coverage: Regression test for #117788

Without the workaround applied, this test will produce malformed mappings that
cause `llvm-cov` to fail.

(And if it does emit well-formed mappings, they should be obviously incorrect.)

tests/coverage/macro_name_span.rs

@@ -0,0 +1,25 @@
+// edition: 2021
+
+// Regression test for <https://github.com/rust-lang/rust/issues/117788>.
+// Under some circumstances, the heuristics that detect macro name spans can
+// get confused and produce incorrect spans beyond the bounds of the span
+// being processed.
+
+// aux-build: macro_name_span_helper.rs
+extern crate macro_name_span_helper;
+
+fn main() {
+    affected_function();
+}
+
+macro_rules! macro_with_an_unreasonably_and_egregiously_long_name {
+    () => {
+        println!("hello");
+    };
+}
+
+macro_name_span_helper::macro_that_defines_a_function! {
+    fn affected_function() {
+        macro_with_an_unreasonably_and_egregiously_long_name!();
+    }
+}