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`

15 files changed, 726 insertions, 0 deletions

diff --git a/tests/codegen-llvm/auxiliary/darwin_objc_aux.rs b/tests/codegen-llvm/auxiliary/darwin_objc_aux.rs
new file mode 100644
index 00000000000..3c35d003c8a
--- /dev/null
+++ b/tests/codegen-llvm/auxiliary/darwin_objc_aux.rs
@@ -0,0 +1,27 @@
+#![crate_type = "lib"]
+#![feature(darwin_objc)]
+
+use std::os::darwin::objc;
+
+#[link(name = "Foundation", kind = "framework")]
+unsafe extern "C" {}
+
+#[inline(always)]
+pub fn inline_get_object_class() -> objc::Class {
+    objc::class!("NSObject")
+}
+
+#[inline(always)]
+pub fn inline_get_alloc_selector() -> objc::SEL {
+    objc::selector!("alloc")
+}
+
+#[inline(never)]
+pub fn never_inline_get_string_class() -> objc::Class {
+    objc::class!("NSString")
+}
+
+#[inline(never)]
+pub fn never_inline_get_init_selector() -> objc::SEL {
+    objc::selector!("init")
+}
diff --git a/tests/codegen-llvm/darwin-no-objc.rs b/tests/codegen-llvm/darwin-no-objc.rs
new file mode 100644
index 00000000000..fda3671fb6d
--- /dev/null
+++ b/tests/codegen-llvm/darwin-no-objc.rs
@@ -0,0 +1,52 @@
+// Test that we don't generate Objective-C definitions or image info unnecessarily.
+
+//@ add-core-stubs
+//@ revisions: i686_apple_darwin
+//@ [i686_apple_darwin] compile-flags: --target i686-apple-darwin
+//@ [i686_apple_darwin] needs-llvm-components: x86
+//@ revisions: x86_64_macos
+//@ [x86_64_macos] compile-flags: --target x86_64-apple-darwin
+//@ [x86_64_macos] needs-llvm-components: x86
+//@ revisions: aarch64_macos
+//@ [aarch64_macos] compile-flags: --target aarch64-apple-darwin
+//@ [aarch64_macos] needs-llvm-components: aarch64
+//@ revisions: i386_ios
+//@ [i386_ios] compile-flags: --target i386-apple-ios
+//@ [i386_ios] needs-llvm-components: x86
+//@ revisions: x86_64_ios
+//@ [x86_64_ios] compile-flags: --target x86_64-apple-ios
+//@ [x86_64_ios] needs-llvm-components: x86
+//@ revisions: armv7s_ios
+//@ [armv7s_ios] compile-flags: --target armv7s-apple-ios
+//@ [armv7s_ios] needs-llvm-components: arm
+//@ revisions: aarch64_ios
+//@ [aarch64_ios] compile-flags: --target aarch64-apple-ios
+//@ [aarch64_ios] needs-llvm-components: aarch64
+//@ revisions: aarch64_ios_sim
+//@ [aarch64_ios_sim] compile-flags: --target aarch64-apple-ios-sim
+//@ [aarch64_ios_sim] needs-llvm-components: aarch64
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items)]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+#[no_mangle]
+pub fn foo() {}
+
+// CHECK-NOT: %struct._class_t
+// CHECK-NOT: %struct._objc_module
+// CHECK-NOT: @OBJC_CLASS_NAME_
+// CHECK-NOT: @"OBJC_CLASS_$_{{[0-9A-Z_a-z]+}}"
+// CHECK-NOT: @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}"
+// CHECK-NOT: @OBJC_METH_VAR_NAME_
+// CHECK-NOT: @OBJC_SELECTOR_REFERENCES_
+// CHECK-NOT: @OBJC_MODULES
+
+// CHECK-NOT: !"Objective-C Version"
+// CHECK-NOT: !"Objective-C Image Info Version"
+// CHECK-NOT: !"Objective-C Image Info Section"
+// CHECK-NOT: !"Objective-C Is Simulated"
+// CHECK-NOT: !"Objective-C Class Properties"
diff --git a/tests/codegen-llvm/darwin-objc-abi-v1.rs b/tests/codegen-llvm/darwin-objc-abi-v1.rs
new file mode 100644
index 00000000000..0fc1de9332a
--- /dev/null
+++ b/tests/codegen-llvm/darwin-objc-abi-v1.rs
@@ -0,0 +1,100 @@
+// ignore-tidy-linelength
+//@ add-core-stubs
+//@ revisions: i686_apple_darwin
+//@ [i686_apple_darwin] compile-flags: --target i686-apple-darwin
+//@ [i686_apple_darwin] needs-llvm-components: x86
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+#[no_mangle]
+pub fn get_class() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_class = "MyClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_class_again() -> *mut () {
+    // Codegen should de-duplicate this class with the one from get_class above.
