coverage: Regression test for "function name is empty" bug

The bug was triggered by a particular usage of the `?` try operator in a
proc-macro expansion.

Thanks to lqd for the minimization.

Co-authored-by: Rémy Rakic <remy.rakic+github@gmail.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/coverage/try-in-macro.rs b/tests/coverage/try-in-macro.rs
new file mode 100644
index 00000000000..ab9d6675418
--- /dev/null
+++ b/tests/coverage/try-in-macro.rs
@@ -0,0 +1,43 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/141577>.
+//!
+//! The changes in <https://github.com/rust-lang/rust/pull/144298> exposed a
+//! latent bug that would sometimes cause the compiler to emit a covfun record
+//! for a function, but not emit a corresponding PGO symbol name entry, because
+//! the function did not have any physical coverage counters. The `llvm-cov`
+//! tool would then fail to resolve the covfun record's function name hash,
+//! and exit with the cryptic error:
+//!
+//! ```text
+//!    malformed instrumentation profile data: function name is empty
+//! ```
+//!
+//! The bug was then triggered in the wild by the macro-expansion of
+//! `#[derive(arbitrary::Arbitrary)]`.
+//!
+//! This test uses a minimized form of the `Arbitrary` derive macro that was
+//! found to still trigger the original bug. The bug could also be triggered
+//! by a bang proc-macro or an attribute proc-macro.
+
+//@ edition: 2024
+//@ revisions: attr bang derive
+//@ proc-macro: try_in_macro_helper.rs
+
+trait Arbitrary {
+    fn try_size_hint() -> Option<usize>;
+}
+
+// Expand via an attribute proc-macro.
+#[cfg_attr(attr, try_in_macro_helper::attr)]
+const _: () = ();
+
+// Expand via a regular bang-style proc-macro.
+#[cfg(bang)]
+try_in_macro_helper::bang!();
+
+// Expand via a derive proc-macro.
+#[cfg_attr(derive, derive(try_in_macro_helper::Arbitrary))]
+enum MyEnum {}
+
+fn main() {
+    MyEnum::try_size_hint();
+}