Auto merge of #127731 - veluca93:abi_checks, r=RalfJung

Emit future-incompatibility lint when calling/declaring functions with vectors that require missing target feature

On some architectures, vector types may have a different ABI depending on whether the relevant target features are enabled. (The ABI when the feature is disabled is often not specified, but LLVM implements some de-facto ABI.)

As discussed in https://github.com/rust-lang/lang-team/issues/235, this turns out to very easily lead to unsound code.

This commit makes it a post-monomorphization error to declare or call functions using those vector types in a context in which the corresponding target features are disabled, if using an ABI for which the difference is relevant. This ensures that these functions are always called with a consistent ABI.

See the [nomination comment](https://github.com/rust-lang/rust/pull/127731#issuecomment-2288558187) for more discussion.

r? RalfJung

Part of https://github.com/rust-lang/rust/issues/116558

1 files changed, 18 insertions, 0 deletions

diff --git a/compiler/rustc_monomorphize/src/errors.rs b/compiler/rustc_monomorphize/src/errors.rs
index d5fae6e23cb..5048a8d5d99 100644
--- a/compiler/rustc_monomorphize/src/errors.rs
+++ b/compiler/rustc_monomorphize/src/errors.rs
@@ -92,3 +92,21 @@ pub(crate) struct StartNotFound;
 pub(crate) struct UnknownCguCollectionMode<'a> {
     pub mode: &'a str,
 }
+
+#[derive(LintDiagnostic)]
+#[diag(monomorphize_abi_error_disabled_vector_type_def)]
+#[help]
+pub(crate) struct AbiErrorDisabledVectorTypeDef<'a> {
+    #[label]
+    pub span: Span,
+    pub required_feature: &'a str,
+}
+
+#[derive(LintDiagnostic)]
+#[diag(monomorphize_abi_error_disabled_vector_type_call)]
+#[help]
+pub(crate) struct AbiErrorDisabledVectorTypeCall<'a> {
+    #[label]
+    pub span: Span,
+    pub required_feature: &'a str,
+}