Auto merge of #118527 - Nadrieril:never_patterns_parse, r=compiler-errors

never_patterns: Parse match arms with no body

Never patterns are meant to signal unreachable cases, and thus don't take bodies:
```rust
let ptr: *const Option<!> = ...;
match *ptr {
    None => { foo(); }
    Some(!),
}
```
This PR makes rustc accept the above, and enforces that an arm has a body xor is a never pattern. This affects parsing of match arms even with the feature off, so this is delicate. (Plus this is my first non-trivial change to the parser).

~~The last commit is optional; it introduces a bit of churn to allow the new suggestions to be machine-applicable. There may be a better solution? I'm not sure.~~ EDIT: I removed that commit

r? `@compiler-errors`

compiler/rustc_lint/src/unused.rs

@@ -1113,15 +1113,17 @@ impl EarlyLintPass for UnusedParens {
             }
             ExprKind::Match(ref _expr, ref arm) => {
                 for a in arm {
-                    self.check_unused_delims_expr(
-                        cx,
-                        &a.body,
-                        UnusedDelimsCtx::MatchArmExpr,
-                        false,
-                        None,
-                        None,
-                        true,
-                    );
+                    if let Some(body) = &a.body {
+                        self.check_unused_delims_expr(
+                            cx,
+                            body,
+                            UnusedDelimsCtx::MatchArmExpr,
+                            false,
+                            None,
+                            None,
+                            true,
+                        );
+                    }
                 }
             }
             _ => {}