {
                if &*tag_obj.sym == "String"
                    && &*tag_prop.sym == "raw"
                    && is_unresolved(tag_obj, self.unresolved_mark)
                {
                    self.eval_tpl(tpl, true)
                } else {
                    JsValue::unknown_empty(true, "tagged template literal is not supported yet")
                }
            }

            Expr::Fn(expr) => {
                if let Some(ident) = &expr.ident {
                    JsValue::Variable(ident.to_id())
                } else {
                    JsValue::Variable((
                        format!("*anonymous function {}*", expr.function.span.lo.0).into(),
                        SyntaxContext::empty(),
                    ))
                }
            }
            Expr::Arrow(expr) => JsValue::Variable((
                format!("*arrow function {}*", expr.span.lo.0).into(),
                SyntaxContext::empty(),
            )),

            Expr::Await(AwaitExpr { arg, .. }) => JsValue::awaited(Box::new(self.eval(arg))),

            Expr::Seq(e) => {
                let mut seq = e.exprs.iter().map(|e| self.eval(e)).peekable();
                let mut side_effects = false;
                let mut last = seq.next().unwrap();
                for e in seq {
                    side_effects |= last.has_side_effects();
                    last = e;
                }
                if side_effects {
                    last.make_unknown(true, "sequence with side effects");
                }
                last
            }

            Expr::Member(MemberExpr {
                obj,
                prop: MemberProp::Ident(prop),
                ..
            }) => {
                let obj = self.eval(obj);
                JsValue::member(Box::new(obj), Box::new(prop.sym.clone().into()))
            }

            Expr::Member(MemberExpr {
                obj,
                prop: MemberProp::Computed(computed),
                ..
            }) => {
                let obj = self.eval(obj);
                let prop = self.eval(&computed.expr);
                JsValue::member(Box::new(obj), Box::new(prop))
            }

            Expr::New(NewExpr {
                callee: box callee,
                args,
                ..
            }) => {
                // We currently do not handle spreads.
                if args.iter().flatten().any(|arg| arg.spread.is_some()) {
                    return JsValue::unknown_empty(true, "spread in new calls is not supported");
                }

                let args: Vec<_> = args
                    .iter()
                    .flatten()
                    .map(|arg| self.eval(&arg.expr))
                    .collect();
                let callee = Box::new(self.eval(callee));

                JsValue::new(callee, args)
            }

            Expr::Call(CallExpr {
                callee: Callee::Expr(box callee),
                args,
                ..
            }) => {
                // We currently do not handle spreads.
                if args.iter().any(|arg| arg.spread.is_some()) {
                    return JsValue::unknown_empty(
                        true,
                        "spread in function calls is not supported",
                    );
                }

                let args = args.iter().map(|arg| self.eval(&arg.expr)).collect();
                if let Expr::Member(MemberExpr { obj, prop, .. }) = unparen(callee) {
                    let obj = Box::new(self.eval(obj));
                    let prop = Box::new(match prop {
                        MemberProp::Ident(i) => i.sym.clone().into(),
                        MemberProp::PrivateName(_) => {
                            return JsValue::unknown_empty(
                                false,
                                "private names in function calls is not supported",
                            );
                        }
                        MemberProp::Computed(ComputedPropName { expr, .. }) => self.eval(expr),
                    });
                    JsValue::member_call(obj, prop, args)
                } else {
                    let callee = Box::new(self.eval(callee));

                    JsValue::call(callee, args)
                }
            }

            Expr::Call(CallExpr {
                callee: Callee::Super(_),
                args,
                ..
            }) => {
                // We currently do not handle spreads.
                if args.iter().any(|arg| arg.spread.is_some()) {
                    return JsValue::unknown_empty(
                        true,
                        "spread in function calls is not supported",
                    );
                }

                let args = args.iter().map(|arg| self.eval(&arg.expr)).collect();

                JsValue::super_call(args)
            }

            Expr::Call(CallExpr {
                callee: Callee::Import(_),
                args,
                ..
            }) => {
                // We currently do not handle spreads.
                if args.iter().any(|arg| arg.spread.is_some()) {
                    return JsValue::unknown_empty(true, "spread in import() is not supported");
                }
                let args = args.iter().map(|arg| self.eval(&arg.expr)).collect();

                let callee = Box::new(JsValue::FreeVar(atom!("import")));

                JsValue::call(callee, args)
            }

            Expr::Array(arr) => {
                if arr.elems.iter().flatten().any(|v| v.spread.is_some()) {
                    return JsValue::unknown_empty(true, "spread is not supported");
                }

                let arr = arr
                    .elems
                    .iter()
                    .map(|e| match e {
                        Some(e) => self.eval(&e.expr),
                        _ => JsValue::Constant(ConstantValue::Undefined),
                    })
                    .collect();
                JsValue::array(arr)
            }

            Expr::Object(obj) => JsValue::object(
                obj.props
                    .iter()
                    .map(|prop| match prop {
                        PropOrSpread::Spread(SpreadElement { expr, .. }) => {
                            ObjectPart::Spread(self.eval(expr))
                        }
                        PropOrSpread::Prop(box Prop::KeyValue(KeyValueProp { key, box value })) => {
                            ObjectPart::KeyValue(self.eval_prop_name(key), self.eval(value))
                        }
                        PropOrSpread::Prop(box Prop::Shorthand(ident)) => ObjectPart::KeyValue(
                            ident.sym.clone().into(),
                            self.eval(&Expr::Ident(ident.clone())),
                        ),
                        _ => ObjectPart::Spread(JsValue::unknown_empty(
                            true,
                            "unsupported object part",
                        )),
                    })
                    .collect(),
            ),

            Expr::MetaProp(MetaPropExpr {
                kind: MetaPropKind::ImportMeta,
                ..
            }) => JsValue::WellKnownObject(WellKnownObjectKind::ImportMeta),

            Expr::Assign(AssignExpr { right, .. }) => self.eval(right),

            _ => JsValue::unknown_empty(true, "unsupported expression"),
        }
    }

    pub fn eval_single_expr_lit(expr_lit: RcStr) -> Result<JsValue> {
        let cm = Lrc::new(SourceMap::default());

        let js_value = try_with_handler(cm, Default::default(), |_| {
            GLOBALS.set(&Default::default(), || {
                let expr = parse_single_expr_lit(expr_lit);
                let eval_context = EvalContext::new(
                    None,
                    Mark::new(),
                    Mark::new(),
                    Default::default(),
                    None,
                    None,
                );

                Ok(eval_context.eval(&expr))
            })
        })
        .map_err(|e| e.to_pretty_error())?;

        Ok(js_value)
    }
}

enum EarlyReturn {
    Always {
        prev_effects: Vec<Effect>,
        start_ast_path: Vec<AstParentKind>,
    },
    Conditional {
        prev_effects: Vec<Effect>,
        start_ast_path: Vec<AstParentKind>,

        condition: Box<JsValue>,
        then: Option<Box<EffectsBlock>>,
        r#else: Option<Box<EffectsBlock>>,
        /// The ast path to the condition.
        condition_ast_path: Vec<AstParentKind>,
        span: Span,

        early_return_condition_value: bool,
    },
}

pub fn as_parent_path_skip(
    ast_path: &AstNodePath<AstParentNodeRef<'_>>,
    skip: usize,
) -> Vec<AstParentKind> {
    ast_path
        .iter()
        .take(ast_path.len() - skip)
        .map(|n| n.kind())
        .collect()
}

struct Analyzer<'a> {
    analyze_mode: AnalyzeMode,

    data: &'a mut VarGraph,
    state: analyzer_state::AnalyzerState,

    effects: Vec<Effect>,
    // Effects collected from hoisted declarations. See https://developer.mozilla.org/en-US/docs/Glossary/Hoisting
    // Tracked separately so we can preserve effects from hoisted declarations even when we don't
    // collect effects from the declaring context.
    hoisted_effects: Vec<Effect>,
    early_return_stack: Vec<EarlyReturn>,

    eval_context: &'a EvalContext,

    var_decl_kind: Option<VarDeclKind>,
}

trait FunctionLike {
    fn is_async(&self) -> bool {
        false
    }
    fn is_generator(&self) -> bool {
        false
    }
    fn span(&self) -> Span;
}

impl FunctionLike for Function {
    fn is_async(&self) -> bool {
        self.is_async
    }
    fn is_generator(&self) -> bool {
        self.is_generator
    }
    fn span(&self) -> Span {
        self.span
    }
}
impl FunctionLike for ArrowExpr {
    fn is_async(&self) -> bool {
        self.is_async
    }
    fn is_generator(&self) -> bool {
        self.is_generator
    }
    fn span(&self) -> Span {
        self.span
    }
}

impl FunctionLike for Constructor {
    fn span(&self) -> Span {
        self.span
    }
}
impl FunctionLike for GetterProp {
    fn span(&self) -> Span {
        self.span
    }
}
impl FunctionLike for SetterProp {
    fn span(&self) -> Span {
        self.span
    }
}

mod analyzer_state {
    use super::*;