+    unsafe extern "C" {
+        #[rustc_objc_class = "MyClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_selector() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_selector = "myMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_selector_again() -> *mut () {
+    // Codegen should de-duplicate this selector with the one from get_selector above.
+    unsafe extern "C" {
+        #[rustc_objc_selector = "myMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_other_class() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_class = "OtherClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_other_selector() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_selector = "otherMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+// CHECK: %struct._objc_module = type { i32, i32, ptr, ptr }
+
+// CHECK: @OBJC_CLASS_NAME_.{{[0-9]+}} = private unnamed_addr constant [8 x i8] c"MyClass\00", section "__TEXT,__cstring,cstring_literals", align 1
+// CHECK: @OBJC_CLASS_REFERENCES_.{{[0-9]+}} = private global ptr @OBJC_CLASS_NAME_.{{[0-9]+}}, section "__OBJC,__cls_refs,literal_pointers,no_dead_strip", align 4
+// CHECK-NOT: @OBJC_CLASS_NAME_
+// CHECK-NOT: @OBJC_CLASS_REFERENCES_
+
+// CHECK: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [9 x i8] c"myMethod\00", section "__TEXT,__cstring,cstring_literals", align 1
+// CHECK: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = private externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}, section "__OBJC,__message_refs,literal_pointers,no_dead_strip", align 4
+// CHECK-NOT: @OBJC_METH_VAR_NAME_
+// CHECK-NOT: @OBJC_SELECTOR_REFERENCES_
+
+// CHECK: @OBJC_CLASS_NAME_.{{[0-9]+}} = private unnamed_addr constant [11 x i8] c"OtherClass\00", section "__TEXT,__cstring,cstring_literals", align 1
+// CHECK: @OBJC_CLASS_REFERENCES_.{{[0-9]+}} = private global ptr @OBJC_CLASS_NAME_.{{[0-9]+}}, section "__OBJC,__cls_refs,literal_pointers,no_dead_strip", align 4
+
+// CHECK: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [12 x i8] c"otherMethod\00", section "__TEXT,__cstring,cstring_literals", align 1
+// CHECK: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = private externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}, section "__OBJC,__message_refs,literal_pointers,no_dead_strip", align 4
+
+// CHECK: @OBJC_CLASS_NAME_.{{[0-9]+}} = private unnamed_addr constant [1 x i8] zeroinitializer, section "__TEXT,__cstring,cstring_literals", align 1
+// CHECK: @OBJC_MODULES = private global %struct._objc_module { i32 7, i32 16, ptr @OBJC_CLASS_NAME_.{{[0-9]+}}, ptr null }, section "__OBJC,__module_info,regular,no_dead_strip", align 4
+
+// CHECK: load ptr, ptr @OBJC_CLASS_REFERENCES_.{{[0-9]+}}, align 4
+// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}}, align 4
+// CHECK: load ptr, ptr @OBJC_CLASS_REFERENCES_.{{[0-9]+}}, align 4
+// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}}, align 4
+
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Version", i32 1}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Version", i32 0}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Section", !"__OBJC,__image_info,regular"}
+// CHECK-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Class Properties", i32 64}
diff --git a/tests/codegen-llvm/darwin-objc-abi-v2.rs b/tests/codegen-llvm/darwin-objc-abi-v2.rs
new file mode 100644
index 00000000000..f142371d582
--- /dev/null
+++ b/tests/codegen-llvm/darwin-objc-abi-v2.rs
@@ -0,0 +1,185 @@
+// ignore-tidy-linelength
+//@ add-core-stubs
+//@ revisions: x86_64_macos
+//@ [x86_64_macos] compile-flags: --target x86_64-apple-darwin
+//@ [x86_64_macos] needs-llvm-components: x86
+//@ revisions: aarch64_macos
+//@ [aarch64_macos] compile-flags: --target aarch64-apple-darwin
+//@ [aarch64_macos] needs-llvm-components: aarch64
+//@ revisions: i386_ios
+//@ [i386_ios] compile-flags: --target i386-apple-ios
+//@ [i386_ios] needs-llvm-components: x86
+//@ revisions: x86_64_ios
+//@ [x86_64_ios] compile-flags: --target x86_64-apple-ios
+//@ [x86_64_ios] needs-llvm-components: x86
+//@ revisions: armv7s_ios
+//@ [armv7s_ios] compile-flags: --target armv7s-apple-ios
+//@ [armv7s_ios] needs-llvm-components: arm
+//@ revisions: aarch64_ios
