remove unnecessary string searchings

remove unnecessary string searchings for checking if function arguments have `&` and `&mut`

Author: TaKO8Ki

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -671,7 +671,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
         // It only make sense when suggesting dereferences for arguments
-        let ObligationCauseCode::FunctionArgumentObligation { .. } = obligation.cause.code() else {
+        let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } = obligation.cause.code() else {
             return false;
         };
         let param_env = obligation.param_env;
@@ -702,19 +702,22 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     Some(steps).filter(|_| self.predicate_may_hold(&obligation))
                 }) {
                     if steps > 0 {
-                        if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(span) {
-                            // Don't care about `&mut` because `DerefMut` is used less
-                            // often and user will not expect autoderef happens.
-                            if src.starts_with('&') && !src.starts_with("&mut ") {
-                                let derefs = "*".repeat(steps);
-                                err.span_suggestion(
-                                    span,
-                                    "consider dereferencing here",
-                                    format!("&{}{}", derefs, &src[1..]),
-                                    Applicability::MachineApplicable,
-                                );
-                                return true;
-                            }
+                        // Don't care about `&mut` because `DerefMut` is used less
+                        // often and user will not expect autoderef happens.
+                        if let Some(hir::Node::Expr(hir::Expr {
+                            kind:
+                                hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Not, expr),
+                            ..
+                        })) = self.tcx.hir().find(*arg_hir_id)
+                        {
+                            let derefs = "*".repeat(steps);
+                            err.span_suggestion_verbose(
+                                expr.span.shrink_to_lo(),
+                                "consider dereferencing here",
+                                derefs,
+                                Applicability::MachineApplicable,
+                            );
+                            return true;
                         }
                     }
                 } else if real_trait_pred != trait_pred {

src/test/ui/traits/suggest-deferences/issue-39029.stderr

@@ -2,10 +2,8 @@ error[E0277]: the trait bound `NoToSocketAddrs: ToSocketAddrs` is not satisfied
   --> $DIR/issue-39029.rs:16:37
    |
 LL |     let _errors = TcpListener::bind(&bad);
-   |                   ----------------- ^^^^
-   |                   |                 |
-   |                   |                 the trait `ToSocketAddrs` is not implemented for `NoToSocketAddrs`
-   |                   |                 help: consider dereferencing here: `&*bad`
+   |                   ----------------- ^^^^ the trait `ToSocketAddrs` is not implemented for `NoToSocketAddrs`
+   |                   |
    |                   required by a bound introduced by this call
    |
    = note: required because of the requirements on the impl of `ToSocketAddrs` for `&NoToSocketAddrs`
@@ -14,6 +12,10 @@ note: required by a bound in `TcpListener::bind`
    |
 LL |     pub fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
    |                    ^^^^^^^^^^^^^ required by this bound in `TcpListener::bind`
+help: consider dereferencing here
+   |
+LL |     let _errors = TcpListener::bind(&*bad);
+   |                                      +
 
 error: aborting due to previous error
 

src/test/ui/traits/suggest-deferences/issue-62530.stderr

@@ -2,17 +2,19 @@ error[E0277]: the trait bound `&String: SomeTrait` is not satisfied
   --> $DIR/issue-62530.rs:13:26
    |
 LL |     takes_type_parameter(&string);  // Error
-   |     -------------------- ^^^^^^^
-   |     |                    |
-   |     |                    the trait `SomeTrait` is not implemented for `&String`
-   |     |                    help: consider dereferencing here: `&*string`
+   |     -------------------- ^^^^^^^ the trait `SomeTrait` is not implemented for `&String`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `takes_type_parameter`
   --> $DIR/issue-62530.rs:4:44
    |
 LL | fn takes_type_parameter<T>(_x: T) where T: SomeTrait {}
    |                                            ^^^^^^^^^ required by this bound in `takes_type_parameter`
+help: consider dereferencing here
+   |
+LL |     takes_type_parameter(&*string);  // Error
+   |                           +
 
 error: aborting due to previous error
 

src/test/ui/traits/suggest-deferences/multiple-0.stderr

@@ -2,17 +2,19 @@ error[E0277]: the trait bound `&Baz: Happy` is not satisfied
   --> $DIR/multiple-0.rs:34:9
    |
 LL |     foo(&baz);
-   |     --- ^^^^
-   |     |   |
-   |     |   the trait `Happy` is not implemented for `&Baz`
-   |     |   help: consider dereferencing here: `&***baz`
+   |     --- ^^^^ the trait `Happy` is not implemented for `&Baz`
+   |     |
    |     required by a bound introduced by this call
    |
 note: required by a bound in `foo`
   --> $DIR/multiple-0.rs:30:26
    |
 LL | fn foo<T>(_: T) where T: Happy {}
    |                          ^^^^^ required by this bound in `foo`
+help: consider dereferencing here
+   |
+LL |     foo(&***baz);
+   |          +++
 
 error: aborting due to previous error