1 files changed, 844 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
new file mode 100644
index 000000000..3b61d9895
--- /dev/null
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -0,0 +1,844 @@
+//! FIXME: write short doc here
+
+use hir_expand::{
+    name::{self, AsName, Name},
+    HirFileId, MacroCallId, MacroCallLoc, MacroDefId, MacroFileKind,
+};
+use ra_cfg::CfgOptions;
+use ra_db::{CrateId, FileId};
+use ra_syntax::{ast, SmolStr};
+use rustc_hash::FxHashMap;
+use test_utils::tested_by;
+
+use crate::{
+    attr::Attr,
+    db::DefDatabase2,
+    nameres::{
+        diagnostics::DefDiagnostic, mod_resolution::ModDir, per_ns::PerNs, raw, CrateDefMap,
+        ModuleData, ReachedFixedPoint, Resolution, ResolveMode,
+    },
+    path::{Path, PathKind},
+    AdtId, AstId, AstItemDef, ConstId, CrateModuleId, EnumId, EnumVariantId, FunctionId,
+    LocationCtx, ModuleDefId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, UnionId,
+};
+
+pub(super) fn collect_defs(db: &impl DefDatabase2, mut def_map: CrateDefMap) -> CrateDefMap {
+    let crate_graph = db.crate_graph();
+
+    // populate external prelude
+    for dep in crate_graph.dependencies(def_map.krate) {
+        let dep_def_map = db.crate_def_map(dep.crate_id);
+        log::debug!("crate dep {:?} -> {:?}", dep.name, dep.crate_id);
+        def_map.extern_prelude.insert(
+            dep.as_name(),
+            ModuleId { krate: dep.crate_id, module_id: dep_def_map.root }.into(),
+        );
+
+        // look for the prelude
+        if def_map.prelude.is_none() {
+            let map = db.crate_def_map(dep.crate_id);
+            if map.prelude.is_some() {
+                def_map.prelude = map.prelude;
+            }
+        }
+    }
+
+    let cfg_options = crate_graph.cfg_options(def_map.krate);
+
+    let mut collector = DefCollector {
+        db,
+        def_map,
+        glob_imports: FxHashMap::default(),
+        unresolved_imports: Vec::new(),
+        unexpanded_macros: Vec::new(),
+        mod_dirs: FxHashMap::default(),
+        macro_stack_monitor: MacroStackMonitor::default(),
+        cfg_options,
+    };
+    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<'a, DB> {
+    db: &'a 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)>,
+    mod_dirs: FxHashMap<CrateModuleId, ModDir>,
+
+    /// 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,
+
+    cfg_options: &'a CfgOptions,
+}
+
+impl<DB> DefCollector<'_, DB>
+where
+    DB: DefDatabase2,
+{
+    fn collect(&mut self) {
+        let crate_graph = self.db.crate_graph();
+        let file_id = crate_graph.crate_root(self.def_map.krate);
+        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,
+            mod_dir: ModDir::root(),
+        }
+        .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!("name resolution is stuck");
+                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, PerNs::none(), import, &import_data)
+        }
+    }
+
+    /// Define a macro with `macro_rules`.
+    ///
+    /// It will define the macro in legacy textual scope, and if it has `#[macro_export]`,
+    /// then it is also defined in the root module scope.
+    /// You can `use` or invoke it by `crate::macro_name` anywhere, before or after the definition.
+    ///
+    /// It is surprising that the macro will never be in the current module scope.
+    /// These code fails with "unresolved import/macro",
+    /// ```rust,compile_fail
+    /// mod m { macro_rules! foo { () => {} } }
+    /// use m::foo as bar;
+    /// ```
+    ///
+    /// ```rust,compile_fail
+    /// macro_rules! foo { () => {} }
+    /// self::foo!();
+    /// crate::foo!();
+    /// ```
+    ///
+    /// Well, this code compiles, bacause the plain path `foo` in `use` is searched
+    /// in the legacy textual scope only.
