Bugfix/comment duplication (rust-lang#5913)

* Fix rust-lang#5871

* Only idempotence test is necessary

* Update src/expr.rs

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>

---------

Co-authored-by: Caleb Cartwright <calebcartwright@users.noreply.github.com>

Author: GambitingMan

src/expr.rs

@@ -1453,7 +1453,7 @@ pub(crate) fn rewrite_paren(
     let remove_nested_parens = context.config.remove_nested_parens();
     loop {
         // 1 = "(" or ")"
-        pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span.lo());
+        pre_span = mk_sp(span.lo() + BytePos(1), subexpr.span().lo());
         post_span = mk_sp(subexpr.span.hi(), span.hi() - BytePos(1));
         pre_comment = rewrite_missing_comment(pre_span, shape, context)?;
         post_comment = rewrite_missing_comment(post_span, shape, context)?;

tests/target/issue-5871.rs

@@ -0,0 +1,8 @@
+#![feature(stmt_expr_attributes)]
+fn okay() -> u32 {
+    (
+        // Comments in parentheses-expressions caused attributes to be duplicated.
+        #[allow(unused_variables)]
+        0
+    )
+}