pklr 5.1.1

use super::*;

pub(super) fn analysis_entries_for_requested_fields(
    entries: &[Entry],
    requested_fields: Option<&HashSet<String>>,
) -> Vec<Entry> {
    let Some(requested_fields) = requested_fields else {
        return entries.to_vec();
    };
    entries
        .iter()
        .filter(|entry| match entry {
            Entry::Property(prop) => {
                has_modifier(&prop.modifiers, Modifier::Local)
                    || requested_fields.contains(&prop.name)
            }
            // These entries are still evaluated outside the property output
            // filter, so their imports must remain visible to the analysis.
            Entry::DynProperty(..)
            | Entry::Predicate(..)
            | Entry::Spread(_)
            | Entry::ForGenerator(_)
            | Entry::WhenGenerator(_)
            | Entry::ClassDef(..)
            | Entry::TypeAlias(..) => true,
            Entry::Elem(_) => false,
        })
        .cloned()
        .collect()
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub(super) enum ImportUse {
    Fields(HashSet<String>),
    Whole,
}

pub(super) fn requested_fields_for_import(
    uses: &HashMap<String, ImportUse>,
    alias: &str,
) -> Option<HashSet<String>> {
    match uses.get(alias) {
        Some(ImportUse::Fields(fields)) => Some(fields.clone()),
        Some(ImportUse::Whole) | None => None,
    }
}

/// The keys a glob import's mapping is read with, when it is read only as
/// `Alias["key"]`. A field read such as `Alias.length` or `Alias.keys` reads
/// the whole mapping, even when a matched module happens to have that name.
pub(super) fn glob_index_keys(
    uses: &HashMap<String, ImportUse>,
    alias: &str,
) -> Option<HashSet<String>> {
    if uses.contains_key(&other_uses_key(alias)) {
        return None;
    }
    requested_fields_for_import(uses, &index_reads_key(alias))
}

/// Marks that `Alias` is used other than as `Alias["key"]`.
fn other_uses_key(alias: &str) -> String {
    format!("{alias}\0*")
}

/// Where `Alias["key"]` reads are recorded alongside `Alias`'s own uses.
fn index_reads_key(alias: &str) -> String {
    format!("{alias}\0[]")
}

pub(super) fn import_field_uses(entries: &[Entry]) -> HashMap<String, ImportUse> {
    let mut uses = HashMap::default();
    let shadows = HashSet::default();
    collect_entry_import_field_uses(entries, &mut uses, &shadows);
    uses
}

pub(super) fn collect_entry_import_field_uses(
    entries: &[Entry],
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
) {
    let mut entry_shadows = shadows.clone();
    entry_shadows.extend(declared_entry_roots(entries));
    for entry in entries {
        match entry {
            Entry::Property(prop) => {
                if let Some(ty) = &prop.type_ann {
                    collect_type_import_field_uses(ty, uses, &entry_shadows);
                }
                if let Some(expr) = &prop.value {
                    collect_expr_import_field_uses(expr, uses, &entry_shadows);
                }
                if let Some(body) = &prop.body {
                    collect_entry_import_field_uses(body, uses, &entry_shadows);
                }
            }
            Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                collect_expr_import_field_uses(key, uses, &entry_shadows);
                collect_expr_import_field_uses(value, uses, &entry_shadows);
            }
            Entry::ForGenerator(fgen) => {
                collect_expr_import_field_uses(&fgen.collection, uses, &entry_shadows);
                let mut body_shadows = entry_shadows.clone();
                body_shadows.insert(fgen.val_var.clone());
                if let Some(key_var) = &fgen.key_var {
                    body_shadows.insert(key_var.clone());
                }
                collect_entry_import_field_uses(&fgen.body, uses, &body_shadows);
            }
            Entry::WhenGenerator(wgen) => {
                collect_expr_import_field_uses(&wgen.condition, uses, &entry_shadows);
                collect_entry_import_field_uses(&wgen.body, uses, &entry_shadows);
                if let Some(else_body) = &wgen.else_body {
                    collect_entry_import_field_uses(else_body, uses, &entry_shadows);
                }
            }
            Entry::Spread(expr) | Entry::Elem(expr) => {
                collect_expr_import_field_uses(expr, uses, &entry_shadows);
            }
            Entry::ClassDef(_, _, _, body) => {
                collect_entry_import_field_uses(body, uses, &entry_shadows);
            }
            // A type alias's constraint runs when a value is checked against it.
            Entry::TypeAlias(_, ty) => collect_type_import_field_uses(ty, uses, &entry_shadows),
        }
    }
}

pub(super) fn collect_expr_import_field_uses(
    expr: &Expr,
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
) {
    match expr {
        Expr::Ident(name) => record_whole_import_use(uses, shadows, name),
        Expr::Field(base, field) | Expr::NullSafeField(base, field) => {
            if let Expr::Ident(name) = base.as_ref() {
                record_field_import_use(uses, shadows, name, field);
            } else {
                collect_expr_import_field_uses(base, uses, shadows);
            }
        }
        // `Alias["key"]` names one matched module of a glob import, which
        // `glob_index_keys` narrows to. An ordinary import read this way is
        // still evaluated whole.
        Expr::Index(base, index)
            if matches!(base.as_ref(), Expr::Ident(_))
                && matches!(index.as_ref(), Expr::String(_)) =>
        {
            if let (Expr::Ident(name), Expr::String(key)) = (base.as_ref(), index.as_ref())
                && !shadows.contains(name)
            {
                uses.insert(name.clone(), ImportUse::Whole);
                record_field_import_use(uses, shadows, &index_reads_key(name), key);
            }
        }
        Expr::Index(base, index) | Expr::Binop(_, base, index) => {
            collect_expr_import_field_uses(base, uses, shadows);
            collect_expr_import_field_uses(index, uses, shadows);
        }
        Expr::New(type_name, entries, generic_params) => {
            if let Some(type_name) = type_name {
                if let Some((root, field)) = type_name.split_once('.') {
                    record_field_import_use(uses, shadows, root, field);
                } else {
                    record_whole_import_use(uses, shadows, type_name);
                }
            }
            for param in generic_params {
                record_type_name_import_use(uses, shadows, param);
            }
            collect_entry_import_field_uses(entries, uses, shadows);
        }
        Expr::Call(callee, args) => {
            if let Some(name) = object_method_import_receiver(callee.as_ref()) {
                record_whole_import_use(uses, shadows, name);
            } else {
                collect_expr_import_field_uses(callee, uses, shadows);
            }
            for arg in args {
                collect_expr_import_field_uses(arg, uses, shadows);
            }
        }
        Expr::If(cond, then_expr, else_expr) => {
            collect_expr_import_field_uses(cond, uses, shadows);
            collect_expr_import_field_uses(then_expr, uses, shadows);
            collect_expr_import_field_uses(else_expr, uses, shadows);
        }
        Expr::Let(name, value, body) => {
            collect_expr_import_field_uses(value, uses, shadows);
            let mut body_shadows = shadows.clone();
            body_shadows.insert(name.clone());
            collect_expr_import_field_uses(body, uses, &body_shadows);
        }
        Expr::Is(value, ty) | Expr::As(value, ty) => {
            collect_expr_import_field_uses(value, uses, shadows);
            collect_type_import_field_uses(ty, uses, shadows);
        }
        Expr::Lambda(params, value) => {
            let mut body_shadows = shadows.clone();
            body_shadows.extend(params.iter().cloned());
            collect_expr_import_field_uses(value, uses, &body_shadows);
        }
        Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => collect_expr_import_field_uses(value, uses, shadows),
        Expr::InferredNew(ty, entries) => {
            collect_type_import_field_uses(ty, uses, shadows);
            collect_entry_import_field_uses(entries, uses, shadows);
        }
        Expr::ObjectBody(entries) => collect_entry_import_field_uses(entries, uses, shadows),
        Expr::StringInterpolation(parts) => {
            for part in parts {
                if let StringInterpPart::Expr(expr) = part {
                    collect_expr_import_field_uses(expr, uses, shadows);
                }
            }
        }
        Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => {}
    }
}

pub(super) fn object_method_import_receiver(expr: &Expr) -> Option<&str> {
    let (base, method) = match expr {
        Expr::Field(base, method) | Expr::NullSafeField(base, method) => (base.as_ref(), method),
        _ => return None,
    };
    if !is_intrinsic_object_method(method) {
        return None;
    }
    match base {
        Expr::Ident(name) => Some(name),
        _ => None,
    }
}

pub(super) fn is_intrinsic_object_method(method: &str) -> bool {
    // Import aliases evaluate to module objects. Only methods dispatched for
    // `Value::Object` are whole-object uses here; list/string method names can
    // still be user-defined exported methods such as `Dep.map()`.
    matches!(
        method,
        "containsKey" | "toMap" | "toMapping" | "mapValues" | "filter" | "toList" | "toDynamic"
    )
}

pub(super) fn collect_type_import_field_uses(
    ty: &crate::parser::TypeExpr,
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
) {
    match ty {
        crate::parser::TypeExpr::Named(name) => {
            if string_literal_type_value(name).is_none() {
                record_type_name_import_use(uses, shadows, name);
            }
        }
        crate::parser::TypeExpr::Nullable(inner) => {
            collect_type_import_field_uses(inner, uses, shadows);
        }
        crate::parser::TypeExpr::Union(types) => {
            for ty in types {
                collect_type_import_field_uses(ty, uses, shadows);
            }
        }
        crate::parser::TypeExpr::Generic(name, params) => {
            record_type_name_import_use(uses, shadows, name);
            for param in params {
                collect_type_import_field_uses(param, uses, shadows);
            }
        }
        crate::parser::TypeExpr::Constrained(base, constraint) => {
            for component in constrained_type_components(base) {
                record_type_name_import_use(uses, shadows, component);
            }
            collect_expr_import_field_uses(constraint, uses, shadows);
        }
    }
}

pub(super) fn record_type_name_import_use(
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
    name: &str,
) {
    if let Some((root, field)) = name.split_once('.') {
        record_field_import_use(uses, shadows, root, field);
    } else {
        record_whole_import_use(uses, shadows, name);
    }
}

pub(super) fn record_field_import_use(
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
    name: &str,
    field: &str,
) {
    if shadows.contains(name) {
        return;
    }
    mark_other_use(uses, name);
    match uses.entry(name.to_string()) {
        std::collections::hash_map::Entry::Occupied(mut entry) => {
            if let ImportUse::Fields(fields) = entry.get_mut() {
                fields.insert(field.to_string());
            }
        }
        std::collections::hash_map::Entry::Vacant(entry) => {
            entry.insert(ImportUse::Fields(HashSet::from_iter([field.to_string()])));
        }
    }
}

pub(super) fn record_whole_import_use(
    uses: &mut HashMap<String, ImportUse>,
    shadows: &HashSet<String>,
    name: &str,
) {
    if !shadows.contains(name) {
        mark_other_use(uses, name);
        uses.insert(name.to_string(), ImportUse::Whole);
    }
}

/// Record that `name` is used other than through a literal index, unless
/// `name` is itself one of the internal per-alias keys.
fn mark_other_use(uses: &mut HashMap<String, ImportUse>, name: &str) {
    if !name.contains('\0') {
        uses.insert(other_uses_key(name), ImportUse::Whole);
    }
}