+    /// ```rust
+    /// macro_rules! foo { () => {} }
+    /// use foo as bar;
+    /// ```
+    fn define_macro(
+        &mut self,
+        module_id: CrateModuleId,
+        name: Name,
+        macro_: MacroDefId,
+        export: bool,
+    ) {
+        // Textual scoping
+        self.define_legacy_macro(module_id, name.clone(), macro_);
+
+        // Module scoping
+        // 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, Resolution::from_macro(macro_))]);
+        }
+    }
+
+    /// Define a legacy textual scoped macro in module
+    ///
+    /// We use a map `legacy_macros` to store all legacy textual scoped macros visable per module.
+    /// It will clone all macros from parent legacy scope, whose definition is prior to
+    /// the definition of current module.
+    /// And also, `macro_use` on a module will import all legacy macros visable inside to
+    /// current legacy scope, with possible shadowing.
+    fn define_legacy_macro(&mut self, module_id: CrateModuleId, name: Name, macro_: MacroDefId) {
+        // Always shadowing
+        self.def_map.modules[module_id].scope.legacy_macros.insert(name, macro_);
+    }
+
+    /// Import macros from `#[macro_use] extern crate`.
+    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(ModuleDefId::ModuleId(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.krate);
+        }
+    }
+
+    /// Import all exported macros from another crate
+    ///
+    /// Exported macros are just all macros in the root module scope.
+    /// Note that it contains not only all `#[macro_export]` macros, but also all aliases
+    /// created by `use` in the root module, ignoring the visibility of `use`.
+    fn import_all_macros_exported(&mut self, current_module_id: CrateModuleId, krate: CrateId) {
+        let def_map = self.db.crate_def_map(krate);
+        for (name, def) in def_map[def_map.root].scope.macros() {
+            // `macro_use` only bring things into legacy scope.
+            self.define_legacy_macro(current_module_id, name.clone(), def);
+        }
+    }
+
+    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,
+    ) -> (PerNs, 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"),
+            );
+            (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: PerNs,
+        import_id: raw::ImportId,
+        import: &raw::ImportData,
+    ) {
+        if import.is_glob {
+            log::debug!("glob import: {:?}", import);
+            match def.take_types() {
+                Some(ModuleDefId::ModuleId(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;
+
+                        // Module scoped macros is included
+                        let items = scope
+                            .items
+                            .iter()
+                            .map(|(name, res)| (name.clone(), res.clone()))
+                            .collect::<Vec<_>>();
+
+                        self.update(module_id, Some(import_id), &items);
+                    } 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;
+
+                        // Module scoped macros is included
+                        let items = scope
+                            .items
+                            .iter()
+                            .map(|(name, res)| (name.clone(), res.clone()))
+                            .collect::<Vec<_>>();
+
+                        self.update(module_id, Some(import_id), &items);
+                        // 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(ModuleDefId::AdtId(AdtId::EnumId(e))) => {
+                    tested_by!(glob_enum);
+                    // glob import from enum => just import all the variants
+                    let enum_data = self.db.enum_data(e);
+                    let resolutions = enum_data
+                        .variants
+                        .iter()
+                        .filter_map(|(local_id, variant_data)| {
+                            let name = variant_data.name.clone()?;
+                            let variant = EnumVariantId { parent: e, local_id };
+                            let res = Resolution {
+                                def: PerNs::both(variant.into(), variant.into()),
+                                import: Some(import_id),
+                            };
+                            Some((name, 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.take_types() {
+                            self.def_map.extern_prelude.insert(name.clone(), def);
+                        }
+                    }
+
+                    let resolution = Resolution { def, import: Some(import_id) };
+                    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, Resolution)],
+    ) {
+        self.update_recursive(module_id, import, resolutions, 0)
+    }
+
+    fn update_recursive(
+        &mut self,
+        module_id: CrateModuleId,
+        import: Option<raw::ImportId>,
+        resolutions: &[(Name, Resolution)],
+        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 {
+            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.macros.is_none() && res.def.macros.is_some() {
+                existing.def.macros = res.def.macros;
+                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;
+            }
+        }
+
+        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.get_macros() {
+                let call_id = self.db.intern_macro(MacroCallLoc { def, ast_id: *ast_id });
+                resolved.push((*module_id, call_id, def));
+                res = ReachedFixedPoint::No;
+                return false;
+            }
+
+            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);
+            let mod_dir = self.mod_dirs[&module_id].clone();
+            ModCollector {
+                def_collector: &mut *self,
+                file_id,
+                module_id,
+                raw_items: &raw_items,
+                mod_dir,
+            }
+            .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,
+    mod_dir: ModDir,
+}
+
+impl<DB> ModCollector<'_, &'_ mut DefCollector<'_, DB>>
+where
+    DB: DefDatabase2,
+{
+    fn collect(&mut self, items: &[raw::RawItem]) {
+        // Note: don't assert that inserted value is fresh: it's simply not true
+        // for macros.