    /// Contains fields of `Analyzer` that should only be modified using helper methods. These are
    /// intentionally private to the rest of the `Analyzer` implementation.
    pub struct AnalyzerState {
        pat_value: Option<JsValue>,
        /// A unique identifier for the current function, based on the span of the function
        /// declaration. [`None`] if we are in the root scope.  These are only used as opaque
        /// identifiers to distinguish function arguments.
        cur_fn_id: Option<u32>,
        /// Return values of the current function.
        ///
        /// This is configured to [Some] by function handlers and filled by the
        /// return statement handler.
        cur_fn_return_values: Option<Vec<JsValue>>,
    }

    impl AnalyzerState {
        pub fn new() -> AnalyzerState {
            AnalyzerState {
                pat_value: None,
                cur_fn_id: None,
                cur_fn_return_values: None,
            }
        }
    }

    impl Analyzer<'_> {
        /// Returns true if we are in a function. False if we are in the root scope.
        pub(super) fn is_in_fn(&self) -> bool {
            self.state.cur_fn_id.is_some()
        }

        /// Returns the identifier of the current function.
        /// must be called only if `is_in_fn` is true
        pub(super) fn cur_fn_ident(&self) -> u32 {
            self.state.cur_fn_id.expect("not in a function")
        }

        /// Adds a return value to the current function.
        /// Panics if we are not in a function scope
        pub(super) fn add_return_value(&mut self, value: JsValue) {
            self.state
                .cur_fn_return_values
                .as_mut()
                .expect("not in a function")
                .push(value);
        }

        /// The RHS (or some part of it) of an pattern or assignment (e.g. `PatAssignTarget`,
        /// `SimpleAssignTarget`, function arguments, etc.), read by the individual parts of LHS
        /// (target).
        ///
        /// Consumes the value, setting it to `None`, and returning the previous value. This avoids
        /// extra clones.
        pub(super) fn take_pat_value(&mut self) -> Option<JsValue> {
            self.state.pat_value.take()
        }

        // Runs `func` (usually something that visits children) with the given
        // [`Analyzer::take_pat_value`], restoring the value back to the previous value (usually
        // `None`) afterwards.
        pub(super) fn with_pat_value<T>(
            &mut self,
            value: Option<JsValue>,
            func: impl FnOnce(&mut Self) -> T,
        ) -> T {
            let prev_value = replace(&mut self.state.pat_value, value);
            let out = func(self);
            self.state.pat_value = prev_value;
            out
        }

        /// Runs `func` with the current function identifier and return values initialized for the
        /// block.
        pub(super) fn enter_fn(
            &mut self,
            function: &impl FunctionLike,
            visitor: impl FnOnce(&mut Self),
        ) -> JsValue {
            let fn_id = function.span().lo.0;
            let prev_fn_id = self.state.cur_fn_id.replace(fn_id);
            let prev_return_values = self.state.cur_fn_return_values.replace(vec![]);

            visitor(self);
            let return_values = self.state.cur_fn_return_values.take().unwrap();

            self.state.cur_fn_id = prev_fn_id;
            self.state.cur_fn_return_values = prev_return_values;
            JsValue::function(
                fn_id,
                function.is_async(),
                function.is_generator(),
                match return_values.len() {
                    0 => JsValue::Constant(ConstantValue::Undefined),
                    1 => return_values.into_iter().next().unwrap(),
                    _ => JsValue::alternatives(return_values),
                },
            )
        }
    }
}

pub fn as_parent_path(ast_path: &AstNodePath<AstParentNodeRef<'_>>) -> Vec<AstParentKind> {
    ast_path.iter().map(|n| n.kind()).collect()
}

pub fn as_parent_path_with(
    ast_path: &AstNodePath<AstParentNodeRef<'_>>,
    additional: AstParentKind,
) -> Vec<AstParentKind> {
    ast_path
        .iter()
        .map(|n| n.kind())
        .chain([additional])
        .collect()
}

fn is_in_try(ast_path: &AstNodePath<AstParentNodeRef<'_>>) -> bool {
    ast_path
        .iter()
        .rev()
        .find_map(|ast_ref| match ast_ref.kind() {
            AstParentKind::ArrowExpr(ArrowExprField::Body)
            | AstParentKind::Function(FunctionField::Body)
            | AstParentKind::Constructor(ConstructorField::Body)
            | AstParentKind::ClassMethod(ClassMethodField::Function)
            | AstParentKind::GetterProp(GetterPropField::Body)
            | AstParentKind::SetterProp(SetterPropField::Body)
            | AstParentKind::MethodProp(MethodPropField::Function) => Some(false),
            AstParentKind::TryStmt(TryStmtField::Block) => Some(true),
            _ => None,
        })
        .unwrap_or(false)
}

enum CallOrNewExpr<'ast> {
    Call(&'ast CallExpr),
    New(&'ast NewExpr),
}
impl CallOrNewExpr<'_> {
    fn as_call(&self) -> Option<&CallExpr> {
        match *self {
            CallOrNewExpr::Call(n) => Some(n),
            CallOrNewExpr::New(_) => None,
        }
    }
    fn as_new(&self) -> Option<&NewExpr> {
        match *self {
            CallOrNewExpr::Call(_) => None,
            CallOrNewExpr::New(n) => Some(n),
        }
    }
}

impl Analyzer<'_> {
    fn add_value(&mut self, id: Id, value: JsValue) {
        if is_unresolved_id(&id, self.eval_context.unresolved_mark) {
            self.data.free_var_ids.insert(id.0.clone(), id.clone());
        }

        let kind = if self.is_in_fn() {
            AssignmentScope::Function
        } else {
            AssignmentScope::ModuleEval
        };
        if let Some(prev) = self.data.values.get_mut(&id) {
            prev.add_alt(value, kind);
        } else {
            self.data.values.insert(id, VarMeta::new(value, kind));
        }
        // TODO(kdy1): We may need to report an error for this.
        // Variables declared with `var` are hoisted, but using undefined as its
        // value does not seem like a good idea.
    }

    fn add_value_from_expr(&mut self, id: Id, value: &Expr) {
        let value = self.eval_context.eval(value);

        self.add_value(id, value);
    }

    fn add_effect(&mut self, effect: Effect) {
        self.effects.push(effect);
    }

    fn check_iife<'ast: 'r, 'r>(
        &mut self,
        n: &'ast CallExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) -> bool {
        fn unparen<'ast: 'r, 'r, T>(
            expr: &'ast Expr,
            ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
            f: impl FnOnce(&'ast Expr, &mut AstNodePath<AstParentNodeRef<'r>>) -> T,
        ) -> T {
            if let Some(inner_expr) = expr.as_paren() {
                let mut ast_path =
                    ast_path.with_guard(AstParentNodeRef::Expr(expr, ExprField::Paren));
                let mut ast_path = ast_path.with_guard(AstParentNodeRef::ParenExpr(
                    inner_expr,
                    ParenExprField::Expr,
                ));
                unparen(&inner_expr.expr, &mut ast_path, f)
            } else {
                f(expr, ast_path)
            }
        }

        if n.args.iter().any(|arg| arg.spread.is_some()) {
            return false;
        }

        let Some(expr) = n.callee.as_expr() else {
            return false;
        };

        let fn_expr = {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::CallExpr(n, CallExprField::Callee));
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::Callee(&n.callee, CalleeField::Expr));
            unparen(expr, &mut ast_path, |expr, ast_path| match expr {
                Expr::Fn(fn_expr @ FnExpr { function, ident }) => {
                    let mut ast_path =
                        ast_path.with_guard(AstParentNodeRef::Expr(expr, ExprField::Fn));
                    {
                        let mut ast_path = ast_path
                            .with_guard(AstParentNodeRef::FnExpr(fn_expr, FnExprField::Ident));
                        self.visit_opt_ident(ident, &mut ast_path);

                        // We cannot analyze recursive IIFE
                        if let Some(ident) = ident
                            && contains_ident_ref(&function.body, ident)
                        {
                            return false;
                        }
                    }

