Merge #7803

7803: Fix non-latin characters doc comment in mbe expansion r=edwin0cheng a=edwin0cheng

Fixes #7781

![Peek 2021-02-28 13-47](https://user-images.githubusercontent.com/11014119/109409237-f58e5580-79cb-11eb-92ed-a6700bbe39b5.gif)

Off-topic: This is a [beautiful poem](http://chinesepoetryinenglishverse.blogspot.com/2013/12/blog-post_4784.html) from by Li Shangyin.

bors r+


Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>

crates/mbe/src/syntax_bridge.rs

@@ -213,7 +213,7 @@ fn doc_comment_text(comment: &ast::Comment) -> SmolStr {
 
     // Quote the string
     // Note that `tt::Literal` expect an escaped string
-    let text = format!("{:?}", text.escape_default().to_string());
+    let text = format!("{:?}", text.escape_debug().to_string());
     text.into()
 }
 

crates/mbe/src/tests.rs

@@ -969,6 +969,29 @@ fn test_meta_doc_comments() {
     );
 }
 
+#[test]
+fn test_meta_doc_comments_non_latin() {
+    parse_macro(
+        r#"
+        macro_rules! foo {
+            ($(#[$ i:meta])+) => (
+                $(#[$ i])+
+                fn bar() {}
+            )
+        }
+"#,
+    ).
+    assert_expand_items(
+        r#"foo! {
+            /// 錦瑟無端五十弦，一弦一柱思華年。
+            /**
+                莊生曉夢迷蝴蝶，望帝春心託杜鵑。
+            */
+        }"#,
+        "# [doc = \" 錦瑟無端五十弦，一弦一柱思華年。\"] # [doc = \"\\\\n                莊生曉夢迷蝴蝶，望帝春心託杜鵑。\\\\n            \"] fn bar () {}",
+    );
+}
+
 #[test]
 fn test_tt_block() {
     parse_macro(