Rollup merge of rust-lang#142024 - m-ou-se:what-tail-expression, r=petrochenkov

Don't refer to 'this tail expression' in expansion.

The user has no clue what the compiler is talking about when it says "this tail expression". It is an implementation detail of the macro that it uses a block with tail expression.

Author: matthiaskrgr

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

@@ -3841,7 +3841,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     .expr_ty_adjusted_opt(inner_expr)
                     .unwrap_or(Ty::new_misc_error(tcx));
                 let span = inner_expr.span;
-                if Some(span) != err.span.primary_span() {
+                if Some(span) != err.span.primary_span()
+                    && !span.in_external_macro(tcx.sess.source_map())
+                {
                     err.span_label(
                         span,
                         if ty.references_error() {

tests/ui/never_type/feature-gate-never_type_fallback.stderr

@@ -2,10 +2,8 @@ error[E0277]: the trait bound `(): T` is not satisfied
   --> $DIR/feature-gate-never_type_fallback.rs:10:9
    |
 LL |     foo(panic!())
-   |     --- ^^^^^^^^
-   |     |   |
-   |     |   the trait `T` is not implemented for `()`
-   |     |   this tail expression is of type `()`
+   |     --- ^^^^^^^^ the trait `T` is not implemented for `()`
+   |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one