+//@ [aarch64_ios] compile-flags: --target aarch64-apple-ios
+//@ [aarch64_ios] needs-llvm-components: aarch64
+//@ revisions: aarch64_ios_sim
+//@ [aarch64_ios_sim] compile-flags: --target aarch64-apple-ios-sim
+//@ [aarch64_ios_sim] needs-llvm-components: aarch64
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+
+extern crate minicore;
+use minicore::*;
+
+#[no_mangle]
+pub fn get_class() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_class = "MyClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_class_again() -> *mut () {
+    // Codegen should de-duplicate this class with the one from get_class above.
+    unsafe extern "C" {
+        #[rustc_objc_class = "MyClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_selector() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_selector = "myMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_selector_again() -> *mut () {
+    // Codegen should de-duplicate this selector with the one from get_selector above.
+    unsafe extern "C" {
+        #[rustc_objc_selector = "myMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_other_class() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_class = "OtherClass"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+#[no_mangle]
+pub fn get_other_selector() -> *mut () {
+    unsafe extern "C" {
+        #[rustc_objc_selector = "otherMethod"]
+        safe static VAL: *mut ();
+    }
+    VAL
+}
+
+// CHECK: %struct._class_t = type { ptr, ptr, ptr, ptr, ptr }
+
+// CHECK: @"OBJC_CLASS_$_MyClass" = external global %struct._class_t
+// CHECK: @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}" = internal global ptr @"OBJC_CLASS_$_MyClass", section "__DATA,__objc_classrefs,regular,no_dead_strip",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+// CHECK-NOT: @"OBJC_CLASS_$_MyClass"
+// CHECK-NOT: @"OBJC_CLASSLIST_REFERENCES_$_
+
+// CHECK: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [9 x i8] c"myMethod\00", section "__TEXT,__objc_methname,cstring_literals", align 1
+// CHECK: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+// CHECK-NOT: @OBJC_METH_VAR_NAME_
+// CHECK-NOT: @OBJC_SELECTOR_REFERENCES_
+
+// CHECK: @"OBJC_CLASS_$_OtherClass" = external global %struct._class_t
+// CHECK: @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}" = internal global ptr @"OBJC_CLASS_$_OtherClass", section "__DATA,__objc_classrefs,regular,no_dead_strip",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [12 x i8] c"otherMethod\00", section "__TEXT,__objc_methname,cstring_literals", align 1
+// CHECK: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK-NOT: @OBJC_CLASS_NAME_
+// CHECK-NOT: @OBJC_MODULES
+
+// CHECK: load ptr, ptr @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}},
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK: load ptr, ptr @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}",
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}},
+// x86_64_macos-SAME: align 8
+// aarch64_macos-SAME: align 8
+// i386_ios-SAME: align 4
+// x86_64_ios-SAME: align 8
+// armv7s_ios-SAME: align 4
+// aarch64_ios-SAME: align 8
+// aarch64_ios_sim-SAME: align 8
+
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Version", i32 2}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Version", i32 0}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
+
+// x86_64_macos-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// aarch64_macos-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// i386_ios: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// x86_64_ios: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// armv7s_ios-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// aarch64_ios-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// aarch64_ios_sim: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Class Properties", i32 64}
diff --git a/tests/codegen-llvm/darwin-objc-cross-crate.rs b/tests/codegen-llvm/darwin-objc-cross-crate.rs
new file mode 100644
index 00000000000..74ad9a27346
--- /dev/null
+++ b/tests/codegen-llvm/darwin-objc-cross-crate.rs
@@ -0,0 +1,58 @@
+// Test that Objective-C class and selector references inlined across crates
+// get defined in this CGU but non-inline references don't.