+        self.def_collector.mod_dirs.insert(self.module_id, self.mod_dir.clone());
+
+        // 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.krate);
+            }
+        }
+
+        // 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 self.is_cfg_enabled(item.attrs()) {
+                if let raw::RawItemKind::Import(import_id) = item.kind {
+                    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 {
+            if self.is_cfg_enabled(item.attrs()) {
+                match item.kind {
+                    raw::RawItemKind::Module(m) => {
+                        self.collect_module(&self.raw_items[m], item.attrs())
+                    }
+                    raw::RawItemKind::Import(import_id) => self
+                        .def_collector
+                        .unresolved_imports
+                        .push((self.module_id, import_id, self.raw_items[import_id].clone())),
+                    raw::RawItemKind::Def(def) => self.define_def(&self.raw_items[def]),
+                    raw::RawItemKind::Macro(mac) => self.collect_macro(&self.raw_items[mac]),
+                }
+            }
+        }
+    }
+
+    fn collect_module(&mut self, module: &raw::ModuleData, attrs: &[Attr]) {
+        let path_attr = self.path_attr(attrs);
+        let is_macro_use = self.is_macro_use(attrs);
+        match module {
+            // inline module, just recurse
+            raw::ModuleData::Definition { name, items, ast_id } => {
+                let module_id =
+                    self.push_child_module(name.clone(), AstId::new(self.file_id, *ast_id), None);
+
+                ModCollector {
+                    def_collector: &mut *self.def_collector,
+                    module_id,
+                    file_id: self.file_id,
+                    raw_items: self.raw_items,
+                    mod_dir: self.mod_dir.descend_into_definition(name, path_attr),
+                }
+                .collect(&*items);
+                if is_macro_use {
+                    self.import_all_legacy_macros(module_id);
+                }
+            }
+            // out of line module, resolve, parse and recurse
+            raw::ModuleData::Declaration { name, ast_id } => {
+                let ast_id = AstId::new(self.file_id, *ast_id);
+                match self.mod_dir.resolve_declaration(
+                    self.def_collector.db,
+                    self.file_id,
+                    name,
+                    path_attr,
+                ) {
+                    Ok((file_id, mod_dir)) => {
+                        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,
+                            mod_dir,
+                        }
+                        .collect(raw_items.items());
+                        if is_macro_use {
+                            self.import_all_legacy_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.legacy_macros = modules[self.module_id].scope.legacy_macros.clone();
+        modules[self.module_id].children.insert(name.clone(), res);
+        let resolution = Resolution {
+            def: PerNs::types(
+                ModuleId { krate: self.def_collector.def_map.krate, module_id: res }.into(),
+            ),
+            import: None,
+        };
+        self.def_collector.update(self.module_id, None, &[(name, resolution)]);
+        res
+    }
+
+    fn define_def(&mut self, def: &raw::DefData) {
+        let module =
+            ModuleId { krate: self.def_collector.def_map.krate, module_id: self.module_id };
+        let ctx = LocationCtx::new(self.def_collector.db, module, self.file_id);
+
+        let name = def.name.clone();
+        let def: PerNs = match def.kind {
+            raw::DefKind::Function(ast_id) => {
+                PerNs::values(FunctionId::from_ast_id(ctx, ast_id).into())
+            }
+            raw::DefKind::Struct(ast_id) => {
+                let s = StructId::from_ast_id(ctx, ast_id).into();
