rust-analyzer/crates/ra_hir/src/nameres/collector.rs

use ra_db::FileId;
use ra_syntax::ast;
use rustc_hash::FxHashMap;
use test_utils::tested_by;

use crate::{
    db::DefDatabase,
    either::Either,
    ids::{AstItemDef, LocationCtx, MacroCallId, MacroCallLoc, MacroDefId, MacroFileKind},
    name::MACRO_RULES,
    nameres::{
        diagnostics::DefDiagnostic,
        mod_resolution::{resolve_submodule, ParentModule},
        raw, CrateDefMap, CrateModuleId, ItemOrMacro, ModuleData, ModuleDef, PerNs,
        ReachedFixedPoint, Resolution, ResolveMode,
    },
    AstId, Const, Enum, Function, HirFileId, MacroDef, Module, Name, Path, Static, Struct, Trait,
    TypeAlias, Union,
};

pub(super) fn collect_defs(db: &impl DefDatabase, mut def_map: CrateDefMap) -> CrateDefMap {
    // populate external prelude
    for dep in def_map.krate.dependencies(db) {
        log::debug!("crate dep {:?} -> {:?}", dep.name, dep.krate);
        if let Some(module) = dep.krate.root_module(db) {
            def_map.extern_prelude.insert(dep.name.clone(), module.into());
        }
        // look for the prelude
        if def_map.prelude.is_none() {
            let map = db.crate_def_map(dep.krate);
            if map.prelude.is_some() {
                def_map.prelude = map.prelude;
            }
        }
    }

    let mut collector = DefCollector {
        db,
        def_map,
        glob_imports: FxHashMap::default(),
        unresolved_imports: Vec::new(),
        unexpanded_macros: Vec::new(),
        macro_stack_monitor: MacroStackMonitor::default(),
    };
    collector.collect();
    collector.finish()
}

#[derive(Default)]
struct MacroStackMonitor {
    counts: FxHashMap<MacroDefId, u32>,

    /// Mainly use for test
    validator: Option<Box<dyn Fn(u32) -> bool>>,
}

impl MacroStackMonitor {
    fn increase(&mut self, macro_def_id: MacroDefId) {
        *self.counts.entry(macro_def_id).or_default() += 1;
    }

    fn decrease(&mut self, macro_def_id: MacroDefId) {
        *self.counts.entry(macro_def_id).or_default() -= 1;
    }

    fn is_poison(&self, macro_def_id: MacroDefId) -> bool {
        let cur = *self.counts.get(&macro_def_id).unwrap_or(&0);

        if let Some(validator) = &self.validator {
            validator(cur)
        } else {
            cur > 100
        }
    }
}

/// Walks the tree of module recursively
struct DefCollector<DB> {
    db: DB,
    def_map: CrateDefMap,
    glob_imports: FxHashMap<CrateModuleId, Vec<(CrateModuleId, raw::ImportId)>>,
    unresolved_imports: Vec<(CrateModuleId, raw::ImportId, raw::ImportData)>,
    unexpanded_macros: Vec<(CrateModuleId, AstId<ast::MacroCall>, Path)>,

    /// Some macro use `$tt:tt which mean we have to handle the macro perfectly
    /// To prevent stack overflow, we add a deep counter here for prevent that.
    macro_stack_monitor: MacroStackMonitor,
}

impl<'a, DB> DefCollector<&'a DB>
where
    DB: DefDatabase,
{
    fn collect(&mut self) {
        let crate_graph = self.db.crate_graph();
        let file_id = crate_graph.crate_root(self.def_map.krate.crate_id());
        let raw_items = self.db.raw_items(file_id.into());
        let module_id = self.def_map.root;
        self.def_map.modules[module_id].definition = Some(file_id);
        ModCollector {
            def_collector: &mut *self,
            module_id,
            file_id: file_id.into(),
            raw_items: &raw_items,
            parent_module: None,
        }
        .collect(raw_items.items());