                    {
                        let mut ast_path = ast_path
                            .with_guard(AstParentNodeRef::FnExpr(fn_expr, FnExprField::Function));
                        // We don't handle the value of the function here, though we could to better
                        // model the value of this 'call'
                        self.enter_fn(&**function, |this| {
                            this.handle_iife_function(function, &mut ast_path, &n.args);
                        });
                    }

                    true
                }

                Expr::Arrow(arrow_expr) => {
                    let mut ast_path =
                        ast_path.with_guard(AstParentNodeRef::Expr(expr, ExprField::Arrow));
                    let args = &n.args;
                    // We don't handle the value of the function here, though we could to better
                    // model the value of this 'call'
                    self.enter_fn(arrow_expr, |this| {
                        this.handle_iife_arrow(arrow_expr, args, &mut ast_path);
                    });
                    true
                }
                _ => false,
            })
        };

        if !fn_expr {
            return false;
        }

        let mut ast_path = ast_path.with_guard(AstParentNodeRef::CallExpr(
            n,
            CallExprField::Args(usize::MAX),
        ));

        self.visit_expr_or_spreads(&n.args, &mut ast_path);

        true
    }

    fn handle_iife_arrow<'ast: 'r, 'r>(
        &mut self,
        arrow_expr: &'ast ArrowExpr,
        args: &[ExprOrSpread],
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let ArrowExpr {
            params,
            body,
            is_async: _,
            is_generator: _,
            return_type,
            span: _,
            type_params,
            ctxt: _,
        } = arrow_expr;
        let mut iter = args.iter();
        for (i, param) in params.iter().enumerate() {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::ArrowExpr(
                arrow_expr,
                ArrowExprField::Params(i),
            ));
            let pat_value = iter.next().map(|arg| self.eval_context.eval(&arg.expr));
            self.with_pat_value(pat_value, |this| this.visit_pat(param, &mut ast_path));
        }
        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::ArrowExpr(
                arrow_expr,
                ArrowExprField::Body,
            ));
            self.visit_block_stmt_or_expr(body, &mut ast_path);
        }

        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::ArrowExpr(
                arrow_expr,
                ArrowExprField::ReturnType,
            ));
            self.visit_opt_ts_type_ann(return_type, &mut ast_path);
        }

        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::ArrowExpr(
                arrow_expr,
                ArrowExprField::TypeParams,
            ));
            self.visit_opt_ts_type_param_decl(type_params, &mut ast_path);
        }
    }

    fn handle_iife_function<'ast: 'r, 'r>(
        &mut self,
        function: &'ast Function,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
        args: &[ExprOrSpread],
    ) {
        let mut iter = args.iter();
        let Function {
            body,
            decorators,
            is_async: _,
            is_generator: _,
            params,
            return_type,
            span: _,
            type_params,
            ctxt: _,
        } = function;
        for (i, param) in params.iter().enumerate() {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Function(
                function,
                FunctionField::Params(i),
            ));
            if let Some(arg) = iter.next() {
                self.with_pat_value(Some(self.eval_context.eval(&arg.expr)), |this| {
                    this.visit_param(param, &mut ast_path)
                });
            } else {
                self.visit_param(param, &mut ast_path);
            }
        }

        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::Function(function, FunctionField::Body));

            self.visit_opt_block_stmt(body, &mut ast_path);
        }

        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Function(
                function,
                FunctionField::Decorators(usize::MAX),
            ));

            self.visit_decorators(decorators, &mut ast_path);
        }

        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Function(
                function,
                FunctionField::ReturnType,
            ));

            self.visit_opt_ts_type_ann(return_type, &mut ast_path);
        }

        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Function(
                function,
                FunctionField::TypeParams,
            ));

            self.visit_opt_ts_type_param_decl(type_params, &mut ast_path);
        }
    }

    fn check_call_expr_for_effects<'ast: 'r, 'n, 'r>(
        &mut self,
        callee: &'n Callee,
        args: impl Iterator<Item = &'ast ExprOrSpread>,
        span: Span,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
        n: CallOrNewExpr<'ast>,
    ) {
        let new = n.as_new().is_some();
        let args = args
            .enumerate()
            .map(|(i, arg)| {
                let mut ast_path = ast_path.with_guard(match n {
                    CallOrNewExpr::Call(n) => AstParentNodeRef::CallExpr(n, CallExprField::Args(i)),
                    CallOrNewExpr::New(n) => AstParentNodeRef::NewExpr(n, NewExprField::Args(i)),
                });
                if arg.spread.is_none() {
                    let value = self.eval_context.eval(&arg.expr);

                    let block_path = match &*arg.expr {
                        Expr::Fn(FnExpr { .. }) => {
                            let mut path = as_parent_path(&ast_path);
                            path.push(AstParentKind::ExprOrSpread(ExprOrSpreadField::Expr));
                            path.push(AstParentKind::Expr(ExprField::Fn));
                            path.push(AstParentKind::FnExpr(FnExprField::Function));
                            path.push(AstParentKind::Function(FunctionField::Body));
                            Some(path)
                        }
                        Expr::Arrow(ArrowExpr {
                            body: box BlockStmtOrExpr::BlockStmt(_),
                            ..
                        }) => {
                            let mut path = as_parent_path(&ast_path);
                            path.push(AstParentKind::ExprOrSpread(ExprOrSpreadField::Expr));
                            path.push(AstParentKind::Expr(ExprField::Arrow));
                            path.push(AstParentKind::ArrowExpr(ArrowExprField::Body));
                            path.push(AstParentKind::BlockStmtOrExpr(
                                BlockStmtOrExprField::BlockStmt,
                            ));
                            Some(path)
                        }
                        Expr::Arrow(ArrowExpr {
                            body: box BlockStmtOrExpr::Expr(_),
                            ..
                        }) => {
                            let mut path = as_parent_path(&ast_path);
                            path.push(AstParentKind::ExprOrSpread(ExprOrSpreadField::Expr));
                            path.push(AstParentKind::Expr(ExprField::Arrow));
                            path.push(AstParentKind::ArrowExpr(ArrowExprField::Body));
                            path.push(AstParentKind::BlockStmtOrExpr(BlockStmtOrExprField::Expr));
                            Some(path)
                        }
                        _ => None,
                    };
                    if let Some(path) = block_path {
                        let old_effects = take(&mut self.effects);
                        arg.visit_with_ast_path(self, &mut ast_path);
                        let effects = replace(&mut self.effects, old_effects);
                        EffectArg::Closure(
                            value,
                            Box::new(EffectsBlock {
                                effects,
                                range: AstPathRange::Exact(path),
                            }),
                        )
                    } else {
                        arg.visit_with_ast_path(self, &mut ast_path);
                        EffectArg::Value(value)
                    }
                } else {
                    arg.visit_with_ast_path(self, &mut ast_path);
                    EffectArg::Spread
                }
            })
            .collect();

        match callee {
            Callee::Import(_) => {
                self.add_effect(Effect::Call {
                    func: Box::new(JsValue::FreeVar(atom!("import"))),
                    args,
                    ast_path: as_parent_path(ast_path),
                    span,
                    in_try: is_in_try(ast_path),
                    new,
                });
            }
            Callee::Expr(box expr) => {
                if let Expr::Member(MemberExpr { obj, prop, .. }) = unparen(expr) {
                    let obj_value = Box::new(self.eval_context.eval(obj));
                    let prop_value = match prop {
                        // TODO avoid clone
                        MemberProp::Ident(i) => Box::new(i.sym.clone().into()),
                        MemberProp::PrivateName(_) => Box::new(JsValue::unknown_empty(
                            false,
                            "private names in member expressions are not supported",
                        )),
                        MemberProp::Computed(ComputedPropName { expr, .. }) => {
                            Box::new(self.eval_context.eval(expr))
                        }
                    };
                    self.add_effect(Effect::MemberCall {
                        obj: obj_value,
                        prop: prop_value,
                        args,
                        ast_path: as_parent_path(ast_path),
                        span,
                        in_try: is_in_try(ast_path),
                        new,
                    });
                } else {
                    let fn_value = Box::new(self.eval_context.eval(expr));
                    self.add_effect(Effect::Call {
                        func: fn_value,
                        args,
                        ast_path: as_parent_path(ast_path),
                        span,
                        in_try: is_in_try(ast_path),
                        new,
                    });
                }
            }
            Callee::Super(_) => self.add_effect(Effect::Call {
                func: Box::new(
                    self.eval_context
                        // Unwrap because `new super(..)` isn't valid anyway
                        .eval(&Expr::Call(n.as_call().unwrap().clone())),
                ),
                args,
                ast_path: as_parent_path(ast_path),
                span,
                in_try: is_in_try(ast_path),
                new,
            }),
        }
    }

    fn check_member_expr_for_effects<'ast: 'r, 'r>(
        &mut self,
        member_expr: &'ast MemberExpr,
        ast_path: &AstNodePath<AstParentNodeRef<'r>>,
    ) {
        if !self.analyze_mode.is_code_gen() {
            return;
        }

        let obj_value = Box::new(self.eval_context.eval(&member_expr.obj));
        let prop_value = match &member_expr.prop {
            // TODO avoid clone
            MemberProp::Ident(i) => Box::new(i.sym.clone().into()),
            MemberProp::PrivateName(_) => {
                return;
            }
            MemberProp::Computed(ComputedPropName { expr, .. }) => {
                Box::new(self.eval_context.eval(expr))
            }
        };
        self.add_effect(Effect::Member {
            obj: obj_value,
            prop: prop_value,
            ast_path: as_parent_path(ast_path),
            span: member_expr.span(),
        });
    }

