coverage: Test for closure body that is a single bang-macro

tests/coverage/macro_in_closure.rs

@@ -0,0 +1,17 @@
+#![feature(coverage_attribute)]
+// edition: 2021
+
+// If a closure body consists entirely of a single bang-macro invocation, the
+// body span ends up inside the macro-expansion, so we need to un-expand it
+// back to the declaration site.
+static NO_BLOCK: fn() = || println!("hello");
+
+static WITH_BLOCK: fn() = || {
+    println!("hello");
+};
+
+#[coverage(off)]
+fn main() {
+    NO_BLOCK();
+    WITH_BLOCK();
+}