Rollup merge of #143532 - compiler-errors:mut-ref-sugg, r=davidtwco

More carefully consider span context when suggesting remove `&mut`

Use `find_ancestor_inside` to compute a relative span that is macro-aware, rather than falling back to using BytePos arithmetic which is wrong for `&mut`.

Fixes #143523

Author: jhpratt

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

@@ -1581,12 +1581,15 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         '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))
-                };
+                let span =
+                    if let Some(borrowed_span) = borrowed.span.find_ancestor_inside(expr.span) {
+                        expr.span.until(borrowed_span)
+                    } else {
+                        break 'outer;
+                    };
 
+                // Double check that the span we extracted actually corresponds to a borrow,
+                // rather than some macro garbage.
                 match self.tcx.sess.source_map().span_to_snippet(span) {
                     Ok(snippet) if snippet.starts_with("&") => {}
                     _ => break 'outer,

tests/ui/suggestions/suggest-remove-refs-6.rs

@@ -0,0 +1,12 @@
+// Regression test for #143523.
+
+trait Trait {}
+
+impl Trait for Vec<i32> {}
+
+fn foo(_: impl Trait) {}
+
+fn main() {
+    foo(&mut vec![1]);
+    //~^ ERROR the trait bound `&mut Vec<{integer}>: Trait` is not satisfied
+}

tests/ui/suggestions/suggest-remove-refs-6.stderr

@@ -0,0 +1,22 @@
+error[E0277]: the trait bound `&mut Vec<{integer}>: Trait` is not satisfied
+  --> $DIR/suggest-remove-refs-6.rs:10:9
+   |
+LL |     foo(&mut vec![1]);
+   |     --- ^^^^^^^^^^^^ the trait `Trait` is not implemented for `&mut Vec<{integer}>`
+   |     |
+   |     required by a bound introduced by this call
+   |
+note: required by a bound in `foo`
+  --> $DIR/suggest-remove-refs-6.rs:7:16
+   |
+LL | fn foo(_: impl Trait) {}
+   |                ^^^^^ required by this bound in `foo`
+help: consider removing the leading `&`-reference
+   |
+LL -     foo(&mut vec![1]);
+LL +     foo(vec![1]);
+   |
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.