3 files changed, 18 insertions, 13 deletions

diff --git a/crates/ra_hir/src/code_model_api.rs b/crates/ra_hir/src/code_model_api.rs
index 57f405f4f..9ae620efd 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, FileId};
-use ra_syntax::{ast, TreeArc, SyntaxNode};
+use ra_syntax::{ast::{self, AstNode, DocCommentsOwner}, TreeArc, SyntaxNode};
 
 use crate::{
     Name, DefId, Path, PerNs, ScopesWithSyntaxMapping, Ty, HirFileId,
@@ -297,7 +297,6 @@ pub struct FnSignature {
     /// True if the first param is `self`. This is relevant to decide whether this
     /// can be called as a method.
     pub(crate) has_self_param: bool,
-    pub(crate) documentation: String,
 }
 
 impl FnSignature {
@@ -318,10 +317,6 @@ impl FnSignature {
     pub fn has_self_param(&self) -> bool {
         self.has_self_param
     }
-
-    pub fn documentation(&self) -> &String {
-        &self.documentation
-    }
 }
 
 impl Function {
@@ -357,6 +352,20 @@ impl Function {
     pub fn generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
         db.generic_params(self.def_id)
     }
+
+    pub fn docs(&self, db: &impl HirDatabase) -> Option<String> {
+        let def_loc = self.def_id.loc(db);
+        let syntax = db.file_item(def_loc.source_item_id);
+        let fn_def = ast::FnDef::cast(&syntax).expect("fn def should point to FnDef node");
+
+        // doc_comment_text unconditionally returns a String
+        let comments = fn_def.doc_comment_text();
+        if comments.is_empty() {
+            None
+        } else {
+            Some(comments)
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
diff --git a/crates/ra_hir/src/code_model_impl/function.rs b/crates/ra_hir/src/code_model_impl/function.rs
index c848f7a82..c68c6bfbf 100644
--- a/crates/ra_hir/src/code_model_impl/function.rs
+++ b/crates/ra_hir/src/code_model_impl/function.rs
@@ -2,7 +2,7 @@ mod scope;
 
 use std::sync::Arc;
 
-use ra_syntax::{TreeArc, ast::{self, NameOwner, DocCommentsOwner}};
+use ra_syntax::{TreeArc, ast::{self, NameOwner}};
 
 use crate::{
     DefId, HirDatabase, Name, AsName, Function, FnSignature, Module,
@@ -73,14 +73,11 @@ impl FnSignature {
             TypeRef::unit()
         };
 
-        let comments = node.doc_comment_text();
-
         let sig = FnSignature {
             name,
             params,
             ret_type,
             has_self_param,
-            documentation: comments,
         };
         Arc::new(sig)
     }
diff --git a/crates/ra_ide_api/src/completion/completion_item.rs b/crates/ra_ide_api/src/completion/completion_item.rs
index dfaadbb20..d70c36889 100644
--- a/crates/ra_ide_api/src/completion/completion_item.rs
+++ b/crates/ra_ide_api/src/completion/completion_item.rs
@@ -259,9 +259,8 @@ impl Builder {
             }
             self.insert_text_format = InsertTextFormat::Snippet;
         }
-        let sig = function.signature(ctx.db);
-        if !sig.documentation().is_empty() {
-            self.documentation = Some(sig.documentation().clone());
+        if let Some(docs) = function.docs(ctx.db) {
+            self.documentation = Some(docs);
         }
 
         self.kind = Some(CompletionItemKind::Function);