+
+// ignore-tidy-linelength
+//@ aux-build: darwin_objc_aux.rs
+//@ revisions: x86_64_macos aarch64_macos
+//@ [x86_64_macos] only-x86_64-apple-darwin
+//@ [aarch64_macos] only-aarch64-apple-darwin
+
+#![crate_type = "lib"]
+#![feature(darwin_objc)]
+
+use std::os::darwin::objc;
+
+extern crate darwin_objc_aux as aux;
+
+#[no_mangle]
+pub fn get_object_class() -> objc::Class {
+    aux::inline_get_object_class()
+}
+
+#[no_mangle]
+pub fn get_alloc_selector() -> objc::SEL {
+    aux::inline_get_alloc_selector()
+}
+
+#[no_mangle]
+pub fn get_string_class() -> objc::Class {
+    aux::never_inline_get_string_class()
+}
+
+#[no_mangle]
+pub fn get_init_selector() -> objc::SEL {
+    aux::never_inline_get_init_selector()
+}
+
+// CHECK: %struct._class_t = type { ptr, ptr, ptr, ptr, ptr }
+
+// CHECK: @"OBJC_CLASS_$_NSObject" = external global %struct._class_t
+// CHECK: @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}" = internal global ptr @"OBJC_CLASS_$_NSObject", section "__DATA,__objc_classrefs,regular,no_dead_strip", align 8
+
+// CHECK: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [6 x i8] c"alloc\00", section "__TEXT,__objc_methname,cstring_literals", align 1
+// CHECK: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}, section "__DATA,__objc_selrefs,literal_pointers,no_dead_strip", align 8
+
+// CHECK-NOT: @"OBJC_CLASS_$_NSString" = external global %struct._class_t
+// CHECK-NOT: @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}" = internal global ptr @"OBJC_CLASS_$_NSString"
+
+// CHECK-NOT: @OBJC_METH_VAR_NAME_.{{[0-9]+}} = private unnamed_addr constant [5 x i8] c"init\00"
+// CHECK-NOT: @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}} = internal externally_initialized global ptr @OBJC_METH_VAR_NAME_.{{[0-9]+}}
+
+// CHECK: load ptr, ptr @"OBJC_CLASSLIST_REFERENCES_$_.{{[0-9]+}}", align 8
+// CHECK: load ptr, ptr @OBJC_SELECTOR_REFERENCES_.{{[0-9]+}}, align 8
+
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Version", i32 2}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Version", i32 0}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
+// CHECK-NOT: !{{[0-9]+}} = !{i32 1, !"Objective-C Is Simulated", i32 32}
+// CHECK: !{{[0-9]+}} = !{i32 1, !"Objective-C Class Properties", i32 64}
diff --git a/tests/ui/README.md b/tests/ui/README.md
index 66c1bb905a7..3b28ef694dd 100644
--- a/tests/ui/README.md
+++ b/tests/ui/README.md
@@ -350,6 +350,12 @@ Tests for FFI with C varargs (`va_list`).
 
 Tests for detection and handling of cyclic trait dependencies.
 
+## `tests/ui/darwin-objc/`: Darwin Objective-C
+
+Tests exercising `#![feature(darwin_objc)]`.