/// `inherited_builtins` are the built-in type names (of
/// `BINDING_BUILTIN_TYPES`) that a module this one amends or extends may
/// redefine: checks here also resolve its type aliases, which this analysis
/// doesn't see.
pub(super) fn expand_requested_fields(
    entries: &[Entry],
    requested: &HashSet<String>,
    inherited_builtins: &[&str],
) -> HashSet<String> {
    let property_names: HashSet<String> = entries
        .iter()
        .filter_map(|entry| match entry {
            Entry::Property(prop) if !has_modifier(&prop.modifiers, Modifier::Local) => {
                Some(prop.name.clone())
            }
            _ => None,
        })
        .collect();
    let mut module_aliases: TypeAliases = entries
        .iter()
        .filter_map(|entry| match entry {
            Entry::TypeAlias(name, ty) => Some((name.as_str(), Some(ty))),
            _ => None,
        })
        .collect();
    // Leave the built-ins an inherited alias may redefine (and this module
    // doesn't) unresolved.
    for builtin in inherited_builtins {
        module_aliases.entry(builtin).or_insert(None);
    }
    // Type aliases and classes evaluate their constraints and defaults when a
    // value is checked or built, so a property using one also depends on what
    // the definition reads.
    let definitions = Definitions {
        types: entries
            .iter()
            .filter_map(|entry| match entry {
                Entry::TypeAlias(name, _) | Entry::ClassDef(name, ..) => {
                    Some((name.as_str(), entry))
                }
                _ => None,
            })
            .collect(),
        values: entries
            .iter()
            .filter_map(|entry| match entry {
                Entry::Property(prop) => Some(prop.name.as_str()),
                _ => None,
            })
            .collect(),
        locals: entries
            .iter()
            .filter_map(|entry| match entry {
                Entry::Property(prop) if has_modifier(&prop.modifiers, Modifier::Local) => {
                    Some((prop.name.as_str(), entry))
                }
                _ => None,
            })
            .collect(),
        module_aliases: &module_aliases,
        classes: ModuleClasses::new(entries),
    };
    let aliases = Some(&module_aliases);
    // An importer reading `dep.ClassName` needs the module properties the
    // class reads through `module` (it is evaluated against them). Other
    // definitions don't see module properties, so they need nothing more.
    let module_reading_definitions = if requested
        .iter()
        .any(|name| definitions.types.contains_key(name.as_str()))
    {
        module_dependent_members(entries)
    } else {
        indexmap::IndexSet::new()
    };
    let mut expanded = requested.clone();
    let mut changed = true;
    while changed {
        changed = false;
        for entry in entries {
            let mut refs = Names::default();
            let shadows = Names::default();
            match entry {
                Entry::Property(prop) if expanded.contains(&prop.name) => {
                    if let Some(ty) = &prop.type_ann {
                        collect_type_refs(ty, &mut refs, &shadows, aliases, Some(&definitions));
                    }
                    if let Some(expr) = &prop.value {
                        collect_expr_refs_in(
                            expr,
                            &mut refs,
                            &shadows,
                            aliases,
                            Some(&definitions),
                        );
                        collect_sibling_field_refs_expr(expr, &mut refs.values, true);
                    }
                    if let Some(body) = &prop.body {
                        collect_entry_refs_in(
                            body,
                            &mut refs,
                            &shadows,
                            aliases,
                            Some(&definitions),
                        );
                        collect_sibling_field_refs_entries(body, &mut refs.values);
                    }
                }
                // A requested class or type alias that reads `module` (an
                // importer reading `dep.ClassName`) depends on what its
                // definition reads.
                Entry::ClassDef(name, ..) | Entry::TypeAlias(name, _)
                    if expanded.contains(name) && module_reading_definitions.contains(name) =>
                {
                    refs.types.insert(name.clone());
                }
                _ => continue,
            }
            // Bodies that change the aliases followed what they reach
            // themselves (see `collect_entry_refs_in`).
            follow_definitions(&definitions, &mut refs, aliases);
            // Only value reads request a property: a type reference that
            // shares a property's name names the type, not the property.
            for dep in refs.values {
                if dep == DYNAMIC_SIBLING_REF {
                    for name in &property_names {
                        if expanded.insert(name.clone()) {
                            changed = true;
                        }
                    }
                    continue;
                }
                if property_names.contains(&dep) && expanded.insert(dep) {
                    changed = true;
                }
            }
        }
    }
    expanded
}

/// Adds to `refs` what the type aliases, classes and locals in `definitions`
/// that `refs` names read (transitively), resolving constraint bases through
/// `aliases`, or through the module's aliases for what a local reaches (it is
/// evaluated at module level). A type alias or class is reached through a
/// type reference, or through a value read of its name when no module
/// property has that name; a local through a value read.
///
/// A type reference that names none of the module's type aliases or classes,
/// and that no value binding around it shadows, may name a property or local
/// holding a class (`new x {}` with `local x = module.C`; also a built-in
/// name such as `String`, which a property can rebind), so it is added to
/// `refs` as a value read too.
fn follow_definitions(definitions: &Definitions, refs: &mut Names, aliases: Option<&TypeAliases>) {
    let shadows = Names::default();
    let types_as_values: Vec<String> = refs
        .unbound_types
        .iter()
        .filter(|name| !definitions.types.contains_key(name.as_str()))
        .cloned()
        .collect();
    refs.values.extend(types_as_values);
    // Each name with whether it was reached through a local, and whether it
    // is a type reference. A name reached both through a local and not is
    // followed both ways, as the aliases may differ.
    let mut pending: Vec<(String, bool, bool)> = refs
        .types
        .iter()
        .map(|name| (name.clone(), false, true))
        .chain(refs.values.iter().map(|name| (name.clone(), false, false)))
        .collect();
    let mut visited = HashSet::default();
    while let Some((name, module_scope, is_type)) = pending.pop() {
        let definition = definitions
            .types
            .get(name.as_str())
            .filter(|_| is_type || !definitions.values.contains(name.as_str()));
        let local = definitions.locals.get(name.as_str()).filter(|_| !is_type);
        if (definition.is_none() && local.is_none())
            || !visited.insert((name, module_scope, is_type))
        {
            continue;
        }
        let mut definition_refs = Names::default();
        if let Some(definition) = definition {
            collect_entry_refs_unnarrowed(
                std::slice::from_ref(*definition),
                &mut definition_refs,
                &shadows,
                if module_scope {
                    Some(definitions.module_aliases)
                } else {
                    aliases
                },
                None,
            );
            // A class body's bare roots read module properties only where
            // `ModuleClasses::module_reads` says so; the rest read the
            // instance.
            if let Entry::ClassDef(class, _, _, body) = definition {
                let reads: HashSet<String> = definitions
                    .classes
                    .module_reads(class, body, &definition_refs.values)
                    .into_iter()
                    .cloned()
                    .collect();
                definition_refs
                    .values
                    .retain(|root| !definitions.classes.is_property(root) || reads.contains(root));
            }
            collect_sibling_field_refs_entries(
                std::slice::from_ref(*definition),
                &mut definition_refs.values,
            );
        }
        let mut local_refs = Names::default();
        if let Some(local) = local {
            collect_entry_refs_unnarrowed(
                std::slice::from_ref(*local),
                &mut local_refs,
                &shadows,
                Some(definitions.module_aliases),
                None,
            );
        }
        // At module level `this` is the module object too.
        if let Some(Entry::Property(prop)) = local {
            if let Some(ty) = &prop.type_ann {
                collect_sibling_field_refs_type(ty, &mut local_refs.values);
            }
            if let Some(expr) = &prop.value {
                collect_sibling_field_refs_expr(expr, &mut local_refs.values, true);
            }
            if let Some(body) = &prop.body {
                collect_sibling_field_refs_entries(body, &mut local_refs.values);
            }
        }
        for (deps, module_scope) in [(definition_refs, module_scope), (local_refs, true)] {
            for dep in deps.unbound_types {
                if !definitions.types.contains_key(dep.as_str()) && refs.values.insert(dep.clone())
                {
                    pending.push((dep.clone(), module_scope, false));
                }
                refs.unbound_types.insert(dep);
            }
            for dep in deps.types {
                refs.types.insert(dep.clone());
                pending.push((dep, module_scope, true));
            }
            for dep in deps.values {
                if dep != "this" {
                    refs.values.insert(dep.clone());
                    pending.push((dep, module_scope, false));
                }
            }
        }
    }
}

pub(super) fn collect_sibling_field_refs_entries(entries: &[Entry], refs: &mut HashSet<String>) {
    for entry in entries {
        match entry {
            Entry::Property(prop) => {
                if let Some(ty) = &prop.type_ann {
                    collect_sibling_field_refs_type(ty, refs);
                }
                if let Some(expr) = &prop.value {
                    collect_sibling_field_refs_expr(expr, refs, false);
                }
                if let Some(body) = &prop.body {
                    collect_sibling_field_refs_entries(body, refs);
                }
            }
            Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                collect_sibling_field_refs_expr(key, refs, false);
                collect_sibling_field_refs_expr(value, refs, false);
            }
            Entry::ForGenerator(fgen) => {
                collect_sibling_field_refs_expr(&fgen.collection, refs, false);
                collect_sibling_field_refs_entries(&fgen.body, refs);
            }
            Entry::WhenGenerator(wgen) => {
                collect_sibling_field_refs_expr(&wgen.condition, refs, false);
                collect_sibling_field_refs_entries(&wgen.body, refs);
                if let Some(else_body) = &wgen.else_body {
                    collect_sibling_field_refs_entries(else_body, refs);
                }
            }
            Entry::Spread(expr) | Entry::Elem(expr) => {
                collect_sibling_field_refs_expr(expr, refs, false);
            }
            Entry::ClassDef(_, _, _, body) => collect_sibling_field_refs_entries(body, refs),
            Entry::TypeAlias(_, ty) => collect_sibling_field_refs_type(ty, refs),
        }
    }
}

/// The names a type check binds for the checked value inside a constraint on
/// `base` (see `eval_type_check`): `this` always, and `length` and `isEmpty`
/// only when the base is a string or collection type, which bind them. For
/// any other base, including aliases and classes that can't be resolved
/// here, those two are kept as references: keeping an unneeded reference only
/// evaluates more, while dropping a needed one breaks the check.
fn constraint_bound_names(base: &str) -> &'static [&'static str] {
    // A nullable base also runs its constraint on `null`, which binds nothing.
    if base.ends_with('?') {
        return &["this"];
    }
    let base = base.trim_start_matches('*');
    // A generic base such as `Listing<String>` checks as its class.
    let base = base.split('<').next().unwrap_or(base).trim();
    if BINDING_BUILTIN_TYPES.contains(&base) {
        &["this", "length", "isEmpty"]
    } else {
        &["this"]
    }
}

/// The built-in types whose constraints bind `length` and `isEmpty`; see
/// `constraint_bound_names`.
pub(super) const BINDING_BUILTIN_TYPES: &[&str] = &[
    "String",
    "List",
    "Listing",
    "Map",
    "Mapping",
    "Set",
    "Collection",
];

/// A module's own type aliases by name, for resolving a constraint's base.
/// `None` marks a name that can't be resolved here: a built-in type that a
/// nested body redeclares, which may no longer bind what the built-in does.
type TypeAliases<'a> = HashMap<&'a str, Option<&'a crate::parser::TypeExpr>>;

/// Names by namespace: those a body refers to, or those bound around it.
/// Pkl keeps types and values apart, so a type named like a module property
/// doesn't read the property, and a local doesn't hide a type of its name.
/// The root of a qualified type name counts as both (see
/// `collect_name_root`), as does a declared class.
#[derive(Clone, Default)]
struct Names {
    /// Value names: identifiers and `module.x`/`this.x` fields read, or
    /// locals and parameters bound.
    values: HashSet<String>,
    /// Type names: roots of annotations, `new T` and class parents, or type
    /// aliases and classes declared.
    types: HashSet<String>,
    /// The unqualified type names in `types` that no enclosing value binding
    /// shadows. One that names none of the module's type aliases or classes
    /// may still name a module property or local holding a class (see
    /// `follow_definitions`).
    unbound_types: HashSet<String>,
}

impl Names {
    fn values(values: &HashSet<String>) -> Self {
        Names {
            values: values.clone(),
            ..Names::default()
        }
    }

    fn extend(&mut self, other: Names) {
        self.values.extend(other.values);
        self.types.extend(other.types);
        self.unbound_types.extend(other.unbound_types);
    }

    /// Adds every name in either namespace to `names`, for callers that only
    /// need to know whether a binding (such as an import) is mentioned.
    fn add_all_to(self, names: &mut HashSet<String>) {
        names.extend(self.values);
        names.extend(self.types);
    }
}

/// A module's own type aliases and classes by name, and the names of its
/// properties, which live in a separate namespace and may share a type's name.
struct Definitions<'a> {
    types: HashMap<&'a str, &'a Entry>,
    values: HashSet<&'a str>,
    /// The module's locals, which are always evaluated and are evaluated
    /// again once the module's properties exist when they reach a class
    /// reading `module` (see `module_dependent_members`). A property reading
    /// one depends on what the local reads, including through its classes.
    locals: HashMap<&'a str, &'a Entry>,
    /// The module's aliases, which a local's checks resolve against wherever
    /// it is read from.
    module_aliases: &'a TypeAliases<'a>,
    /// Which bare roots in a followed class body read module properties
    /// rather than the instance's own.
    classes: ModuleClasses<'a>,
}

impl Definitions<'_> {
    /// The names in `values` that can only mean a type alias or class: no
    /// module property has that name.
    fn unshadowed_values<'n>(
        &self,
        values: &'n HashSet<String>,
    ) -> impl Iterator<Item = &'n String> {
        values.iter().filter(|name| {
            self.types.contains_key(name.as_str()) && !self.values.contains(name.as_str())
        })
    }
}

/// Adds to `out` the name of every type alias or class declared directly in
/// `entries`, except a type alias that redeclares one of `aliases`
/// identically, which reads the same either way.
fn collect_entries_type_decls<'e>(
    entries: &'e [Entry],
    aliases: &TypeAliases,
    out: &mut HashSet<&'e str>,
) {
    for entry in entries {
        match entry {
            Entry::TypeAlias(name, ty) => {
                if aliases
                    .get(name.as_str())
                    .is_none_or(|outer| *outer != Some(ty))
                {
                    out.insert(name);
                }
            }
            Entry::ClassDef(name, ..) => {
                out.insert(name);
            }
            _ => {}
        }
    }
}

