Make &-removal suggestion verbose

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

@@ -1358,26 +1358,41 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
-        let span = obligation.cause.span;
+        let mut span = obligation.cause.span;
-
+        while span.desugaring_kind().is_some() {
+            // Remove all the hir desugaring contexts while maintaining the macro contexts.
+            span.remove_mark();
+        }
         let mut suggested = false;
-        if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
-            let refs_number =
-                snippet.chars().filter(|c| !c.is_whitespace()).take_while(|c| *c == '&').count();
-            if let Some('\'') = snippet.chars().filter(|c| !c.is_whitespace()).nth(refs_number) {
-                // Do not suggest removal of borrow from type arguments.
-                return false;
-            }
 
-            // Skipping binder here, remapping below
+        let mut expr_finder = super::FindExprBySpan { span, result: None };
-            let mut suggested_ty = trait_pred.self_ty().skip_binder();
+        let Some(hir::Node::Expr(body)) = self.tcx.hir().find(obligation.cause.body_id) else {
+            return false;
+        };
+        expr_finder.visit_expr(&body);
+        let mut count = 0;
+        let mut suggestions = vec![];
+        let Some(mut expr) = expr_finder.result else { return false; };
+        // Skipping binder here, remapping below
+        let mut suggested_ty = trait_pred.self_ty().skip_binder();
+
+        'outer: loop {
+            while let hir::ExprKind::AddrOf(_, _, borrowed) = expr.kind {
+                count += 1;
+                let span = if expr.span.eq_ctxt(borrowed.span) {
+                    expr.span.until(borrowed.span)
+                } else {
+                    expr.span.with_hi(expr.span.lo() + BytePos(1))
+                };
+                suggestions.push((span, String::new()));
 
-            for refs_remaining in 0..refs_number {
                 let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
                     break;
                 };
                 suggested_ty = *inner_ty;
 
+                expr = borrowed;
+
                 // Remapping bound vars here
                 let trait_pred_and_suggested_ty =
                     trait_pred.map_bound(|trait_pred| (trait_pred, suggested_ty));
@@ -1388,25 +1403,33 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 );
 
                 if self.predicate_may_hold(&new_obligation) {
-                    let sp = self
+                    let msg = if count == 1 {
-                        .tcx
-                        .sess
-                        .source_map()
-                        .span_take_while(span, |c| c.is_whitespace() || *c == '&');
-
-                    let remove_refs = refs_remaining + 1;
-
-                    let msg = if remove_refs == 1 {
                         "consider removing the leading `&`-reference".to_string()
                     } else {
-                        format!("consider removing {} leading `&`-references", remove_refs)
+                        format!("consider removing {count} leading `&`-references")
                     };
 
-                    err.span_suggestion_short(sp, &msg, "", Applicability::MachineApplicable);
+                    err.multipart_suggestion_verbose(
+                        &msg,
+                        suggestions,
+                        Applicability::MachineApplicable,
+                    );
                     suggested = true;
-                    break;
+                    break 'outer;
                 }
             }
+            if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
+                && let hir::def::Res::Local(hir_id) = path.res
+                && let Some(hir::Node::Pat(binding)) = self.tcx.hir().find(hir_id)
+                && let parent_hir_id = self.tcx.hir().get_parent_node(binding.hir_id)
+                && let Some(hir::Node::Local(local)) = self.tcx.hir().find(parent_hir_id)
+                && let None = local.ty
+                && let Some(binding_expr) = local.init
+            {
+                expr = binding_expr;
+            } else {
+                break 'outer;
+            }
         }
         suggested
     }

tests/ui/impl-trait/in-trait/issue-102140.stderr

@@ -2,11 +2,15 @@ error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
   --> $DIR/issue-102140.rs:23:22
    |
 LL |         MyTrait::foo(&self)
-   |         ------------ -^^^^
+   |         ------------ ^^^^^ the trait `MyTrait` is not implemented for `&dyn MyTrait`
-   |         |            |
+   |         |
-   |         |            the trait `MyTrait` is not implemented for `&dyn MyTrait`
-   |         |            help: consider removing the leading `&`-reference
    |         required by a bound introduced by this call
+   |
+help: consider removing the leading `&`-reference
+   |
+LL -         MyTrait::foo(&self)
+LL +         MyTrait::foo(self)
+   |
 
 error[E0277]: the trait bound `&dyn MyTrait: MyTrait` is not satisfied
   --> $DIR/issue-102140.rs:23:9

tests/ui/not-panic/not-panic-safe.stderr

@@ -2,10 +2,7 @@ error[E0277]: the type `&mut i32` may not be safely transferred across an unwind
   --> $DIR/not-panic-safe.rs:8:14
    |
 LL |     assert::<&mut i32>();
-   |              -^^^^^^^
+   |              ^^^^^^^^ `&mut i32` may not be safely transferred across an unwind boundary
-   |              |
-   |              `&mut i32` may not be safely transferred across an unwind boundary
-   |              help: consider removing the leading `&`-reference
    |
    = help: the trait `UnwindSafe` is not implemented for `&mut i32`
    = note: `UnwindSafe` is implemented for `&i32`, but not for `&mut i32`

