Merge #2235

2235: Handle macro-generated expressions slightly less wrong r=matklad a=matklad



Co-authored-by: Aleksey Kladov <[email protected]>

7 files changed, 156 insertions, 100 deletions

diff --git a/crates/ra_hir/src/expr.rs b/crates/ra_hir/src/expr.rs
index 82955fa55..d19f5d14c 100644
--- a/crates/ra_hir/src/expr.rs
+++ b/crates/ra_hir/src/expr.rs
@@ -40,8 +40,8 @@ pub(crate) fn body_with_source_map_query(
             (src.file_id, src.ast.body())
         }
     };
-    let resolver = hir_def::body::MacroResolver::new(db, def.module(db).id);
-    let (body, source_map) = Body::new(db, resolver, file_id, params, body);
+    let expander = hir_def::body::Expander::new(db, file_id, def.module(db).id);
+    let (body, source_map) = Body::new(db, expander, params, body);
     (Arc::new(body), Arc::new(source_map))
 }
 
diff --git a/crates/ra_hir/src/expr/scope.rs b/crates/ra_hir/src/expr/scope.rs
index fe5e836f2..afba66069 100644
--- a/crates/ra_hir/src/expr/scope.rs
+++ b/crates/ra_hir/src/expr/scope.rs
@@ -166,6 +166,7 @@ fn compute_expr_scopes(expr: ExprId, body: &Body, scopes: &mut ExprScopes, scope
 
 #[cfg(test)]
 mod tests {
+    use hir_expand::Source;
     use ra_db::{fixture::WithFixture, SourceDatabase};
     use ra_syntax::{algo::find_node_at_offset, ast, AstNode};
     use test_utils::{assert_eq_text, extract_offset};
@@ -189,7 +190,10 @@ mod tests {
         let analyzer = SourceAnalyzer::new(&db, file_id, marker.syntax(), None);
 
         let scopes = analyzer.scopes();
-        let expr_id = analyzer.body_source_map().node_expr(&marker.into()).unwrap();
+        let expr_id = analyzer
+            .body_source_map()
+            .node_expr(Source { file_id: file_id.into(), ast: &marker.into() })
+            .unwrap();
         let scope = scopes.scope_for(expr_id);
 
         let actual = scopes
diff --git a/crates/ra_hir/src/from_source.rs b/crates/ra_hir/src/from_source.rs
index 2c441b0f4..4b561c63d 100644
--- a/crates/ra_hir/src/from_source.rs
+++ b/crates/ra_hir/src/from_source.rs
@@ -145,7 +145,8 @@ impl Local {
             Some(res)
         })?;
         let (_body, source_map) = db.body_with_source_map(parent);
-        let pat_id = source_map.node_pat(&src.ast.into())?;
+        let src = src.map(ast::Pat::from);
+        let pat_id = source_map.node_pat(src.as_ref())?;
         Some(Local { parent, pat_id })
     }
 }
diff --git a/crates/ra_hir/src/source_binder.rs b/crates/ra_hir/src/source_binder.rs
index f28e9c931..88eed1137 100644
--- a/crates/ra_hir/src/source_binder.rs
+++ b/crates/ra_hir/src/source_binder.rs
@@ -7,8 +7,11 @@
 //! purely for "IDE needs".
 use std::sync::Arc;
 
-use hir_def::path::known;
-use hir_expand::name::AsName;
+use hir_def::{
+    expr::{ExprId, PatId},
+    path::known,
+};
+use hir_expand::{name::AsName, Source};
 use ra_db::FileId;
 use ra_syntax::{
     ast::{self, AstNode},
@@ -93,6 +96,8 @@ fn def_with_body_from_child_node(
 /// original source files. It should not be used inside the HIR itself.
 #[derive(Debug)]
 pub struct SourceAnalyzer {
+    // FIXME: this doesn't handle macros at all
+    file_id: FileId,
     resolver: Resolver,
     body_owner: Option<DefWithBody>,
     body_source_map: Option<Arc<BodySourceMap>>,
@@ -147,7 +152,7 @@ impl SourceAnalyzer {
             let source_map = def.body_source_map(db);
             let scopes = db.expr_scopes(def);
             let scope = match offset {
-                None => scope_for(&scopes, &source_map, &node),
+                None => scope_for(&scopes, &source_map, file_id.into(), &node),
                 Some(offset) => scope_for_offset(&scopes, &source_map, file_id.into(), offset),
             };
             let resolver = expr::resolver_for_scope(db, def, scope);
@@ -157,6 +162,7 @@ impl SourceAnalyzer {
                 body_source_map: Some(source_map),
                 infer: Some(def.infer(db)),
                 scopes: Some(scopes),
+                file_id,
             }
         } else {
             SourceAnalyzer {
@@ -168,17 +174,28 @@ impl SourceAnalyzer {
                 body_source_map: None,
                 infer: None,
                 scopes: None,
+                file_id,
             }
         }
     }
 