/// Type names mentioned by `ty` (identifiers in its named, generic and
/// constraint-base types; not in constraint expressions).
fn mentioned_type_names<'t>(ty: &'t crate::parser::TypeExpr, out: &mut Vec<&'t str>) {
    fn names_in<'s>(text: &'s str, out: &mut Vec<&'s str>) {
        out.extend(
            text.split(|c: char| !(c.is_alphanumeric() || c == '_'))
                .filter(|name| !name.is_empty()),
        );
    }
    match ty {
        crate::parser::TypeExpr::Named(name) | crate::parser::TypeExpr::Constrained(name, _) => {
            names_in(name, out)
        }
        crate::parser::TypeExpr::Nullable(inner) => mentioned_type_names(inner, out),
        crate::parser::TypeExpr::Union(types) => {
            for ty in types {
                mentioned_type_names(ty, out);
            }
        }
        crate::parser::TypeExpr::Generic(name, params) => {
            names_in(name, out);
            for param in params {
                mentioned_type_names(param, out);
            }
        }
    }
}

/// `aliases` without each alias whose meaning may differ where the `declared`
/// type names are in scope: one that is itself declared, or whose definition,
/// followed through the other `aliases`, mentions a declared name. Such an
/// alias named after a built-in that `constraint_bound_names` reads is marked
/// unresolvable rather than dropped, since dropped it would read as the
/// built-in. `None` when every alias is kept.
fn narrow_aliases<'a>(
    aliases: &TypeAliases<'a>,
    declared: &HashSet<&str>,
) -> Option<TypeAliases<'a>> {
    if declared.is_empty() {
        return None;
    }
    let affected = |start: &'a str| {
        let mut seen = HashSet::default();
        let mut pending = vec![start];
        while let Some(name) = pending.pop() {
            if declared.contains(name) {
                return true;
            }
            if !seen.insert(name) {
                continue;
            }
            if let Some(Some(ty)) = aliases.get(name) {
                mentioned_type_names(ty, &mut pending);
            }
        }
        false
    };
    let mut changed = false;
    let kept: TypeAliases<'a> = aliases
        .iter()
        .filter_map(|(name, ty)| {
            if ty.is_none() || !affected(name) {
                return Some((*name, *ty));
            }
            changed = true;
            BINDING_BUILTIN_TYPES
                .contains(name)
                .then_some((*name, None))
        })
        .collect();
    changed.then_some(kept)
}

/// `aliases` with each of the `declared` names that `constraint_bound_names`
/// would read as a built-in marked unresolvable, since where the declaration
/// is in scope the built-in's bindings may no longer apply. A built-in that
/// `entries` only redeclares as one type alias which binds the same names
/// (such as `typealias String = List`) stays resolved, to that definition, when
/// nothing in `aliases` already gave it another meaning: it binds them before
/// and after the declaration alike, and a deeper body that redeclares what
/// the definition refers to still sees it. `None` when `aliases` is
/// unchanged.
fn with_builtins_unresolved<'a>(
    aliases: &TypeAliases<'a>,
    entries: &'a [Entry],
    declared: &HashSet<&str>,
) -> Option<TypeAliases<'a>> {
    let redeclared: Vec<&str> = BINDING_BUILTIN_TYPES
        .iter()
        .copied()
        .filter(|builtin| declared.contains(builtin) && aliases.get(builtin) != Some(&None))
        .collect();
    if redeclared.is_empty() {
        return None;
    }
    let mut marked = aliases.clone();
    for builtin in &redeclared {
        marked.insert(builtin, None);
    }
    // Resolve the new definitions with every redeclared built-in unresolved,
    // so one that reaches another still counts as unknown.
    let binding_definition = |builtin: &str| {
        if aliases.contains_key(builtin) {
            return None;
        }
        let mut definitions = entries.iter().filter_map(|entry| match entry {
            Entry::TypeAlias(name, ty) if name == builtin => Some(Some(ty)),
            Entry::ClassDef(name, ..) if name == builtin => Some(None),
            _ => None,
        });
        match (definitions.next(), definitions.next()) {
            (Some(Some(ty)), None) if alias_binds_collection_names(ty, &marked) => Some(ty),
            _ => None,
        }
    };
    let kept: Vec<_> = redeclared
        .iter()
        .filter_map(|builtin| Some((*builtin, binding_definition(builtin)?)))
        .collect();
    for (builtin, ty) in kept {
        marked.insert(builtin, Some(ty));
    }
    Some(marked)
}

/// Whether a check against the type alias definition `ty` binds `length` and
/// `isEmpty`, resolving through `aliases`.
fn alias_binds_collection_names(ty: &crate::parser::TypeExpr, aliases: &TypeAliases) -> bool {
    match ty {
        crate::parser::TypeExpr::Named(base)
        | crate::parser::TypeExpr::Generic(base, _)
        | crate::parser::TypeExpr::Constrained(base, _) => {
            constraint_bound_names_resolving(base, Some(aliases)).contains(&"length")
        }
        crate::parser::TypeExpr::Nullable(_) | crate::parser::TypeExpr::Union(_) => false,
    }
}

/// `constraint_bound_names`, after following `base` through `aliases` (with
/// cycle protection) to the type it names. A base that resolves to a nullable
/// or union type, to an unresolvable name, or that loops, binds only `this`;
/// a name that isn't one of
/// `aliases` (a class, an imported alias, an unknown name) is left to
/// `constraint_bound_names` as is.
fn constraint_bound_names_resolving(
    base: &str,
    aliases: Option<&TypeAliases>,
) -> &'static [&'static str] {
    let Some(aliases) = aliases else {
        return constraint_bound_names(base);
    };
    let mut base = base;
    let mut seen = HashSet::default();
    loop {
        if base.ends_with('?') {
            return &["this"];
        }
        let name = base.trim_start_matches('*');
        let name = name.split('<').next().unwrap_or(name).trim();
        let Some(ty) = aliases.get(name) else {
            return constraint_bound_names(base);
        };
        let Some(ty) = ty else {
            return &["this"];
        };
        if !seen.insert(name) {
            return &["this"];
        }
        base = match ty {
            crate::parser::TypeExpr::Named(name) | crate::parser::TypeExpr::Generic(name, _) => {
                name
            }
            crate::parser::TypeExpr::Constrained(base, _) => base,
            crate::parser::TypeExpr::Nullable(_) | crate::parser::TypeExpr::Union(_) => {
                return &["this"];
            }
        };
    }
}

/// `module.field` reads in a type's constraints, which run when a value is
/// checked against it.
fn collect_sibling_field_refs_type(ty: &crate::parser::TypeExpr, refs: &mut HashSet<String>) {
    match ty {
        crate::parser::TypeExpr::Constrained(_, constraint) => {
            collect_sibling_field_refs_expr(constraint, refs, false);
        }
        crate::parser::TypeExpr::Nullable(inner) => collect_sibling_field_refs_type(inner, refs),
        crate::parser::TypeExpr::Union(types) | crate::parser::TypeExpr::Generic(_, types) => {
            for ty in types {
                collect_sibling_field_refs_type(ty, refs);
            }
        }
        crate::parser::TypeExpr::Named(_) => {}
    }
}

pub(super) fn collect_sibling_field_refs_expr(
    expr: &Expr,
    refs: &mut HashSet<String>,
    include_this: bool,
) {
    match expr {
        Expr::Field(base, field) | Expr::NullSafeField(base, field) => {
            if is_module_sibling_ref(base, include_this) {
                refs.insert(field.clone());
            }
            collect_sibling_field_refs_expr(base, refs, include_this);
        }
        Expr::Index(base, index) => {
            if is_module_sibling_ref(base, include_this) {
                if let Expr::String(key) = index.as_ref() {
                    refs.insert(key.to_string());
                } else {
                    refs.insert(DYNAMIC_SIBLING_REF.to_string());
                }
            }
            collect_sibling_field_refs_expr(base, refs, include_this);
            collect_sibling_field_refs_expr(index, refs, include_this);
        }
        Expr::Binop(_, left, right) => {
            collect_sibling_field_refs_expr(left, refs, include_this);
            collect_sibling_field_refs_expr(right, refs, include_this);
        }
        Expr::New(type_name, entries, _) => {
            // `new module.C {}` reads the module member `C`.
            if let Some((root, rest)) = type_name.as_deref().and_then(|name| name.split_once('.'))
                && (root == "module" || (include_this && root == "this"))
            {
                let member = rest.split('.').next().unwrap_or(rest);
                refs.insert(member.to_string());
            }
            collect_sibling_field_refs_entries(entries, refs);
        }
        Expr::InferredNew(_, entries) | Expr::ObjectBody(entries) => {
            collect_sibling_field_refs_entries(entries, refs);
        }
        Expr::Call(callee, args) => {
            collect_sibling_field_refs_expr(callee, refs, include_this);
            for arg in args {
                collect_sibling_field_refs_expr(arg, refs, include_this);
            }
        }
        Expr::If(cond, then_expr, else_expr) => {
            collect_sibling_field_refs_expr(cond, refs, include_this);
            collect_sibling_field_refs_expr(then_expr, refs, include_this);
            collect_sibling_field_refs_expr(else_expr, refs, include_this);
        }
        Expr::Let(_, value, body) => {
            collect_sibling_field_refs_expr(value, refs, include_this);
            collect_sibling_field_refs_expr(body, refs, include_this);
        }
        Expr::Is(value, ty) | Expr::As(value, ty) => {
            collect_sibling_field_refs_expr(value, refs, include_this);
            // `module.field` reads in the checked type's constraints.
            collect_sibling_field_refs_type(ty, refs);
        }
        Expr::Lambda(_, body) => collect_sibling_field_refs_expr(body, refs, include_this),
        Expr::Unop(_, body)
        | Expr::Throw(body)
        | Expr::Trace(body, _)
        | Expr::Read(body, _)
        | Expr::ReadOrNull(body, _)
        | Expr::ReadGlob(body, _) => {
            collect_sibling_field_refs_expr(body, refs, include_this);
        }
        Expr::StringInterpolation(parts) => {
            for part in parts {
                if let StringInterpPart::Expr(expr) = part {
                    collect_sibling_field_refs_expr(expr, refs, include_this);
                }
            }
        }
        Expr::Ident(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..)
        | Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_) => {}
    }
}

pub(super) fn property_reference_names(prop: &Property) -> HashSet<String> {
    let mut refs = HashSet::default();
    let shadows = HashSet::default();
    if let Some(expr) = &prop.value {
        collect_expr_refs(expr, &mut refs, &shadows);
        collect_sibling_field_refs_expr(expr, &mut refs, true);
        if has_modifier(&prop.modifiers, Modifier::Local) && is_module_sibling_ref(expr, true) {
            refs.insert(DYNAMIC_SIBLING_REF.to_string());
        }
    }
    if let Some(body) = &prop.body {
        collect_entry_refs(body, &mut refs, &shadows);
        collect_sibling_field_refs_entries(body, &mut refs);
    }
    refs
}

pub(super) fn is_module_sibling_ref(expr: &Expr, include_this: bool) -> bool {
    matches!(expr, Expr::Ident(name) if name == "module" || (include_this && name == "this"))
}

/// The member a module-level entry declares: a property (local or not), a
/// class, or a type alias.
pub(super) fn module_member_name(entry: &Entry) -> Option<&str> {
    match entry {
        Entry::Property(prop) => Some(&prop.name),
        Entry::ClassDef(name, ..) | Entry::TypeAlias(name, _) => Some(name),
        _ => None,
    }
}

/// The other module members that evaluating `entry` can read.  This keeps
/// the current class-scope analysis while making the dependency planner cover
/// locals, classes, aliases, and ordinary properties uniformly.
fn module_member_dependencies(entry: &Entry) -> HashSet<String> {
    let mut refs = referenced_roots(std::slice::from_ref(entry));
    match entry {
        Entry::Property(prop) => {
            refs.extend(property_reference_names(prop));
            if let Some(ty) = &prop.type_ann {
                collect_sibling_field_refs_type(ty, &mut refs);
            }
        }
        Entry::ClassDef(_, _, parent, body) => {
            // Keep qualified `module.x` reads separate from lexical class
            // member references. A class property named `x` shadows a bare
            // `x`, but must not erase this explicit dependency on the
            // module's `x` when we remove those lexical members below.
            let mut module_refs = HashSet::default();
            collect_sibling_field_refs_entries(body, &mut module_refs);
            collect_sibling_field_refs_entries(body, &mut refs);
            if let Some((root, rest)) = parent.as_deref().and_then(|name| name.split_once('.'))
                && root == "module"
            {
                refs.insert(rest.split('.').next().unwrap_or(rest).to_string());
            }
            for entry in body.iter() {
                if let Entry::Property(prop) = entry {
                    refs.remove(&prop.name);
                }
            }
            refs.extend(module_refs);
        }
        Entry::TypeAlias(_, ty) => collect_sibling_field_refs_type(ty, &mut refs),
        _ => {}
    }
    refs
}

