Fix a crash with non-ascii whitespace in doc-comments

crates/ra_ide/src/hover.rs

@@ -743,4 +743,21 @@ fn func(foo: i32) { if true { <|>foo; }; }
             &["u32"],
         );
     }
+
+    #[test]
+    fn test_hover_non_ascii_space_doc() {
+        check_hover_result(
+            "
+            //- /lib.rs
+            ///　<- `\u{3000}` here
+            fn foo() {
+            }
+
+            fn bar() {
+                fo<|>o();
+            }
+            ",
+            &["fn foo()\n```\n\n<- `\u{3000}` here"],
+        );
+    }
 }

crates/ra_syntax/src/ast/traits.rs

@@ -126,8 +126,8 @@ pub trait DocCommentsOwner: AstNode {
 
                 // Determine if the prefix or prefix + 1 char is stripped
                 let pos =
-                    if line.chars().nth(prefix_len).map(|c| c.is_whitespace()).unwrap_or(false) {
-                        prefix_len + 1
+                    if let Some(ws) = line.chars().nth(prefix_len).filter(|c| c.is_whitespace()) {
+                        prefix_len + ws.len_utf8()
                     } else {
                         prefix_len
                     };