Rollup merge of #145660 - jbatez:darwin_objc, r=jdonszelmann,madsmtm,tmandry

initial implementation of the darwin_objc unstable feature

Tracking issue: https://github.com/rust-lang/rust/issues/145496

This feature makes it possible to reference Objective-C classes and selectors using the same ABI used by native Objective-C on Apple/Darwin platforms. Without it, Rust code interacting with Objective-C must resort to loading classes and selectors using costly string-based lookups at runtime. With it, these references can be loaded efficiently at dynamic load time.

r? ```@tmandry```

try-job: `*apple*`
try-job: `x86_64-gnu-nopt`

1 files changed, 28 insertions, 0 deletions

diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
index 32ea9005a97..2c2b14c8a68 100644
--- a/compiler/rustc_attr_parsing/src/session_diagnostics.rs
+++ b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -460,6 +460,34 @@ pub(crate) struct NullOnLinkSection {
 }
 
 #[derive(Diagnostic)]
+#[diag(attr_parsing_null_on_objc_class)]
+pub(crate) struct NullOnObjcClass {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(attr_parsing_null_on_objc_selector)]
+pub(crate) struct NullOnObjcSelector {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(attr_parsing_objc_class_expected_string_literal)]
+pub(crate) struct ObjcClassExpectedStringLiteral {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(attr_parsing_objc_selector_expected_string_literal)]
+pub(crate) struct ObjcSelectorExpectedStringLiteral {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(attr_parsing_stability_outside_std, code = E0734)]
 pub(crate) struct StabilityOutsideStd {
     #[primary_span]