Display a banner when nightly-only tests are being skipped
diff --git a/tests/zzz_stable.rs b/tests/zzz_stable.rs
new file mode 100644
index 0000000..87bac22
--- /dev/null
+++ b/tests/zzz_stable.rs
@@ -0,0 +1,23 @@
+#![cfg(syn_disable_nightly_tests)]
+
+extern crate colored;
+
+use colored::Colorize;
+
+const MSG: &str = "
+‖
+‖ WARNING:
+‖ This is not a nightly compiler so not all tests were able to
+‖ run. Syn includes tests that compare Syn's parser against the
+‖ compiler's parser, which requires access to unstable libsyntax
+‖ data structures and a nightly compiler.
+‖
+";
+
+#[test]
+fn notice() {
+ panic!(MSG
+ .replace("WARNING", &"WARNING".bold().to_string())
+ .yellow()
+ .to_string());
+}