New ui tests for new soft feature gates

src/test/ui/feature-gates/soft-syntax-gates-without-errors.rs

@@ -0,0 +1,26 @@
+// check-pass
+// This file is used to test the behavior of the early-pass syntax warnings.
+// If macro syntax is stabilized, replace with a different unstable syntax.
+
+#[cfg(FALSE)]
+macro b() {}
+//~^ WARN: `macro` is experimental
+//~| WARN: unstable syntax
+
+macro_rules! identity {
+    ($($x:tt)*) => ($($x)*);
+}
+
+#[cfg(FALSE)]
+identity! {
+    macro d() {} // No error
+}
+
+identity! {
+    #[cfg(FALSE)]
+    macro e() {}
+    //~^ WARN: `macro` is experimental
+    //~| WARN: unstable syntax
+}
+
+fn main() {}