    /// Ends a conditional block. All early returns are integrated into the
    /// effects. Returns true if the whole block always early returns.
    fn end_early_return_block(&mut self) -> bool {
        let mut always_returns = false;
        while let Some(early_return) = self.early_return_stack.pop() {
            match early_return {
                EarlyReturn::Always {
                    prev_effects,
                    start_ast_path,
                } => {
                    self.effects = prev_effects;
                    if self.analyze_mode.is_code_gen() {
                        self.effects.push(Effect::Unreachable { start_ast_path });
                    }
                    always_returns = true;
                }
                EarlyReturn::Conditional {
                    prev_effects,
                    start_ast_path,
                    condition,
                    then,
                    r#else,
                    condition_ast_path,
                    span,
                    early_return_condition_value,
                } => {
                    let block = Box::new(EffectsBlock {
                        effects: take(&mut self.effects),
                        range: AstPathRange::StartAfter(start_ast_path),
                    });
                    self.effects = prev_effects;
                    let kind = match (then, r#else, early_return_condition_value) {
                        (None, None, false) => ConditionalKind::If { then: block },
                        (None, None, true) => ConditionalKind::IfElseMultiple {
                            then: vec![block],
                            r#else: vec![],
                        },
                        (Some(then), None, false) => ConditionalKind::IfElseMultiple {
                            then: vec![then, block],
                            r#else: vec![],
                        },
                        (Some(then), None, true) => ConditionalKind::IfElse {
                            then,
                            r#else: block,
                        },
                        (Some(then), Some(r#else), false) => ConditionalKind::IfElseMultiple {
                            then: vec![then, block],
                            r#else: vec![r#else],
                        },
                        (Some(then), Some(r#else), true) => ConditionalKind::IfElseMultiple {
                            then: vec![then],
                            r#else: vec![r#else, block],
                        },
                        (None, Some(r#else), false) => ConditionalKind::IfElse {
                            then: block,
                            r#else,
                        },
                        (None, Some(r#else), true) => ConditionalKind::IfElseMultiple {
                            then: vec![],
                            r#else: vec![r#else, block],
                        },
                    };
                    self.effects.push(Effect::Conditional {
                        condition,
                        kind: Box::new(kind),
                        ast_path: condition_ast_path,
                        span,
                    })
                }
            }
        }
        always_returns
    }
}

impl VisitAstPath for Analyzer<'_> {
    fn visit_import_specifier<'ast: 'r, 'r>(
        &mut self,
        _import_specifier: &'ast ImportSpecifier,
        _ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        // Skip these nodes entirely: We gather imports in a separate pass
    }

    fn visit_assign_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast AssignExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        // LHS
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::AssignExpr(n, AssignExprField::Left));

            let pat_value = match (n.op, n.left.as_ident()) {
                (AssignOp::Assign, _) => self.eval_context.eval(&n.right),
                (AssignOp::AndAssign | AssignOp::OrAssign | AssignOp::NullishAssign, Some(_)) => {
                    // We can handle the right value as alternative to the existing value
                    self.eval_context.eval(&n.right)
                }
                (AssignOp::AddAssign, Some(key)) => {
                    let left = self.eval_context.eval(&Expr::Ident(key.clone().into()));
                    let right = self.eval_context.eval(&n.right);
                    JsValue::add(vec![left, right])
                }
                _ => JsValue::unknown_empty(true, "unsupported assign operation"),
            };
            self.with_pat_value(Some(pat_value), |this| {
                n.left.visit_children_with_ast_path(this, &mut ast_path)
            });
        }

        // RHS
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::AssignExpr(n, AssignExprField::Right));
            self.visit_expr(&n.right, &mut ast_path);
        }
    }

    fn visit_update_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast UpdateExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        if let Some(key) = n.arg.as_ident() {
            self.add_value(
                key.to_id(),
                JsValue::unknown_empty(true, "updated with update expression"),
            );
        }

        let mut ast_path =
            ast_path.with_guard(AstParentNodeRef::UpdateExpr(n, UpdateExprField::Arg));
        self.visit_expr(&n.arg, &mut ast_path);
    }

    fn visit_call_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast CallExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        // We handle `define(function (require) {})` here.
        if let Callee::Expr(callee) = &n.callee
            && n.args.len() == 1
            && let Some(require_var_id) = extract_var_from_umd_factory(callee, &n.args)
        {
            self.add_value(
                require_var_id,
                JsValue::unknown_if(
                    self.eval_context
                        .imports
                        .get_attributes(n.callee.span())
                        .ignore,
                    JsValue::WellKnownFunction(WellKnownFunctionKind::Require),
                    true,
                    "ignored require",
                ),
            );
        }

        if self.check_iife(n, ast_path) {
            return;
        }

        // special behavior of IIFEs
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::CallExpr(n, CallExprField::Callee));
            n.callee.visit_with_ast_path(self, &mut ast_path);
        }

        self.check_call_expr_for_effects(
            &n.callee,
            n.args.iter(),
            n.span(),
            ast_path,
            CallOrNewExpr::Call(n),
        );
    }

    fn visit_new_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast NewExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::NewExpr(n, NewExprField::Callee));
            n.callee.visit_with_ast_path(self, &mut ast_path);
        }

        self.check_call_expr_for_effects(
            &Callee::Expr(n.callee.clone()),
            n.args.iter().flatten(),
            n.span(),
            ast_path,
            CallOrNewExpr::New(n),
        );
    }

    fn visit_member_expr<'ast: 'r, 'r>(
        &mut self,
        member_expr: &'ast MemberExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.check_member_expr_for_effects(member_expr, ast_path);
        member_expr.visit_children_with_ast_path(self, ast_path);
    }

    fn visit_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast Expr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let old = self.var_decl_kind;
        self.var_decl_kind = None;
        n.visit_children_with_ast_path(self, ast_path);
        self.var_decl_kind = old;
    }

    fn visit_params<'ast: 'r, 'r>(
        &mut self,
        n: &'ast [Param],
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let cur_fn_ident = self.cur_fn_ident();
        for (index, p) in n.iter().enumerate() {
            self.with_pat_value(Some(JsValue::Argument(cur_fn_ident, index)), |this| {
                let mut ast_path = ast_path.with_index_guard(index);
                p.visit_with_ast_path(this, &mut ast_path);
            });
        }
    }

    fn visit_param<'ast: 'r, 'r>(
        &mut self,
        n: &'ast Param,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let old = self.var_decl_kind;
        let Param {
            decorators,
            pat,
            span: _,
        } = n;
        self.var_decl_kind = None;
        self.with_pat_value(None, |this| {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Param(
                n,
                ParamField::Decorators(usize::MAX),
            ));
            this.visit_decorators(decorators, &mut ast_path);
        });
        {
            let mut ast_path = ast_path.with_guard(AstParentNodeRef::Param(n, ParamField::Pat));
            self.visit_pat(pat, &mut ast_path);
        }
        self.var_decl_kind = old;
    }

    fn visit_fn_decl<'ast: 'r, 'r>(
        &mut self,
        decl: &'ast FnDecl,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let fn_value = self.enter_fn(&*decl.function, |this| {
            decl.visit_children_with_ast_path(this, ast_path);
        });
        // Take all effects produced by the function and move them to hoisted effects since
        // function declarations are hoisted.
        // This accounts for the fact that even with `if (false) { function f() {} }` `f` is
        // hoisted out of the condition. so we still need to process effects for it.
        // TODO(lukesandberg): shouldn't this just be the effects associated with the function.
        self.hoisted_effects.append(&mut self.effects);