+    fn expr_id(&self, expr: &ast::Expr) -> Option<ExprId> {
+        let src = Source { file_id: self.file_id.into(), ast: expr };
+        self.body_source_map.as_ref()?.node_expr(src)
+    }
+
+    fn pat_id(&self, pat: &ast::Pat) -> Option<PatId> {
+        let src = Source { file_id: self.file_id.into(), ast: pat };
+        self.body_source_map.as_ref()?.node_pat(src)
+    }
+
     pub fn type_of(&self, _db: &impl HirDatabase, expr: &ast::Expr) -> Option<crate::Ty> {
-        let expr_id = self.body_source_map.as_ref()?.node_expr(expr)?;
+        let expr_id = self.expr_id(expr)?;
         Some(self.infer.as_ref()?[expr_id].clone())
     }
 
     pub fn type_of_pat(&self, _db: &impl HirDatabase, pat: &ast::Pat) -> Option<crate::Ty> {
-        let pat_id = self.body_source_map.as_ref()?.node_pat(pat)?;
+        let pat_id = self.pat_id(pat)?;
         Some(self.infer.as_ref()?[pat_id].clone())
     }
 
@@ -191,22 +208,22 @@ impl SourceAnalyzer {
     }
 
     pub fn resolve_method_call(&self, call: &ast::MethodCallExpr) -> Option<Function> {
-        let expr_id = self.body_source_map.as_ref()?.node_expr(&call.clone().into())?;
+        let expr_id = self.expr_id(&call.clone().into())?;
         self.infer.as_ref()?.method_resolution(expr_id)
     }
 
     pub fn resolve_field(&self, field: &ast::FieldExpr) -> Option<crate::StructField> {
-        let expr_id = self.body_source_map.as_ref()?.node_expr(&field.clone().into())?;
+        let expr_id = self.expr_id(&field.clone().into())?;
         self.infer.as_ref()?.field_resolution(expr_id)
     }
 
     pub fn resolve_record_literal(&self, record_lit: &ast::RecordLit) -> Option<crate::VariantDef> {
-        let expr_id = self.body_source_map.as_ref()?.node_expr(&record_lit.clone().into())?;
+        let expr_id = self.expr_id(&record_lit.clone().into())?;
         self.infer.as_ref()?.variant_resolution_for_expr(expr_id)
     }
 
     pub fn resolve_record_pattern(&self, record_pat: &ast::RecordPat) -> Option<crate::VariantDef> {
-        let pat_id = self.body_source_map.as_ref()?.node_pat(&record_pat.clone().into())?;
+        let pat_id = self.pat_id(&record_pat.clone().into())?;
         self.infer.as_ref()?.variant_resolution_for_pat(pat_id)
     }
 
