Rollup merge of #55138 - zackmdavis:the_paren_trap, r=pnkfelix

in which unused-parens suggestions heed what the user actually wrote

Aaron Hill pointed out that unnecessary parens around a macro call (paradigmatically, `format!`) yielded a suggestion of hideous macro-expanded code. `span_to_snippet` is fallable as far as the type system is concerned, so the pretty-printing can live on in the oft-neglected `else` branch.

Resolves #55109.

src/test/ui/lint/suggestions.rs

@@ -56,7 +56,7 @@ fn main() {
     while true {
     //~^ WARN denote infinite loops
     //~| HELP use `loop`
-        let mut a = (1);
+        let mut registry_no = (format!("NX-{}", 74205));
         //~^ WARN does not need to be mutable
         //~| HELP remove this `mut`
         //~| WARN unnecessary parentheses
@@ -72,6 +72,6 @@ fn main() {
             //~^ WARN this pattern is redundant
             //~| HELP remove this
         }
-        println!("{} {}", a, b);
+        println!("{} {}", registry_no, b);
     }
 }

src/test/ui/lint/suggestions.stderr

@@ -1,8 +1,8 @@
 warning: unnecessary parentheses around assigned value
-  --> $DIR/suggestions.rs:59:21
+  --> $DIR/suggestions.rs:59:31
    |
-LL |         let mut a = (1);
-   |                     ^^^ help: remove these parentheses
+LL |         let mut registry_no = (format!("NX-{}", 74205));
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove these parentheses
    |
 note: lint level defined here
   --> $DIR/suggestions.rs:13:21
@@ -21,8 +21,8 @@ LL | #[no_debug] // should suggest removal of deprecated attribute
 warning: variable does not need to be mutable
   --> $DIR/suggestions.rs:59:13
    |
-LL |         let mut a = (1);
-   |             ----^
+LL |         let mut registry_no = (format!("NX-{}", 74205));
+   |             ----^^^^^^^^^^^
    |             |
    |             help: remove this `mut`
    |