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Greg Parker
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[runtime] Register a hook for class name lookup from libobjc (swiftlang#20650)
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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@@ -798,6 +798,22 @@ 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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// RUN: %empty-directory(%t)
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// RUN: %target-build-swift-dylib(%t/libresilient_struct.%target-dylib-extension) -Xfrontend -enable-resilience -Xfrontend -enable-class-resilience %S/../../Inputs/resilient_struct.swift -emit-module -emit-module-path %t/resilient_struct.swiftmodule -module-name resilient_struct
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// RUN: %target-codesign %t/libresilient_struct.%target-dylib-extension
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// RUN: %target-build-swift-dylib(%t/libresilient_class.%target-dylib-extension) -Xfrontend -enable-resilience -Xfrontend -enable-class-resilience %S/../../Inputs/resilient_class.swift -emit-module -emit-module-path %t/resilient_class.swiftmodule -module-name resilient_class -I%t -L%t -lresilient_struct
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// RUN: %target-codesign %t/libresilient_class.%target-dylib-extension
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// RUN: %target-build-swift %s -L %t -I %t -lresilient_struct -lresilient_class -o %t/main -Xlinker -rpath -Xlinker %t
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// RUN: %target-codesign %t/main
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// RUN: %target-run %t/main %t/libresilient_struct.%target-dylib-extension %t/libresilient_class.%target-dylib-extension
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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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import resilient_struct
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import resilient_class
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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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class ResilientSuperclass : ResilientOutsideParent {
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var supervalue = 10
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}
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class ResilientSubclass : ResilientSuperclass {
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var subvalue = 20
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}
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class ResilientFieldSuperclassSwift {
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var supervalue = ResilientInt(i: 1)
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}
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class ResilientFieldSubclassSwift : ResilientFieldSuperclassSwift {
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var subvalue = ResilientInt(i: 2)
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}
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class ResilientFieldSuperclassObjC : NSObject {
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var supervalue = ResilientInt(i: 3)
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}
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class ResilientFieldSubclassObjC : ResilientFieldSuperclassObjC {
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var subvalue = ResilientInt(i: 4)
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}
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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("ResilientSubclass")
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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.ResilientSubclass")
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requireClass(named: "main.ResilientSuperclass")
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expectEqual(ResilientSuperclass().supervalue, 10)
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expectEqual(ResilientSubclass().supervalue, 10)
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expectEqual(ResilientSubclass().subvalue, 20)
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}
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testSuite.test("ResilientField")
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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.ResilientFieldSubclassSwift")
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requireClass(named: "main.ResilientFieldSuperclassSwift")
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requireClass(named: "main.ResilientFieldSubclassObjC")
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requireClass(named: "main.ResilientFieldSuperclassObjC")
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expectEqual(ResilientFieldSuperclassSwift().supervalue.i, 1)
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expectEqual(ResilientFieldSubclassSwift().supervalue.i, 1)
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expectEqual(ResilientFieldSubclassSwift().subvalue.i, 2)
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expectEqual(ResilientFieldSuperclassObjC().supervalue.i, 3)
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expectEqual(ResilientFieldSubclassObjC().supervalue.i, 3)
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expectEqual(ResilientFieldSubclassObjC().subvalue.i, 4)
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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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