@@ -264,13 +281,13 @@ impl SourceAnalyzer {
 
     pub fn resolve_path(&self, db: &impl HirDatabase, path: &ast::Path) -> Option<PathResolution> {
         if let Some(path_expr) = path.syntax().parent().and_then(ast::PathExpr::cast) {
-            let expr_id = self.body_source_map.as_ref()?.node_expr(&path_expr.into())?;
+            let expr_id = self.expr_id(&path_expr.into())?;
             if let Some(assoc) = self.infer.as_ref()?.assoc_resolutions_for_expr(expr_id) {
                 return Some(PathResolution::AssocItem(assoc));
             }
         }
         if let Some(path_pat) = path.syntax().parent().and_then(ast::PathPat::cast) {
-            let pat_id = self.body_source_map.as_ref()?.node_pat(&path_pat.into())?;
+            let pat_id = self.pat_id(&path_pat.into())?;
             if let Some(assoc) = self.infer.as_ref()?.assoc_resolutions_for_pat(pat_id) {
                 return Some(PathResolution::AssocItem(assoc));
             }
@@ -285,7 +302,7 @@ impl SourceAnalyzer {
         let name = name_ref.as_name();
         let source_map = self.body_source_map.as_ref()?;
         let scopes = self.scopes.as_ref()?;
-        let scope = scope_for(scopes, source_map, name_ref.syntax());
+        let scope = scope_for(scopes, source_map, self.file_id.into(), name_ref.syntax());
         let ret = scopes
             .scope_chain(scope)
             .flat_map(|scope| scopes.entries(scope).iter())
@@ -418,11 +435,12 @@ impl SourceAnalyzer {
 fn scope_for(
     scopes: &ExprScopes,
     source_map: &BodySourceMap,
+    file_id: HirFileId,
     node: &SyntaxNode,
 ) -> Option<ScopeId> {
     node.ancestors()
         .filter_map(ast::Expr::cast)
-        .filter_map(|it| source_map.node_expr(&it))
+        .filter_map(|it| source_map.node_expr(Source { file_id, ast: &it }))
         .find_map(|it| scopes.scope_for(it))
 }
 
diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index ac8f8261b..75bba31c2 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -3,9 +3,12 @@ mod lower;
 
 use std::{ops::Index, sync::Arc};
 
-use hir_expand::{either::Either, HirFileId, MacroDefId, Source};
+use hir_expand::{
+    either::Either, hygiene::Hygiene, AstId, HirFileId, MacroCallLoc, MacroDefId, MacroFileKind,
+    Source,
+};
 use ra_arena::{map::ArenaMap, Arena};
-use ra_syntax::{ast, AstPtr};
+use ra_syntax::{ast, AstNode, AstPtr};
 use rustc_hash::FxHashMap;
 
 use crate::{
@@ -16,25 +19,87 @@ use crate::{
     ModuleId,
 };
 
-pub struct MacroResolver {
+pub struct Expander {
     crate_def_map: Arc<CrateDefMap>,
+    current_file_id: HirFileId,
+    hygiene: Hygiene,
     module: ModuleId,
 }
 
-impl MacroResolver {
-    pub fn new(db: &impl DefDatabase2, module: ModuleId) -> MacroResolver {
-        MacroResolver { crate_def_map: db.crate_def_map(module.krate), module }
+impl Expander {
+    pub fn new(db: &impl DefDatabase2, current_file_id: HirFileId, module: ModuleId) -> Expander {
+        let crate_def_map = db.crate_def_map(module.krate);
+        let hygiene = Hygiene::new(db, current_file_id);
+        Expander { crate_def_map, current_file_id, hygiene, module }
     }
 
-    pub(crate) fn resolve_path_as_macro(
-        &self,
+    fn expand(
+        &mut self,
         db: &impl DefDatabase2,
-        path: &Path,
-    ) -> Option<MacroDefId> {
+        macro_call: ast::MacroCall,
+    ) -> Option<(Mark, ast::Expr)> {
+        let ast_id = AstId::new(
+            self.current_file_id,
+            db.ast_id_map(self.current_file_id).ast_id(&macro_call),
+        );
+
+        if let Some(path) = macro_call.path().and_then(|path| self.parse_path(path)) {
+            if let Some(def) = self.resolve_path_as_macro(db, &path) {
+                let call_id = db.intern_macro(MacroCallLoc { def, ast_id });
+                let file_id = call_id.as_file(MacroFileKind::Expr);
+                if let Some(node) = db.parse_or_expand(file_id) {
+                    if let Some(expr) = ast::Expr::cast(node) {
+                        log::debug!("macro expansion {:#?}", expr.syntax());
+                        let mark = self.enter(db, file_id);
+                        return Some((mark, expr));
+                    }
+                }
+            }
+        }
+
+        // FIXME: Instead of just dropping the error from expansion
+        // report it
+        None
+    }
+
+    fn enter(&mut self, db: &impl DefDatabase2, file_id: HirFileId) -> Mark {
+        let mark = Mark { file_id: self.current_file_id };
+        self.hygiene = Hygiene::new(db, file_id);
+        self.current_file_id = file_id;
+        mark
+    }
+
+    fn exit(&mut self, db: &impl DefDatabase2, mark: Mark) {
+        self.hygiene = Hygiene::new(db, mark.file_id);
+        self.current_file_id = mark.file_id;
+        std::mem::forget(mark);
+    }
+
+    fn to_source<T>(&self, ast: T) -> Source<T> {
+        Source { file_id: self.current_file_id, ast }
+    }
+
+    fn parse_path(&mut self, path: ast::Path) -> Option<Path> {
+        Path::from_src(path, &self.hygiene)
+    }
+
+    fn resolve_path_as_macro(&self, db: &impl DefDatabase2, path: &Path) -> Option<MacroDefId> {
         self.crate_def_map.resolve_path(db, self.module.module_id, path).0.get_macros()
     }
 }
 