/// A class's parent and body.
type ClassInfo<'e> = (Option<&'e str>, &'e [Entry]);

/// The classes visible somewhere, by name: the module's, and the nested ones
/// in scope there, which hide the module's of the same name except from
/// `module.Name`.
#[derive(Clone, Default)]
struct ClassMap<'e> {
    module: std::rc::Rc<HashMap<&'e str, ClassInfo<'e>>>,
    nested: HashMap<&'e str, ClassInfo<'e>>,
}

impl<'e> ClassMap<'e> {
    fn module(classes: HashMap<&'e str, ClassInfo<'e>>) -> Self {
        ClassMap {
            module: std::rc::Rc::new(classes),
            nested: HashMap::default(),
        }
    }

    fn get(&self, name: &str) -> Option<&ClassInfo<'e>> {
        self.nested.get(name).or_else(|| self.module.get(name))
    }

    /// Adds the classes declared directly in `body`, hiding outer ones.
    fn extend_with_body(&mut self, body: &'e [Entry]) {
        self.nested
            .extend(body.iter().filter_map(|entry| match entry {
                Entry::ClassDef(name, _, parent, inner) => {
                    Some((name.as_str(), (parent.as_deref(), inner.as_slice())))
                }
                _ => None,
            }));
    }
}

/// The non-local properties a class whose parent is `parent` inherits from
/// the ancestors in `classes`. `module.Parent` names the module's class, as
/// does any parent of a module class.
fn ancestor_properties<'e>(classes: &ClassMap<'e>, parent: Option<&'e str>) -> HashSet<&'e str> {
    let mut names = HashSet::default();
    let mut seen = HashSet::default();
    let mut next = parent.map(|parent| (parent, false));
    while let Some((name, in_module)) = next {
        let (qualified, name) = match name.strip_prefix("module.") {
            Some(name) => (true, name),
            None => (in_module, name),
        };
        // A nested class hides the module's of its name, except from
        // `module.Name` and from module classes' own parents.
        let (in_module, info) = match classes.nested.get(name).filter(|_| !qualified) {
            Some(info) => (false, Some(info)),
            None => (true, classes.module.get(name)),
        };
        let Some((parent, body)) = info else {
            break;
        };
        if !seen.insert((in_module, name)) {
            break;
        }
        names.extend(body.iter().filter_map(|entry| match entry {
            Entry::Property(prop) if !has_modifier(&prop.modifiers, Modifier::Local) => {
                Some(prop.name.as_str())
            }
            _ => None,
        }));
        next = parent.map(|parent| (parent, in_module));
    }
    names
}

/// A module's non-local properties and its classes, for deciding which bare
/// roots in a class body read the module's properties.
struct ModuleClasses<'a> {
    properties: HashSet<&'a str>,
    classes: ClassMap<'a>,
}

impl<'a> ModuleClasses<'a> {
    fn new(entries: &'a [Entry]) -> Self {
        Self {
            properties: entries
                .iter()
                .filter_map(|entry| match entry {
                    Entry::Property(prop) if !has_modifier(&prop.modifiers, Modifier::Local) => {
                        Some(prop.name.as_str())
                    }
                    _ => None,
                })
                .collect(),
            classes: ClassMap::module(
                entries
                    .iter()
                    .filter_map(|entry| match entry {
                        Entry::ClassDef(name, _, parent, body) => {
                            Some((name.as_str(), (parent.as_deref(), body.as_slice())))
                        }
                        _ => None,
                    })
                    .collect(),
            ),
        }
    }

    /// Whether `name` is one of the module's non-local properties.
    fn is_property(&self, name: &str) -> bool {
        self.properties.contains(name)
    }

    /// The `roots` (bare roots read in the body of the module-level `class`)
    /// that read module properties. A bare root naming a module property
    /// reads it like `module.name` unless the instance has a property of that
    /// name when the read happens. The body's locals are evaluated before its
    /// properties, and each property is bound in declaration order, so a
    /// property the body declares only hides the module's from the entries
    /// after it, and from methods none of the defaults up to it run. The
    /// body's defaults are first evaluated before the parent's members are
    /// merged in, so an inherited property is likewise only seen by methods
    /// the defaults don't run.
    fn module_reads<'r>(
        &self,
        class: &str,
        body: &[Entry],
        roots: &'r HashSet<String>,
    ) -> Vec<&'r String> {
        let mut inherited = None;
        let mut eager = None;
        roots
            .iter()
            .filter(|root| {
                if !self.is_property(root) {
                    return false;
                }
                let declared = body.iter().rposition(
                    |entry| matches!(entry, Entry::Property(prop) if prop.name == **root),
                );
                if let Some(declared) = declared {
                    return eager
                        .get_or_insert_with(|| EagerReads::new(body, &self.classes))
                        .upto(declared)
                        .contains(root.as_str());
                }
                if !inherited
                    .get_or_insert_with(|| self.inherited_properties(class))
                    .contains(root.as_str())
                {
                    return true;
                }
                eager
                    .get_or_insert_with(|| EagerReads::new(body, &self.classes))
                    .all
                    .contains(root.as_str())
            })
            .collect()
    }

    /// The non-local properties `class` inherits from ancestors declared in
    /// this module.
    fn inherited_properties(&self, class: &str) -> HashSet<&'a str> {
        let parent = self.classes.get(class).and_then(|(parent, _)| *parent);
        ancestor_properties(&self.classes, parent)
    }
}

/// The names a class body reads while its defaults are evaluated: those of
/// its non-method entries, and of the methods they run. A method (a property
/// or local whose value is a lambda) runs when they read it (calling it by
/// name, as a member of the instance, or any of them once the instance
/// escapes; see `InstanceReads`), except that a property whose value is just
/// the method (`callback = getMin`) only stores it: the method then runs when
/// they read that property. Other method bodies only run on a built instance.
struct EagerReads<'e> {
    body: &'e [Entry],
    /// The classes the body's nested classes may extend: the enclosing
    /// scope's and the body's own.
    classes: ClassMap<'e>,
    methods: HashSet<&'e str>,
    stored: HashMap<&'e str, &'e str>,
    /// What all of the body's defaults read.
    all: HashSet<String>,
    /// The methods all of the body's defaults run.
    runs: HashSet<&'e str>,
}

impl<'e> EagerReads<'e> {
    fn is_method(entry: &Entry) -> bool {
        matches!(entry, Entry::Property(prop) if matches!(prop.value, Some(Expr::Lambda(..))))
    }

    fn is_local(entry: &Entry) -> bool {
        matches!(entry, Entry::Property(prop) if has_modifier(&prop.modifiers, Modifier::Local))
    }

    /// `scope` holds the classes the body's nested classes may extend.
    fn new(body: &'e [Entry], scope: &ClassMap<'e>) -> Self {
        let mut classes = scope.clone();
        classes.extend_with_body(body);
        let mut reads = EagerReads {
            body,
            classes,
            methods: body
                .iter()
                .filter_map(|entry| match entry {
                    Entry::Property(prop) if Self::is_method(entry) => Some(prop.name.as_str()),
                    _ => None,
                })
                .collect(),
            stored: stored_methods(body, Self::is_method),
            all: HashSet::default(),
            runs: HashSet::default(),
        };
        let defaults = body
            .iter()
            .filter(|entry| reads.is_default(entry))
            .collect();
        (reads.all, reads.runs) = reads.reads(defaults);
        reads
    }

    fn is_default(&self, entry: &Entry) -> bool {
        !Self::is_method(entry)
            && !matches!(entry, Entry::Property(prop) if self.stored.contains_key(prop.name.as_str()))
    }

    /// What the entries a class property at index `upto` doesn't hide its
    /// name from read: the defaults at or before it, the locals and nested
    /// classes (evaluated before any property), and the local methods any
    /// default runs (which capture the scope the locals see).
    fn upto(&self, upto: usize) -> HashSet<String> {
        let seeds = self
            .body
            .iter()
            .enumerate()
            .filter(|(index, entry)| match entry {
                Entry::Property(prop) if Self::is_method(entry) => {
                    Self::is_local(entry) && self.runs.contains(prop.name.as_str())
                }
                _ => {
                    self.is_default(entry)
                        && (*index <= upto
                            || Self::is_local(entry)
                            || matches!(entry, Entry::ClassDef(..)))
                }
            })
            .map(|(_, entry)| entry)
            .collect();
        self.reads(seeds).0
    }

    /// What `seeds` read, with the methods they run (transitively). A nested
    /// class reads only what its own defaults do (see `class_default_reads`),
    /// and once they use it, what the methods they call on it (by name, as
    /// any object's member) read from outside it.
    fn reads(&self, seeds: Vec<&'e Entry>) -> (HashSet<String>, HashSet<&'e str>) {
        let body = self.body;
        let (nested, seeds): (Vec<&Entry>, Vec<&Entry>) = seeds
            .into_iter()
            .partition(|entry| matches!(entry, Entry::ClassDef(..)));
        let mut refs = referenced_roots_of(&seeds);
        for class in &nested {
            if let Entry::ClassDef(_, _, _, class_body) = class {
                refs.extend(class_default_reads(class_body, &self.classes));
            }
        }
        let mut fields = HashSet::default();
        let mut instance = InstanceReads {
            members: HashSet::default(),
            escapes: false,
        };
        for seed in &seeds {
            let seed = std::slice::from_ref(*seed);
            collect_field_names_entries(seed, &mut fields);
            instance.entries(seed, 0);
        }
        let mut followed = HashSet::default();
        // The nested classes the code followed so far uses, at any depth.
        let mut used: Vec<NestedClass<'e>> = Vec::new();
        let mut used_keys: HashSet<*const Entry> = HashSet::default();
        let mut followed_nested: HashSet<*const Entry> = HashSet::default();
        loop {
            let mut nested_reads = false;
            for entry in body {
                if let Entry::ClassDef(name, _, parent, class_body) = entry
                    && refs.contains(name)
                    && used_keys.insert(std::ptr::from_ref(entry))
                {
                    used.push(NestedClass {
                        body: class_body,
                        parent: parent.as_deref(),
                        chain: vec![(body, None)],
                    });
                }
            }
            let mut index = 0;
            while index < used.len() {
                let class = used[index].clone();
                index += 1;
                let scope = class.scope(&self.classes);
                let shadow = class.shadow(&scope);
                // Its methods called here, and the ones they call. Reading a
                // property that only stores a method (see `stored`) calls it.
                let stored = stored_methods(class.body, Self::is_method);
                let mut called = fields.clone();
                loop {
                    let calls_all = called.contains(DYNAMIC_SIBLING_REF);
                    let next: Vec<&Entry> = class
                        .body
                        .iter()
                        .filter(|entry| match entry {
                            Entry::Property(prop) if Self::is_method(entry) => {
                                (calls_all
                                    || called.contains(&prop.name)
                                    || stored.iter().any(|(property, method)| {
                                        *method == prop.name && called.contains(*property)
                                    }))
                                    && followed_nested.insert(std::ptr::from_ref(*entry))
                            }
                            _ => false,
                        })
                        .collect();
                    if next.is_empty() {
                        break;
                    }
                    for method in next {
                        let method = std::slice::from_ref(method);
                        let roots = referenced_roots(method);
                        called.extend(roots.iter().cloned());
                        collect_field_names_entries(method, &mut called);
                        // Other classes' methods it calls run here too.
                        collect_field_names_entries(method, &mut fields);
                        // The nested classes it builds (its own, or ones an
                        // enclosing class declares): their defaults run here,
                        // and their methods may.
                        for root in &roots {
                            if let Some((entry, found)) = class.lookup(root)
                                && used_keys.insert(std::ptr::from_ref(entry))
                            {
                                let found_scope = found.scope(&self.classes);
                                let enclosing = found.enclosing_names(&found_scope);
                                refs.extend(
                                    class_default_reads(found.body, &found_scope)
                                        .into_iter()
                                        .filter(|root| !enclosing.contains(root.as_str())),
                                );
                                used.push(found);
                            }
                        }
                        refs.extend(
                            roots
                                .into_iter()
                                .filter(|root| !shadow.contains(root.as_str())),
                        );
                        nested_reads = true;
                    }
                }
            }
            let calls_all = instance.escapes;
            let read = |name: &str| refs.contains(name) || instance.members.contains(name);
            let mut runs: HashSet<&str> = self
                .methods
                .iter()
                .copied()
                .filter(|method| calls_all || read(method))
                .collect();
            runs.extend(
                self.stored
                    .iter()
                    .filter(|(property, _)| read(property))
                    .map(|(_, method)| *method),
            );
            let next: Vec<&Entry> = body
                .iter()
                .filter(|entry| match entry {
                    Entry::Property(prop) if Self::is_method(entry) => {
                        runs.contains(prop.name.as_str()) && followed.insert(prop.name.as_str())
                    }
                    _ => false,
                })
                .collect();
            if next.is_empty() && !nested_reads {
                return (refs, followed);
            }
            for method in next {
                let method = std::slice::from_ref(method);
                refs.extend(referenced_roots(method));
                collect_field_names_entries(method, &mut fields);
                instance.entries(method, 0);
            }
        }
    }
}

