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, 31 insertions, 0 deletions

diff --git a/tests/coverage/auxiliary/try_in_macro_helper.rs b/tests/coverage/auxiliary/try_in_macro_helper.rs
new file mode 100644
index 00000000000..27d2af15b05
--- /dev/null
+++ b/tests/coverage/auxiliary/try_in_macro_helper.rs
@@ -0,0 +1,31 @@
+//@ edition: 2024
+// (The proc-macro crate doesn't need to be instrumented.)
+//@ compile-flags: -Cinstrument-coverage=off
+
+use proc_macro::TokenStream;
+
+/// Minimized form of `#[derive(arbitrary::Arbitrary)]` that still triggers
+/// the original bug.
+const CODE: &str = "
+    impl Arbitrary for MyEnum {
+        fn try_size_hint() -> Option<usize> {
+            Some(0)?;
+            None
+        }
+    }
+";
+
+#[proc_macro_attribute]
+pub fn attr(_attr: TokenStream, _item: TokenStream) -> TokenStream {
+    CODE.parse().unwrap()
+}
+
+#[proc_macro]
+pub fn bang(_item: TokenStream) -> TokenStream {
+    CODE.parse().unwrap()
+}
+
+#[proc_macro_derive(Arbitrary)]
+pub fn derive_arbitrary(_item: TokenStream) -> TokenStream {
+    CODE.parse().unwrap()
+}