+struct Mark {
+    file_id: HirFileId,
+}
+
+impl Drop for Mark {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            panic!("dropped mark")
+        }
+    }
+}
+
 /// The body of an item (function, const etc.).
 #[derive(Debug, Eq, PartialEq)]
 pub struct Body {
@@ -70,9 +135,9 @@ pub type PatSource = Source<PatPtr>;
 /// this properly for macros.
 #[derive(Default, Debug, Eq, PartialEq)]
 pub struct BodySourceMap {
-    expr_map: FxHashMap<ExprPtr, ExprId>,
+    expr_map: FxHashMap<ExprSource, ExprId>,
     expr_map_back: ArenaMap<ExprId, ExprSource>,
-    pat_map: FxHashMap<PatPtr, PatId>,
+    pat_map: FxHashMap<PatSource, PatId>,
     pat_map_back: ArenaMap<PatId, PatSource>,
     field_map: FxHashMap<(ExprId, usize), AstPtr<ast::RecordField>>,
 }
@@ -80,12 +145,11 @@ pub struct BodySourceMap {
 impl Body {
     pub fn new(
         db: &impl DefDatabase2,
-        resolver: MacroResolver,
-        file_id: HirFileId,
+        expander: Expander,
         params: Option<ast::ParamList>,
         body: Option<ast::Expr>,
     ) -> (Body, BodySourceMap) {
-        lower::lower(db, resolver, file_id, params, body)
+        lower::lower(db, expander, params, body)
     }
 
     pub fn params(&self) -> &[PatId] {
@@ -126,16 +190,18 @@ impl BodySourceMap {
         self.expr_map_back.get(expr).copied()
     }
 
-    pub fn node_expr(&self, node: &ast::Expr) -> Option<ExprId> {
-        self.expr_map.get(&Either::A(AstPtr::new(node))).cloned()
+    pub fn node_expr(&self, node: Source<&ast::Expr>) -> Option<ExprId> {
+        let src = node.map(|it| Either::A(AstPtr::new(it)));
+        self.expr_map.get(&src).cloned()
     }
 
     pub fn pat_syntax(&self, pat: PatId) -> Option<PatSource> {
         self.pat_map_back.get(pat).copied()
     }
 
-    pub fn node_pat(&self, node: &ast::Pat) -> Option<PatId> {
-        self.pat_map.get(&Either::A(AstPtr::new(node))).cloned()
+    pub fn node_pat(&self, node: Source<&ast::Pat>) -> Option<PatId> {
+        let src = node.map(|it| Either::A(AstPtr::new(it)));
+        self.pat_map.get(&src).cloned()
     }
 
     pub fn field_syntax(&self, expr: ExprId, field: usize) -> AstPtr<ast::RecordField> {
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index 2aa863c9e..f6d79ddf0 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -2,9 +2,7 @@
 
 use hir_expand::{
     either::Either,
-    hygiene::Hygiene,
     name::{self, AsName, Name},
-    AstId, HirFileId, MacroCallLoc, MacroFileKind, Source,
 };
 use ra_arena::Arena;
 use ra_syntax::{
@@ -16,7 +14,7 @@ use ra_syntax::{
 };
 
 use crate::{
-    body::{Body, BodySourceMap, MacroResolver, PatPtr},
+    body::{Body, BodySourceMap, Expander, PatPtr},
     builtin_type::{BuiltinFloat, BuiltinInt},
     db::DefDatabase2,
     expr::{
@@ -30,16 +28,13 @@ use crate::{
 
