Add test for #[rustc_per_edition].

src/test/ui/editions/auxiliary/per-edition.rs

@@ -0,0 +1,27 @@
+// edition:2015
+
+#![feature(rustc_attrs)]
+
+#[rustc_per_edition]
+pub type I32OrStr = (
+    i32, // 2015
+    &'static str, // 2018+
+);
+
+pub type I32 = I32OrStr;
+
+pub use I32OrStr as Magic;
+
+#[macro_export]
+macro_rules! int {
+    () => {
+        $crate::I32OrStr
+    }
+}
+
+#[macro_export]
+macro_rules! x {
+    () => {
+        X
+    }
+}

src/test/ui/editions/rustc-per-edition.rs

@@ -0,0 +1,24 @@
+// check-pass
+// edition:2021
+// aux-build:per-edition.rs
+
+#![feature(rustc_attrs)]
+
+#[macro_use]
+extern crate per_edition;
+
+#[rustc_per_edition]
+type X = (
+    u32, // 2015
+    &'static str, // 2018,
+    f64, // 2021+
+);
+
+fn main() {
+    let _: X = 6.28;
+    let _: per_edition::I32 = 1i32;
+    let _: per_edition::I32OrStr = "hello";
+    let _: per_edition::Magic = "world";
+    let _: per_edition::int!() = 2i32;
+    let _: per_edition::x!() = 3u32;
+}