+
+See [Tracking Issue for `darwin_objc` #145496](https://github.com/rust-lang/rust/issues/145496).
+
 ## `tests/ui/dataflow_const_prop/`
 
 Contains a single regression test for const prop in `SwitchInt` pass crashing when `ptr2int` transmute is involved.
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-arg.rs b/tests/ui/darwin-objc/darwin-objc-bad-arg.rs
new file mode 100644
index 00000000000..70eb83aa052
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-arg.rs
@@ -0,0 +1,36 @@
+// Test that `objc::class!` and `objc::selector!` only take string literals.
+
+//@ edition: 2024
+//@ only-apple
+
+#![feature(darwin_objc)]
+
+use std::os::darwin::objc;
+
+pub fn main() {
+    let s = "NSObject";
+    objc::class!(s);
+    //~^ ERROR attribute value must be a literal
+
+    objc::class!(NSObject);
+    //~^ ERROR attribute value must be a literal
+
+    objc::class!(123);
+    //~^ ERROR `objc::class!` expected a string literal
+
+    objc::class!("NSObject\0");
+    //~^ ERROR `objc::class!` may not contain null characters
+
+    let s = "alloc";
+    objc::selector!(s);
+    //~^ ERROR attribute value must be a literal
+
+    objc::selector!(alloc);
+    //~^ ERROR attribute value must be a literal
+
+    objc::selector!(123);
+    //~^ ERROR `objc::selector!` expected a string literal
+
+    objc::selector!("alloc\0");
+    //~^ ERROR `objc::selector!` may not contain null characters
+}
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-arg.stderr b/tests/ui/darwin-objc/darwin-objc-bad-arg.stderr
new file mode 100644
index 00000000000..99eeb27e30c
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-arg.stderr
@@ -0,0 +1,50 @@
+error: attribute value must be a literal
+  --> $DIR/darwin-objc-bad-arg.rs:12:18
+   |
+LL |     objc::class!(s);
+   |                  ^
+
+error: attribute value must be a literal
+  --> $DIR/darwin-objc-bad-arg.rs:15:18
+   |
+LL |     objc::class!(NSObject);
+   |                  ^^^^^^^^
+
+error: `objc::class!` expected a string literal
+  --> $DIR/darwin-objc-bad-arg.rs:18:18
+   |
+LL |     objc::class!(123);
+   |                  ^^^
+
+error: `objc::class!` may not contain null characters
+  --> $DIR/darwin-objc-bad-arg.rs:21:18
+   |
+LL |     objc::class!("NSObject\0");
+   |                  ^^^^^^^^^^^^
+
+error: attribute value must be a literal
+  --> $DIR/darwin-objc-bad-arg.rs:25:21
+   |
+LL |     objc::selector!(s);
+   |                     ^
+
+error: attribute value must be a literal
+  --> $DIR/darwin-objc-bad-arg.rs:28:21
+   |
+LL |     objc::selector!(alloc);
+   |                     ^^^^^
+
+error: `objc::selector!` expected a string literal
+  --> $DIR/darwin-objc-bad-arg.rs:31:21
+   |
+LL |     objc::selector!(123);
+   |                     ^^^
+
+error: `objc::selector!` may not contain null characters
+  --> $DIR/darwin-objc-bad-arg.rs:34:21
+   |
+LL |     objc::selector!("alloc\0");
+   |                     ^^^^^^^^^
+
+error: aborting due to 8 previous errors
+
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-const.rs b/tests/ui/darwin-objc/darwin-objc-bad-const.rs
new file mode 100644
index 00000000000..ccf28697b48
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-const.rs
@@ -0,0 +1,17 @@
+// Test that `objc::class!` and `objc::selector!` aren't `const` expressions.
+// The system gives them their final values at dynamic load time.