        self.add_value(decl.ident.to_id(), fn_value);
    }

    fn visit_fn_expr<'ast: 'r, 'r>(
        &mut self,
        expr: &'ast FnExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let fn_value = self.enter_fn(&*expr.function, |this| {
            expr.visit_children_with_ast_path(this, ast_path);
        });
        if let Some(ident) = &expr.ident {
            self.add_value(ident.to_id(), fn_value);
        } else {
            self.add_value(
                (
                    format!("*anonymous function {}*", expr.function.span.lo.0).into(),
                    SyntaxContext::empty(),
                ),
                fn_value,
            );
        }
    }

    fn visit_arrow_expr<'ast: 'r, 'r>(
        &mut self,
        expr: &'ast ArrowExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let fn_value = self.enter_fn(expr, |this| {
            let fn_id = this.cur_fn_ident();
            for (index, p) in expr.params.iter().enumerate() {
                this.with_pat_value(Some(JsValue::Argument(fn_id, index)), |this| {
                    let mut ast_path = ast_path.with_guard(AstParentNodeRef::ArrowExpr(
                        expr,
                        ArrowExprField::Params(index),
                    ));
                    p.visit_with_ast_path(this, &mut ast_path);
                });
            }

            {
                let mut ast_path =
                    ast_path.with_guard(AstParentNodeRef::ArrowExpr(expr, ArrowExprField::Body));
                expr.body.visit_with_ast_path(this, &mut ast_path);
                // If body is a single expression treat it as a Block with an return statement
                if let BlockStmtOrExpr::Expr(inner_expr) = &*expr.body {
                    let implicit_return_value = this.eval_context.eval(inner_expr);
                    this.add_return_value(implicit_return_value);
                }
            }
        });
        self.add_value(
            (
                format!("*arrow function {}*", expr.span.lo.0).into(),
                SyntaxContext::empty(),
            ),
            fn_value,
        );
    }

    fn visit_class_decl<'ast: 'r, 'r>(
        &mut self,
        decl: &'ast ClassDecl,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.add_value_from_expr(
            decl.ident.to_id(),
            // TODO avoid clone
            &Expr::Class(ClassExpr {
                ident: Some(decl.ident.clone()),
                class: decl.class.clone(),
            }),
        );
        decl.visit_children_with_ast_path(self, ast_path);
    }

    fn visit_getter_prop<'ast: 'r, 'r>(
        &mut self,
        node: &'ast GetterProp,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(node, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_setter_prop<'ast: 'r, 'r>(
        &mut self,
        node: &'ast SetterProp,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(node, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_constructor<'ast: 'r, 'r>(
        &mut self,
        node: &'ast Constructor,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(node, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_class_method<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ClassMethod,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(&*node.function, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_private_method<'ast: 'r, 'r>(
        &mut self,
        node: &'ast PrivateMethod,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(&*node.function, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_method_prop<'ast: 'r, 'r>(
        &mut self,
        node: &'ast MethodProp,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.enter_fn(&*node.function, |this| {
            node.visit_children_with_ast_path(this, ast_path);
        });
    }

    fn visit_var_decl<'ast: 'r, 'r>(
        &mut self,
        n: &'ast VarDecl,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let old = self.var_decl_kind;
        self.var_decl_kind = Some(n.kind);
        n.visit_children_with_ast_path(self, ast_path);
        self.var_decl_kind = old;
    }

    fn visit_var_declarator<'ast: 'r, 'r>(
        &mut self,
        n: &'ast VarDeclarator,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        // LHS
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::VarDeclarator(n, VarDeclaratorField::Name));

            if self.var_decl_kind.is_some()
                && let Some(init) = &n.init
            {
                // For case like
                //
                // if (shouldRun()) {
                //   var x = true;
                // }
                // if (x) {
                // }
                //
                // The variable `x` is undefined

                let should_include_undefined = matches!(self.var_decl_kind, Some(VarDeclKind::Var))
                    && is_lexically_block_scope(&mut ast_path);
                let init_value = self.eval_context.eval(init);
                let pat_value = Some(if should_include_undefined {
                    JsValue::alternatives(vec![
                        init_value,
                        JsValue::Constant(ConstantValue::Undefined),
                    ])
                } else {
                    init_value
                });
                self.with_pat_value(pat_value, |this| {
                    this.visit_pat(&n.name, &mut ast_path);
                });
            } else {
                // Don't use `with_pat_value(None, ...)` here. A `VarDecl` can occur inside of a
                // `ForOfStmt` with no `init` field, but still have a `pat_value` set that we want
                // to inherit.
                self.visit_pat(&n.name, &mut ast_path);
            }
        }

        // RHS
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::VarDeclarator(n, VarDeclaratorField::Init));

            self.visit_opt_expr(&n.init, &mut ast_path);
        }
    }

    fn visit_for_in_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast ForInStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::ForInStmt(n, ForInStmtField::Right));
            n.right.visit_with_ast_path(self, &mut ast_path);
        }

        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::ForInStmt(n, ForInStmtField::Left));
            self.with_pat_value(
                // TODO this should really be
                // `Some(JsValue::iteratedKeys(Box::new(self.eval_context.eval(&n.right))))`
                Some(JsValue::unknown_empty(
                    false,
                    "for-in variable currently not analyzed",
                )),
                |this| {
                    n.left.visit_with_ast_path(this, &mut ast_path);
                },
            )
        }

        let mut ast_path =
            ast_path.with_guard(AstParentNodeRef::ForInStmt(n, ForInStmtField::Body));

        let prev_early_return_stack = take(&mut self.early_return_stack);
        n.body.visit_with_ast_path(self, &mut ast_path);
        self.end_early_return_block();
        self.early_return_stack = prev_early_return_stack;
    }

    fn visit_for_of_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast ForOfStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::ForOfStmt(n, ForOfStmtField::Right));
            n.right.visit_with_ast_path(self, &mut ast_path);
        }

        let iterable = self.eval_context.eval(&n.right);

        // TODO n.await is ignored (async interables)
        self.with_pat_value(Some(JsValue::iterated(Box::new(iterable))), |this| {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::ForOfStmt(n, ForOfStmtField::Left));
            n.left.visit_with_ast_path(this, &mut ast_path);
        });

        let mut ast_path =
            ast_path.with_guard(AstParentNodeRef::ForOfStmt(n, ForOfStmtField::Body));

        let prev_early_return_stack = take(&mut self.early_return_stack);
        n.body.visit_with_ast_path(self, &mut ast_path);
        self.end_early_return_block();
        self.early_return_stack = prev_early_return_stack;
    }

    fn visit_for_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast ForStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let prev_early_return_stack = take(&mut self.early_return_stack);
        n.visit_children_with_ast_path(self, ast_path);
        self.end_early_return_block();
        self.early_return_stack = prev_early_return_stack;
    }

    fn visit_while_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast WhileStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let prev_early_return_stack = take(&mut self.early_return_stack);
        n.visit_children_with_ast_path(self, ast_path);
        self.end_early_return_block();
        self.early_return_stack = prev_early_return_stack;
    }

    fn visit_do_while_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast DoWhileStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let prev_early_return_stack = take(&mut self.early_return_stack);
        n.visit_children_with_ast_path(self, ast_path);
        self.end_early_return_block();
        self.early_return_stack = prev_early_return_stack;
    }

    fn visit_simple_assign_target<'ast: 'r, 'r>(
        &mut self,
        n: &'ast SimpleAssignTarget,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let value = self.take_pat_value();
        if let SimpleAssignTarget::Ident(i) = n {
            n.visit_children_with_ast_path(self, ast_path);

            self.add_value(
                i.to_id(),
                value.unwrap_or_else(|| {
                    JsValue::unknown(JsValue::Variable(i.to_id()), false, "pattern without value")
                }),
            );
            return;
        }

        n.visit_children_with_ast_path(self, ast_path);
    }

    fn visit_assign_target_pat<'ast: 'r, 'r>(
        &mut self,
        pat: &'ast AssignTargetPat,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let value = self
            .take_pat_value()
            .unwrap_or_else(|| JsValue::unknown_empty(false, "pattern without value"));
        match pat {
            AssignTargetPat::Array(arr) => {
                let mut ast_path = ast_path.with_guard(AstParentNodeRef::AssignTargetPat(
                    pat,
                    AssignTargetPatField::Array,
                ));
                self.handle_array_pat_with_value(arr, value, &mut ast_path);
            }
            AssignTargetPat::Object(obj) => {
                let mut ast_path = ast_path.with_guard(AstParentNodeRef::AssignTargetPat(
                    pat,
                    AssignTargetPatField::Object,
                ));
                self.handle_object_pat_with_value(obj, value, &mut ast_path);
            }
            AssignTargetPat::Invalid(_) => {}
        }
    }

    fn visit_pat<'ast: 'r, 'r>(
        &mut self,
        pat: &'ast Pat,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let value = self.take_pat_value();
        match pat {
            Pat::Ident(i) => {
                self.add_value(
                    i.to_id(),
                    value.unwrap_or_else(|| {
                        JsValue::unknown(
                            JsValue::Variable(i.to_id()),
                            false,
                            "pattern without value",
                        )
                    }),
                );
            }

