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

Author: Zalathar

tests/coverage/macro_in_closure.cov-map

@@ -0,0 +1,16 @@
+Function name: macro_in_closure::NO_BLOCK::{closure#0}
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 07, 1c, 00, 2d]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 7, 28) to (start + 0, 45)
+
+Function name: macro_in_closure::WITH_BLOCK::{closure#0}
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 09, 1e, 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 + 9, 30) to (start + 2, 2)
+

tests/coverage/macro_in_closure.coverage

@@ -0,0 +1,18 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |// edition: 2021
+   LL|       |
+   LL|       |// If a closure body consists entirely of a single bang-macro invocation, the
+   LL|       |// body span ends up inside the macro-expansion, so we need to un-expand it
+   LL|       |// back to the declaration site.
+   LL|      1|static NO_BLOCK: fn() = || println!("hello");
+   LL|       |
+   LL|      1|static WITH_BLOCK: fn() = || {
+   LL|      1|    println!("hello");
+   LL|      1|};
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    NO_BLOCK();
+   LL|       |    WITH_BLOCK();
+   LL|       |}
+

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();
+}