coverage: Regression test for #117788

This test isn't able to reproduce the malformed mappings that cause `llvm-cov`
to fail, but does reproduce the underlying problem in a way that results in
obviously incorrect mappings if the workaround is not present.

Author: Zalathar

tests/coverage/macro_name_span.cov-map

@@ -0,0 +1,16 @@
+Function name: macro_name_span::affected_function
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 0e, 1b, 00, 20]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 14, 27) to (start + 0, 32)
+
+Function name: macro_name_span::main
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 08, 01, 02, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 8, 1) to (start + 2, 2)
+

tests/coverage/macro_name_span.coverage

@@ -0,0 +1,33 @@
+   LL|       |// edition: 2021
+   LL|       |
+   LL|       |// Regression test for <https://github.com/rust-lang/rust/issues/117788>.
+   LL|       |// Under some circumstances, the heuristics that detect macro name spans can
+   LL|       |// get confused and produce incorrect spans beyond the bounds of the span
+   LL|       |// being processed.
+   LL|       |
+   LL|      1|fn main() {
+   LL|      1|    affected_function();
+   LL|      1|}
+   LL|       |
+   LL|       |macro_rules! macro_that_defines_a_function {
+   LL|       |    (fn $name:ident () $body:tt) => {
+   LL|      1|        fn $name () -> () $body
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|       |// These comment lines are not executable and should not have counters.
+   LL|       |// If they do have counters, it means that a span from the above $body has
+   LL|       |// been extended beyond its proper bounds.
+   LL|       |
+   LL|       |macro_rules! macro_with_an_unreasonably_and_egregiously_long_name {
+   LL|       |    () => {
+   LL|       |        println!("hello");
+   LL|       |    };
+   LL|       |}
+   LL|       |
+   LL|       |macro_that_defines_a_function! {
+   LL|       |    fn affected_function() {
+   LL|       |        macro_with_an_unreasonably_and_egregiously_long_name!();
+   LL|       |    }
+   LL|       |}
+

tests/coverage/macro_name_span.rs

@@ -0,0 +1,32 @@
+// 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.
+
+fn main() {
+    affected_function();
+}
+
+macro_rules! macro_that_defines_a_function {
+    (fn $name:ident () $body:tt) => {
+        fn $name () -> () $body
+    }
+}
+
+// These comment lines are not executable and should not have counters.
+// If they do have counters, it means that a span from the above $body has
+// been extended beyond its proper bounds.
+
+macro_rules! macro_with_an_unreasonably_and_egregiously_long_name {
+    () => {
+        println!("hello");
+    };
+}
+
+macro_that_defines_a_function! {
+    fn affected_function() {
+        macro_with_an_unreasonably_and_egregiously_long_name!();
+    }
+}