        // main name resolution fixed-point loop.
        let mut i = 0;
        loop {
            self.db.check_canceled();
            match (self.resolve_imports(), self.resolve_macros()) {
                (ReachedFixedPoint::Yes, ReachedFixedPoint::Yes) => break,
                _ => i += 1,
            }
            if i == 1000 {
                log::error!("diverging name resolution");
                break;
            }
        }

        let unresolved_imports = std::mem::replace(&mut self.unresolved_imports, Vec::new());
        // show unresolved imports in completion, etc
        for (module_id, import, import_data) in unresolved_imports {
            self.record_resolved_import(module_id, Either::A(PerNs::none()), import, &import_data)
        }
    }

    fn define_macro(
        &mut self,
        module_id: CrateModuleId,
        name: Name,
        macro_id: MacroDefId,
        export: bool,
    ) {
        let def = Either::B(MacroDef { id: macro_id });

        // In Rust, `#[macro_export]` macros are unconditionally visible at the
        // crate root, even if the parent modules is **not** visible.
        if export {
            self.update(self.def_map.root, None, &[(name.clone(), def.clone())]);

            // Exported macros are collected in crate level ready for
            // glob import with `#[macro_use]`.
            self.def_map.exported_macros.insert(name.clone(), macro_id);
        }
        self.update(module_id, None, &[(name.clone(), def)]);
        self.define_textual_macro(module_id, name.clone(), macro_id);
    }

    /// Define a macro in current textual scope.
    ///
    /// We use a map `textual_macros` to store all textual macros visable per module.
    /// It will clone all macros from parent textual scope, whose definition is prior to
    /// the definition of current module.
    /// And also, `macro_use` on a module will import all textual macros visable inside to
    /// current textual scope, with possible shadowing.
    ///
    /// In a single module, the order of definition/usage of textual scoped macros matters.
    /// But we ignore it here to make it easy to implement.
    fn define_textual_macro(&mut self, module_id: CrateModuleId, name: Name, macro_id: MacroDefId) {
        // Always shadowing
        self.def_map.modules[module_id]
            .scope
            .textual_macros
            .insert(name, MacroDef { id: macro_id });
    }

    /// Import macros from `#[macro_use] extern crate`.
    ///
    /// They are non-scoped, and will only be inserted into mutable `global_macro_scope`.
    fn import_macros_from_extern_crate(
        &mut self,
        current_module_id: CrateModuleId,
        import: &raw::ImportData,
    ) {
        log::debug!(
            "importing macros from extern crate: {:?} ({:?})",
            import,
            self.def_map.edition,
        );

        let res = self.def_map.resolve_name_in_extern_prelude(
            &import
                .path
                .as_ident()
                .expect("extern crate should have been desugared to one-element path"),
        );

        if let Some(ModuleDef::Module(m)) = res.take_types() {
            tested_by!(macro_rules_from_other_crates_are_visible_with_macro_use);
            self.import_all_macros_exported(current_module_id, m);
        }
    }

    fn import_all_macros_exported(&mut self, current_module_id: CrateModuleId, module: Module) {
        let item_map = self.db.crate_def_map(module.krate);
        for (name, &macro_id) in &item_map.exported_macros {
            self.define_textual_macro(current_module_id, name.clone(), macro_id);
        }
    }

    fn resolve_imports(&mut self) -> ReachedFixedPoint {
        let mut imports = std::mem::replace(&mut self.unresolved_imports, Vec::new());
        let mut resolved = Vec::new();
        imports.retain(|(module_id, import, import_data)| {
            let (def, fp) = self.resolve_import(*module_id, import_data);
            if fp == ReachedFixedPoint::Yes {
                resolved.push((*module_id, def, *import, import_data.clone()))
            }
            fp == ReachedFixedPoint::No
        });
        self.unresolved_imports = imports;
        // Resolves imports, filling-in module scopes
        let result =
            if resolved.is_empty() { ReachedFixedPoint::Yes } else { ReachedFixedPoint::No };
        for (module_id, def, import, import_data) in resolved {
            self.record_resolved_import(module_id, def, import, &import_data)
        }
        result
    }

