Make a ui test to take the role of libproc_macro #[test] tests

Author: dtolnay

src/test/ui/proc-macro/auxiliary/api/mod.rs

@@ -0,0 +1,16 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![crate_name = "proc_macro_api_tests"]
+#![deny(dead_code)] // catch if a test function is never called
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn run(input: TokenStream) -> TokenStream {
+    assert!(input.is_empty());
+    TokenStream::new()
+}

src/test/ui/proc-macro/test.rs

@@ -0,0 +1,12 @@
+// check-pass
+// aux-build:api/mod.rs
+
+//! This is for everything that *would* be a #[test] inside of libproc_macro,
+//! except for the fact that proc_macro objects are not capable of existing
+//! inside of an ordinary Rust test execution, only inside a macro.
+
+extern crate proc_macro_api_tests;
+
+proc_macro_api_tests::run!();
+
+fn main() {}