Auto merge of #129935 - RalfJung:unsupported_calling_conventions, r=compiler-errors

make unsupported_calling_conventions a hard error

This has been a future-compat lint (not shown in dependencies) since Rust 1.55, released 3 years ago. Hopefully that was enough time so this can be made a hard error now. Given that long timeframe, I think it's justified to skip the "show in dependencies" stage. There were [not many crates hitting this](rust-lang/rust#86231 (comment)) even when the lint was originally added.

This should get cratered, and I assume then it needs a t-compiler FCP. (t-compiler because this looks entirely like an implementation oversight -- for the vast majority of ABIs, we already have a hard error, but some were initially missed, and we are finally fixing that.)

Fixes rust-lang/rust#87678

Author: bors

tests/ui/missing_const_for_fn/could_be_const.fixed

@@ -1,7 +1,7 @@
 #![warn(clippy::missing_const_for_fn)]
 #![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
-#![allow(unsupported_calling_conventions)]
-#![feature(const_trait_impl)]
+#![feature(const_trait_impl, abi_vectorcall)]
+
 
 use std::mem::transmute;
 
@@ -212,8 +212,8 @@ mod extern_fn {
     //~^ ERROR: this could be a `const fn`
     const extern "system-unwind" fn system_unwind() {}
     //~^ ERROR: this could be a `const fn`
-    pub const extern "stdcall" fn std_call() {}
+    pub const extern "vectorcall" fn std_call() {}
     //~^ ERROR: this could be a `const fn`
-    pub const extern "stdcall-unwind" fn std_call_unwind() {}
+    pub const extern "vectorcall-unwind" fn std_call_unwind() {}
     //~^ ERROR: this could be a `const fn`
 }

tests/ui/missing_const_for_fn/could_be_const.rs

@@ -1,7 +1,7 @@
 #![warn(clippy::missing_const_for_fn)]
 #![allow(incomplete_features, clippy::let_and_return, clippy::missing_transmute_annotations)]
-#![allow(unsupported_calling_conventions)]
-#![feature(const_trait_impl)]
+#![feature(const_trait_impl, abi_vectorcall)]
+
 
 use std::mem::transmute;
 
@@ -212,8 +212,8 @@ mod extern_fn {
     //~^ ERROR: this could be a `const fn`
     extern "system-unwind" fn system_unwind() {}
     //~^ ERROR: this could be a `const fn`
-    pub extern "stdcall" fn std_call() {}
+    pub extern "vectorcall" fn std_call() {}
     //~^ ERROR: this could be a `const fn`
-    pub extern "stdcall-unwind" fn std_call_unwind() {}
+    pub extern "vectorcall-unwind" fn std_call_unwind() {}
     //~^ ERROR: this could be a `const fn`
 }

tests/ui/missing_const_for_fn/could_be_const.stderr

@@ -319,23 +319,23 @@ LL |     const extern "system-unwind" fn system_unwind() {}
 error: this could be a `const fn`
   --> tests/ui/missing_const_for_fn/could_be_const.rs:215:5
    |
-LL |     pub extern "stdcall" fn std_call() {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     pub extern "vectorcall" fn std_call() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: make the function `const`
    |
-LL |     pub const extern "stdcall" fn std_call() {}
+LL |     pub const extern "vectorcall" fn std_call() {}
    |         +++++
 
 error: this could be a `const fn`
   --> tests/ui/missing_const_for_fn/could_be_const.rs:217:5
    |
-LL |     pub extern "stdcall-unwind" fn std_call_unwind() {}
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     pub extern "vectorcall-unwind" fn std_call_unwind() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: make the function `const`
    |
-LL |     pub const extern "stdcall-unwind" fn std_call_unwind() {}
+LL |     pub const extern "vectorcall-unwind" fn std_call_unwind() {}
    |         +++++
 
 error: aborting due to 26 previous errors