+
+//@ edition: 2024
+//@ only-apple
+
+#![feature(darwin_objc)]
+
+use std::os::darwin::objc;
+
+pub const CLASS: objc::Class = objc::class!("NSObject");
+//~^ ERROR cannot access extern static `CLASS::VAL` [E0080]
+
+pub const SELECTOR: objc::SEL = objc::selector!("alloc");
+//~^ ERROR cannot access extern static `SELECTOR::VAL` [E0080]
+
+pub fn main() {}
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-const.stderr b/tests/ui/darwin-objc/darwin-objc-bad-const.stderr
new file mode 100644
index 00000000000..43d0b7d761f
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-const.stderr
@@ -0,0 +1,19 @@
+error[E0080]: cannot access extern static `CLASS::VAL`
+  --> $DIR/darwin-objc-bad-const.rs:11:32
+   |
+LL | pub const CLASS: objc::Class = objc::class!("NSObject");
+   |                                ^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `CLASS` failed here
+   |
+   = note: this error originates in the macro `objc::class` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0080]: cannot access extern static `SELECTOR::VAL`
+  --> $DIR/darwin-objc-bad-const.rs:14:33
+   |
+LL | pub const SELECTOR: objc::SEL = objc::selector!("alloc");
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `SELECTOR` failed here
+   |
+   = note: this error originates in the macro `objc::selector` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-ref.rs b/tests/ui/darwin-objc/darwin-objc-bad-ref.rs
new file mode 100644
index 00000000000..fb1437366dd
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-ref.rs
@@ -0,0 +1,31 @@
+// Test that `objc::class!` and `objc::selector!` can't be returned by reference.
+// A single instance may have multiple addresses (e.g. across dylib boundaries).
+
+//@ edition: 2024
+//@ only-apple
+
+#![feature(darwin_objc)]
+
+use std::os::darwin::objc;
+
+pub fn class_ref<'a>() -> &'a objc::Class {
+    &objc::class!("NSObject")
+    //~^ ERROR cannot return reference to temporary value [E0515]
+}
+
+pub fn class_ref_static() -> &'static objc::Class {
+    &objc::class!("NSObject")
+    //~^ ERROR cannot return reference to temporary value [E0515]
+}
+
+pub fn selector_ref<'a>() -> &'a objc::SEL {
+    &objc::selector!("alloc")
+    //~^ ERROR cannot return reference to temporary value [E0515]
+}
+
+pub fn selector_ref_static() -> &'static objc::SEL {
+    &objc::selector!("alloc")
+    //~^ ERROR cannot return reference to temporary value [E0515]
+}
+
+pub fn main() {}
diff --git a/tests/ui/darwin-objc/darwin-objc-bad-ref.stderr b/tests/ui/darwin-objc/darwin-objc-bad-ref.stderr
new file mode 100644
index 00000000000..b09e6a75c84
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-bad-ref.stderr
@@ -0,0 +1,39 @@
+error[E0515]: cannot return reference to temporary value
+  --> $DIR/darwin-objc-bad-ref.rs:12:5
+   |
+LL |     &objc::class!("NSObject")
+   |     ^------------------------
+   |     ||
+   |     |temporary value created here
+   |     returns a reference to data owned by the current function
+
+error[E0515]: cannot return reference to temporary value
+  --> $DIR/darwin-objc-bad-ref.rs:17:5
+   |
+LL |     &objc::class!("NSObject")
+   |     ^------------------------
+   |     ||
+   |     |temporary value created here
+   |     returns a reference to data owned by the current function
+
+error[E0515]: cannot return reference to temporary value
+  --> $DIR/darwin-objc-bad-ref.rs:22:5
+   |
+LL |     &objc::selector!("alloc")
+   |     ^------------------------
+   |     ||
+   |     |temporary value created here
+   |     returns a reference to data owned by the current function
+
+error[E0515]: cannot return reference to temporary value
+  --> $DIR/darwin-objc-bad-ref.rs:27:5
+   |
+LL |     &objc::selector!("alloc")
+   |     ^------------------------
+   |     ||
+   |     |temporary value created here
+   |     returns a reference to data owned by the current function
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0515`.
diff --git a/tests/ui/darwin-objc/darwin-objc-class-selector.rs b/tests/ui/darwin-objc/darwin-objc-class-selector.rs
new file mode 100644
index 00000000000..b9a2fc3634f
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-class-selector.rs
@@ -0,0 +1,31 @@
+// Call `[NSObject class]` using `objc::class!` and `objc::selector!`.