    fn resolve_import(
        &self,
        module_id: CrateModuleId,
        import: &raw::ImportData,
    ) -> (ItemOrMacro, ReachedFixedPoint) {
        log::debug!("resolving import: {:?} ({:?})", import, self.def_map.edition);
        if import.is_extern_crate {
            let res = self.def_map.resolve_name_in_extern_prelude(
                &import
                    .path
                    .as_ident()
                    .expect("extern crate should have been desugared to one-element path"),
            );
            (Either::A(res), ReachedFixedPoint::Yes)
        } else {
            let res = self.def_map.resolve_path_fp_with_macro(
                self.db,
                ResolveMode::Import,
                module_id,
                &import.path,
            );

            (res.resolved_def, res.reached_fixedpoint)
        }
    }

    fn record_resolved_import(
        &mut self,
        module_id: CrateModuleId,
        def: ItemOrMacro,
        import_id: raw::ImportId,
        import: &raw::ImportData,
    ) {
        if import.is_glob {
            log::debug!("glob import: {:?}", import);
            match def.a().and_then(|item| item.take_types()) {
                Some(ModuleDef::Module(m)) => {
                    if import.is_prelude {
                        tested_by!(std_prelude);
                        self.def_map.prelude = Some(m);
                    } else if m.krate != self.def_map.krate {
                        tested_by!(glob_across_crates);
                        // glob import from other crate => we can just import everything once
                        let item_map = self.db.crate_def_map(m.krate);
                        let scope = &item_map[m.module_id].scope;
                        let items = scope
                            .items
                            .iter()
                            .map(|(name, res)| (name.clone(), Either::A(res.clone())));
                        let macros =
                            scope.macros.iter().map(|(name, res)| (name.clone(), Either::B(*res)));

                        let all = items.chain(macros).collect::<Vec<_>>();
                        self.update(module_id, Some(import_id), &all);
                    } else {
                        // glob import from same crate => we do an initial
                        // import, and then need to propagate any further
                        // additions
                        let scope = &self.def_map[m.module_id].scope;
                        let items = scope
                            .items
                            .iter()
                            .map(|(name, res)| (name.clone(), Either::A(res.clone())));
                        let macros =
                            scope.macros.iter().map(|(name, res)| (name.clone(), Either::B(*res)));

                        let all = items.chain(macros).collect::<Vec<_>>();

                        self.update(module_id, Some(import_id), &all);
                        // record the glob import in case we add further items
                        self.glob_imports
                            .entry(m.module_id)
                            .or_default()
                            .push((module_id, import_id));
                    }
                }
                Some(ModuleDef::Enum(e)) => {
                    tested_by!(glob_enum);
                    // glob import from enum => just import all the variants
                    let variants = e.variants(self.db);
                    let resolutions = variants
                        .into_iter()
                        .filter_map(|variant| {
                            let res = Resolution {
                                def: PerNs::both(variant.into(), variant.into()),
                                import: Some(import_id),
                            };
                            let name = variant.name(self.db)?;
                            Some((name, Either::A(res)))
                        })
                        .collect::<Vec<_>>();
                    self.update(module_id, Some(import_id), &resolutions);
                }
                Some(d) => {
                    log::debug!("glob import {:?} from non-module/enum {:?}", import, d);
                }
                None => {
                    log::debug!("glob import {:?} didn't resolve as type", import);
                }
            }
        } else {
            match import.path.segments.last() {
                Some(last_segment) => {
                    let name = import.alias.clone().unwrap_or_else(|| last_segment.name.clone());
                    log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def);

