Rollup merge of rust-lang#127301 - estebank:fix-suggestions, r=Urgau

Tweak some structured suggestions to be more verbose and accurate

Addressing some issues I found while working on rust-lang#127282.
```
error: this URL is not a hyperlink
  --> $DIR/auxiliary/include-str-bare-urls.md:1:11
   |
LL | HEADS UP! https://example.com MUST SHOW UP IN THE STDERR FILE!
   |           ^^^^^^^^^^^^^^^^^^^
   |
   = note: bare URLs are not automatically turned into clickable links
note: the lint level is defined here
  --> $DIR/include-str-bare-urls.rs:14:9
   |
LL | #![deny(rustdoc::bare_urls)]
   |         ^^^^^^^^^^^^^^^^^^
help: use an automatic link instead
   |
LL | HEADS UP! <https://example.com> MUST SHOW UP IN THE STDERR FILE!
   |           +                   +
```
```
error[E0384]: cannot assign twice to immutable variable `v`
  --> $DIR/assign-imm-local-twice.rs:7:5
   |
LL |     v = 1;
   |     ----- first assignment to `v`
LL |     println!("v={}", v);
LL |     v = 2;
   |     ^^^^^ cannot assign twice to immutable variable
   |
help: consider making this binding mutable
   |
LL |     let mut v: isize;
   |         +++
```
```
error[E0393]: the type parameter `Rhs` must be explicitly specified
  --> $DIR/issue-22560.rs:9:23
   |
LL | trait Sub<Rhs=Self> {
   | ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
   |                       ^^^
   |
   = note: because of the default `Self` reference, type parameters must be specified on object types
help: set the type parameter to the desired type
   |
LL | type Test = dyn Add + Sub<Rhs>;
   |                          +++++
```
```
error[E0596]: cannot borrow `v` as mutable, as it is not declared as mutable
  --> $DIR/issue-33819.rs:4:34
   |
LL |         Some(ref v) => { let a = &mut v; },
   |                                  ^^^^^^ cannot borrow as mutable
   |
help: try removing `&mut` here
   |
LL -         Some(ref v) => { let a = &mut v; },
LL +         Some(ref v) => { let a = v; },
   |
```
```
help: remove the invocation before committing it to a version control system
   |
LL -     dbg!();
   |
```
```
error[E0308]: mismatched types
  --> $DIR/issue-39974.rs:1:21
   |
LL | const LENGTH: f64 = 2;
   |                     ^ expected `f64`, found integer
   |
help: use a float literal
   |
LL | const LENGTH: f64 = 2.0;
   |                      ++
```
```
error[E0529]: expected an array or slice, found `Vec<i32>`
  --> $DIR/match-ergonomics.rs:8:9
   |
LL |         [&v] => {},
   |         ^^^^ pattern cannot match with input type `Vec<i32>`
   |
help: consider slicing here
   |
LL |     match x[..] {
   |            ++++
```
```
error[E0609]: no field `0` on type `[u32; 1]`
  --> $DIR/parenthesized-deref-suggestion.rs:10:21
   |
LL |     (x as [u32; 1]).0;
   |                     ^ unknown field
   |
help: instead of using tuple indexing, use array indexing
   |
LL |     (x as [u32; 1])[0];
   |                    ~ +
```

Author: matthiaskrgr

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -3757,13 +3757,11 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         assigned_span: Span,
         err_place: Place<'tcx>,
     ) {
-        let (from_arg, local_decl, local_name) = match err_place.as_local() {
-            Some(local) => (
-                self.body.local_kind(local) == LocalKind::Arg,
-                Some(&self.body.local_decls[local]),
-                self.local_names[local],
-            ),
-            None => (false, None, None),
+        let (from_arg, local_decl) = match err_place.as_local() {
+            Some(local) => {
+                (self.body.local_kind(local) == LocalKind::Arg, Some(&self.body.local_decls[local]))
+            }
+            None => (false, None),
         };
 
         // If root local is initialized immediately (everything apart from let
@@ -3795,13 +3793,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             err.span_label(assigned_span, format!("first assignment to {place_description}"));
         }
         if let Some(decl) = local_decl
-            && let Some(name) = local_name
             && decl.can_be_made_mutable()
         {
-            err.span_suggestion(
-                decl.source_info.span,
+            err.span_suggestion_verbose(
+                decl.source_info.span.shrink_to_lo(),
                 "consider making this binding mutable",
-                format!("mut {name}"),
+                "mut ".to_string(),
                 Applicability::MachineApplicable,
             );
             if !from_arg
@@ -3813,10 +3810,10 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     }))
                 )
             {
-                err.span_suggestion(
-                    decl.source_info.span,
+                err.span_suggestion_verbose(
+                    decl.source_info.span.shrink_to_lo(),
                     "to modify the original value, take a borrow instead",
-                    format!("ref mut {name}"),
+                    "ref mut ".to_string(),
                     Applicability::MaybeIncorrect,
                 );
             }

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -408,21 +408,21 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                                     fn_decl.implicit_self,
                                     hir::ImplicitSelfKind::RefImm | hir::ImplicitSelfKind::RefMut
                                 ) {
-                                    err.span_suggestion(
-                                        upvar_ident.span,
+                                    err.span_suggestion_verbose(
+                                        upvar_ident.span.shrink_to_lo(),
                                         "consider changing this to be mutable",
-                                        format!("mut {}", upvar_ident.name),
+                                        "mut ",
                                         Applicability::MachineApplicable,
                                     );
                                     break;
                                 }
                             }
                         }
                     } else {
-                        err.span_suggestion(
-                            upvar_ident.span,
+                        err.span_suggestion_verbose(
+                            upvar_ident.span.shrink_to_lo(),
                             "consider changing this to be mutable",
-                            format!("mut {}", upvar_ident.name),
+                            "mut ",
                             Applicability::MachineApplicable,
                         );
                     }
@@ -449,8 +449,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     .is_ok_and(|snippet| snippet.starts_with("&mut ")) =>
             {
                 err.span_label(span, format!("cannot {act}"));
-                err.span_suggestion(
-                    span,
+                err.span_suggestion_verbose(
+                    span.with_hi(span.lo() + BytePos(5)),
                     "try removing `&mut` here",
                     "",
                     Applicability::MaybeIncorrect,
@@ -755,13 +755,16 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 pat: hir::Pat { kind: hir::PatKind::Ref(_, _), .. },
                 ..
             }) = node
-            && let Ok(name) =
-                self.infcx.tcx.sess.source_map().span_to_snippet(local_decl.source_info.span)
         {
-            err.span_suggestion(
-                pat_span,
+            err.multipart_suggestion(
                 "consider changing this to be mutable",
-                format!("&(mut {name})"),
+                vec![
+                    (pat_span.until(local_decl.source_info.span), "&(mut ".to_string()),
+                    (
+                        local_decl.source_info.span.shrink_to_hi().with_hi(pat_span.hi()),
+                        ")".to_string(),
+                    ),
+                ],
                 Applicability::MachineApplicable,
             );
             return;