 pub(super) fn lower(
     db: &impl DefDatabase2,
-    resolver: MacroResolver,
-    file_id: HirFileId,
+    expander: Expander,
     params: Option<ast::ParamList>,
     body: Option<ast::Expr>,
 ) -> (Body, BodySourceMap) {
     ExprCollector {
-        resolver,
+        expander,
         db,
-        original_file_id: file_id,
-        current_file_id: file_id,
         source_map: BodySourceMap::default(),
         body: Body {
             exprs: Arena::default(),
@@ -53,9 +48,7 @@ pub(super) fn lower(
 
 struct ExprCollector<DB> {
     db: DB,
-    resolver: MacroResolver,
-    original_file_id: HirFileId,
-    current_file_id: HirFileId,
+    expander: Expander,
 
     body: Body,
     source_map: BodySourceMap,
@@ -101,12 +94,9 @@ where
     fn alloc_expr(&mut self, expr: Expr, ptr: AstPtr<ast::Expr>) -> ExprId {
         let ptr = Either::A(ptr);
         let id = self.body.exprs.alloc(expr);
-        if self.current_file_id == self.original_file_id {
-            self.source_map.expr_map.insert(ptr, id);
-        }
-        self.source_map
-            .expr_map_back
-            .insert(id, Source { file_id: self.current_file_id, ast: ptr });
+        let src = self.expander.to_source(ptr);
+        self.source_map.expr_map.insert(src, id);
+        self.source_map.expr_map_back.insert(id, src);
         id
     }
     // desugared exprs don't have ptr, that's wrong and should be fixed
@@ -117,20 +107,16 @@ where
     fn alloc_expr_field_shorthand(&mut self, expr: Expr, ptr: AstPtr<ast::RecordField>) -> ExprId {
         let ptr = Either::B(ptr);
         let id = self.body.exprs.alloc(expr);
-        if self.current_file_id == self.original_file_id {
-            self.source_map.expr_map.insert(ptr, id);
-        }
-        self.source_map
-            .expr_map_back
-            .insert(id, Source { file_id: self.current_file_id, ast: ptr });
+        let src = self.expander.to_source(ptr);
+        self.source_map.expr_map.insert(src, id);
+        self.source_map.expr_map_back.insert(id, src);
         id
     }
     fn alloc_pat(&mut self, pat: Pat, ptr: PatPtr) -> PatId {
         let id = self.body.pats.alloc(pat);
-        if self.current_file_id == self.original_file_id {
-            self.source_map.pat_map.insert(ptr, id);
-        }
-        self.source_map.pat_map_back.insert(id, Source { file_id: self.current_file_id, ast: ptr });
+        let src = self.expander.to_source(ptr);
+        self.source_map.pat_map.insert(src, id);
+        self.source_map.pat_map_back.insert(id, src);
         id
     }
 