/// A class nested in a class body, at any depth, as `EagerReads` follows it.
#[derive(Clone)]
struct NestedClass<'e> {
    body: &'e [Entry],
    parent: Option<&'e str>,
    /// The bodies enclosing it, outermost (the followed class's) first, each
    /// with its class's parent. The last one declares it.
    chain: Vec<(&'e [Entry], Option<&'e str>)>,
}

impl<'e> NestedClass<'e> {
    /// The classes visible where it is declared, nearer ones winning.
    fn scope(&self, classes: &ClassMap<'e>) -> ClassMap<'e> {
        let mut scope = classes.clone();
        for (body, _) in &self.chain {
            scope.extend_with_body(body);
        }
        scope
    }

    /// The names the instances of the nested classes around it bind
    /// (declared or inherited), which its own code reads lexically. The
    /// outermost body's are left to `EagerReads`.
    fn enclosing_names(&self, scope: &ClassMap<'e>) -> HashSet<&'e str> {
        let mut names = HashSet::default();
        for (body, parent) in self.chain.iter().skip(1) {
            names.extend(instance_names(scope, *parent, body));
        }
        names
    }

    /// The names its methods read from its own instance or lexically from
    /// those around it.
    fn shadow(&self, scope: &ClassMap<'e>) -> HashSet<&'e str> {
        let mut names = self.enclosing_names(scope);
        names.extend(instance_names(scope, self.parent, self.body));
        names
    }

    /// The nested class `name` names from inside it: one it declares, or
    /// else the nearest enclosing body's.
    fn lookup(&self, name: &str) -> Option<(&'e Entry, NestedClass<'e>)> {
        let mut chain = self.chain.clone();
        chain.push((self.body, self.parent));
        while let Some(&(body, _)) = chain.last() {
            if let Some(entry) = body
                .iter()
                .find(|entry| matches!(entry, Entry::ClassDef(class, ..) if class == name))
                && let Entry::ClassDef(_, _, parent, inner) = entry
            {
                return Some((
                    entry,
                    NestedClass {
                        body: inner,
                        parent: parent.as_deref(),
                        chain,
                    },
                ));
            }
            chain.pop();
        }
        None
    }
}

/// The names an instance of a class with this `parent` and `body` has
/// itself: its properties and those it inherits from `classes`.
fn instance_names<'e>(
    classes: &ClassMap<'e>,
    parent: Option<&'e str>,
    body: &'e [Entry],
) -> HashSet<&'e str> {
    let mut names = ancestor_properties(classes, parent);
    names.extend(body.iter().filter_map(|entry| match entry {
        Entry::Property(prop) => Some(prop.name.as_str()),
        _ => None,
    }));
    names
}

/// `referenced_roots` for entries of one body that aren't contiguous: a
/// local or method any of them declares shadows its name in all of them.
fn referenced_roots_of(entries: &[&Entry]) -> HashSet<String> {
    let mut shadows = HashSet::default();
    for entry in entries {
        shadows.extend(declared_entry_roots(std::slice::from_ref(*entry)));
    }
    let mut refs = HashSet::default();
    for entry in entries {
        collect_entry_refs(std::slice::from_ref(*entry), &mut refs, &shadows);
    }
    refs
}

/// The properties of a class `body` that store one of its methods (those
/// `is_method` accepts) rather than compute a value (`callback = getMin` or
/// `= this.getMin`), with the method each stores.
fn stored_methods(body: &[Entry], is_method: fn(&Entry) -> bool) -> HashMap<&str, &str> {
    let methods: HashSet<&str> = body
        .iter()
        .filter_map(|entry| match entry {
            Entry::Property(prop) if is_method(entry) => Some(prop.name.as_str()),
            _ => None,
        })
        .collect();
    body.iter()
        .filter_map(|entry| match entry {
            Entry::Property(prop) if !has_modifier(&prop.modifiers, Modifier::Local) => {
                let method = match prop.value.as_ref()? {
                    Expr::Ident(name) => name,
                    Expr::Field(base, name) if matches!(&**base, Expr::Ident(this) if this == "this") => {
                        name
                    }
                    _ => return None,
                };
                methods
                    .contains(method.as_str())
                    .then_some((prop.name.as_str(), method.as_str()))
            }
            _ => None,
        })
        .collect()
}

/// The names a class body's defaults read from its enclosing scope while
/// they are evaluated (see `EagerReads`): those it doesn't bind itself
/// by then. A name inherited from its parent is kept, as is one any default
/// reads before the body's own property of that name is bound.
fn class_default_reads<'e>(body: &'e [Entry], scope: &ClassMap<'e>) -> HashSet<String> {
    let eager = EagerReads::new(body, scope);
    eager
        .all
        .iter()
        .filter(|root| {
            body.iter()
                .rposition(|entry| matches!(entry, Entry::Property(prop) if prop.name == **root))
                .is_none_or(|declared| eager.upto(declared).contains(*root))
        })
        .cloned()
        .collect()
}

/// Adds to `out` every member name `entries` read from any object (`x.name`,
/// `x?.name`, `x["name"]`), or `DYNAMIC_SIBLING_REF` for a computed key or a
/// value passed to a call that may be an object (which may read any of its
/// members).
fn collect_field_names_entries(entries: &[Entry], out: &mut HashSet<String>) {
    for entry in entries {
        match entry {
            Entry::Property(prop) => {
                if let Some(value) = &prop.value {
                    collect_field_names_expr(value, out);
                }
                if let Some(body) = &prop.body {
                    collect_field_names_entries(body, out);
                }
            }
            Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                collect_field_names_expr(key, out);
                collect_field_names_expr(value, out);
            }
            Entry::ForGenerator(fgen) => {
                collect_field_names_expr(&fgen.collection, out);
                collect_field_names_entries(&fgen.body, out);
            }
            Entry::WhenGenerator(wgen) => {
                collect_field_names_expr(&wgen.condition, out);
                collect_field_names_entries(&wgen.body, out);
                if let Some(else_body) = &wgen.else_body {
                    collect_field_names_entries(else_body, out);
                }
            }
            Entry::Spread(expr) | Entry::Elem(expr) => collect_field_names_expr(expr, out),
            Entry::ClassDef(..) | Entry::TypeAlias(..) => {}
        }
    }
}

/// Whether `expr` may evaluate to an object: anything but literals, string
/// interpolations, and operators on them.
fn may_be_object(expr: &Expr) -> bool {
    match expr {
        Expr::Null | Expr::Bool(_) | Expr::Int(_) | Expr::Float(_) | Expr::String(_) => false,
        Expr::Binop(_, left, right) => may_be_object(left) || may_be_object(right),
        Expr::Unop(_, value) => may_be_object(value),
        // An interpolation is always a string.
        Expr::StringInterpolation(_) => false,
        _ => true,
    }
}

fn collect_field_names_expr(expr: &Expr, out: &mut HashSet<String>) {
    match expr {
        Expr::Field(base, name) | Expr::NullSafeField(base, name) => {
            out.insert(name.clone());
            collect_field_names_expr(base, out);
        }
        Expr::Index(base, index) => {
            match index.as_ref() {
                Expr::String(key) => {
                    out.insert(key.to_string());
                }
                _ => {
                    out.insert(DYNAMIC_SIBLING_REF.to_string());
                }
            }
            collect_field_names_expr(base, out);
            collect_field_names_expr(index, out);
        }
        Expr::New(_, entries, _) | Expr::ObjectBody(entries) | Expr::InferredNew(_, entries) => {
            collect_field_names_entries(entries, out)
        }
        Expr::Binop(op, left, right) => {
            // `x |> f` passes `x` to `f` like `f(x)`.
            if matches!(op, BinOp::Pipe) && may_be_object(left) {
                out.insert(DYNAMIC_SIBLING_REF.to_string());
            }
            collect_field_names_expr(left, out);
            collect_field_names_expr(right, out);
        }
        Expr::Call(callee, args) => {
            // An object passed to a call may have any of its members read
            // there.
            if args.iter().any(may_be_object) {
                out.insert(DYNAMIC_SIBLING_REF.to_string());
            }
            collect_field_names_expr(callee, out);
            for arg in args {
                collect_field_names_expr(arg, out);
            }
        }
        Expr::If(cond, then_expr, else_expr) => {
            collect_field_names_expr(cond, out);
            collect_field_names_expr(then_expr, out);
            collect_field_names_expr(else_expr, out);
        }
        Expr::Let(_, value, body) => {
            collect_field_names_expr(value, out);
            collect_field_names_expr(body, out);
        }
        Expr::Lambda(_, value) => collect_field_names_expr(value, out),
        Expr::Is(value, _)
        | Expr::As(value, _)
        | Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => collect_field_names_expr(value, out),
        Expr::StringInterpolation(parts) => {
            for part in parts {
                if let StringInterpPart::Expr(expr) = part {
                    collect_field_names_expr(expr, out);
                }
            }
        }
        Expr::Ident(_)
        | Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => {}
    }
}

/// How to evaluate the module-level members of a body (see
/// `module_evaluation_plan`).
pub(super) struct EvaluationPlan {
    /// Entry indices, each member after the members it reads.
    pub(super) order: Vec<usize>,
    /// For each entry, the entries that read it.
    dependents: Vec<Vec<usize>>,
}

impl EvaluationPlan {
    /// `failed`, and every entry that reads one of them directly or
    /// transitively, in evaluation order.
    pub(super) fn affected_by(&self, failed: &HashSet<usize>) -> Vec<usize> {
        let mut affected = vec![false; self.dependents.len()];
        let mut stack: Vec<usize> = failed.iter().copied().collect();
        while let Some(index) = stack.pop() {
            if !std::mem::replace(&mut affected[index], true) {
                stack.extend(&self.dependents[index]);
            }
        }
        self.order
            .iter()
            .copied()
            .filter(|&index| affected[index])
            .collect()
    }
}

/// The order in which to evaluate the module-level `entries`: every member
/// after the members it reads, so a member may read one declared after it.
/// Entries that don't depend on each other, and members on a cycle, keep
/// declaration order. A dynamic read through the module object
/// (`module[key]`) may reach any member, so it comes after the other members
/// unless they read it.
pub(super) fn module_evaluation_plan(entries: &[Entry]) -> EvaluationPlan {
    // A one-entry module has no sibling dependency to discover. This keeps
    // the fixed evaluation cost of the planner out of simple configurations.
    if entries.len() <= 1 {
        return EvaluationPlan {
            order: (0..entries.len()).collect(),
            dependents: std::iter::repeat_with(Vec::new)
                .take(entries.len())
                .collect(),
        };
    }
    let mut by_name: HashMap<&str, Vec<usize>> = HashMap::default();
    for (index, entry) in entries.iter().enumerate() {
        if let Some(name) = module_member_name(entry) {
            by_name.entry(name).or_default().push(index);
        }
    }
    let mut dynamic = vec![false; entries.len()];
    let static_deps: Vec<Vec<usize>> = entries
        .iter()
        .enumerate()
        .map(|(index, entry)| {
            if module_member_name(entry).is_none() {
                return Vec::new();
            }
            let refs = module_member_dependencies(entry);
            dynamic[index] = refs.contains(DYNAMIC_SIBLING_REF);
            let mut deps: Vec<usize> = refs
                .iter()
                .filter_map(|name| by_name.get(name.as_str()))
                .flatten()
                .copied()
                .filter(|&dep| dep != index)
                .collect();
            deps.sort_unstable();
            deps.dedup();
            deps
        })
        .collect();
    // Whether `from` reads `to`, directly or through other members.
    let reaches = |from: usize, to: usize| {
        let mut seen = vec![false; entries.len()];
        let mut stack = vec![from];
        while let Some(i) = stack.pop() {
            if i == to {
                return true;
            }
            if !std::mem::replace(&mut seen[i], true) {
                stack.extend(&static_deps[i]);
            }
        }
        false
    };
    let deps: Vec<Vec<usize>> = (0..entries.len())
        .map(|i| {
            let mut deps = static_deps[i].clone();
            if dynamic[i] {
                deps.extend((0..entries.len()).filter(|&j| {
                    j != i
                        && !dynamic[j]
                        && module_member_name(&entries[j]).is_some()
                        && !reaches(j, i)
                }));
                deps.sort_unstable();
                deps.dedup();
            }
            deps
        })
        .collect();
    // 0 = unvisited, 1 = in progress, 2 = done.
    fn visit(i: usize, deps: &[Vec<usize>], state: &mut [u8], order: &mut Vec<usize>) {
        if state[i] != 0 {
            return;
        }
        state[i] = 1;
        for &j in &deps[i] {
            visit(j, deps, state, order);
        }
        state[i] = 2;
        order.push(i);
    }
    let mut state = vec![0u8; entries.len()];
    let mut order = Vec::with_capacity(entries.len());
    // Locals, classes and type aliases come first unless they read a
    // property: objects built from them capture the scope they were
    // evaluated in, which stays small before the properties join it.
    let is_property = |entry: &Entry| matches!(entry, Entry::Property(prop) if !has_modifier(&prop.modifiers, Modifier::Local));
    for i in (0..entries.len()).filter(|&i| !is_property(&entries[i])) {
        visit(i, &deps, &mut state, &mut order);
    }
    for i in 0..entries.len() {
        visit(i, &deps, &mut state, &mut order);
    }
    let mut dependents = vec![Vec::new(); entries.len()];
    for (index, deps) in deps.iter().enumerate() {
        for &dep in deps {
            dependents[dep].push(index);
        }
    }
    EvaluationPlan { order, dependents }
}

