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Greg Parker
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[runtime] Register a hook for class name lookup from libobjc
libobjc needs to look up classes by name. Some Swift classes, such as instantiated generics and their subclasses, are created only on demand. Now a by-name lookup from libobjc counts as a demand for those classes. rdar://problem/27808571
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‎include/swift/Runtime/Metadata.h

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@@ -495,6 +495,11 @@ SWIFT_RUNTIME_EXPORT
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const ClassMetadata *
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swift_getObjCClassFromMetadata(const Metadata *theClass);
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// Get the ObjC class object from class type metadata,
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// or nullptr if the type isn't an ObjC class.
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const ClassMetadata *
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swift_getObjCClassFromMetadataConditional(const Metadata *theClass);
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SWIFT_RUNTIME_EXPORT
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const ClassMetadata *
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swift_getObjCClassFromObject(HeapObject *object);

‎stdlib/public/runtime/Metadata.cpp

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@@ -756,6 +756,22 @@ swift::swift_getObjCClassFromMetadata(const Metadata *theMetadata) {
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return theClass;
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}
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const ClassMetadata *
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swift::swift_getObjCClassFromMetadataConditional(const Metadata *theMetadata) {
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// If it's an ordinary class, return it.
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if (auto theClass = dyn_cast<ClassMetadata>(theMetadata)) {
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return theClass;
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}
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// Unwrap ObjC class wrappers.
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if (auto wrapper = dyn_cast<ObjCClassWrapperMetadata>(theMetadata)) {
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return wrapper->Class;
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}
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// Not an ObjC class after all.
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return nil;
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}
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#endif
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/***************************************************************************/

‎stdlib/public/runtime/MetadataLookup.cpp

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@@ -47,6 +47,7 @@ using namespace reflection;
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#include <objc/runtime.h>
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#include <objc/message.h>
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#include <objc/objc.h>
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#include <dlfcn.h>
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#endif
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/// Produce a Demangler value suitable for resolving runtime type metadata
@@ -1284,6 +1285,63 @@ swift_stdlib_getTypeByMangledName(
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return swift_checkMetadataState(MetadataState::Complete, metadata).Value;
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}
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#if SWIFT_OBJC_INTEROP
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// Return the ObjC class for the given type name.
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// This gets installed as a callback from libobjc.
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// FIXME: delete this #if and dlsym once we don't
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// need to build with older libobjc headers
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#if !OBJC_GETCLASSHOOK_DEFINED
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using objc_hook_getClass = BOOL(*)(const char * _Nonnull name,
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Class _Nullable * _Nonnull outClass);
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#endif
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static objc_hook_getClass OldGetClassHook;
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static BOOL
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getObjCClassByMangledName(const char * _Nonnull typeName,
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Class _Nullable * _Nonnull outClass) {
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auto metadata = swift_stdlib_getTypeByMangledName(typeName, strlen(typeName),
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/* no substitutions */
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nullptr, nullptr);
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if (metadata) {
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auto objcClass =
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reinterpret_cast<Class>(
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const_cast<ClassMetadata *>(
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swift_getObjCClassFromMetadataConditional(metadata)));
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if (objcClass) {
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*outClass = objcClass;
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return YES;
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}
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}
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return OldGetClassHook(typeName, outClass);
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}
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__attribute__((constructor))
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static void installGetClassHook() {
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// FIXME: delete this #if and dlsym once we don't
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// need to build with older libobjc headers
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#if !OBJC_GETCLASSHOOK_DEFINED
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using objc_hook_getClass = BOOL(*)(const char * _Nonnull name,
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Class _Nullable * _Nonnull outClass);
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auto objc_setHook_getClass =
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(void(*)(objc_hook_getClass _Nonnull,
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objc_hook_getClass _Nullable * _Nonnull))
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dlsym(RTLD_DEFAULT, "objc_setHook_getClass");
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#endif
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#pragma clang diagnostic push
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#pragma clang diagnostic ignored "-Wunguarded-availability"
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if (objc_setHook_getClass) {
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objc_setHook_getClass(getObjCClassByMangledName, &OldGetClassHook);
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}
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#pragma clang diagnostic pop
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}
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#endif
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unsigned SubstGenericParametersFromMetadata::
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buildDescriptorPath(const ContextDescriptor *context) const {
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// Terminating condition: we don't have a context.

