3 files changed, 26 insertions, 40 deletions

diff --git a/crates/ra_hir/src/code_model_api.rs b/crates/ra_hir/src/code_model_api.rs
index 3f882a736..5f61bb589 100644
--- a/crates/ra_hir/src/code_model_api.rs
+++ b/crates/ra_hir/src/code_model_api.rs
@@ -2,7 +2,7 @@ use std::sync::Arc;
 
 use relative_path::RelativePathBuf;
 use ra_db::{CrateId, Cancelable, FileId};
-use ra_syntax::{ast, TreeArc, SyntaxNode, AstNode};
+use ra_syntax::{ast, TreeArc, SyntaxNode};
 
 use crate::{
     Name, DefId, Path, PerNs, ScopesWithSyntaxMapping, Ty, HirFileId,
@@ -12,6 +12,7 @@ use crate::{
     expr::BodySyntaxMapping,
     ty::InferenceResult,
     adt::VariantData,
+    code_model_impl::def_id_to_ast,
 };
 
 /// hir::Crate describes a single crate. It's the main interface with which
@@ -186,13 +187,7 @@ impl Struct {
         &self,
         db: &impl HirDatabase,
     ) -> Cancelable<(HirFileId, TreeArc<ast::StructDef>)> {
-        let (file_id, syntax) = self.def_id.source(db);
-        Ok((
-            file_id,
-            ast::StructDef::cast(&syntax)
-                .expect("struct def should point to StructDef node")
-                .to_owned(),
-        ))
+        Ok(def_id_to_ast(db, self.def_id))
     }
 }
 
@@ -219,13 +214,7 @@ impl Enum {
     }
 
     pub fn source(&self, db: &impl HirDatabase) -> Cancelable<(HirFileId, TreeArc<ast::EnumDef>)> {
-        let (file_id, syntax) = self.def_id.source(db);
-        Ok((
-            file_id,
-            ast::EnumDef::cast(&syntax)
-                .expect("enum def should point to EnumDef node")
-                .to_owned(),
-        ))
+        Ok(def_id_to_ast(db, self.def_id))
     }
 }
 
@@ -259,13 +248,7 @@ impl EnumVariant {
         &self,
         db: &impl HirDatabase,
     ) -> Cancelable<(HirFileId, TreeArc<ast::EnumVariant>)> {
-        let (file_id, syntax) = self.def_id.source(db);
-        Ok((
-            file_id,
-            ast::EnumVariant::cast(&syntax)
-                .expect("variant def should point to EnumVariant node")
-                .to_owned(),
-        ))
+        Ok(def_id_to_ast(db, self.def_id))
     }
 }
 
@@ -304,7 +287,7 @@ impl Function {
     }
 
     pub fn source(&self, db: &impl HirDatabase) -> Cancelable<(HirFileId, TreeArc<ast::FnDef>)> {
-        Ok(self.source_impl(db))
+        Ok(def_id_to_ast(db, self.def_id))
     }
 
     pub fn body_syntax_mapping(&self, db: &impl HirDatabase) -> Cancelable<Arc<BodySyntaxMapping>> {
diff --git a/crates/ra_hir/src/code_model_impl.rs b/crates/ra_hir/src/code_model_impl.rs
index 1f28fab74..0cea9f7b6 100644
--- a/crates/ra_hir/src/code_model_impl.rs
+++ b/crates/ra_hir/src/code_model_impl.rs
@@ -1,3 +1,18 @@
 mod krate; // `crate` is invalid ident :(
 mod module;
 pub(crate) mod function;
+
+use ra_syntax::{AstNode, TreeArc};
+
+use crate::{HirDatabase, DefId, HirFileId};
+
+pub(crate) fn def_id_to_ast<N: AstNode>(
+    db: &impl HirDatabase,
+    def_id: DefId,
+) -> (HirFileId, TreeArc<N>) {
+    let (file_id, syntax) = def_id.source(db);
+    let ast = N::cast(&syntax)
+        .unwrap_or_else(|| panic!("def points to wrong source {:?} {:?}", def_id, syntax))
+        .to_owned();
+    (file_id, ast)
+}
diff --git a/crates/ra_hir/src/code_model_impl/function.rs b/crates/ra_hir/src/code_model_impl/function.rs
index daf49e791..1ce939e05 100644
--- a/crates/ra_hir/src/code_model_impl/function.rs
+++ b/crates/ra_hir/src/code_model_impl/function.rs
@@ -3,16 +3,14 @@ mod scope;
 use std::sync::Arc;
 
 use ra_db::Cancelable;
-use ra_syntax::{
-    TreeArc,
-    ast::{self, AstNode, NameOwner},
-};
+use ra_syntax::{TreeArc, ast::{self, NameOwner}};
 
 use crate::{
-    DefId, DefKind, HirDatabase, Name, AsName, Function, FnSignature, Module, HirFileId,
+    DefId, HirDatabase, Name, AsName, Function, FnSignature, Module,
     type_ref::{TypeRef, Mutability},
     expr::Body,
     impl_block::ImplBlock,
+    code_model_impl::def_id_to_ast,
 };
 
 pub use self::scope::{FnScopes, ScopesWithSyntaxMapping, ScopeEntryWithSyntax};
@@ -22,16 +20,6 @@ impl Function {
         Function { def_id }
     }
 
-    pub(crate) fn source_impl(&self, db: &impl HirDatabase) -> (HirFileId, TreeArc<ast::FnDef>) {
-        let def_loc = self.def_id.loc(db);
-        assert!(def_loc.kind == DefKind::Function);
-        let syntax = db.file_item(def_loc.source_item_id);
-        (
-            def_loc.source_item_id.file_id,
-            ast::FnDef::cast(&syntax).unwrap().to_owned(),
-        )
-    }
-
     pub(crate) fn body(&self, db: &impl HirDatabase) -> Cancelable<Arc<Body>> {
         db.body_hir(self.def_id)
     }
@@ -48,8 +36,8 @@ impl Function {
 
 impl FnSignature {
     pub(crate) fn fn_signature_query(db: &impl HirDatabase, def_id: DefId) -> Arc<FnSignature> {
-        let func = Function::new(def_id);
-        let node = func.source_impl(db).1; // TODO we're using source_impl here to avoid returning Cancelable... this is a bit hacky
+        // FIXME: we're using def_id_to_ast here to avoid returning Cancelable... this is a bit hacky
+        let node: TreeArc<ast::FnDef> = def_id_to_ast(db, def_id).1;
         let name = node
             .name()
             .map(|n| n.as_name())