/// Names, in declaration order, of the module members in `entries` that must
/// be evaluated again once the module's properties are available: classes
/// whose bodies read `module` or a module property by name (`a = min`), and
/// the members that reference such a member
/// (a subclass, a type alias naming it, a local, or a module function
/// building an instance).
pub(super) fn module_dependent_members(entries: &[Entry]) -> indexmap::IndexSet<String> {
    // A member qualified through the module object (`module.C`, or `this.C`
    // where `this` is the module) is a reference to `C` like a bare `C`.
    fn qualified_member(name: &str, include_this: bool) -> Option<&str> {
        let (root, rest) = name.split_once('.')?;
        (root == "module" || (include_this && root == "this"))
            .then(|| rest.split('.').next().unwrap_or(rest))
    }
    // Only a class that reads the module's properties starts a dependency
    // chain. Most modules have no classes, so check for one first.
    if !entries
        .iter()
        .any(|entry| matches!(entry, Entry::ClassDef(..)))
    {
        return indexmap::IndexSet::new();
    }
    let classes = ModuleClasses::new(entries);
    let members: Vec<(&String, bool, HashSet<String>)> = entries
        .iter()
        .filter_map(|entry| match entry {
            Entry::ClassDef(name, _, parent, body) => {
                let mut refs = referenced_roots(body);
                let reads_module = !classes.module_reads(name, body, &refs).is_empty();
                if reads_module {
                    refs.insert("module".to_string());
                }
                // Inside a class body `this` is the instance, so only
                // `module.C` names a module member.
                collect_sibling_field_refs_entries(body, &mut refs);
                if let Some(parent) = parent {
                    let mut parent_refs = Names::default();
                    collect_name_root(parent, &mut parent_refs, &Names::default());
                    parent_refs.add_all_to(&mut refs);
                    refs.extend(qualified_member(parent, false).map(str::to_string));
                }
                Some((name, true, refs))
            }
            Entry::TypeAlias(name, ty) => {
                let mut refs = HashSet::default();
                collect_type_names(ty, &mut refs);
                // `typealias Ok = Int(module.C.v == "b")` reads `C` when a
                // value is checked against it.
                collect_sibling_field_refs_type(ty, &mut refs);
                if let Some(target) = type_alias_target(ty) {
                    refs.extend(qualified_member(target, true).map(str::to_string));
                }
                Some((name, false, refs))
            }
            // Locals, and module functions (a non-local property whose value
            // is a lambda). Other module properties are evaluated in order by
            // the property pass and already see the refreshed classes.
            Entry::Property(prop)
                if has_modifier(&prop.modifiers, Modifier::Local)
                    || matches!(prop.value, Some(Expr::Lambda(..))) =>
            {
                let value = prop.value.as_ref()?;
                let mut refs = HashSet::default();
                collect_expr_refs(value, &mut refs, &HashSet::default());
                // At module level `this` is the module object too.
                collect_sibling_field_refs_expr(value, &mut refs, true);
                Some((&prop.name, false, refs))
            }
            _ => None,
        })
        .collect();
    let mut dependent = HashSet::default();
    loop {
        let before = dependent.len();
        for (name, is_class, refs) in &members {
            // A dynamic `module[key]` read can reach any tracked member.
            if !dependent.contains(name.as_str())
                && ((refs.contains(DYNAMIC_SIBLING_REF) && !dependent.is_empty())
                    || refs.iter().any(|root| {
                        (*is_class && root == "module") || dependent.contains(root.as_str())
                    }))
            {
                dependent.insert(name.to_string());
            }
        }
        if dependent.len() == before {
            break;
        }
    }
    // Refresh order: each member after the members it reads, so a function
    // or class declared before a class it uses sees that class's new value.
    // Ties and cycles keep declaration order; a dynamic `module[key]` read
    // may reach any member, so it comes after the members without one.
    let tracked: Vec<&(&String, bool, HashSet<String>)> = members
        .iter()
        .filter(|(name, ..)| dependent.contains(name.as_str()))
        .collect();
    let index: HashMap<&str, usize> = tracked
        .iter()
        .enumerate()
        .map(|(i, (name, ..))| (name.as_str(), i))
        .collect();
    let dynamic: Vec<bool> = tracked
        .iter()
        .map(|(_, _, refs)| refs.contains(DYNAMIC_SIBLING_REF))
        .collect();
    let static_deps: Vec<Vec<usize>> = tracked
        .iter()
        .enumerate()
        .map(|(i, (_, _, refs))| {
            let mut deps: Vec<usize> = refs
                .iter()
                .filter_map(|name| index.get(name.as_str()).copied())
                .filter(|&j| j != i)
                .collect();
            deps.sort_unstable();
            deps
        })
        .collect();
    // Whether `from` reads `to`, directly or through other members.
    let reaches = |from: usize, to: usize| {
        let mut seen = vec![false; tracked.len()];
        let mut stack = vec![from];
        while let Some(i) = stack.pop() {
            if i == to {
                return true;
            }
            if !std::mem::replace(&mut seen[i], true) {
                stack.extend(&static_deps[i]);
            }
        }
        false
    };
    // A dynamic reader goes after the other members, except those that read
    // it: ordering it after them would put it after its own dependents.
    let deps: Vec<Vec<usize>> = (0..tracked.len())
        .map(|i| {
            let mut deps = static_deps[i].clone();
            if dynamic[i] {
                deps.extend(
                    (0..tracked.len()).filter(|&j| j != i && !dynamic[j] && !reaches(j, i)),
                );
                deps.sort_unstable();
                deps.dedup();
            }
            deps
        })
        .collect();
    // 0 = unvisited, 1 = in progress, 2 = done.
    fn visit(i: usize, deps: &[Vec<usize>], state: &mut [u8], order: &mut Vec<usize>) {
        if state[i] != 0 {
            return;
        }
        state[i] = 1;
        for &j in &deps[i] {
            visit(j, deps, state, order);
        }
        state[i] = 2;
        order.push(i);
    }
    let mut state = vec![0u8; tracked.len()];
    let mut order = Vec::with_capacity(tracked.len());
    for i in 0..tracked.len() {
        visit(i, &deps, &mut state, &mut order);
    }
    order.into_iter().map(|i| tracked[i].0.clone()).collect()
}

/// The class or alias a type alias binds to at runtime (`typealias A = C`,
/// `C?` or `C(constraint)`), as `eval_type_alias` resolves it.
pub(super) fn type_alias_target(ty: &crate::parser::TypeExpr) -> Option<&str> {
    match ty {
        crate::parser::TypeExpr::Named(target)
        | crate::parser::TypeExpr::Constrained(target, _) => Some(target),
        crate::parser::TypeExpr::Nullable(inner) => match inner.as_ref() {
            crate::parser::TypeExpr::Named(target) => Some(target),
            _ => None,
        },
        _ => None,
    }
}

/// Every name `entries` read or name as a type (an import used only in a
/// type annotation, such as `x is Dep.Foo`, is still referenced).
pub(super) fn referenced_roots(entries: &[Entry]) -> HashSet<String> {
    let mut refs = HashSet::default();
    let shadows = HashSet::default();
    collect_entry_refs(entries, &mut refs, &shadows);
    refs
}

/// Adds to `refs` every name `entries` read or name as a type.
pub(super) fn collect_entry_refs(
    entries: &[Entry],
    refs: &mut HashSet<String>,
    shadows: &HashSet<String>,
) {
    let mut collected = Names::default();
    let shadows = Names::values(shadows);
    collect_entry_refs_in(entries, &mut collected, &shadows, None, None);
    collected.add_all_to(refs);
}

/// Like `collect_entry_refs`, but resolves a constraint's base through the
/// module's own type aliases (see `constraint_bound_names_resolving`).
fn collect_entry_refs_in(
    entries: &[Entry],
    refs: &mut Names,
    shadows: &Names,
    aliases: Option<&TypeAliases>,
    definitions: Option<&Definitions>,
) {
    // A type alias or class declared in this body takes effect only from its
    // declaration on (a local evaluated earlier still sees the module's
    // aliases), and it can change what a module alias's definition refers to
    // (`typealias String = Int` under an identical `typealias S = String`). So
    // stop resolving the module aliases whose definitions reach a name this
    // body declares (other than by an identical redeclaration), keeping the
    // conservative reading of their constraints, and leave a redeclared
    // built-in unresolved (even without module aliases).
    let no_aliases = TypeAliases::default();
    let narrowed = {
        let aliases = aliases.unwrap_or(&no_aliases);
        let mut declared = HashSet::default();
        collect_entries_type_decls(entries, aliases, &mut declared);
        let narrowed = narrow_aliases(aliases, &declared);
        with_builtins_unresolved(narrowed.as_ref().unwrap_or(aliases), entries, &declared)
            .or(narrowed)
    };
    // A definition's constraints resolve aliases where the check happens, so
    // when following `definitions` and this body changes the aliases, follow
    // the ones reached from here with this body's aliases, and leave only
    // what they read to the caller: drop the type references followed here,
    // but keep value reads (a name shared with a module property reads the
    // property).
    if let (Some(narrowed), Some(definitions)) = (&narrowed, definitions) {
        let mut body_refs = Names::default();
        collect_entry_refs_unnarrowed(
            entries,
            &mut body_refs,
            shadows,
            Some(narrowed),
            Some(definitions),
        );
        follow_definitions(definitions, &mut body_refs, Some(narrowed));
        let followed: HashSet<String> = definitions
            .unshadowed_values(&body_refs.values)
            .cloned()
            .collect();
        body_refs.values.retain(|name| !followed.contains(name));
        body_refs
            .types
            .retain(|name| !definitions.types.contains_key(name.as_str()));
        refs.extend(body_refs);
        return;
    }
    collect_entry_refs_unnarrowed(
        entries,
        refs,
        shadows,
        narrowed.as_ref().or(aliases),
        definitions,
    );
}

/// `collect_entry_refs_in` without narrowing `aliases` for the types
/// `entries` declare, for a module-level definition followed on its own.
fn collect_entry_refs_unnarrowed(
    entries: &[Entry],
    refs: &mut Names,
    shadows: &Names,
    aliases: Option<&TypeAliases>,
    definitions: Option<&Definitions>,
) {
    let mut entry_shadows = shadows.clone();
    entry_shadows.extend(declared_entry_names(entries));
    for entry in entries {
        match entry {
            Entry::Property(prop) => {
                if let Some(ty) = &prop.type_ann {
                    collect_type_refs(ty, refs, &entry_shadows, aliases, definitions);
                }
                if let Some(expr) = &prop.value {
                    collect_expr_refs_in(expr, refs, &entry_shadows, aliases, definitions);
                }
                if let Some(body) = &prop.body {
                    collect_entry_refs_in(body, refs, &entry_shadows, aliases, definitions);
                }
            }
            Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                collect_expr_refs_in(key, refs, &entry_shadows, aliases, definitions);
                collect_expr_refs_in(value, refs, &entry_shadows, aliases, definitions);
            }
            Entry::ForGenerator(fgen) => {
                collect_expr_refs_in(&fgen.collection, refs, &entry_shadows, aliases, definitions);
                let mut body_shadows = entry_shadows.clone();
                body_shadows.values.insert(fgen.val_var.clone());
                if let Some(key_var) = &fgen.key_var {
                    body_shadows.values.insert(key_var.clone());
                }
                collect_entry_refs_in(&fgen.body, refs, &body_shadows, aliases, definitions);
            }
            Entry::WhenGenerator(wgen) => {
                collect_expr_refs_in(&wgen.condition, refs, &entry_shadows, aliases, definitions);
                collect_entry_refs_in(&wgen.body, refs, &entry_shadows, aliases, definitions);
                if let Some(else_body) = &wgen.else_body {
                    collect_entry_refs_in(else_body, refs, &entry_shadows, aliases, definitions);
                }
            }
            Entry::Spread(expr) | Entry::Elem(expr) => {
                collect_expr_refs_in(expr, refs, &entry_shadows, aliases, definitions)
            }
            Entry::ClassDef(_, _, parent, body) => {
                if let Some(parent) = parent {
                    collect_name_root(parent, refs, &entry_shadows);
                }
                collect_entry_refs_in(body, refs, &entry_shadows, aliases, definitions);
            }
            Entry::TypeAlias(_, ty) => {
                collect_type_refs(ty, refs, &entry_shadows, aliases, definitions)
            }
        }
    }
}

