Rollup merge of #143698 - benschulz:unused-parens-2, r=lcnr,compiler-errors

Fix unused_parens false positive

Resolves rust-lang/rust#143653.

The "no bounds exception" was indiscriminately set to `OneBound` for referents and pointees. However, if the reference or pointer type itself appears in no-bounds position, any constraints it has must be propagated.

```rust
// unused parens: not in no-bounds position
fn foo(_: Box<(dyn Send)>) {}

// unused parens: in no-bounds position, but one-bound exception applies
fn bar(_: Box<dyn Fn(&u32) -> &(dyn Send)>) {}

// *NOT* unused parens: in no-bounds position, but no exceptions to be made
fn baz(_: Box<dyn Fn(&u32) -> &(dyn Send) + Send>) {}
```

3 files changed, 43 insertions, 0 deletions

diff --git a/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.fixed b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.fixed
new file mode 100644
index 00000000000..4b0bca3d44a
--- /dev/null
+++ b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.fixed
@@ -0,0 +1,12 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+#![allow(warnings)]
+trait MyTrait {}
+
+fn foo(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait) + Send + Sync>) {}
+
+//~v ERROR unnecessary parentheses around type
+fn bar(_: Box<dyn FnMut(&mut u32) -> &mut dyn MyTrait>) {}
+
+fn main() {}
diff --git a/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.rs b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.rs
new file mode 100644
index 00000000000..4eefd3dc81a
--- /dev/null
+++ b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.rs
@@ -0,0 +1,12 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+#![allow(warnings)]
+trait MyTrait {}
+
+fn foo(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait) + Send + Sync>) {}
+
+//~v ERROR unnecessary parentheses around type
+fn bar(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait)>) {}
+
+fn main() {}
diff --git a/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.stderr b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.stderr
new file mode 100644
index 00000000000..89455e3db73
--- /dev/null
+++ b/tests/ui/lint/unused/unused-parens-false-positive-issue-143653.stderr
@@ -0,0 +1,19 @@
+error: unnecessary parentheses around type
+  --> $DIR/unused-parens-false-positive-issue-143653.rs:10:43
+   |
+LL | fn bar(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait)>) {}
+   |                                           ^           ^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-parens-false-positive-issue-143653.rs:3:9
+   |
+LL | #![deny(unused_parens)]
+   |         ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL - fn bar(_: Box<dyn FnMut(&mut u32) -> &mut (dyn MyTrait)>) {}
+LL + fn bar(_: Box<dyn FnMut(&mut u32) -> &mut dyn MyTrait>) {}
+   |
+
+error: aborting due to 1 previous error
+