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`

3 files changed, 100 insertions, 3 deletions

diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
index d5d51f2e79a..262b8213977 100644
--- a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -2,7 +2,10 @@ use rustc_hir::attrs::{CoverageAttrKind, OptimizeAttr, SanitizerSet, UsedBy};
 use rustc_session::parse::feature_err;
 
 use super::prelude::*;
-use crate::session_diagnostics::{NakedFunctionIncompatibleAttribute, NullOnExport};
+use crate::session_diagnostics::{
+    NakedFunctionIncompatibleAttribute, NullOnExport, NullOnObjcClass, NullOnObjcSelector,
+    ObjcClassExpectedStringLiteral, ObjcSelectorExpectedStringLiteral,
+};
 
 pub(crate) struct OptimizeParser;
 
@@ -150,6 +153,70 @@ impl<S: Stage> SingleAttributeParser<S> for ExportNameParser {
     }
 }
 
+pub(crate) struct ObjcClassParser;
+
+impl<S: Stage> SingleAttributeParser<S> for ObjcClassParser {
+    const PATH: &[rustc_span::Symbol] = &[sym::rustc_objc_class];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::ForeignStatic)]);
+    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "ClassName");
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        let Some(nv) = args.name_value() else {
+            cx.expected_name_value(cx.attr_span, None);
+            return None;
+        };
+        let Some(classname) = nv.value_as_str() else {
+            // `#[rustc_objc_class = ...]` is expected to be used as an implementatioin detail
+            // inside a standard library macro, but `cx.expected_string_literal` exposes too much.
+            // Use a custom error message instead.
+            cx.emit_err(ObjcClassExpectedStringLiteral { span: nv.value_span });
+            return None;
+        };
+        if classname.as_str().contains('\0') {
+            // `#[rustc_objc_class = ...]` will be converted to a null-terminated string,
+            // so it may not contain any null characters.
+            cx.emit_err(NullOnObjcClass { span: nv.value_span });
+            return None;
+        }
+        Some(AttributeKind::ObjcClass { classname, span: cx.attr_span })
+    }
+}
+
+pub(crate) struct ObjcSelectorParser;
+
+impl<S: Stage> SingleAttributeParser<S> for ObjcSelectorParser {
+    const PATH: &[rustc_span::Symbol] = &[sym::rustc_objc_selector];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::ForeignStatic)]);
+    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "methodName");
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        let Some(nv) = args.name_value() else {
+            cx.expected_name_value(cx.attr_span, None);
+            return None;
+        };
+        let Some(methname) = nv.value_as_str() else {
+            // `#[rustc_objc_selector = ...]` is expected to be used as an implementatioin detail
+            // inside a standard library macro, but `cx.expected_string_literal` exposes too much.
+            // Use a custom error message instead.
+            cx.emit_err(ObjcSelectorExpectedStringLiteral { span: nv.value_span });
+            return None;
+        };
+        if methname.as_str().contains('\0') {
+            // `#[rustc_objc_selector = ...]` will be converted to a null-terminated string,
+            // so it may not contain any null characters.
+            cx.emit_err(NullOnObjcSelector { span: nv.value_span });
+            return None;
+        }
+        Some(AttributeKind::ObjcSelector { methname, span: cx.attr_span })
+    }
+}
+
 #[derive(Default)]
 pub(crate) struct NakedParser {
     span: Option<Span>,
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index d7998048be5..58b13292484 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -20,8 +20,8 @@ use crate::attributes::allow_unstable::{
 use crate::attributes::body::CoroutineParser;
 use crate::attributes::codegen_attrs::{
     ColdParser, CoverageParser, ExportNameParser, ForceTargetFeatureParser, NakedParser,
-    NoMangleParser, OptimizeParser, SanitizeParser, TargetFeatureParser, TrackCallerParser,
-    UsedParser,
+    NoMangleParser, ObjcClassParser, ObjcSelectorParser, OptimizeParser, SanitizeParser,
+    TargetFeatureParser, TrackCallerParser, UsedParser,
 };
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::crate_level::{
@@ -185,6 +185,8 @@ attribute_parsers!(
         Single<LinkageParser>,
         Single<MoveSizeLimitParser>,
         Single<MustUseParser>,
+        Single<ObjcClassParser>,
+        Single<ObjcSelectorParser>,
         Single<OptimizeParser>,
         Single<PathAttributeParser>,
         Single<PatternComplexityLimitParser>,
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]