tests/ui/suggestions/suggest-remove-refs-1.stderr

@@ -2,13 +2,15 @@ error[E0277]: `&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
   --> $DIR/suggest-remove-refs-1.rs:6:19
    |
 LL |     for (i, _) in &v.iter().enumerate() {
-   |                   -^^^^^^^^^^^^^^^^^^^^
+   |                   ^^^^^^^^^^^^^^^^^^^^^ `&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
-   |                   |
-   |                   `&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
-   |                   help: consider removing the leading `&`-reference
    |
    = help: the trait `Iterator` is not implemented for `&Enumerate<std::slice::Iter<'_, {integer}>>`
    = note: required for `&Enumerate<std::slice::Iter<'_, {integer}>>` to implement `IntoIterator`
+help: consider removing the leading `&`-reference
+   |
+LL -     for (i, _) in &v.iter().enumerate() {
+LL +     for (i, _) in v.iter().enumerate() {
+   |
 
 error: aborting due to previous error
 

tests/ui/suggestions/suggest-remove-refs-2.stderr

@@ -2,13 +2,15 @@ error[E0277]: `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterat
   --> $DIR/suggest-remove-refs-2.rs:6:19
    |
 LL |     for (i, _) in & & & & &v.iter().enumerate() {
-   |                   ---------^^^^^^^^^^^^^^^^^^^^
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
-   |                   |
-   |                   `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
-   |                   help: consider removing 5 leading `&`-references
    |
    = help: the trait `Iterator` is not implemented for `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>`
    = note: required for `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` to implement `IntoIterator`
+help: consider removing 5 leading `&`-references
+   |
+LL -     for (i, _) in & & & & &v.iter().enumerate() {
+LL +     for (i, _) in v.iter().enumerate() {
+   |
 
 error: aborting due to previous error
 

tests/ui/suggestions/suggest-remove-refs-3.stderr

@@ -1,18 +1,20 @@
 error[E0277]: `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
   --> $DIR/suggest-remove-refs-3.rs:6:19
    |
-LL |        for (i, _) in & & &
+LL |       for (i, _) in & & &
-   |  ____________________^
+   |  ___________________^
-   | | ___________________|
+LL | |         & &v
-   | ||
+LL | |         .iter()
-LL | ||         & &v
+LL | |         .enumerate() {
-   | ||___________- help: consider removing 5 leading `&`-references
+   | |____________________^ `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
-LL | |          .iter()
-LL | |          .enumerate() {
-   | |_____________________^ `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` is not an iterator
    |
    = help: the trait `Iterator` is not implemented for `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>`
    = note: required for `&&&&&Enumerate<std::slice::Iter<'_, {integer}>>` to implement `IntoIterator`
+help: consider removing 5 leading `&`-references
+   |
+LL -     for (i, _) in & & &
+LL +     for (i, _) in v
+   |
 
 error: aborting due to previous error
 

tests/ui/suggestions/suggest-remove-refs-4.fixed

@@ -0,0 +1,5 @@
+// run-rustfix
+fn main() {
+    let foo = [1,2,3].iter();
+    for _i in foo {} //~ ERROR E0277
+}

tests/ui/suggestions/suggest-remove-refs-4.rs

@@ -0,0 +1,5 @@
+// run-rustfix
+fn main() {
+    let foo = &[1,2,3].iter();
+    for _i in &foo {} //~ ERROR E0277
+}

tests/ui/suggestions/suggest-remove-refs-4.stderr

@@ -0,0 +1,17 @@
+error[E0277]: `&&std::slice::Iter<'_, {integer}>` is not an iterator
+  --> $DIR/suggest-remove-refs-4.rs:4:15
+   |
+LL |     for _i in &foo {}
+   |               ^^^^ `&&std::slice::Iter<'_, {integer}>` is not an iterator
+   |
+   = help: the trait `Iterator` is not implemented for `&&std::slice::Iter<'_, {integer}>`
+   = note: required for `&&std::slice::Iter<'_, {integer}>` to implement `IntoIterator`
+help: consider removing 2 leading `&`-references
+   |
+LL ~     let foo = [1,2,3].iter();
+LL ~     for _i in foo {}
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/typeck/issue-57404.stderr

@@ -2,14 +2,17 @@ error[E0277]: `&mut ()` is not a tuple
   --> $DIR/issue-57404.rs:6:41
    |
 LL |     handlers.unwrap().as_mut().call_mut(&mut ());
-   |                                -------- -^^^^^^
+   |                                -------- ^^^^^^^ the trait `Tuple` is not implemented for `&mut ()`
-   |                                |        |
+   |                                |
-   |                                |        the trait `Tuple` is not implemented for `&mut ()`
-   |                                |        help: consider removing the leading `&`-reference
    |                                required by a bound introduced by this call
    |
 note: required by a bound in `call_mut`
   --> $SRC_DIR/core/src/ops/function.rs:LL:COL
+help: consider removing the leading `&`-reference
+   |
+LL -     handlers.unwrap().as_mut().call_mut(&mut ());
+LL +     handlers.unwrap().as_mut().call_mut(());
+   |
 
 error: aborting due to previous error