                    // extern crates in the crate root are special-cased to insert entries into the extern prelude: rust-lang/rust#54658
                    if import.is_extern_crate && module_id == self.def_map.root {
                        if let Some(def) = def.a().and_then(|item| item.take_types()) {
                            self.def_map.extern_prelude.insert(name.clone(), def);
                        }
                    }

                    let resolution = match def {
                        Either::A(item) => {
                            Either::A(Resolution { def: item, import: Some(import_id) })
                        }
                        Either::B(macro_) => Either::B(macro_),
                    };

                    self.update(module_id, Some(import_id), &[(name, resolution)]);
                }
                None => tested_by!(bogus_paths),
            }
        }
    }

    fn update(
        &mut self,
        module_id: CrateModuleId,
        import: Option<raw::ImportId>,
        resolutions: &[(Name, Either<Resolution, MacroDef>)],
    ) {
        self.update_recursive(module_id, import, resolutions, 0)
    }

    fn update_recursive(
        &mut self,
        module_id: CrateModuleId,
        import: Option<raw::ImportId>,
        resolutions: &[(Name, Either<Resolution, MacroDef>)],
        depth: usize,
    ) {
        if depth > 100 {
            // prevent stack overflows (but this shouldn't be possible)
            panic!("infinite recursion in glob imports!");
        }
        let module_items = &mut self.def_map.modules[module_id].scope;
        let mut changed = false;
        for (name, res) in resolutions {
            match res {
                // item
                Either::A(res) => {
                    let existing = module_items.items.entry(name.clone()).or_default();

                    if existing.def.types.is_none() && res.def.types.is_some() {
                        existing.def.types = res.def.types;
                        existing.import = import.or(res.import);
                        changed = true;
                    }
                    if existing.def.values.is_none() && res.def.values.is_some() {
                        existing.def.values = res.def.values;
                        existing.import = import.or(res.import);
                        changed = true;
                    }

                    if existing.def.is_none()
                        && res.def.is_none()
                        && existing.import.is_none()
                        && res.import.is_some()
                    {
                        existing.import = res.import;
                    }
                }
                // macro
                Either::B(res) => {
                    // Always shadowing
                    module_items.macros.insert(name.clone(), *res);
                }
            }
        }

        if !changed {
            return;
        }
        let glob_imports = self
            .glob_imports
            .get(&module_id)
            .into_iter()
            .flat_map(|v| v.iter())
            .cloned()
            .collect::<Vec<_>>();
        for (glob_importing_module, glob_import) in glob_imports {
            // We pass the glob import so that the tracked import in those modules is that glob import
            self.update_recursive(glob_importing_module, Some(glob_import), resolutions, depth + 1);
        }
    }

    fn resolve_macros(&mut self) -> ReachedFixedPoint {
        let mut macros = std::mem::replace(&mut self.unexpanded_macros, Vec::new());
        let mut resolved = Vec::new();
        let mut res = ReachedFixedPoint::Yes;
        macros.retain(|(module_id, ast_id, path)| {
            let resolved_res = self.def_map.resolve_path_fp_with_macro(
                self.db,
                ResolveMode::Other,
                *module_id,
                path,
            );

            if let Some(def) = resolved_res.resolved_def.b() {
                let call_id = MacroCallLoc { def: def.id, ast_id: *ast_id }.id(self.db);
                resolved.push((*module_id, call_id, def.id));
                res = ReachedFixedPoint::No;
                return false;
            }

            if resolved_res.reached_fixedpoint != ReachedFixedPoint::Yes {
                let crate_name = &path.segments[0].name;

                // FIXME:
                // $crate are not handled in resolver right now
                if crate_name.to_string() == "$crate" {
                    return true;
                }