+                PerNs::both(s, s)
+            }
+            raw::DefKind::Union(ast_id) => {
+                let s = UnionId::from_ast_id(ctx, ast_id).into();
+                PerNs::both(s, s)
+            }
+            raw::DefKind::Enum(ast_id) => PerNs::types(EnumId::from_ast_id(ctx, ast_id).into()),
+            raw::DefKind::Const(ast_id) => PerNs::values(ConstId::from_ast_id(ctx, ast_id).into()),
+            raw::DefKind::Static(ast_id) => {
+                PerNs::values(StaticId::from_ast_id(ctx, ast_id).into())
+            }
+            raw::DefKind::Trait(ast_id) => PerNs::types(TraitId::from_ast_id(ctx, ast_id).into()),
+            raw::DefKind::TypeAlias(ast_id) => {
+                PerNs::types(TypeAliasId::from_ast_id(ctx, ast_id).into())
+            }
+        };
+        let resolution = Resolution { def, import: None };
+        self.def_collector.update(self.module_id, None, &[(name, resolution)])
+    }
+
+    fn collect_macro(&mut self, mac: &raw::MacroData) {
+        let ast_id = AstId::new(self.file_id, mac.ast_id);
+
+        // 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 { ast_id, krate: self.def_collector.def_map.krate };
+                self.def_collector.define_macro(self.module_id, name.clone(), macro_id, mac.export);
+            }
+            return;
+        }
+
+        // Case 2: try to resolve in legacy 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_legacy_macro(&name)
+        }) {
+            let macro_call_id =
+                self.def_collector.db.intern_macro(MacroCallLoc { def: macro_def, ast_id });
+
+            self.def_collector.collect_macro_expansion(self.module_id, macro_call_id, macro_def);
+            return;
+        }
+
+        // Case 3: resolve in module scope, expand during name resolution.
+        // We rewrite simple path `macro_name` to `self::macro_name` to force resolve in module scope only.
+        let mut path = mac.path.clone();
+        if path.is_ident() {
+            path.kind = PathKind::Self_;
+        }
+        self.def_collector.unexpanded_macros.push((self.module_id, ast_id, path));
+    }
+
+    fn import_all_legacy_macros(&mut self, module_id: CrateModuleId) {
+        let macros = self.def_collector.def_map[module_id].scope.legacy_macros.clone();
+        for (name, macro_) in macros {
+            self.def_collector.define_legacy_macro(self.module_id, name.clone(), macro_);
+        }
+    }
+
+    fn is_cfg_enabled(&self, attrs: &[Attr]) -> bool {
+        attrs.iter().all(|attr| attr.is_cfg_enabled(&self.def_collector.cfg_options) != Some(false))
+    }
+
+    fn path_attr<'a>(&self, attrs: &'a [Attr]) -> Option<&'a SmolStr> {
+        attrs.iter().find_map(|attr| attr.as_path())
+    }
+
+    fn is_macro_use<'a>(&self, attrs: &'a [Attr]) -> bool {
+        attrs.iter().any(|attr| attr.is_simple_atom("macro_use"))
+    }
+}
+
+fn is_macro_rules(path: &Path) -> bool {
+    path.as_ident() == Some(&name::MACRO_RULES)
+}
+
+#[cfg(test)]
+mod tests {
+    use ra_arena::Arena;
+    use ra_db::{fixture::WithFixture, SourceDatabase};
+    use rustc_hash::FxHashSet;
+
+    use crate::{db::DefDatabase2, test_db::TestDB};
+
+    use super::*;
+
+    fn do_collect_defs(
+        db: &impl DefDatabase2,
+        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(),
+            mod_dirs: FxHashMap::default(),
+            macro_stack_monitor: monitor,
+            cfg_options: &CfgOptions::default(),
+        };
+        collector.collect();
+        collector.finish()
+    }
+
+    fn do_limited_resolve(code: &str, limit: u32, poison_limit: u32) -> CrateDefMap {
+        let (db, _file_id) = TestDB::with_single_file(&code);
+        let krate = db.crate_graph().iter().next().unwrap();
+
+        let def_map = {
+            let edition = db.crate_graph().edition(krate);
+            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(),
+                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);
+    }
+}