            Pat::Array(arr) => {
                let mut ast_path = ast_path.with_guard(AstParentNodeRef::Pat(pat, PatField::Array));
                let value =
                    value.unwrap_or_else(|| JsValue::unknown_empty(false, "pattern without value"));
                self.handle_array_pat_with_value(arr, value, &mut ast_path);
            }

            Pat::Object(obj) => {
                let mut ast_path =
                    ast_path.with_guard(AstParentNodeRef::Pat(pat, PatField::Object));
                let value =
                    value.unwrap_or_else(|| JsValue::unknown_empty(false, "pattern without value"));
                self.handle_object_pat_with_value(obj, value, &mut ast_path);
            }

            _ => pat.visit_children_with_ast_path(self, ast_path),
        }
    }

    fn visit_return_stmt<'ast: 'r, 'r>(
        &mut self,
        stmt: &'ast ReturnStmt,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        stmt.visit_children_with_ast_path(self, ast_path);

        // Technically a top level return is illegal, but node supports it due to how module
        // wrapping works.
        if self.is_in_fn() {
            let return_value = stmt
                .arg
                .as_deref()
                .map(|e| self.eval_context.eval(e))
                .unwrap_or(JsValue::Constant(ConstantValue::Undefined));

            self.add_return_value(return_value);
        }

        self.early_return_stack.push(EarlyReturn::Always {
            prev_effects: take(&mut self.effects),
            start_ast_path: as_parent_path(ast_path),
        });
    }

    fn visit_ident<'ast: 'r, 'r>(
        &mut self,
        ident: &'ast Ident,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        // Note: `Ident` is (generally) only used for nodes referencing a variable, as it has scope
        // information. In other cases (e.g. object literals, properties of member expressions),
        // `IdentName` is used instead.

        // Note: The `Ident` children of `ImportSpecifier` are not visited because
        // `visit_import_specifier` bails out.

        // Attempt to add import effects.
        if let Some((esm_reference_index, export)) =
            self.eval_context.imports.get_binding(&ident.to_id())
        {
            // Optimization: Look for a MemberExpr to see if we only access a few members from the
            // module, add those specific effects instead of depending on the entire module.
            //
            // export.is_none() checks for a namespace import (*).
            if export.is_none()
                && !self
                    .eval_context
                    .imports
                    .should_import_all(esm_reference_index)
                && let Some(AstParentNodeRef::MemberExpr(member, MemberExprField::Obj)) =
                    ast_path.get(ast_path.len() - 2)
                && let Some(prop) = self.eval_context.eval_member_prop(&member.prop)
                && let Some(prop_str) = prop.as_str()
            {
                // a namespace member access like
                // `import * as ns from "..."; ns.exportName`
                self.add_effect(Effect::ImportedBinding {
                    esm_reference_index,
                    export: Some(prop_str.into()),
                    // point to the MemberExpression instead
                    ast_path: as_parent_path_skip(ast_path, 1),
                    span: member.span(),
                });
            } else {
                self.add_effect(Effect::ImportedBinding {
                    esm_reference_index,
                    export,
                    ast_path: as_parent_path(ast_path),
                    span: ident.span(),
                })
            }
            return;
        }

        // If this identifier is free, produce an effect so we can potentially replace it later.
        if self.analyze_mode.is_code_gen()
            && let JsValue::FreeVar(var) = self.eval_context.eval_ident(ident)
        {
            // TODO(lukesandberg): we should consider filtering effects here, e.g. there is no
            // benefit in an Effect for `window` or `Math`
            self.add_effect(Effect::FreeVar {
                var,
                ast_path: as_parent_path(ast_path),
                span: ident.span(),
            })
        }
    }

    fn visit_this_expr<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ThisExpr,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        // TODO: would it be better to compute this while traversing?
        // `this` is rebound within functions and class method members
        if ast_path.iter().rev().any(|node| {
            matches!(
                node.kind(),
                AstParentKind::MethodProp(MethodPropField::Function)
                    | AstParentKind::GetterProp(GetterPropField::Body)
                    | AstParentKind::SetterProp(SetterPropField::Body)
                    | AstParentKind::Constructor(ConstructorField::Body)
                    | AstParentKind::ClassMethod(ClassMethodField::Function)
                    | AstParentKind::ClassDecl(ClassDeclField::Class)
                    | AstParentKind::ClassExpr(ClassExprField::Class)
                    | AstParentKind::Function(FunctionField::Body)
                    | AstParentKind::Function(FunctionField::Params(_))
            )
        }) {
            // We are in some scope that will rebind this
            return;
        }

        if self.analyze_mode.is_code_gen() {
            // Otherwise 'this' is free
            self.add_effect(Effect::FreeVar {
                var: atom!("this"),
                ast_path: as_parent_path(ast_path),
                span: node.span(),
            })
        }
    }

    fn visit_meta_prop_expr<'ast: 'r, 'r>(
        &mut self,
        expr: &'ast MetaPropExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        if self.analyze_mode.is_code_gen() && expr.kind == MetaPropKind::ImportMeta {
            // MetaPropExpr also covers `new.target`. Only consider `import.meta`
            // an effect.
            self.add_effect(Effect::ImportMeta {
                span: expr.span,
                ast_path: as_parent_path(ast_path),
            })
        }
    }

    fn visit_program<'ast: 'r, 'r>(
        &mut self,
        program: &'ast Program,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        self.effects = take(&mut self.data.effects);
        program.visit_children_with_ast_path(self, ast_path);
        self.end_early_return_block();
        self.effects.append(&mut self.hoisted_effects);
        self.data.effects = take(&mut self.effects);
    }

    fn visit_cond_expr<'ast: 'r, 'r>(
        &mut self,
        expr: &'ast CondExpr,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::CondExpr(expr, CondExprField::Test));
            expr.test.visit_with_ast_path(self, &mut ast_path);
        }

        let prev_effects = take(&mut self.effects);
        let then = {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::CondExpr(expr, CondExprField::Cons));
            expr.cons.visit_with_ast_path(self, &mut ast_path);
            Box::new(EffectsBlock {
                effects: take(&mut self.effects),
                range: AstPathRange::Exact(as_parent_path(&ast_path)),
            })
        };
        let r#else = {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::CondExpr(expr, CondExprField::Alt));
            expr.alt.visit_with_ast_path(self, &mut ast_path);
            Box::new(EffectsBlock {
                effects: take(&mut self.effects),
                range: AstPathRange::Exact(as_parent_path(&ast_path)),
            })
        };
        self.effects = prev_effects;

        self.add_conditional_effect(
            &expr.test,
            ast_path,
            AstParentKind::CondExpr(CondExprField::Test),
            expr.span(),
            ConditionalKind::Ternary { then, r#else },
        );
    }

    fn visit_if_stmt<'ast: 'r, 'r>(
        &mut self,
        stmt: &'ast IfStmt,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::IfStmt(stmt, IfStmtField::Test));
            stmt.test.visit_with_ast_path(self, &mut ast_path);
        }
        let prev_effects = take(&mut self.effects);
        let prev_early_return_stack = take(&mut self.early_return_stack);
        let then_returning;
        let then = {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::IfStmt(stmt, IfStmtField::Cons));
            stmt.cons.visit_with_ast_path(self, &mut ast_path);
            then_returning = self.end_early_return_block();
            Box::new(EffectsBlock {
                effects: take(&mut self.effects),
                range: AstPathRange::Exact(as_parent_path(&ast_path)),
            })
        };
        let mut else_returning = false;
        let r#else = stmt.alt.as_ref().map(|alt| {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::IfStmt(stmt, IfStmtField::Alt));
            alt.visit_with_ast_path(self, &mut ast_path);
            else_returning = self.end_early_return_block();
            Box::new(EffectsBlock {
                effects: take(&mut self.effects),
                range: AstPathRange::Exact(as_parent_path(&ast_path)),
            })
        });
        self.early_return_stack = prev_early_return_stack;
        self.effects = prev_effects;
        self.add_conditional_if_effect_with_early_return(
            &stmt.test,
            ast_path,
            AstParentKind::IfStmt(IfStmtField::Test),
            stmt.span(),
            (!then.is_empty()).then_some(then),
            r#else.and_then(|block| (!block.is_empty()).then_some(block)),
            then_returning,
            else_returning,
        );
    }

