preserve multiline string trailing whitespace

crates/compiler/fmt/src/expr.rs

@@ -627,8 +627,8 @@ fn fmt_str_body(body: &str, buf: &mut Buf) {
             '\u{200c}' => buf.push_str("\\u(200c)"),
             '\u{feff}' => buf.push_str("\\u(feff)"),
             // Don't change anything else in the string
-            ' ' => buf.spaces(1),
-            '\n' => buf.newline(),
+            ' ' => buf.push_str_allow_spaces(" "),
+            '\n' => buf.push_str_allow_spaces("\n"),
             _ => buf.push(c),
         }
     }

crates/compiler/test_syntax/tests/test_fmt.rs

@@ -6379,6 +6379,13 @@ mod test_fmt {
         );
     }
 
+    #[test]
+    fn preserve_multiline_string_trailing_whitespace() {
+        expr_formats_same(indoc!(
+            "x =\n    \"\"\"\n    foo\n    bar                \n    baz\n    \"\"\"\nx"
+        ));
+    }
+
     // this is a parse error atm
     //    #[test]
     //    fn multiline_apply() {