Do not consider using a semicolon when a return would work better

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

@@ -393,12 +393,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 | ExprKind::If(..)
                 | ExprKind::Match(..)
                 | ExprKind::Block(..) => {
-                    err.span_suggestion(
-                        cause_span.shrink_to_hi(),
-                        "try adding a semicolon",
-                        ";".to_string(),
-                        Applicability::MachineApplicable,
-                    );
+                    self.suggest_return_or_semicolon(err, expression, cause_span);
                 }
                 _ => (),
             }
@@ -475,4 +470,31 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.tcx.sess.parse_sess.expr_parentheses_needed(err, *sp, None);
         }
     }
+
+    pub(in super::super) fn suggest_return_or_semicolon(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expression: &'tcx hir::Expr<'tcx>,
+        cause_span: Span,
+    ) {
+        if let Some(ref ret_coercion) = self.ret_coercion {
+            let ret_ty = ret_coercion.borrow().expected_ty();
+            let return_expr_ty = self.check_expr_with_hint(expression, ret_ty.clone());
+            if self.can_coerce(return_expr_ty, ret_ty) {
+                err.span_suggestion_short(
+                    cause_span.shrink_to_lo(),
+                    "try adding return",
+                    "return ".to_string(),
+                    Applicability::MachineApplicable,
+                );
+                return;
+            }
+        }
+        err.span_suggestion(
+            cause_span.shrink_to_hi(),
+            "try adding a semicolon",
+            ";".to_string(),
+            Applicability::MachineApplicable,
+        );
+    }
 }

src/test/ui/typeck/issue-52284.rs

@@ -0,0 +1,14 @@
+struct Alef();
+struct Bet();
+fn gimel() -> Alef {
+  if true {
+    Alef() //~ERROR
+  }
+  if true {
+    Bet() //~ERROR
+  }
+  Alef()
+}
+fn main() {
+  gimel();
+}

src/test/ui/typeck/issue-52284.stderr

@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-52284.rs:5:5
+   |
+LL | /   if true {
+LL | |     Alef()
+   | |     ^^^^^^ expected `()`, found struct `Alef`
+LL | |   }
+   | |___- expected this to be `()`
+   |
+help: try adding return
+   |
+LL |     return Alef()
+   |     ^^^^^^
+help: consider using a semicolon here
+   |
+LL |   };
+   |    ^
+
+error[E0308]: mismatched types
+  --> $DIR/issue-52284.rs:8:5
+   |
+LL | /   if true {
+LL | |     Bet()
+   | |     ^^^^^ expected `()`, found struct `Bet`
+LL | |   }
+   | |___- expected this to be `()`
+   |
+help: try adding a semicolon
+   |
+LL |     Bet();
+   |          ^
+help: consider using a semicolon here
+   |
+LL |   };
+   |    ^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.