compiler_rt: implement __isPlatformVersionAtLeast (Objective-C @available expressions) for Darwin (#10232)

CMakeLists.txt

@@ -497,6 +497,7 @@ set(ZIG_STAGE2_SOURCES
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/muloti4.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/multi3.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negXf2.zig"
+    "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/os_version_check.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/popcountdi2.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/shift.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/stack_probe.zig"

lib/std/special/compiler_rt.zig

@@ -7,6 +7,7 @@ const abi = builtin.abi;
 
 const is_gnu = abi.isGnu();
 const is_mingw = os_tag == .windows and is_gnu;
+const is_darwin = std.Target.Os.Tag.isDarwin(os_tag);
 
 const linkage = if (is_test)
     std.builtin.GlobalLinkage.Internal
@@ -336,6 +337,11 @@ comptime {
         const __popcountdi2 = @import("compiler_rt/popcountdi2.zig").__popcountdi2;
         @export(__popcountdi2, .{ .name = "__popcountdi2", .linkage = linkage });
 
+        if (is_darwin) {
+            const __isPlatformVersionAtLeast = @import("compiler_rt/os_version_check.zig").__isPlatformVersionAtLeast;
+            @export(__isPlatformVersionAtLeast, .{ .name = "__isPlatformVersionAtLeast", .linkage = linkage });
+        }
+
         const __mulsi3 = @import("compiler_rt/int.zig").__mulsi3;
         @export(__mulsi3, .{ .name = "__mulsi3", .linkage = linkage });
         const __muldi3 = @import("compiler_rt/muldi3.zig").__muldi3;

lib/std/special/compiler_rt/os_version_check.zig

@@ -0,0 +1,50 @@
+const testing = @import("std").testing;
+const builtin = @import("builtin");
+
+// Ported from llvm-project 13.0.0 d7b669b3a30345cfcdb2fde2af6f48aa4b94845d
+//
+// https://github.com/llvm/llvm-project/blob/llvmorg-13.0.0/compiler-rt/lib/builtins/os_version_check.c
+
+// The compiler generates calls to __isPlatformVersionAtLeast() when Objective-C's @available
+// function is invoked.
+//
+// Old versions of clang would instead emit calls to __isOSVersionAtLeast(), which is still
+// supported in clang's compiler-rt implementation today in case anyone tries to link an object file
+// produced with an old clang version. This requires dynamically loading frameworks, parsing a
+// system plist file, and generally adds a fair amount of complexity to the implementation and so
+// our implementation differs by simply removing that backwards compatability support. We only use
+// the newer codepath, which merely calls out to the Darwin _availability_version_check API which is
+// available on macOS 10.15+, iOS 13+, tvOS 13+ and watchOS 6+.
+
+inline fn constructVersion(major: u32, minor: u32, subminor: u32) u32 {
+    return ((major & 0xffff) << 16) | ((minor & 0xff) << 8) | (subminor & 0xff);
+}
+
+// Darwin-only
+pub fn __isPlatformVersionAtLeast(platform: u32, major: u32, minor: u32, subminor: u32) callconv(.C) i32 {
+    return @boolToInt(_availability_version_check(1, &[_]dyld_build_version_t{
+        .{
+            .platform = platform,
+            .version = constructVersion(major, minor, subminor),
+        },
+    }));
+}
+
+// _availability_version_check darwin API support.
+const dyld_platform_t = u32;
+const dyld_build_version_t = extern struct {
+    platform: dyld_platform_t,
+    version: u32,
+};
+// Darwin-only
+extern "c" fn _availability_version_check(count: u32, versions: [*c]const dyld_build_version_t) bool;
+
+test "isPlatformVersionAtLeast" {
+    if (!builtin.os.tag.isDarwin()) return error.SkipZigTest;
+
+    // Note: this test depends on the actual host OS version since it is merely calling into the
+    // native Darwin API.
+    const macos_platform_constant = 1;
+    try testing.expect(__isPlatformVersionAtLeast(macos_platform_constant, 10, 0, 15) == 1);
+    try testing.expect(__isPlatformVersionAtLeast(macos_platform_constant, 99, 0, 0) == 0);
+}