// Wrap only the locals needed by the selected element. Forcing unrelated
// locals here can recurse when a local itself reads super.first or super.last.
pub(super) fn with_listing_locals(expr: &Expr, locals: &[(String, Expr)]) -> Expr {
    let mut expr = expr.clone();
    let mut refs = HashSet::default();
    collect_expr_refs(&expr, &mut refs, &HashSet::default());
    for (name, value) in locals.iter().rev() {
        if refs.remove(name) {
            collect_expr_refs(value, &mut refs, &HashSet::default());
            expr = Expr::Let(name.clone(), Box::new(value.clone()), Box::new(expr));
        }
    }
    expr
}

/// Names a type expression needs when it is resolved later in a detached
/// scope. This includes roots named in the type itself and values read by a
/// constraint.
pub(super) fn type_reference_names(ty: &crate::parser::TypeExpr) -> HashSet<String> {
    let mut collected = Names::default();
    collect_type_refs(ty, &mut collected, &Names::default(), None, None);
    let mut refs = HashSet::default();
    collected.add_all_to(&mut refs);
    refs
}

fn collect_type_names(ty: &crate::parser::TypeExpr, refs: &mut HashSet<String>) {
    refs.extend(type_reference_names(ty));
}

/// Adds to `refs` every name `expr` reads or names as a type.
pub(super) fn collect_expr_refs(
    expr: &Expr,
    refs: &mut HashSet<String>,
    shadows: &HashSet<String>,
) {
    let mut collected = Names::default();
    let shadows = Names::values(shadows);
    collect_expr_refs_in(expr, &mut collected, &shadows, None, None);
    collected.add_all_to(refs);
}

fn collect_expr_refs_in(
    expr: &Expr,
    refs: &mut Names,
    shadows: &Names,
    aliases: Option<&TypeAliases>,
    definitions: Option<&Definitions>,
) {
    match expr {
        Expr::Ident(name) => {
            if !shadows.values.contains(name) {
                refs.values.insert(name.clone());
            }
        }
        Expr::New(type_name, entries, generic_params) => {
            if let Some(type_name) = type_name {
                collect_name_root(type_name, refs, shadows);
            }
            for param in generic_params {
                collect_name_root(param, refs, shadows);
            }
            collect_entry_refs_in(entries, refs, shadows, aliases, definitions);
        }
        Expr::Field(base, _) | Expr::NullSafeField(base, _) => {
            collect_expr_refs_in(base, refs, shadows, aliases, definitions);
        }
        Expr::Index(base, index) | Expr::Binop(_, base, index) => {
            collect_expr_refs_in(base, refs, shadows, aliases, definitions);
            collect_expr_refs_in(index, refs, shadows, aliases, definitions);
        }
        Expr::Call(callee, args) => {
            collect_expr_refs_in(callee, refs, shadows, aliases, definitions);
            for arg in args {
                collect_expr_refs_in(arg, refs, shadows, aliases, definitions);
            }
        }
        Expr::If(cond, then_expr, else_expr) => {
            collect_expr_refs_in(cond, refs, shadows, aliases, definitions);
            collect_expr_refs_in(then_expr, refs, shadows, aliases, definitions);
            collect_expr_refs_in(else_expr, refs, shadows, aliases, definitions);
        }
        Expr::Let(name, value, body) => {
            collect_expr_refs_in(value, refs, shadows, aliases, definitions);
            let mut body_shadows = shadows.clone();
            body_shadows.values.insert(name.clone());
            collect_expr_refs_in(body, refs, &body_shadows, aliases, definitions);
        }
        Expr::Is(value, ty) | Expr::As(value, ty) => {
            collect_expr_refs_in(value, refs, shadows, aliases, definitions);
            collect_type_refs(ty, refs, shadows, aliases, definitions);
        }
        Expr::Lambda(params, value) => {
            let mut body_shadows = shadows.clone();
            body_shadows.values.extend(params.iter().cloned());
            collect_expr_refs_in(value, refs, &body_shadows, aliases, definitions);
        }
        Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => {
            collect_expr_refs_in(value, refs, shadows, aliases, definitions)
        }
        Expr::InferredNew(ty, entries) => {
            collect_type_refs(ty, refs, shadows, aliases, definitions);
            collect_entry_refs_in(entries, refs, shadows, aliases, definitions);
        }
        Expr::ObjectBody(entries) => {
            collect_entry_refs_in(entries, refs, shadows, aliases, definitions)
        }
        Expr::StringInterpolation(parts) => {
            for part in parts {
                if let StringInterpPart::Expr(expr) = part {
                    collect_expr_refs_in(expr, refs, shadows, aliases, definitions);
                }
            }
        }
        Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => {}
    }
}

fn collect_type_refs(
    ty: &crate::parser::TypeExpr,
    refs: &mut Names,
    shadows: &Names,
    aliases: Option<&TypeAliases>,
    definitions: Option<&Definitions>,
) {
    match ty {
        crate::parser::TypeExpr::Named(name) => collect_name_root(name, refs, shadows),
        crate::parser::TypeExpr::Nullable(inner) => {
            collect_type_refs(inner, refs, shadows, aliases, definitions)
        }
        crate::parser::TypeExpr::Union(types) => {
            for ty in types {
                collect_type_refs(ty, refs, shadows, aliases, definitions);
            }
        }
        crate::parser::TypeExpr::Generic(name, params) => {
            collect_name_root(name, refs, shadows);
            for param in params {
                collect_type_refs(param, refs, shadows, aliases, definitions);
            }
        }
        crate::parser::TypeExpr::Constrained(base, constraint) => {
            for component in constrained_type_components(base) {
                collect_name_root(component, refs, shadows);
            }
            // A type check binds the checked value's own names inside the
            // constraint, so they are not references to the enclosing scope.
            let mut constraint_shadows = shadows.clone();
            constraint_shadows.values.extend(
                constraint_bound_names_resolving(base, aliases)
                    .iter()
                    .map(|name| name.to_string()),
            );
            collect_expr_refs_in(constraint, refs, &constraint_shadows, aliases, definitions);
        }
    }
}

fn collect_name_root(name: &str, refs: &mut Names, shadows: &Names) {
    let root = name.split('.').next().unwrap_or(name);
    if root.is_empty() {
        return;
    }
    let qualified = root.len() < name.len();
    if !shadows.types.contains(root) {
        refs.types.insert(root.to_string());
        if !qualified && !shadows.values.contains(root) {
            refs.unbound_types.insert(root.to_string());
        }
    }
    // The root of a qualified name (`Dep.Item`) is a module, which may be a
    // property holding one (`Dep = import(...)`), so it's read as a value too.
    if qualified && !shadows.values.contains(root) {
        refs.values.insert(root.to_string());
    }
}

pub(super) fn constrained_type_components(name: &str) -> impl Iterator<Item = &str> {
    name.trim_start_matches('*')
        .trim_end_matches('?')
        .split(['<', '>', ','])
        .map(str::trim)
        .filter(|component| !component.is_empty())
}

/// `declared_entry_roots` by namespace.
fn declared_entry_names(entries: &[Entry]) -> Names {
    let mut names = Names::default();
    for entry in entries {
        match entry {
            // A class is bound as a value too (`ok = C`, `C.a`); a type alias
            // is not.
            Entry::ClassDef(name, ..) => {
                names.types.insert(name.clone());
                names.values.insert(name.clone());
            }
            Entry::TypeAlias(name, _) => {
                names.types.insert(name.clone());
            }
            Entry::Property(prop)
                if has_modifier(&prop.modifiers, Modifier::Local)
                    || matches!(prop.value, Some(Expr::Lambda(..))) =>
            {
                names.values.insert(prop.name.clone());
            }
            _ => {}
        }
    }
    names
}

pub(super) fn declared_entry_roots(entries: &[Entry]) -> HashSet<String> {
    entries
        .iter()
        .filter_map(|entry| match entry {
            Entry::ClassDef(name, ..) | Entry::TypeAlias(name, _) => Some(name.clone()),
            Entry::Property(prop)
                if has_modifier(&prop.modifiers, Modifier::Local)
                    || matches!(prop.value, Some(Expr::Lambda(..))) =>
            {
                Some(prop.name.clone())
            }
            _ => None,
        })
        .collect()
}

/// Every name an expression could resolve in its enclosing scope, ignoring
/// shadowing. Over-approximating is safe for deciding what a lambda captures:
/// a local of an object built in the body may be read before it is declared,
/// so an enclosing binding of the same name must stay reachable.
pub(super) fn collect_unshadowed_names(expr: &Expr, names: &mut HashSet<String>) {
    match expr {
        Expr::Ident(name) => {
            names.insert(name.clone());
        }
        Expr::New(type_name, entries, generic_params) => {
            if type_name.is_some() || !generic_params.is_empty() {
                mark_type_use(names);
            }
            collect_unshadowed_entry_names(entries, names);
        }
        Expr::Field(base, _) | Expr::NullSafeField(base, _) => {
            collect_unshadowed_names(base, names);
        }
        Expr::Index(base, index) | Expr::Binop(_, base, index) => {
            collect_unshadowed_names(base, names);
            collect_unshadowed_names(index, names);
        }
        Expr::Call(callee, args) => {
            collect_unshadowed_names(callee, names);
            for arg in args {
                collect_unshadowed_names(arg, names);
            }
        }
        Expr::If(cond, then_expr, else_expr) => {
            collect_unshadowed_names(cond, names);
            collect_unshadowed_names(then_expr, names);
            collect_unshadowed_names(else_expr, names);
        }
        Expr::Let(_, value, body) => {
            collect_unshadowed_names(value, names);
            collect_unshadowed_names(body, names);
        }
        Expr::Is(value, ty) | Expr::As(value, ty) => {
            collect_unshadowed_names(value, names);
            collect_unshadowed_type_names(ty, names);
        }
        Expr::Lambda(_, value) => collect_unshadowed_names(value, names),
        Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => collect_unshadowed_names(value, names),
        Expr::InferredNew(ty, entries) => {
            collect_unshadowed_type_names(ty, names);
            collect_unshadowed_entry_names(entries, names);
        }
        Expr::ObjectBody(entries) => collect_unshadowed_entry_names(entries, names),
        Expr::StringInterpolation(parts) => {
            for part in parts {
                if let StringInterpPart::Expr(expr) = part {
                    collect_unshadowed_names(expr, names);
                }
            }
        }
        Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => {}
    }
}

fn collect_unshadowed_entry_names(entries: &[Entry], names: &mut HashSet<String>) {
    for entry in entries {
        match entry {
            Entry::Property(prop) => {
                if let Some(ty) = &prop.type_ann {
                    collect_unshadowed_type_names(ty, names);
                }
                if let Some(expr) = &prop.value {
                    collect_unshadowed_names(expr, names);
                }
                if let Some(body) = &prop.body {
                    collect_unshadowed_entry_names(body, names);
                }
            }
            Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                collect_unshadowed_names(key, names);
                collect_unshadowed_names(value, names);
            }
            Entry::ForGenerator(fgen) => {
                collect_unshadowed_names(&fgen.collection, names);
                collect_unshadowed_entry_names(&fgen.body, names);
            }
            Entry::WhenGenerator(wgen) => {
                collect_unshadowed_names(&wgen.condition, names);
                collect_unshadowed_entry_names(&wgen.body, names);
                if let Some(else_body) = &wgen.else_body {
                    collect_unshadowed_entry_names(else_body, names);
                }
            }
            Entry::Spread(expr) | Entry::Elem(expr) => collect_unshadowed_names(expr, names),
            Entry::ClassDef(_, _, parent, body) => {
                if parent.is_some() {
                    mark_type_use(names);
                }
                collect_unshadowed_entry_names(body, names);
            }
            Entry::TypeAlias(_, ty) => collect_unshadowed_type_names(ty, names),
        }
    }
}

fn collect_unshadowed_type_names(ty: &crate::parser::TypeExpr, names: &mut HashSet<String>) {
    mark_type_use(names);
    // A constraint is an ordinary expression evaluated against the value.
    if let crate::parser::TypeExpr::Constrained(_, constraint) = ty {
        collect_unshadowed_names(constraint, names);
    }
    match ty {
        crate::parser::TypeExpr::Nullable(inner) => collect_unshadowed_type_names(inner, names),
        crate::parser::TypeExpr::Union(types) | crate::parser::TypeExpr::Generic(_, types) => {
            for ty in types {
                collect_unshadowed_type_names(ty, names);
            }
        }
        _ => {}
    }
}