                // FIXME:
                // Currently `#[cfg(test)]` are ignored and cargo-metadata do not insert
                // dev-dependencies of dependencies. For example,
                // if we depend on parking lot, and parking lot has a dev-dependency on lazy_static.
                // Then `lazy_static` wil not included in `CrateGraph`
                // We can fix that by proper handling `cfg(test)`.
                //
                // So right now we set the fixpoint to No only if its crate is in CrateGraph
                // See issue #1282 for details
                let krate =
                    match self.def_map.resolve_name_in_extern_prelude(crate_name).take_types() {
                        Some(ModuleDef::Module(m)) => m.krate(self.db),
                        _ => return true,
                    };
                if krate.is_none() {
                    return true;
                }

                res = resolved_res.reached_fixedpoint;
            }

            true
        });

        self.unexpanded_macros = macros;

        for (module_id, macro_call_id, macro_def_id) in resolved {
            self.collect_macro_expansion(module_id, macro_call_id, macro_def_id);
        }

        res
    }

    fn collect_macro_expansion(
        &mut self,
        module_id: CrateModuleId,
        macro_call_id: MacroCallId,
        macro_def_id: MacroDefId,
    ) {
        if self.def_map.poison_macros.contains(&macro_def_id) {
            return;
        }

        self.macro_stack_monitor.increase(macro_def_id);

        if !self.macro_stack_monitor.is_poison(macro_def_id) {
            let file_id: HirFileId = macro_call_id.as_file(MacroFileKind::Items);
            let raw_items = self.db.raw_items(file_id);
            ModCollector {
                def_collector: &mut *self,
                file_id,
                module_id,
                raw_items: &raw_items,
                parent_module: None,
            }
            .collect(raw_items.items());
        } else {
            log::error!("Too deep macro expansion: {:?}", macro_call_id);
            self.def_map.poison_macros.insert(macro_def_id);
        }

        self.macro_stack_monitor.decrease(macro_def_id);
    }

    fn finish(self) -> CrateDefMap {
        self.def_map
    }
}

/// Walks a single module, populating defs, imports and macros
struct ModCollector<'a, D> {
    def_collector: D,
    module_id: CrateModuleId,
    file_id: HirFileId,
    raw_items: &'a raw::RawItems,
    parent_module: Option<ParentModule<'a>>,
}

impl<DB> ModCollector<'_, &'_ mut DefCollector<&'_ DB>>
where
    DB: DefDatabase,
{
    fn collect(&mut self, items: &[raw::RawItem]) {
        // Prelude module is always considered to be `#[macro_use]`.
        if let Some(prelude_module) = self.def_collector.def_map.prelude {
            if prelude_module.krate != self.def_collector.def_map.krate {
                tested_by!(prelude_is_macro_use);
                self.def_collector.import_all_macros_exported(self.module_id, prelude_module);
            }
        }

        // This should be processed eagerly instead of deferred to resolving.
        // `#[macro_use] extern crate` is hoisted to imports macros before collecting
        // any other items.
        for item in items {
            if let raw::RawItem::Import(import_id) = *item {
                let import = self.raw_items[import_id].clone();
                if import.is_extern_crate && import.is_macro_use {
                    self.def_collector.import_macros_from_extern_crate(self.module_id, &import);
                }
            }
        }

        for item in items {
            match *item {
                raw::RawItem::Module(m) => self.collect_module(&self.raw_items[m]),
                raw::RawItem::Import(import_id) => self.def_collector.unresolved_imports.push((
                    self.module_id,
                    import_id,
                    self.raw_items[import_id].clone(),
                )),
                raw::RawItem::Def(def) => self.define_def(&self.raw_items[def]),
                raw::RawItem::Macro(mac) => self.collect_macro(&self.raw_items[mac]),
            }
        }
    }

    fn collect_module(&mut self, module: &raw::ModuleData) {
        match module {
            // inline module, just recurse
            raw::ModuleData::Definition { name, items, ast_id, attr_path, is_macro_use } => {
                let module_id =
                    self.push_child_module(name.clone(), ast_id.with_file_id(self.file_id), None);
                let parent_module = ParentModule { name, attr_path: attr_path.as_ref() };

