use correct file for diagnostics

closes #1475

2 files changed, 22 insertions, 9 deletions

diff --git a/crates/ra_hir/src/diagnostics.rs b/crates/ra_hir/src/diagnostics.rs
index f5f2e65f3..c97f0656d 100644
--- a/crates/ra_hir/src/diagnostics.rs
+++ b/crates/ra_hir/src/diagnostics.rs
@@ -1,6 +1,6 @@
 use std::{any::Any, fmt};
 
-use ra_syntax::{ast, AstPtr, SyntaxNode, SyntaxNodePtr, TextRange, TreeArc};
+use ra_syntax::{ast, AstNode, AstPtr, SyntaxNode, SyntaxNodePtr, TextRange, TreeArc};
 use relative_path::RelativePathBuf;
 
 use crate::{HirDatabase, HirFileId, Name};
@@ -27,11 +27,17 @@ pub trait Diagnostic: Any + Send + Sync + fmt::Debug + 'static {
     fn as_any(&self) -> &(dyn Any + Send + 'static);
 }
 
+pub trait AstDiagnostic {
+    type AST;
+    fn ast(&self, db: &impl HirDatabase) -> Self::AST;
+}
+
 impl dyn Diagnostic {
     pub fn syntax_node(&self, db: &impl HirDatabase) -> TreeArc<SyntaxNode> {
         let node = db.parse_or_expand(self.file()).unwrap();
         self.syntax_node_ptr().to_node(&*node).to_owned()
     }
+
     pub fn downcast_ref<D: Diagnostic>(&self) -> Option<&D> {
         self.as_any().downcast_ref()
     }
@@ -135,3 +141,13 @@ impl Diagnostic for MissingFields {
         self
     }
 }
+
+impl AstDiagnostic for MissingFields {
+    type AST = TreeArc<ast::NamedFieldList>;
+
+    fn ast(&self, db: &impl HirDatabase) -> Self::AST {
+        let root = db.parse_or_expand(self.file()).unwrap();
+        let node = self.syntax_node_ptr().to_node(&*root);
+        ast::NamedFieldList::cast(&node).unwrap().to_owned()
+    }
+}
diff --git a/crates/ra_ide_api/src/diagnostics.rs b/crates/ra_ide_api/src/diagnostics.rs
index 9ab455b0e..a46289cba 100644
--- a/crates/ra_ide_api/src/diagnostics.rs
+++ b/crates/ra_ide_api/src/diagnostics.rs
@@ -1,7 +1,7 @@
 use std::cell::RefCell;
 
 use hir::{
-    diagnostics::{Diagnostic as _, DiagnosticSink},
+    diagnostics::{AstDiagnostic, Diagnostic as _, DiagnosticSink},
     source_binder,
 };
 use itertools::Itertools;
@@ -9,7 +9,7 @@ use ra_assists::ast_editor::{AstBuilder, AstEditor};
 use ra_db::SourceDatabase;
 use ra_prof::profile;
 use ra_syntax::{
-    ast::{self, AstNode, NamedField, NamedFieldList},
+    ast::{self, AstNode, NamedField},
     Location, SyntaxNode, TextRange, T,
 };
 use ra_text_edit::{TextEdit, TextEditBuilder};
@@ -34,9 +34,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
         fix: None,
     }));
 
-    let source_file = parse.tree;
-
-    for node in source_file.syntax().descendants() {
+    for node in parse.tree.syntax().descendants() {
         check_unnecessary_braces_in_use_statement(&mut res, file_id, node);
         check_struct_shorthand_initialization(&mut res, file_id, node);
     }
@@ -61,9 +59,8 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
         })
     })
     .on::<hir::diagnostics::MissingFields, _>(|d| {
-        let syntax_node = d.syntax_node_ptr();
-        let node = NamedFieldList::cast(syntax_node.to_node(source_file.syntax())).unwrap();
-        let mut ast_editor = AstEditor::new(node);
+        let node = d.ast(db);
+        let mut ast_editor = AstEditor::new(&*node);
         for f in d.missed_fields.iter() {
             ast_editor.append_field(&AstBuilder::<NamedField>::from_name(f));
         }