make suggestion text more legible

Author: Young-Flash

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1970,15 +1970,10 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
         {
             if !ident_span.from_expansion() {
                 let (span, text) = match self.r.tcx.sess.source_map().span_to_snippet(ident_span) {
-                    Ok(var_name) => {
+                    Ok(ref name) if let Some(name) = name.strip_prefix("let") => {
                         // a special case for #117894
-                        let text = var_name.strip_prefix("let").and_then(|rest| {
-                            match rest.starts_with("_") {
-                                true => rest.strip_prefix("_").map(String::from),
-                                false => Some(rest.to_string())
-                            }
-                        }).unwrap_or(var_name);
-                        (ident_span, format!("let {}", text))
+                        let name = name.strip_prefix("_").unwrap_or(name);
+                        (ident_span, format!("let {name}"))
                     },
                     _ => (ident_span.shrink_to_lo(), "let ".to_string())
                 };

tests/ui/suggestions/issue-104086-suggest-let.stderr

@@ -7,7 +7,7 @@ LL |     x = x = x;
 help: you might have meant to introduce a new binding
    |
 LL |     let x = x = x;
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/issue-104086-suggest-let.rs:2:9
@@ -30,7 +30,7 @@ LL |     x = y = y = y;
 help: you might have meant to introduce a new binding
    |
 LL |     let x = y = y = y;
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `y` in this scope
   --> $DIR/issue-104086-suggest-let.rs:7:9
@@ -59,7 +59,7 @@ LL |     x = y = y;
 help: you might have meant to introduce a new binding
    |
 LL |     let x = y = y;
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `y` in this scope
   --> $DIR/issue-104086-suggest-let.rs:13:9
@@ -82,7 +82,7 @@ LL |     x = x = y;
 help: you might have meant to introduce a new binding
    |
 LL |     let x = x = y;
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/issue-104086-suggest-let.rs:18:9
@@ -105,7 +105,7 @@ LL |     x = x; // will suggest add `let`
 help: you might have meant to introduce a new binding
    |
 LL |     let x = x; // will suggest add `let`
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/issue-104086-suggest-let.rs:23:9
@@ -122,7 +122,7 @@ LL |     x = y // will suggest add `let`
 help: you might have meant to introduce a new binding
    |
 LL |     let x = y // will suggest add `let`
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `y` in this scope
   --> $DIR/issue-104086-suggest-let.rs:27:9

tests/ui/suggestions/suggest-let-for-assignment.stderr

@@ -7,7 +7,7 @@ LL |     demo = 1;
 help: you might have meant to introduce a new binding
    |
 LL |     let demo = 1;
-   |     ~~~~~~~~
+   |     +++
 
 error[E0425]: cannot find value `demo` in this scope
   --> $DIR/suggest-let-for-assignment.rs:5:10
@@ -24,7 +24,7 @@ LL |     x = "x";
 help: you might have meant to introduce a new binding
    |
 LL |     let x = "x";
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/suggest-let-for-assignment.rs:8:23
@@ -81,7 +81,7 @@ LL |     y = 1 + 2;
 help: you might have meant to introduce a new binding
    |
 LL |     let y = 1 + 2;
-   |     ~~~~~
+   |     +++
 
 error[E0425]: cannot find value `y` in this scope
   --> $DIR/suggest-let-for-assignment.rs:22:23