                ModCollector {
                    def_collector: &mut *self.def_collector,
                    module_id,
                    file_id: self.file_id,
                    raw_items: self.raw_items,
                    parent_module: Some(parent_module),
                }
                .collect(&*items);
                if *is_macro_use {
                    self.import_all_textual_macros(module_id);
                }
            }
            // out of line module, resolve, parse and recurse
            raw::ModuleData::Declaration { name, ast_id, attr_path, is_macro_use } => {
                let ast_id = ast_id.with_file_id(self.file_id);
                let is_root = self.def_collector.def_map.modules[self.module_id].parent.is_none();
                match resolve_submodule(
                    self.def_collector.db,
                    self.file_id,
                    name,
                    is_root,
                    attr_path.as_ref(),
                    self.parent_module,
                ) {
                    Ok(file_id) => {
                        let module_id = self.push_child_module(name.clone(), ast_id, Some(file_id));
                        let raw_items = self.def_collector.db.raw_items(file_id.into());
                        ModCollector {
                            def_collector: &mut *self.def_collector,
                            module_id,
                            file_id: file_id.into(),
                            raw_items: &raw_items,
                            parent_module: None,
                        }
                        .collect(raw_items.items());
                        if *is_macro_use {
                            self.import_all_textual_macros(module_id);
                        }
                    }
                    Err(candidate) => self.def_collector.def_map.diagnostics.push(
                        DefDiagnostic::UnresolvedModule {
                            module: self.module_id,
                            declaration: ast_id,
                            candidate,
                        },
                    ),
                };
            }
        }
    }

    fn push_child_module(
        &mut self,
        name: Name,
        declaration: AstId<ast::Module>,
        definition: Option<FileId>,
    ) -> CrateModuleId {
        let modules = &mut self.def_collector.def_map.modules;
        let res = modules.alloc(ModuleData::default());
        modules[res].parent = Some(self.module_id);
        modules[res].declaration = Some(declaration);
        modules[res].definition = definition;
        modules[res].scope.textual_macros = modules[self.module_id].scope.textual_macros.clone();
        modules[self.module_id].children.insert(name.clone(), res);
        let resolution = Resolution {
            def: PerNs::types(
                Module { krate: self.def_collector.def_map.krate, module_id: res }.into(),
            ),
            import: None,
        };
        self.def_collector.update(self.module_id, None, &[(name, Either::A(resolution))]);
        res
    }

    fn define_def(&mut self, def: &raw::DefData) {
        let module = Module { krate: self.def_collector.def_map.krate, module_id: self.module_id };
        let ctx = LocationCtx::new(self.def_collector.db, module, self.file_id);

        macro_rules! def {
            ($kind:ident, $ast_id:ident) => {
                $kind { id: AstItemDef::from_ast_id(ctx, $ast_id) }.into()
            };
        }
        let name = def.name.clone();
        let def: PerNs<ModuleDef> = match def.kind {
            raw::DefKind::Function(ast_id) => PerNs::values(def!(Function, ast_id)),
            raw::DefKind::Struct(ast_id) => {
                let s = def!(Struct, ast_id);
                PerNs::both(s, s)
            }
            raw::DefKind::Union(ast_id) => {
                let s = def!(Union, ast_id);
                PerNs::both(s, s)
            }
            raw::DefKind::Enum(ast_id) => PerNs::types(def!(Enum, ast_id)),
            raw::DefKind::Const(ast_id) => PerNs::values(def!(Const, ast_id)),
            raw::DefKind::Static(ast_id) => PerNs::values(def!(Static, ast_id)),
            raw::DefKind::Trait(ast_id) => PerNs::types(def!(Trait, ast_id)),
            raw::DefKind::TypeAlias(ast_id) => PerNs::types(def!(TypeAlias, ast_id)),
        };
        let resolution = Resolution { def, import: None };
        self.def_collector.update(self.module_id, None, &[(name, Either::A(resolution))])
    }

    fn collect_macro(&mut self, mac: &raw::MacroData) {
        // Case 1: macro rules, define a macro in crate-global mutable scope
        if is_macro_rules(&mac.path) {
            if let Some(name) = &mac.name {
                let macro_id = MacroDefId(mac.ast_id.with_file_id(self.file_id));
                self.def_collector.define_macro(self.module_id, name.clone(), macro_id, mac.export)
            }
            return;
        }

        let ast_id = mac.ast_id.with_file_id(self.file_id);

