2 files changed, 32 insertions, 24 deletions

diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index 010d35e55..57ba45b45 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -149,13 +149,16 @@ pub type PatSource = InFile<PatPtr>;
 #[derive(Default, Debug, Eq, PartialEq)]
 pub struct BodySourceMap {
     expr_map: FxHashMap<ExprSource, ExprId>,
-    expr_map_back: ArenaMap<ExprId, ExprSource>,
+    expr_map_back: ArenaMap<ExprId, Result<ExprSource, SyntheticSyntax>>,
     pat_map: FxHashMap<PatSource, PatId>,
-    pat_map_back: ArenaMap<PatId, PatSource>,
+    pat_map_back: ArenaMap<PatId, Result<PatSource, SyntheticSyntax>>,
     field_map: FxHashMap<(ExprId, usize), AstPtr<ast::RecordField>>,
     expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
 }
 
+#[derive(Default, Debug, Eq, PartialEq, Clone, Copy)]
+pub struct SyntheticSyntax;
+
 impl Body {
     pub(crate) fn body_with_source_map_query(
         db: &impl DefDatabase,
@@ -219,8 +222,8 @@ impl Index<PatId> for Body {
 }
 
 impl BodySourceMap {
-    pub fn expr_syntax(&self, expr: ExprId) -> Option<ExprSource> {
-        self.expr_map_back.get(expr).copied()
+    pub fn expr_syntax(&self, expr: ExprId) -> Result<ExprSource, SyntheticSyntax> {
+        self.expr_map_back[expr]
     }
 
     pub fn node_expr(&self, node: InFile<&ast::Expr>) -> Option<ExprId> {
@@ -238,8 +241,8 @@ impl BodySourceMap {
         self.expr_map.get(&src).cloned()
     }
 
-    pub fn pat_syntax(&self, pat: PatId) -> Option<PatSource> {
-        self.pat_map_back.get(pat).copied()
+    pub fn pat_syntax(&self, pat: PatId) -> Result<PatSource, SyntheticSyntax> {
+        self.pat_map_back[pat]
     }
 
     pub fn node_pat(&self, node: InFile<&ast::Pat>) -> Option<PatId> {
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index c18e6879b..ec1b0c2e7 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -14,9 +14,10 @@ use ra_syntax::{
 };
 use test_utils::tested_by;
 
+use super::{ExprSource, PatSource};
 use crate::{
     adt::StructKind,
-    body::{Body, BodySourceMap, Expander, PatPtr},
+    body::{Body, BodySourceMap, Expander, PatPtr, SyntheticSyntax},
     builtin_type::{BuiltinFloat, BuiltinInt},
     db::DefDatabase,
     expr::{
@@ -102,44 +103,48 @@ where
 
     fn alloc_expr(&mut self, expr: Expr, ptr: AstPtr<ast::Expr>) -> ExprId {
         let ptr = Either::Left(ptr);
-        let id = self.body.exprs.alloc(expr);
         let src = self.expander.to_source(ptr);
+        let id = self.make_expr(expr, Ok(src));
         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
     // somehow.
     fn alloc_expr_desugared(&mut self, expr: Expr) -> ExprId {
-        self.body.exprs.alloc(expr)
+        self.make_expr(expr, Err(SyntheticSyntax))
     }
     fn alloc_expr_field_shorthand(&mut self, expr: Expr, ptr: AstPtr<ast::RecordField>) -> ExprId {
         let ptr = Either::Right(ptr);
-        let id = self.body.exprs.alloc(expr);
         let src = self.expander.to_source(ptr);
+        let id = self.make_expr(expr, Ok(src));
         self.source_map.expr_map.insert(src, id);
+        id
+    }
+    fn empty_block(&mut self) -> ExprId {
+        self.alloc_expr_desugared(Expr::Block { statements: Vec::new(), tail: None })
+    }
+    fn missing_expr(&mut self) -> ExprId {
+        self.alloc_expr_desugared(Expr::Missing)
+    }
+    fn make_expr(&mut self, expr: Expr, src: Result<ExprSource, SyntheticSyntax>) -> ExprId {
+        let id = self.body.exprs.alloc(expr);
         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);
         let src = self.expander.to_source(ptr);
+        let id = self.make_pat(pat, Ok(src));
         self.source_map.pat_map.insert(src, id);
-        self.source_map.pat_map_back.insert(id, src);
         id
     }
-
-    fn empty_block(&mut self) -> ExprId {
-        let block = Expr::Block { statements: Vec::new(), tail: None };
-        self.body.exprs.alloc(block)
-    }
-
-    fn missing_expr(&mut self) -> ExprId {
-        self.body.exprs.alloc(Expr::Missing)
-    }
-
     fn missing_pat(&mut self) -> PatId {
-        self.body.pats.alloc(Pat::Missing)
+        self.make_pat(Pat::Missing, Err(SyntheticSyntax))
+    }
+    fn make_pat(&mut self, pat: Pat, src: Result<PatSource, SyntheticSyntax>) -> PatId {
+        let id = self.body.pats.alloc(pat);
+        self.source_map.pat_map_back.insert(id, src);
+        id
     }
 
     fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {