Update code based on PR comments

This patch does the following:
- Refactor some repeated lines into a single one
- Split the `ungated_async_fn_caller` lint into multiple lines, and make
  one of those lines only print out on nightly
- Use test revisions instead of copying an existing test

Author: bryangarza

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -350,7 +350,8 @@ lint_builtin_mutable_transmutes =
 
 lint_builtin_unstable_features = unstable feature
 
-lint_ungated_async_fn_track_caller = `#[track_caller]` on async functions is a no-op, unless the `closure_track_caller` feature is enabled
+lint_ungated_async_fn_track_caller = `#[track_caller]` on async functions is a no-op
+     .suggestion = enable this feature
 
 lint_builtin_unreachable_pub = unreachable `pub` {$what}
     .suggestion = consider restricting its visibility

compiler/rustc_lint/src/builtin.rs

@@ -1371,10 +1371,16 @@ impl<'tcx> LateLintPass<'tcx> for UngatedAsyncFnTrackCaller {
             if let Some(attr) = maybe_track_caller {
                 cx.struct_span_lint(
                     UNGATED_ASYNC_FN_TRACK_CALLER,
-                    span.with_hi(attr.span.hi()),
+                    attr.span,
                     fluent::lint_ungated_async_fn_track_caller,
-                    |lint| lint,
-                    );
+                    |lint| {
+                        lint.span_label(span, "this function will not propagate the caller location");
+                        if cx.tcx.sess.is_nightly_build() {
+                            lint.span_suggestion(attr.span, fluent::suggestion, "#[closure_track_caller]", Applicability::MachineApplicable);
+                        }
+                        lint
+                    }
+                );
             }
         }
     }

src/test/ui/async-await/track-caller/issue-104588-no-op-panic-track-caller.rs

@@ -1,7 +1,7 @@
 // check-pass
 // edition:2021
 
-#[track_caller] //~ WARN `#[track_caller]` on async functions is a no-op, unless the `closure_track_caller` feature is enabled
+#[track_caller] //~ WARN `#[track_caller]` on async functions is a no-op
 async fn foo() {}
 
 fn main() {

src/test/ui/async-await/track-caller/issue-104588-no-op-panic-track-caller.stderr

@@ -1,10 +1,10 @@
-warning: `#[track_caller]` on async functions is a no-op, unless the `closure_track_caller` feature is enabled
-  --> $DIR/issue-104588-no-op-track-caller.rs:4:16
+warning: `#[track_caller]` on async functions is a no-op
+  --> $DIR/issue-104588-no-op-track-caller.rs:4:1
    |
-LL |   #[track_caller]
-   |  ________________^
-LL | | async fn foo() {}
-   | |_
+LL | #[track_caller]
+   | ^^^^^^^^^^^^^^^ help: enable this feature: `#[closure_track_caller]`
+LL | async fn foo() {}
+   | ----------------- this function will not propagate the caller location
    |
    = note: `#[warn(ungated_async_fn_track_caller)]` on by default
 

src/test/ui/async-await/track-caller/issue-104588-no-op-track-caller.rs

@@ -0,0 +1,14 @@
+warning: `#[track_caller]` on async functions is a no-op
+  --> $DIR/panic-track-caller.rs:50:1
+   |
+LL |   #[track_caller]
+   |   ^^^^^^^^^^^^^^^ help: enable this feature: `#[closure_track_caller]`
+LL | / async fn bar_track_caller() {
+LL | |     panic!()
+LL | | }
+   | |_- this function will not propagate the caller location
+   |
+   = note: `#[warn(ungated_async_fn_track_caller)]` on by default
+
+warning: 1 warning emitted
+

src/test/ui/async-await/track-caller/issue-104588-no-op-track-caller.stderr

@@ -1,7 +1,9 @@
 // run-pass
 // edition:2021
+// revisions: feat nofeat
 // needs-unwind
-#![feature(closure_track_caller)]
+
+#![cfg_attr(feat, feature(closure_track_caller))]
 
 use std::future::Future;
 use std::panic;
@@ -45,7 +47,7 @@ async fn foo() {
     bar().await
 }
 
-#[track_caller]
+#[track_caller] //[nofeat]~ WARN `#[track_caller]` on async functions is a no-op
 async fn bar_track_caller() {
     panic!()
 }
@@ -84,7 +86,9 @@ fn panicked_at(f: impl FnOnce() + panic::UnwindSafe) -> u32 {
 }
 
 fn main() {
-    assert_eq!(panicked_at(|| block_on(foo())), 41);
-    assert_eq!(panicked_at(|| block_on(foo_track_caller())), 54);
-    assert_eq!(panicked_at(|| block_on(foo_assoc())), 67);
+    assert_eq!(panicked_at(|| block_on(foo())), 43);
+    #[cfg(feat)]
+    assert_eq!(panicked_at(|| block_on(foo_track_caller())), 56);
+    #[cfg(nofeat)]
+    assert_eq!(panicked_at(|| block_on(foo_track_caller())), 52);
 }