‎test/Interpreter/SDK/objc_getClass.swift

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@@ -0,0 +1,142 @@
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// RUN: %target-run-simple-swift
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// REQUIRES: executable_test
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// REQUIRES: objc_interop
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// Test Swift's hook for objc_getClass()
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import StdlibUnittest
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import ObjectiveC
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import Foundation
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// Old OS versions do not have this hook.
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let getClassHookMissing = {
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nil == dlsym(UnsafeMutableRawPointer(bitPattern: -2),
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"objc_setHook_getClass")
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}()
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var testSuite = TestSuite("objc_getClass")
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class SwiftSuperclass { }
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class SwiftSubclass : SwiftSuperclass { }
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class ObjCSuperclass : NSObject { }
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class ObjCSubclass : ObjCSuperclass { }
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class MangledSwiftSuperclass { }
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class MangledSwiftSubclass : MangledSwiftSuperclass { }
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class MangledObjCSuperclass : NSObject { }
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class MangledObjCSubclass : MangledObjCSuperclass { }
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class GenericSwiftClass<Value> {
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let value: Value
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init(value: Value) { self.value = value }
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}
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class ConstrainedSwiftSuperclass : GenericSwiftClass<String> {
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init() { super.init(value:"") }
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}
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class ConstrainedSwiftSubclass : ConstrainedSwiftSuperclass { }
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class MangledGenericSwiftClass<Value> {
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let value: Value
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init(value: Value) { self.value = value }
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}
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class MangledConstrainedSwiftSuperclass : MangledGenericSwiftClass<String> {
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init() { super.init(value:"") }
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}
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class MangledConstrainedSwiftSubclass : MangledConstrainedSwiftSuperclass { }
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class GenericObjCClass<Value> : NSObject {
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let value: Value
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init(value: Value) { self.value = value }
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}
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class ConstrainedObjCSuperclass : GenericObjCClass<String> {
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init() { super.init(value:"") }
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}
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class ConstrainedObjCSubclass : ConstrainedObjCSuperclass { }
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class MangledGenericObjCClass<Value> : NSObject {
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let value: Value
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init(value: Value) { self.value = value }
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}
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class MangledConstrainedObjCSuperclass : MangledGenericObjCClass<String> {
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init() { super.init(value:"") }
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}
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class MangledConstrainedObjCSubclass : MangledConstrainedObjCSuperclass { }
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func requireClass(named name: String, demangledName: String) {
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for _ in 1...2 {
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let cls: AnyClass? = NSClassFromString(name)
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expectNotNil(cls, "class named \(name) unexpectedly not found")
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expectEqual(NSStringFromClass(cls!), demangledName,
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"class named \(name) has the wrong name");
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}
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}
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func requireClass(named name: String) {
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return requireClass(named: name, demangledName: name)
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}
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testSuite.test("Basic") {
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requireClass(named: "main.SwiftSubclass")
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requireClass(named: "main.SwiftSuperclass")
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requireClass(named: "main.ObjCSubclass")
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requireClass(named: "main.ObjCSuperclass")
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}
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testSuite.test("BasicMangled") {
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requireClass(named: "_TtC4main20MangledSwiftSubclass",
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demangledName: "main.MangledSwiftSubclass")
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requireClass(named: "_TtC4main22MangledSwiftSuperclass",
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demangledName: "main.MangledSwiftSuperclass")
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requireClass(named: "_TtC4main19MangledObjCSubclass",
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demangledName: "main.MangledObjCSubclass")
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requireClass(named: "_TtC4main21MangledObjCSuperclass",
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demangledName: "main.MangledObjCSuperclass")
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}
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testSuite.test("Generic")
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.skip(.custom({ getClassHookMissing },
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reason: "objc_getClass hook not present"))
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.code {
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requireClass(named: "main.ConstrainedSwiftSubclass")
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requireClass(named: "main.ConstrainedSwiftSuperclass")
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requireClass(named: "main.ConstrainedObjCSubclass")
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requireClass(named: "main.ConstrainedObjCSuperclass")
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}
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testSuite.test("GenericMangled")
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.skip(.custom({ getClassHookMissing },
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reason: "objc_getClass hook not present"))
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.code {
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requireClass(named: "_TtC4main24ConstrainedSwiftSubclass",
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demangledName: "main.ConstrainedSwiftSubclass")
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requireClass(named: "_TtC4main26ConstrainedSwiftSuperclass",
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demangledName: "main.ConstrainedSwiftSuperclass")
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requireClass(named: "_TtC4main23ConstrainedObjCSubclass",
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demangledName: "main.ConstrainedObjCSubclass")
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requireClass(named: "_TtC4main25ConstrainedObjCSuperclass",
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demangledName: "main.ConstrainedObjCSuperclass")
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}
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testSuite.test("NotPresent") {
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// This class does not exist.
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expectNil(NSClassFromString("main.ThisClassDoesNotExist"));
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// This name is improperly mangled
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expectNil(NSClassFromString("_TtC5main"));
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// Swift.Int is not a class type.
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expectNil(NSClassFromString("Si"))
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}
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runAllTests()
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