        // Case 2: try to resolve in textual scope and expand macro_rules, triggering
        // recursive item collection.
        if let Some(macro_def) = mac.path.as_ident().and_then(|name| {
            self.def_collector.def_map[self.module_id].scope.get_textual_macro(&name)
        }) {
            let def = macro_def.id;
            let macro_call_id = MacroCallLoc { def, ast_id }.id(self.def_collector.db);

            self.def_collector.collect_macro_expansion(self.module_id, macro_call_id, def);
            return;
        }

        // Case 3: path to a macro from another crate, expand during name resolution
        self.def_collector.unexpanded_macros.push((self.module_id, ast_id, mac.path.clone()))
    }

    fn import_all_textual_macros(&mut self, module_id: CrateModuleId) {
        let macros = self.def_collector.def_map[module_id].scope.textual_macros.clone();
        for (name, macro_) in macros {
            self.def_collector.define_textual_macro(self.module_id, name.clone(), macro_.id);
        }
    }
}

fn is_macro_rules(path: &Path) -> bool {
    path.as_ident() == Some(&MACRO_RULES)
}

#[cfg(test)]
mod tests {
    use ra_db::SourceDatabase;

    use super::*;
    use crate::{db::DefDatabase, mock::MockDatabase, Crate};
    use ra_arena::Arena;
    use rustc_hash::FxHashSet;

    fn do_collect_defs(
        db: &impl DefDatabase,
        def_map: CrateDefMap,
        monitor: MacroStackMonitor,
    ) -> CrateDefMap {
        let mut collector = DefCollector {
            db,
            def_map,
            glob_imports: FxHashMap::default(),
            unresolved_imports: Vec::new(),
            unexpanded_macros: Vec::new(),
            macro_stack_monitor: monitor,
        };
        collector.collect();
        collector.finish()
    }

    fn do_limited_resolve(code: &str, limit: u32, poison_limit: u32) -> CrateDefMap {
        let (db, _source_root, _) = MockDatabase::with_single_file(&code);
        let crate_id = db.crate_graph().iter().next().unwrap();
        let krate = Crate { crate_id };

        let def_map = {
            let edition = krate.edition(&db);
            let mut modules: Arena<CrateModuleId, ModuleData> = Arena::default();
            let root = modules.alloc(ModuleData::default());
            CrateDefMap {
                krate,
                edition,
                extern_prelude: FxHashMap::default(),
                prelude: None,
                root,
                modules,
                poison_macros: FxHashSet::default(),
                exported_macros: FxHashMap::default(),
                diagnostics: Vec::new(),
            }
        };

        let mut monitor = MacroStackMonitor::default();
        monitor.validator = Some(Box::new(move |count| {
            assert!(count < limit);
            count >= poison_limit
        }));

        do_collect_defs(&db, def_map, monitor)
    }

    #[test]
    fn test_macro_expand_limit_width() {
        do_limited_resolve(
            r#"
        macro_rules! foo {
            ($($ty:ty)*) => { foo!($($ty)*, $($ty)*); }
        }
foo!(KABOOM);
        "#,
            16,
            1000,
        );
    }

    #[test]
    fn test_macro_expand_poisoned() {
        let def = do_limited_resolve(
            r#"
        macro_rules! foo {
            ($ty:ty) => { foo!($ty); }
        }
foo!(KABOOM);
        "#,
            100,
            16,
        );

        assert_eq!(def.poison_macros.len(), 1);
    }

    #[test]
    fn test_macro_expand_normal() {
        let def = do_limited_resolve(
            r#"
        macro_rules! foo {
            ($ident:ident) => { struct $ident {} }
        }
foo!(Bar);
        "#,
            16,
            16,
        );

        assert_eq!(def.poison_macros.len(), 0);
    }
}