Add test for Rust hygiene bug.

Author: de-vri-es

tests/check.rs

@@ -104,6 +104,20 @@ fn non_debug_refs() {
 	assert!(let I(10) = & &I(10));
 }
 
+#[test]
+fn test_hygiene_bug() {
+	// Test to see if we work around a hygiene bug in the Rust compiler.
+	// See https://github.com/rust-lang/rust/issues/74036
+	// and https://github.com/rust-lang/rust/issues/67062
+	macro_rules! assert_square {
+		($val:expr, $expected:expr) => { assert!($val * $val == $expected) }
+	};
+
+	// If the hygiene bug is not fixed, this evaluates as 2 + 2 * 2 + 2 instead of (2 + 2) * (2 + ).
+	// So it will fail with assert!(8 == 16).
+	assert_square!(2 + 2, 16);
+}
+
 #[test]
 fn no_copy() {
 	let a = String::new();