tests: migrate unsupported-abi-transmute.rs to extern "rust-invalid"

Author: workingjubilee

tests/ui/abi/unsupported-abi-transmute.rs

@@ -1,15 +1,12 @@
-//@ add-core-stubs
-//@ compile-flags: --crate-type=lib --target x86_64-unknown-none
-//@ needs-llvm-components: x86
+// Check we error before unsupported ABIs reach codegen stages.
+
 //@ edition: 2018
-#![no_core]
-#![feature(no_core, lang_items)]
-extern crate minicore;
-use minicore::*;
+//@ compile-flags: --crate-type=lib
+#![feature(rustc_attrs)]
 
-// Check we error before unsupported ABIs reach codegen stages.
+use core::mem;
 
 fn anything() {
-    let a = unsafe { mem::transmute::<usize, extern "thiscall" fn(i32)>(4) }(2);
+    let a = unsafe { mem::transmute::<usize, extern "rust-invalid" fn(i32)>(4) }(2);
     //~^ ERROR: is not a supported ABI for the current target [E0570]
 }

tests/ui/abi/unsupported-abi-transmute.stderr

@@ -1,8 +1,8 @@
-error[E0570]: "thiscall" is not a supported ABI for the current target
-  --> $DIR/unsupported-abi-transmute.rs:13:53
+error[E0570]: "rust-invalid" is not a supported ABI for the current target
+  --> $DIR/unsupported-abi-transmute.rs:10:53
    |
-LL |     let a = unsafe { mem::transmute::<usize, extern "thiscall" fn(i32)>(4) }(2);
-   |                                                     ^^^^^^^^^^
+LL |     let a = unsafe { mem::transmute::<usize, extern "rust-invalid" fn(i32)>(4) }(2);
+   |                                                     ^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/abi/unsupported-in-impls.rs

@@ -1,6 +1,9 @@
 // Test for https://github.com/rust-lang/rust/issues/86232
 // Due to AST-to-HIR lowering nuances, we used to allow unsupported ABIs to "leak" into the HIR
 // without being checked, as we would check after generating the ExternAbi.
+// Checking afterwards only works if we examine every HIR construct that contains an ExternAbi,
+// and those may be very different in HIR, even if they read the same in source.
+// This made it very easy to make mistakes.
 //
 // Here we test that an unsupported ABI in various impl-related positions will be rejected,
 // both in the original declarations and the actual implementations.