    fn visit_try_stmt<'ast: 'r, 'r>(
        &mut self,
        stmt: &'ast TryStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let prev_effects = take(&mut self.effects);
        let prev_early_return_stack = take(&mut self.early_return_stack);
        let mut block = {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::TryStmt(stmt, TryStmtField::Block));
            stmt.block.visit_with_ast_path(self, &mut ast_path);
            self.end_early_return_block();
            take(&mut self.effects)
        };
        let mut handler = if let Some(handler) = stmt.handler.as_ref() {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::TryStmt(stmt, TryStmtField::Handler));
            handler.visit_with_ast_path(self, &mut ast_path);
            self.end_early_return_block();
            take(&mut self.effects)
        } else {
            vec![]
        };
        self.early_return_stack = prev_early_return_stack;
        self.effects = prev_effects;
        self.effects.append(&mut block);
        self.effects.append(&mut handler);
        if let Some(finalizer) = stmt.finalizer.as_ref() {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::TryStmt(stmt, TryStmtField::Finalizer));
            finalizer.visit_with_ast_path(self, &mut ast_path);
            // If a finally block early returns the parent block does too.
            if self.end_early_return_block() {
                self.early_return_stack.push(EarlyReturn::Always {
                    prev_effects: take(&mut self.effects),
                    start_ast_path: as_parent_path(&ast_path),
                });
            }
        };
    }

    fn visit_switch_case<'ast: 'r, 'r>(
        &mut self,
        case: &'ast SwitchCase,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        let prev_effects = take(&mut self.effects);
        let prev_early_return_stack = take(&mut self.early_return_stack);
        case.visit_children_with_ast_path(self, ast_path);
        self.end_early_return_block();
        let mut effects = take(&mut self.effects);
        self.early_return_stack = prev_early_return_stack;
        self.effects = prev_effects;
        self.effects.append(&mut effects);
    }

    fn visit_block_stmt<'ast: 'r, 'r>(
        &mut self,
        n: &'ast BlockStmt,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        enum ScopeType {
            Function,
            Block,
            ControlFlow,
        }
        let block_type = if ast_path.len() < 2 {
            ScopeType::Block
        } else if matches!(
            &ast_path[ast_path.len() - 2..],
            [
                AstParentNodeRef::IfStmt(_, IfStmtField::Cons),
                AstParentNodeRef::Stmt(_, StmtField::Block)
            ] | [
                AstParentNodeRef::IfStmt(_, IfStmtField::Alt),
                AstParentNodeRef::Stmt(_, StmtField::Block)
            ] | [_, AstParentNodeRef::TryStmt(_, TryStmtField::Block,)]
                | [
                    AstParentNodeRef::TryStmt(_, TryStmtField::Handler),
                    AstParentNodeRef::CatchClause(_, CatchClauseField::Body)
                ]
                | [
                    AstParentNodeRef::LabeledStmt(_, LabeledStmtField::Body),
                    AstParentNodeRef::Stmt(_, StmtField::Block)
                ]
        ) {
            ScopeType::ControlFlow
        } else if matches!(
            &ast_path[ast_path.len() - 2..],
            [_, AstParentNodeRef::Function(_, FunctionField::Body)]
                | [
                    AstParentNodeRef::ArrowExpr(_, ArrowExprField::Body),
                    AstParentNodeRef::BlockStmtOrExpr(_, BlockStmtOrExprField::BlockStmt)
                ]
                | [_, AstParentNodeRef::GetterProp(_, GetterPropField::Body)]
                | [_, AstParentNodeRef::SetterProp(_, SetterPropField::Body)]
                | [_, AstParentNodeRef::Constructor(_, ConstructorField::Body)]
        ) {
            ScopeType::Function
        } else {
            ScopeType::Block
        };
        match block_type {
            ScopeType::Function => {
                let early_return_stack = take(&mut self.early_return_stack);
                let mut effects = take(&mut self.effects);
                let hoisted_effects = take(&mut self.hoisted_effects);
                n.visit_children_with_ast_path(self, ast_path);
                if !self.end_early_return_block() {
                    // NOTE: this only occurs if the function has a return statement on one branch
                    // but not another. if there are no return statements,
                    // `end_early_return_block` will return false.
                    self.add_return_value(JsValue::Constant(ConstantValue::Undefined));
                }
                self.effects.append(&mut self.hoisted_effects);
                effects.append(&mut self.effects);
                self.hoisted_effects = hoisted_effects;
                self.effects = effects;
                self.early_return_stack = early_return_stack;
            }
            ScopeType::Block => {
                n.visit_children_with_ast_path(self, ast_path);
                if self.end_early_return_block() {
                    self.early_return_stack.push(EarlyReturn::Always {
                        prev_effects: take(&mut self.effects),
                        start_ast_path: as_parent_path(ast_path),
                    });
                }
            }
            ScopeType::ControlFlow => {
                n.visit_children_with_ast_path(self, ast_path);
            }
        }
    }

    fn visit_unary_expr<'ast: 'r, 'r>(
        &mut self,
        n: &'ast UnaryExpr,
        ast_path: &mut swc_core::ecma::visit::AstNodePath<'r>,
    ) {
        if n.op == UnaryOp::TypeOf && self.analyze_mode.is_code_gen() {
            let arg_value = Box::new(self.eval_context.eval(&n.arg));

            self.add_effect(Effect::TypeOf {
                arg: arg_value,
                ast_path: as_parent_path(ast_path),
                span: n.span(),
            });
        }

        n.visit_children_with_ast_path(self, ast_path);
    }

    fn visit_labeled_stmt<'ast: 'r, 'r>(
        &mut self,
        stmt: &'ast LabeledStmt,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        let mut prev_effects = take(&mut self.effects);
        let prev_early_return_stack = take(&mut self.early_return_stack);

        stmt.visit_children_with_ast_path(self, ast_path);

        self.end_early_return_block();

        let effects = take(&mut self.effects);

        prev_effects.push(Effect::Conditional {
            condition: Box::new(JsValue::unknown_empty(true, "labeled statement")),
            kind: Box::new(ConditionalKind::Labeled {
                body: Box::new(EffectsBlock {
                    effects,
                    range: AstPathRange::Exact(as_parent_path_with(
                        ast_path,
                        AstParentKind::LabeledStmt(LabeledStmtField::Body),
                    )),
                }),
            }),
            ast_path: as_parent_path(ast_path),
            span: stmt.span,
        });

        self.effects = prev_effects;
        self.early_return_stack = prev_early_return_stack;
    }
}

fn is_lexically_block_scope(ast_path: &mut AstNodePath<AstParentNodeRef>) -> bool {
    let mut iter = ast_path.iter().rev().peekable();

    while let Some(cur) = iter.next() {
        // If it's a block statement, we need to check if it's Function#body
        if matches!(cur.kind(), AstParentKind::BlockStmt(..)) {
            if let Some(next) = iter.peek() {
                return !matches!(next.kind(), AstParentKind::Function(FunctionField::Body));
            }
            return false;
        }
    }

