Make unused_parens's suggestion considering expr's attributes.

compiler/rustc_lint/src/unused.rs

@@ -804,7 +804,15 @@ trait UnusedDelimLint {
                 .find_ancestor_inside(value.span)
                 .map(|span| (value.span.with_hi(span.lo()), value.span.with_lo(span.hi()))),
             ast::ExprKind::Paren(ref expr) => {
-                expr.span.find_ancestor_inside(value.span).map(|expr_span| {
+                // For the expr with attributes, like `let _ = (#[inline] || println!("Hello!"));`,
+                // the span should contains the attributes, or the suggestion will remove them.
+                let expr_span_with_attrs =
+                    if let Some(attr_lo) = expr.attrs.iter().map(|attr| attr.span.lo()).min() {
+                        expr.span.with_lo(attr_lo)
+                    } else {
+                        expr.span
+                    };
+                expr_span_with_attrs.find_ancestor_inside(value.span).map(|expr_span| {
                     (value.span.with_hi(expr_span.lo()), value.span.with_lo(expr_span.hi()))
                 })
             }

tests/ui/lint/unused/unused-parens-for-stmt-expr-attributes-issue-129833.fixed

@@ -0,0 +1,15 @@
+//@ run-rustfix
+// Check the `unused_parens` suggestion for paren_expr with attributes.
+// The suggestion should retain attributes in the front.
+
+#![feature(stmt_expr_attributes)]
+#![deny(unused_parens)]
+
+pub fn foo() -> impl Fn() {
+    let _ = #[inline] #[allow(dead_code)] || println!("Hello!"); //~ERROR unnecessary parentheses
+    #[inline] #[allow(dead_code)] || println!("Hello!") //~ERROR unnecessary parentheses
+}
+
+fn main() {
+    let _ = foo();
+}

tests/ui/lint/unused/unused-parens-for-stmt-expr-attributes-issue-129833.rs

@@ -0,0 +1,15 @@
+//@ run-rustfix
+// Check the `unused_parens` suggestion for paren_expr with attributes.
+// The suggestion should retain attributes in the front.
+
+#![feature(stmt_expr_attributes)]
+#![deny(unused_parens)]
+
+pub fn foo() -> impl Fn() {
+    let _ = (#[inline] #[allow(dead_code)] || println!("Hello!")); //~ERROR unnecessary parentheses
+    (#[inline] #[allow(dead_code)] || println!("Hello!")) //~ERROR unnecessary parentheses
+}
+
+fn main() {
+    let _ = foo();
+}

tests/ui/lint/unused/unused-parens-for-stmt-expr-attributes-issue-129833.stderr

@@ -0,0 +1,31 @@
+error: unnecessary parentheses around assigned value
+  --> $DIR/unused-parens-for-stmt-expr-attributes-issue-129833.rs:9:13
+   |
+LL |     let _ = (#[inline] #[allow(dead_code)] || println!("Hello!"));
+   |             ^                                                   ^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-parens-for-stmt-expr-attributes-issue-129833.rs:6:9
+   |
+LL | #![deny(unused_parens)]
+   |         ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL -     let _ = (#[inline] #[allow(dead_code)] || println!("Hello!"));
+LL +     let _ = #[inline] #[allow(dead_code)] || println!("Hello!");
+   |
+
+error: unnecessary parentheses around block return value
+  --> $DIR/unused-parens-for-stmt-expr-attributes-issue-129833.rs:10:5
+   |
+LL |     (#[inline] #[allow(dead_code)] || println!("Hello!"))
+   |     ^                                                   ^
+   |
+help: remove these parentheses
+   |
+LL -     (#[inline] #[allow(dead_code)] || println!("Hello!"))
+LL +     #[inline] #[allow(dead_code)] || println!("Hello!")
+   |
+
+error: aborting due to 2 previous errors
+