macros: always emit return statement (#4636)

Fixes #4635

tests-build/tests/fail/macros_invalid_input.stderr

@@ -1,97 +1,101 @@
 error: the `async` keyword is missing from the function declaration
- --> $DIR/macros_invalid_input.rs:4:1
+ --> tests/fail/macros_invalid_input.rs:6:1
   |
-4 | fn main_is_not_async() {}
+6 | fn main_is_not_async() {}
   | ^^
 
 error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
- --> $DIR/macros_invalid_input.rs:6:15
+ --> tests/fail/macros_invalid_input.rs:8:15
   |
-6 | #[tokio::main(foo)]
+8 | #[tokio::main(foo)]
   |               ^^^
 
 error: Must have specified ident
- --> $DIR/macros_invalid_input.rs:9:15
-  |
-9 | #[tokio::main(threadpool::bar)]
-  |               ^^^^^^^^^^^^^^^
+  --> tests/fail/macros_invalid_input.rs:11:15
+   |
+11 | #[tokio::main(threadpool::bar)]
+   |               ^^^^^^^^^^^^^^^
 
 error: the `async` keyword is missing from the function declaration
-  --> $DIR/macros_invalid_input.rs:13:1
+  --> tests/fail/macros_invalid_input.rs:15:1
    |
-13 | fn test_is_not_async() {}
+15 | fn test_is_not_async() {}
    | ^^
 
 error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
-  --> $DIR/macros_invalid_input.rs:15:15
+  --> tests/fail/macros_invalid_input.rs:17:15
    |
-15 | #[tokio::test(foo)]
+17 | #[tokio::test(foo)]
    |               ^^^
 
 error: Unknown attribute foo is specified; expected one of: `flavor`, `worker_threads`, `start_paused`, `crate`
-  --> $DIR/macros_invalid_input.rs:18:15
+  --> tests/fail/macros_invalid_input.rs:20:15
    |
-18 | #[tokio::test(foo = 123)]
+20 | #[tokio::test(foo = 123)]
    |               ^^^^^^^^^
 
 error: Failed to parse value of `flavor` as string.
-  --> $DIR/macros_invalid_input.rs:21:24
+  --> tests/fail/macros_invalid_input.rs:23:24
    |
-21 | #[tokio::test(flavor = 123)]
+23 | #[tokio::test(flavor = 123)]
    |                        ^^^
 
 error: No such runtime flavor `foo`. The runtime flavors are `current_thread` and `multi_thread`.
-  --> $DIR/macros_invalid_input.rs:24:24
+  --> tests/fail/macros_invalid_input.rs:26:24
    |
-24 | #[tokio::test(flavor = "foo")]
+26 | #[tokio::test(flavor = "foo")]
    |                        ^^^^^
 
 error: The `start_paused` option requires the `current_thread` runtime flavor. Use `#[tokio::test(flavor = "current_thread")]`
-  --> $DIR/macros_invalid_input.rs:27:55
+  --> tests/fail/macros_invalid_input.rs:29:55
    |
-27 | #[tokio::test(flavor = "multi_thread", start_paused = false)]
+29 | #[tokio::test(flavor = "multi_thread", start_paused = false)]
    |                                                       ^^^^^
 
 error: Failed to parse value of `worker_threads` as integer.
-  --> $DIR/macros_invalid_input.rs:30:57
+  --> tests/fail/macros_invalid_input.rs:32:57
    |
-30 | #[tokio::test(flavor = "multi_thread", worker_threads = "foo")]
+32 | #[tokio::test(flavor = "multi_thread", worker_threads = "foo")]
    |                                                         ^^^^^
 
 error: The `worker_threads` option requires the `multi_thread` runtime flavor. Use `#[tokio::test(flavor = "multi_thread")]`
-  --> $DIR/macros_invalid_input.rs:33:59
+  --> tests/fail/macros_invalid_input.rs:35:59
    |
-33 | #[tokio::test(flavor = "current_thread", worker_threads = 4)]
+35 | #[tokio::test(flavor = "current_thread", worker_threads = 4)]
    |                                                           ^
 
 error: Failed to parse value of `crate` as ident.
-  --> $DIR/macros_invalid_input.rs:36:23
+  --> tests/fail/macros_invalid_input.rs:38:23
    |
-36 | #[tokio::test(crate = 456)]
+38 | #[tokio::test(crate = 456)]
    |                       ^^^
 
 error: Failed to parse value of `crate` as ident: "456"
-  --> $DIR/macros_invalid_input.rs:39:23
+  --> tests/fail/macros_invalid_input.rs:41:23
    |
-39 | #[tokio::test(crate = "456")]
+41 | #[tokio::test(crate = "456")]
    |                       ^^^^^
 
 error: Failed to parse value of `crate` as ident: "abc::edf"
-  --> $DIR/macros_invalid_input.rs:42:23
+  --> tests/fail/macros_invalid_input.rs:44:23
    |
-42 | #[tokio::test(crate = "abc::edf")]
+44 | #[tokio::test(crate = "abc::edf")]
    |                       ^^^^^^^^^^
 
 error: second test attribute is supplied
-  --> $DIR/macros_invalid_input.rs:46:1
+  --> tests/fail/macros_invalid_input.rs:48:1
    |
-46 | #[test]
+48 | #[test]
    | ^^^^^^^
 
 error: duplicated attribute
-  --> $DIR/macros_invalid_input.rs:46:1
+  --> tests/fail/macros_invalid_input.rs:48:1
    |
-46 | #[test]
+48 | #[test]
    | ^^^^^^^
    |
-   = note: `-D duplicate-macro-attributes` implied by `-D warnings`
+note: the lint level is defined here
+  --> tests/fail/macros_invalid_input.rs:1:9
+   |
+1  | #![deny(duplicate_macro_attributes)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^