    // This `var` is not in a block scope
    false
}

impl Analyzer<'_> {
    fn add_conditional_if_effect_with_early_return(
        &mut self,
        test: &Expr,
        ast_path: &AstNodePath<AstParentNodeRef<'_>>,
        condition_ast_kind: AstParentKind,
        span: Span,
        then: Option<Box<EffectsBlock>>,
        r#else: Option<Box<EffectsBlock>>,
        early_return_when_true: bool,
        early_return_when_false: bool,
    ) {
        if then.is_none() && r#else.is_none() && !early_return_when_false && !early_return_when_true
        {
            return;
        }
        let condition = Box::new(self.eval_context.eval(test));
        if condition.is_unknown() {
            if let Some(mut then) = then {
                self.effects.append(&mut then.effects);
            }
            if let Some(mut r#else) = r#else {
                self.effects.append(&mut r#else.effects);
            }
            return;
        }
        match (early_return_when_true, early_return_when_false) {
            (true, false) => {
                self.early_return_stack.push(EarlyReturn::Conditional {
                    prev_effects: take(&mut self.effects),
                    start_ast_path: as_parent_path(ast_path),
                    condition,
                    then,
                    r#else,
                    condition_ast_path: as_parent_path_with(ast_path, condition_ast_kind),
                    span,
                    early_return_condition_value: true,
                });
            }
            (false, true) => {
                self.early_return_stack.push(EarlyReturn::Conditional {
                    prev_effects: take(&mut self.effects),
                    start_ast_path: as_parent_path(ast_path),
                    condition,
                    then,
                    r#else,
                    condition_ast_path: as_parent_path_with(ast_path, condition_ast_kind),
                    span,
                    early_return_condition_value: false,
                });
            }
            (false, false) | (true, true) => {
                let kind = match (then, r#else) {
                    (Some(then), Some(r#else)) => ConditionalKind::IfElse { then, r#else },
                    (Some(then), None) => ConditionalKind::If { then },
                    (None, Some(r#else)) => ConditionalKind::Else { r#else },
                    (None, None) => {
                        // No effects, ignore
                        return;
                    }
                };
                self.add_effect(Effect::Conditional {
                    condition,
                    kind: Box::new(kind),
                    ast_path: as_parent_path_with(ast_path, condition_ast_kind),
                    span,
                });
                if early_return_when_false && early_return_when_true {
                    self.early_return_stack.push(EarlyReturn::Always {
                        prev_effects: take(&mut self.effects),
                        start_ast_path: as_parent_path(ast_path),
                    });
                }
            }
        }
    }

    fn add_conditional_effect(
        &mut self,
        test: &Expr,
        ast_path: &AstNodePath<AstParentNodeRef<'_>>,
        ast_kind: AstParentKind,
        span: Span,
        mut cond_kind: ConditionalKind,
    ) {
        let condition = Box::new(self.eval_context.eval(test));
        if condition.is_unknown() {
            match &mut cond_kind {
                ConditionalKind::If { then } => {
                    self.effects.append(&mut then.effects);
                }
                ConditionalKind::Else { r#else } => {
                    self.effects.append(&mut r#else.effects);
                }
                ConditionalKind::IfElse { then, r#else }
                | ConditionalKind::Ternary { then, r#else } => {
                    self.effects.append(&mut then.effects);
                    self.effects.append(&mut r#else.effects);
                }
                ConditionalKind::IfElseMultiple { then, r#else } => {
                    for block in then {
                        self.effects.append(&mut block.effects);
                    }
                    for block in r#else {
                        self.effects.append(&mut block.effects);
                    }
                }
                ConditionalKind::And { expr }
                | ConditionalKind::Or { expr }
                | ConditionalKind::NullishCoalescing { expr } => {
                    self.effects.append(&mut expr.effects);
                }
                ConditionalKind::Labeled { body } => {
                    self.effects.append(&mut body.effects);
                }
            }
        } else {
            self.add_effect(Effect::Conditional {
                condition,
                kind: Box::new(cond_kind),
                ast_path: as_parent_path_with(ast_path, ast_kind),
                span,
            });
        }
    }

    fn handle_array_pat_with_value<'ast: 'r, 'r>(
        &mut self,
        arr: &'ast ArrayPat,
        pat_value: JsValue,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        match pat_value {
            JsValue::Array { items, .. } => {
                for (idx, (elem_pat, value_item)) in arr
                    .elems
                    .iter()
                    // TODO: This does not handle inline spreads correctly
                    // e.g. `let [a,..b,c] = [1,2,3]`
                    .zip(items.into_iter().map(Some).chain(iter::repeat(None)))
                    .enumerate()
                {
                    self.with_pat_value(value_item, |this| {
                        let mut ast_path = ast_path
                            .with_guard(AstParentNodeRef::ArrayPat(arr, ArrayPatField::Elems(idx)));
                        elem_pat.visit_with_ast_path(this, &mut ast_path);
                    });
                }
            }
            value => {
                for (idx, elem) in arr.elems.iter().enumerate() {
                    let pat_value = Some(JsValue::member(
                        Box::new(value.clone()),
                        Box::new(JsValue::Constant(ConstantValue::Num(ConstantNumber(
                            idx as f64,
                        )))),
                    ));
                    self.with_pat_value(pat_value, |this| {
                        let mut ast_path = ast_path
                            .with_guard(AstParentNodeRef::ArrayPat(arr, ArrayPatField::Elems(idx)));
                        elem.visit_with_ast_path(this, &mut ast_path);
                    });
                }
            }
        }
    }

    fn handle_object_pat_with_value<'ast: 'r, 'r>(
        &mut self,
        obj: &'ast ObjectPat,
        pat_value: JsValue,
        ast_path: &mut AstNodePath<AstParentNodeRef<'r>>,
    ) {
        for (i, prop) in obj.props.iter().enumerate() {
            let mut ast_path =
                ast_path.with_guard(AstParentNodeRef::ObjectPat(obj, ObjectPatField::Props(i)));
            match prop {
                ObjectPatProp::KeyValue(kv) => {
                    let mut ast_path = ast_path.with_guard(AstParentNodeRef::ObjectPatProp(
                        prop,
                        ObjectPatPropField::KeyValue,
                    ));
                    let KeyValuePatProp { key, value } = kv;
                    let key_value = self.eval_context.eval_prop_name(key);
                    {
                        let mut ast_path = ast_path.with_guard(AstParentNodeRef::KeyValuePatProp(
                            kv,
                            KeyValuePatPropField::Key,
                        ));
                        key.visit_with_ast_path(self, &mut ast_path);
                    }
                    let pat_value = Some(JsValue::member(
                        Box::new(pat_value.clone()),
                        Box::new(key_value),
                    ));
                    self.with_pat_value(pat_value, |this| {
                        let mut ast_path = ast_path.with_guard(AstParentNodeRef::KeyValuePatProp(
                            kv,
                            KeyValuePatPropField::Value,
                        ));
                        value.visit_with_ast_path(this, &mut ast_path);
                    });
                }
                ObjectPatProp::Assign(assign) => {
                    let mut ast_path = ast_path.with_guard(AstParentNodeRef::ObjectPatProp(
                        prop,
                        ObjectPatPropField::Assign,
                    ));
                    let AssignPatProp { key, value, .. } = assign;
                    let key_value = key.sym.clone().into();
                    {
                        let mut ast_path = ast_path.with_guard(AstParentNodeRef::AssignPatProp(
                            assign,
                            AssignPatPropField::Key,
                        ));
                        key.visit_with_ast_path(self, &mut ast_path);
                    }
                    self.add_value(
                        key.to_id(),
                        if let Some(box value) = value {
                            let value = self.eval_context.eval(value);
                            JsValue::alternatives(vec![
                                JsValue::member(Box::new(pat_value.clone()), Box::new(key_value)),
                                value,
                            ])
                        } else {
                            JsValue::member(Box::new(pat_value.clone()), Box::new(key_value))
                        },
                    );
                    {
                        let mut ast_path = ast_path.with_guard(AstParentNodeRef::AssignPatProp(
                            assign,
                            AssignPatPropField::Value,
                        ));
                        value.visit_with_ast_path(self, &mut ast_path);
                    }
                }

                _ => prop.visit_with_ast_path(self, &mut ast_path),
            }
        }
    }
}

fn extract_var_from_umd_factory(callee: &Expr, args: &[ExprOrSpread]) -> Option<Id> {
    match unparen(callee) {
        Expr::Ident(Ident { sym, .. }) => {
            if &**sym == "define"
                && let Expr::Fn(FnExpr { function, .. }) = &*args[0].expr
            {
                let params = &*function.params;
                if params.len() == 1
                    && let Pat::Ident(param) = &params[0].pat
                    && &*param.id.sym == "require"
                {
                    return Some(param.to_id());
                }
            }
        }

        // umd may use (function (factory){
        //   // Somewhere, define(['require', 'exports'], factory)
        // }(function (require, exports){}))
        //
        // In all module system which has `require`, `require` in the factory function can be
        // treated as a well-known require.
        Expr::Fn(FnExpr { function, .. }) => {
            let params = &*function.params;
            if params.len() == 1
                && let Some(FnExpr { function, .. }) =
                    args.first().and_then(|arg| arg.expr.as_fn_expr())
            {
                let params = &*function.params;
                if !params.is_empty()
                    && let Pat::Ident(param) = &params[0].pat
                    && &*param.id.sym == "require"
                {
                    return Some(param.to_id());
                }
            }
        }

        _ => {}
    }

    None
}