Refine "remove semicolon" suggestion in trait selection

Don't suggest it if the last statement doesn't have a semicolon

Fixes rust-lang#81098

See also rust-lang#54771 for why this suggestion was added

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

@@ -899,8 +899,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     // no return, suggest removal of semicolon on last statement.
                     // Once that is added, close #54771.
                     if let Some(ref stmt) = blk.stmts.last() {
-                        let sp = self.tcx.sess.source_map().end_point(stmt.span);
-                        err.span_label(sp, "consider removing this semicolon");
+                        if let hir::StmtKind::Semi(_) = stmt.kind {
+                            let sp = self.tcx.sess.source_map().end_point(stmt.span);
+                            err.span_label(sp, "consider removing this semicolon");
+                        }
                     }
                 }
             }

src/test/ui/suggestions/issue-81098.rs

@@ -0,0 +1,13 @@
+// Don't suggest removing a semicolon if the last statement isn't an expression with semicolon
+// (#81098)
+fn wat() -> impl core::fmt::Display { //~ ERROR: `()` doesn't implement `std::fmt::Display`
+    fn why() {}
+}
+
+// Do it if the last statement is an expression with semicolon
+// (#54771)
+fn ok() -> impl core::fmt::Display { //~ ERROR: `()` doesn't implement `std::fmt::Display`
+    1;
+}
+
+fn main() {}

src/test/ui/suggestions/issue-81098.stderr

@@ -0,0 +1,23 @@
+error[E0277]: `()` doesn't implement `std::fmt::Display`
+  --> $DIR/issue-81098.rs:3:13
+   |
+LL | fn wat() -> impl core::fmt::Display {
+   |             ^^^^^^^^^^^^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
+   |
+   = help: the trait `std::fmt::Display` is not implemented for `()`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+
+error[E0277]: `()` doesn't implement `std::fmt::Display`
+  --> $DIR/issue-81098.rs:9:12
+   |
+LL | fn ok() -> impl core::fmt::Display {
+   |            ^^^^^^^^^^^^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
+LL |     1;
+   |      - consider removing this semicolon
+   |
+   = help: the trait `std::fmt::Display` is not implemented for `()`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.