/// Recorded by [`collect_unshadowed_names`] when the expression names a type
/// or class anywhere (`new T`, `is`/`as`, type annotations, constraints, class
/// parents). Type names come in many spellings (defaults, generics, quoted
/// names containing separators), and resolving them looks up bindings in ways
/// a name list cannot capture reliably, so callers that see this capture the
/// whole scope.
pub(super) const NAMES_A_TYPE: &str = "\0type";

fn mark_type_use(names: &mut HashSet<String>) {
    names.insert(NAMES_A_TYPE.to_string());
}

/// Whether `name` appears as an identifier anywhere in `entries`, including
/// nested bodies, lambdas and type constraints, ignoring shadowing. Cheaper
/// than collecting every name when only one matters.
pub(super) fn entries_mention(entries: &[Entry], name: &str) -> bool {
    entries.iter().any(|entry| entry_mentions(entry, name))
}

fn property_mentions(prop: &Property, name: &str) -> bool {
    prop.type_ann
        .as_ref()
        .is_some_and(|ty| type_mentions(ty, name))
        || prop
            .value
            .as_ref()
            .is_some_and(|expr| expr_mentions(expr, name))
        || prop
            .body
            .as_ref()
            .is_some_and(|body| entries_mention(body, name))
}

fn entry_mentions(entry: &Entry, name: &str) -> bool {
    match entry {
        Entry::Property(prop) => property_mentions(prop, name),
        Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
            expr_mentions(key, name) || expr_mentions(value, name)
        }
        Entry::ForGenerator(fgen) => {
            expr_mentions(&fgen.collection, name) || entries_mention(&fgen.body, name)
        }
        Entry::WhenGenerator(wgen) => {
            expr_mentions(&wgen.condition, name)
                || entries_mention(&wgen.body, name)
                || wgen
                    .else_body
                    .as_ref()
                    .is_some_and(|body| entries_mention(body, name))
        }
        Entry::Spread(expr) | Entry::Elem(expr) => expr_mentions(expr, name),
        Entry::ClassDef(_, _, parent, body) => {
            parent
                .as_deref()
                .is_some_and(|parent| type_name_mentions(parent, name))
                || entries_mention(body, name)
        }
        Entry::TypeAlias(_, ty) => type_mentions(ty, name),
    }
}

/// Whether a type name as written (`outer.Step`, `*Foo<Bar>?`, a quoted name)
/// contains `name` as an identifier, so a type resolved through that binding
/// counts as a mention.
fn type_name_mentions(type_name: &str, name: &str) -> bool {
    type_name
        .split(|c: char| !(c.is_alphanumeric() || c == '_' || c == '$'))
        .any(|token| token == name)
}

fn expr_mentions(expr: &Expr, name: &str) -> bool {
    match expr {
        Expr::Ident(ident) => ident == name,
        Expr::New(type_name, entries, generic_params) => {
            type_name
                .iter()
                .chain(generic_params)
                .any(|type_name| type_name_mentions(type_name, name))
                || entries_mention(entries, name)
        }
        Expr::ObjectBody(entries) => entries_mention(entries, name),
        Expr::InferredNew(ty, entries) => type_mentions(ty, name) || entries_mention(entries, name),
        Expr::Field(base, _) | Expr::NullSafeField(base, _) => expr_mentions(base, name),
        Expr::Index(base, index) | Expr::Binop(_, base, index) => {
            expr_mentions(base, name) || expr_mentions(index, name)
        }
        Expr::Call(callee, args) => {
            expr_mentions(callee, name) || args.iter().any(|arg| expr_mentions(arg, name))
        }
        Expr::If(cond, then_expr, else_expr) => {
            expr_mentions(cond, name)
                || expr_mentions(then_expr, name)
                || expr_mentions(else_expr, name)
        }
        Expr::Let(_, value, body) => expr_mentions(value, name) || expr_mentions(body, name),
        Expr::Is(value, ty) | Expr::As(value, ty) => {
            expr_mentions(value, name) || type_mentions(ty, name)
        }
        Expr::Lambda(_, value) => expr_mentions(value, name),
        Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => expr_mentions(value, name),
        Expr::StringInterpolation(parts) => parts.iter().any(|part| match part {
            StringInterpPart::Expr(expr) => expr_mentions(expr, name),
            StringInterpPart::Literal(_) => false,
        }),
        Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => false,
    }
}

/// Whether an expression evaluated directly as a Mapping entry needs the
/// Mapping's `this`. Nested objects bind their own receiver, while lambdas
/// retain the direct entry's lexical receiver.
pub(super) fn mapping_entry_mentions_this(expr: &Expr) -> bool {
    match expr {
        Expr::Ident(name) => name == "this",
        Expr::Field(base, _) | Expr::NullSafeField(base, _) => mapping_entry_mentions_this(base),
        Expr::Index(base, index) | Expr::Binop(_, base, index) => {
            mapping_entry_mentions_this(base) || mapping_entry_mentions_this(index)
        }
        Expr::Call(callee, args) => {
            mapping_entry_mentions_this(callee) || args.iter().any(mapping_entry_mentions_this)
        }
        Expr::If(cond, then_expr, else_expr) => {
            mapping_entry_mentions_this(cond)
                || mapping_entry_mentions_this(then_expr)
                || mapping_entry_mentions_this(else_expr)
        }
        Expr::Let(name, value, body) => {
            mapping_entry_mentions_this(value)
                || (name != "this" && mapping_entry_mentions_this(body))
        }
        Expr::Lambda(params, body) => {
            !params.iter().any(|param| param == "this") && mapping_entry_mentions_this(body)
        }
        // A constructed or amended object provides its own `this`; a type
        // constraint likewise binds `this` to the checked value.
        Expr::New(..) | Expr::InferredNew(..) | Expr::ObjectBody(..) => false,
        Expr::Is(value, _) | Expr::As(value, _) => mapping_entry_mentions_this(value),
        Expr::Unop(_, value)
        | Expr::Throw(value)
        | Expr::Trace(value, _)
        | Expr::Read(value, _)
        | Expr::ReadOrNull(value, _)
        | Expr::ReadGlob(value, _) => mapping_entry_mentions_this(value),
        Expr::StringInterpolation(parts) => parts.iter().any(|part| match part {
            StringInterpPart::Expr(expr) => mapping_entry_mentions_this(expr),
            StringInterpPart::Literal(_) => false,
        }),
        Expr::Null
        | Expr::Bool(_)
        | Expr::Int(_)
        | Expr::Float(_)
        | Expr::String(_)
        | Expr::Import(..)
        | Expr::ImportGlob(..) => false,
    }
}

/// How a class body's expressions reach the class instance: `this` in the
/// body itself (and in its methods), `outer` one object body down, and
/// `outer.outer` (and so on) further down. Names
/// read as `ref.name` or `ref["name"]` go to `members`; any other use of the
/// reference (bound by a `let`, passed to a call, indexed by a computed key)
/// sets `escapes`, after which any member may be read.
struct InstanceReads {
    members: HashSet<String>,
    escapes: bool,
}

impl InstanceReads {
    /// How many object bodies below the class body `expr` names the
    /// instance, if it is `this` or a chain of `outer`s.
    fn reference_depth(expr: &Expr) -> Option<usize> {
        match expr {
            Expr::Ident(name) if name == "this" => Some(0),
            Expr::Ident(name) if name == "outer" => Some(1),
            Expr::Field(base, field) if field == "outer" => match Self::reference_depth(base)? {
                0 => None,
                depth => Some(depth + 1),
            },
            _ => None,
        }
    }

    fn entries(&mut self, entries: &[Entry], depth: usize) {
        for entry in entries {
            match entry {
                Entry::Property(prop) => {
                    if let Some(value) = &prop.value {
                        self.expr(value, depth);
                    }
                    // A property's object body is one level further down.
                    if let Some(body) = &prop.body {
                        self.entries(body, depth + 1);
                    }
                }
                Entry::DynProperty(key, value) | Entry::Predicate(key, value) => {
                    self.expr(key, depth);
                    self.expr(value, depth);
                }
                Entry::Spread(expr) | Entry::Elem(expr) => self.expr(expr, depth),
                Entry::ForGenerator(fgen) => {
                    self.expr(&fgen.collection, depth);
                    self.entries(&fgen.body, depth);
                }
                Entry::WhenGenerator(wgen) => {
                    self.expr(&wgen.condition, depth);
                    self.entries(&wgen.body, depth);
                    if let Some(else_body) = &wgen.else_body {
                        self.entries(else_body, depth);
                    }
                }
                Entry::ClassDef(..) | Entry::TypeAlias(..) => {}
            }
        }
    }

    fn expr(&mut self, expr: &Expr, depth: usize) {
        let is_reference = |expr: &Expr| Self::reference_depth(expr) == Some(depth);
        match expr {
            // The instance used as a value.
            _ if is_reference(expr) => self.escapes = true,
            Expr::Field(base, field) | Expr::NullSafeField(base, field) if is_reference(base) => {
                self.members.insert(field.clone());
            }
            Expr::Index(base, index) if is_reference(base) => match index.as_ref() {
                Expr::String(key) => {
                    self.members.insert(key.to_string());
                }
                index => {
                    self.escapes = true;
                    self.expr(index, depth);
                }
            },
            // `this` or an `outer` chain naming some other object.
            Expr::Field(base, _) | Expr::NullSafeField(base, _)
                if Self::reference_depth(base).is_some() => {}
            Expr::Ident(_) => {}
            Expr::New(_, entries, _)
            | Expr::ObjectBody(entries)
            | Expr::InferredNew(_, entries) => self.entries(entries, depth + 1),
            Expr::Field(base, _) | Expr::NullSafeField(base, _) => self.expr(base, depth),
            Expr::Index(left, right) | Expr::Binop(_, left, right) => {
                self.expr(left, depth);
                self.expr(right, depth);
            }
            Expr::Call(callee, args) => {
                self.expr(callee, depth);
                for arg in args {
                    self.expr(arg, depth);
                }
            }
            Expr::If(cond, then_expr, else_expr) => {
                self.expr(cond, depth);
                self.expr(then_expr, depth);
                self.expr(else_expr, depth);
            }
            Expr::Let(_, value, body) => {
                self.expr(value, depth);
                self.expr(body, depth);
            }
            // A type's constraints bind `this` to the checked value.
            Expr::Is(value, _) | Expr::As(value, _) => self.expr(value, depth),
            Expr::Lambda(_, value) => self.expr(value, depth),
            Expr::Unop(_, value)
            | Expr::Throw(value)
            | Expr::Trace(value, _)
            | Expr::Read(value, _)
            | Expr::ReadOrNull(value, _)
            | Expr::ReadGlob(value, _) => self.expr(value, depth),
            Expr::StringInterpolation(parts) => {
                for part in parts {
                    if let StringInterpPart::Expr(expr) = part {
                        self.expr(expr, depth);
                    }
                }
            }
            Expr::Null
            | Expr::Bool(_)
            | Expr::Int(_)
            | Expr::Float(_)
            | Expr::String(_)
            | Expr::Import(..)
            | Expr::ImportGlob(..) => {}
        }
    }
}

pub(super) fn type_mentions(ty: &crate::parser::TypeExpr, name: &str) -> bool {
    match ty {
        crate::parser::TypeExpr::Constrained(base, constraint) => {
            type_name_mentions(base, name) || expr_mentions(constraint, name)
        }
        crate::parser::TypeExpr::Nullable(inner) => type_mentions(inner, name),
        crate::parser::TypeExpr::Union(types) => types.iter().any(|ty| type_mentions(ty, name)),
        crate::parser::TypeExpr::Generic(base, types) => {
            type_name_mentions(base, name) || types.iter().any(|ty| type_mentions(ty, name))
        }
        crate::parser::TypeExpr::Named(type_name) => type_name_mentions(type_name, name),
    }
}