Trim whitespace in RemoveLet primary span

Separate `RemoveLet` span into primary span for `let` and removal
suggestion span for `let `, so that primary span does not include
whitespace.

Fixes: rust-lang#133031

Signed-off-by: Tyrone Wu <wudevelops@gmail.com>

Author: tyrone-wu

Diff for: compiler/rustc_parse/src/errors.rs

@@ -650,8 +650,9 @@ pub(crate) struct LeftArrowOperator {
 #[diag(parse_remove_let)]
 pub(crate) struct RemoveLet {
     #[primary_span]
-    #[suggestion(applicability = "machine-applicable", code = "", style = "verbose")]
     pub span: Span,
+    #[suggestion(applicability = "machine-applicable", code = "", style = "verbose")]
+    pub suggestion: Span,
 }
 
 #[derive(Diagnostic)]

Diff for: compiler/rustc_parse/src/parser/pat.rs

@@ -685,7 +685,7 @@ impl<'a> Parser<'a> {
             self.bump();
             // Trim extra space after the `let`
             let span = lo.with_hi(self.token.span.lo());
-            self.dcx().emit_err(RemoveLet { span });
+            self.dcx().emit_err(RemoveLet { span: lo, suggestion: span });
             lo = self.token.span;
         }
 

Diff for: tests/ui/parser/unnecessary-let.fixed

@@ -0,0 +1,13 @@
+//@ run-rustfix
+
+fn main() {
+    for _x in [1, 2, 3] {}
+    //~^ ERROR expected pattern, found `let`
+    //~| ERROR missing `in` in `for` loop
+
+    match 1 {
+        1 => {}
+        //~^ ERROR expected pattern, found `let`
+        _ => {}
+    }
+}

Diff for: tests/ui/parser/unnecessary-let.rs

@@ -1,5 +1,7 @@
+//@ run-rustfix
+
 fn main() {
-    for let x of [1, 2, 3] {}
+    for let _x of [1, 2, 3] {}
     //~^ ERROR expected pattern, found `let`
     //~| ERROR missing `in` in `for` loop
 

Diff for: tests/ui/parser/unnecessary-let.stderr

@@ -1,31 +1,31 @@
 error: expected pattern, found `let`
-  --> $DIR/unnecessary-let.rs:2:9
+  --> $DIR/unnecessary-let.rs:4:9
    |
-LL |     for let x of [1, 2, 3] {}
-   |         ^^^^
+LL |     for let _x of [1, 2, 3] {}
+   |         ^^^
    |
 help: remove the unnecessary `let` keyword
    |
-LL -     for let x of [1, 2, 3] {}
-LL +     for x of [1, 2, 3] {}
+LL -     for let _x of [1, 2, 3] {}
+LL +     for _x of [1, 2, 3] {}
    |
 
 error: missing `in` in `for` loop
-  --> $DIR/unnecessary-let.rs:2:15
+  --> $DIR/unnecessary-let.rs:4:16
    |
-LL |     for let x of [1, 2, 3] {}
-   |               ^^
+LL |     for let _x of [1, 2, 3] {}
+   |                ^^
    |
 help: try using `in` here instead
    |
-LL |     for let x in [1, 2, 3] {}
-   |               ~~
+LL |     for let _x in [1, 2, 3] {}
+   |                ~~
 
 error: expected pattern, found `let`
-  --> $DIR/unnecessary-let.rs:7:9
+  --> $DIR/unnecessary-let.rs:9:9
    |
 LL |         let 1 => {}
-   |         ^^^^
+   |         ^^^
    |
 help: remove the unnecessary `let` keyword
    |