+
+//@ edition: 2024
+//@ only-apple
+//@ run-pass
+
+#![feature(darwin_objc)]
+
+use std::mem::transmute;
+use std::os::darwin::objc;
+
+#[link(name = "Foundation", kind = "framework")]
+unsafe extern "C" {}
+
+#[link(name = "objc", kind = "dylib")]
+unsafe extern "C" {
+    unsafe fn objc_msgSend();
+}
+
+fn main() {
+    let msg_send_fn = unsafe {
+        transmute::<
+            unsafe extern "C" fn(),
+            unsafe extern "C" fn(objc::Class, objc::SEL) -> objc::Class,
+        >(objc_msgSend)
+    };
+    let static_sel = objc::selector!("class");
+    let static_class = objc::class!("NSObject");
+    let runtime_class = unsafe { msg_send_fn(static_class, static_sel) };
+    assert_eq!(static_class, runtime_class);
+}
diff --git a/tests/ui/darwin-objc/darwin-objc-class.rs b/tests/ui/darwin-objc/darwin-objc-class.rs
new file mode 100644
index 00000000000..851149d8726
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-class.rs
@@ -0,0 +1,39 @@
+// Test that `objc::class!` returns the same thing as `objc_lookUpClass`.
+
+//@ edition: 2024
+//@ only-apple
+//@ run-pass
+
+#![feature(darwin_objc)]
+
+use std::ffi::c_char;
+use std::os::darwin::objc;
+
+#[link(name = "Foundation", kind = "framework")]
+unsafe extern "C" {}
+
+#[link(name = "objc")]
+unsafe extern "C" {
+    fn objc_lookUpClass(methname: *const c_char) -> objc::Class;
+}
+
+fn get_object_class() -> objc::Class {
+    objc::class!("NSObject")
+}
+
+fn lookup_object_class() -> objc::Class {
+    unsafe { objc_lookUpClass(c"NSObject".as_ptr()) }
+}
+
+fn get_string_class() -> objc::Class {
+    objc::class!("NSString")
+}
+
+fn lookup_string_class() -> objc::Class {
+    unsafe { objc_lookUpClass(c"NSString".as_ptr()) }
+}
+
+fn main() {
+    assert_eq!(get_object_class(), lookup_object_class());
+    assert_eq!(get_string_class(), lookup_string_class());
+}
diff --git a/tests/ui/darwin-objc/darwin-objc-selector.rs b/tests/ui/darwin-objc/darwin-objc-selector.rs
new file mode 100644
index 00000000000..008ae4c4ca4
--- /dev/null
+++ b/tests/ui/darwin-objc/darwin-objc-selector.rs
@@ -0,0 +1,36 @@
+// Test that `objc::selector!` returns the same thing as `sel_registerName`.
+
+//@ edition: 2024
+//@ only-apple
+//@ run-pass
+
+#![feature(darwin_objc)]
+
+use std::ffi::c_char;
+use std::os::darwin::objc;
+
+#[link(name = "objc")]
+unsafe extern "C" {
+    fn sel_registerName(methname: *const c_char) -> objc::SEL;
+}
+
+fn get_alloc_selector() -> objc::SEL {
+    objc::selector!("alloc")
+}
+
+fn register_alloc_selector() -> objc::SEL {
+    unsafe { sel_registerName(c"alloc".as_ptr()) }
+}
+
+fn get_init_selector() -> objc::SEL {
+    objc::selector!("initWithCString:encoding:")
+}
+
+fn register_init_selector() -> objc::SEL {
+    unsafe { sel_registerName(c"initWithCString:encoding:".as_ptr()) }
+}
+
+fn main() {
+    assert_eq!(get_alloc_selector(), register_alloc_selector());
+    assert_eq!(get_init_selector(), register_init_selector());
+}