@@ -272,7 +258,7 @@ where
             ast::Expr::PathExpr(e) => {
                 let path = e
                     .path()
-                    .and_then(|path| self.parse_path(path))
+                    .and_then(|path| self.expander.parse_path(path))
                     .map(Expr::Path)
                     .unwrap_or(Expr::Missing);
                 self.alloc_expr(path, syntax_ptr)
@@ -288,7 +274,8 @@ where
             ast::Expr::ParenExpr(e) => {
                 let inner = self.collect_expr_opt(e.expr());
                 // make the paren expr point to the inner expression as well
-                self.source_map.expr_map.insert(Either::A(syntax_ptr), inner);
+                let src = self.expander.to_source(Either::A(syntax_ptr));
+                self.source_map.expr_map.insert(src, inner);
                 inner
             }
             ast::Expr::ReturnExpr(e) => {
@@ -296,7 +283,7 @@ where
                 self.alloc_expr(Expr::Return { expr }, syntax_ptr)
             }
             ast::Expr::RecordLit(e) => {
-                let path = e.path().and_then(|path| self.parse_path(path));
+                let path = e.path().and_then(|path| self.expander.parse_path(path));
                 let mut field_ptrs = Vec::new();
                 let record_lit = if let Some(nfl) = e.record_field_list() {
                     let fields = nfl
@@ -443,32 +430,14 @@ where
             // FIXME implement HIR for these:
             ast::Expr::Label(_e) => self.alloc_expr(Expr::Missing, syntax_ptr),
             ast::Expr::RangeExpr(_e) => self.alloc_expr(Expr::Missing, syntax_ptr),
-            ast::Expr::MacroCall(e) => {
-                let ast_id = AstId::new(
-                    self.current_file_id,
-                    self.db.ast_id_map(self.current_file_id).ast_id(&e),
-                );
-
-                if let Some(path) = e.path().and_then(|path| self.parse_path(path)) {
-                    if let Some(def) = self.resolver.resolve_path_as_macro(self.db, &path) {
-                        let call_id = self.db.intern_macro(MacroCallLoc { def, ast_id });
-                        let file_id = call_id.as_file(MacroFileKind::Expr);
-                        if let Some(node) = self.db.parse_or_expand(file_id) {
-                            if let Some(expr) = ast::Expr::cast(node) {
-                                log::debug!("macro expansion {:#?}", expr.syntax());
-                                let old_file_id =
-                                    std::mem::replace(&mut self.current_file_id, file_id);
-                                let id = self.collect_expr(expr);
-                                self.current_file_id = old_file_id;
-                                return id;
-                            }
-                        }
-                    }
+            ast::Expr::MacroCall(e) => match self.expander.expand(self.db, e) {
+                Some((mark, expansion)) => {
+                    let id = self.collect_expr(expansion);
+                    self.expander.exit(self.db, mark);
+                    id
                 }
-                // FIXME: Instead of just dropping the error from expansion
-                // report it
-                self.alloc_expr(Expr::Missing, syntax_ptr)
-            }
+                None => self.alloc_expr(Expr::Missing, syntax_ptr),
+            },
         }
     }
 
@@ -519,7 +488,7 @@ where
                 Pat::Bind { name, mode: annotation, subpat }
             }
             ast::Pat::TupleStructPat(p) => {
-                let path = p.path().and_then(|path| self.parse_path(path));
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
                 let args = p.args().map(|p| self.collect_pat(p)).collect();
                 Pat::TupleStruct { path, args }
             }
@@ -529,7 +498,7 @@ where
                 Pat::Ref { pat, mutability }
             }
             ast::Pat::PathPat(p) => {
-                let path = p.path().and_then(|path| self.parse_path(path));
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
                 path.map(Pat::Path).unwrap_or(Pat::Missing)
             }
             ast::Pat::TuplePat(p) => {
@@ -538,7 +507,7 @@ where
             }
             ast::Pat::PlaceholderPat(_) => Pat::Wild,
             ast::Pat::RecordPat(p) => {
-                let path = p.path().and_then(|path| self.parse_path(path));
+                let path = p.path().and_then(|path| self.expander.parse_path(path));
                 let record_field_pat_list =
                     p.record_field_pat_list().expect("every struct should have a field list");
                 let mut fields: Vec<_> = record_field_pat_list
@@ -579,11 +548,6 @@ where
             self.missing_pat()
         }
     }
-
-    fn parse_path(&mut self, path: ast::Path) -> Option<Path> {
-        let hygiene = Hygiene::new(self.db, self.current_file_id);
-        Path::from_src(path, &hygiene)
-    }
 }
 
 impl From<ast::BinOp> for BinaryOp {
diff --git a/crates/ra_hir_expand/src/lib.rs b/crates/ra_hir_expand/src/lib.rs
index c6ffa2c6f..930789b0f 100644
--- a/crates/ra_hir_expand/src/lib.rs
+++ b/crates/ra_hir_expand/src/lib.rs
@@ -223,7 +223,7 @@ impl<N: AstNode> AstId<N> {
     }
 }
 
-#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash)]
 pub struct Source<T> {
     pub file_id: HirFileId,
     pub ast: T,
@@ -233,6 +233,9 @@ impl<T> Source<T> {
     pub fn map<F: FnOnce(T) -> U, U>(self, f: F) -> Source<U> {
         Source { file_id: self.file_id, ast: f(self.ast) }
     }
+    pub fn as_ref(&self) -> Source<&T> {
+        Source { file_id: self.file_id, ast: &self.ast }
+    }
     pub fn file_syntax(&self, db: &impl db::AstDatabase) -> SyntaxNode {
         db.parse_or_expand(self.file_id).expect("source created from invalid file")
     }