[ClangImporter] Forward generic parameters while importing generic @compatibility_alias

When importing @compatibility_alias declarations check if underlying declaration
is generic and if so, forward generic environment and generic parameters (if any)
to newly created typealias declaration, otherwise there is going to be a mismatch
between type associated with typealias and its declaration which leads to crashes.

Resolves: rdar://problem/39849926

Author: xedin

lib/ClangImporter/ImportDecl.cpp

@@ -4966,6 +4966,12 @@ namespace {
                     Impl.importSourceLoc(decl->getLocation()),
                     /*genericparams=*/nullptr, dc);
 
+      if (auto *GTD = dyn_cast<GenericTypeDecl>(typeDecl)) {
+        typealias->setGenericEnvironment(GTD->getGenericEnvironment());
+        if (GTD->isGeneric())
+          typealias->setGenericParams(GTD->getGenericParams()->clone(typealias));
+      }
+
       typealias->setUnderlyingType(Impl.getSugaredTypeReference(typeDecl));
       return typealias;
     }

test/ClangImporter/Inputs/custom-modules/ObjCIRExtras.h

@@ -60,8 +60,16 @@
 @interface SwiftNameTestErrorSub : SwiftNameTestError
 @end
 
+@interface SwiftGenericNameTest<T> : NSObject
+@end
+
+@interface SwiftConstrGenericNameTest<T:NSNumber *> : NSNumber
+@end
+
 int global_int SWIFT_NAME(GlobalInt);
 
 @compatibility_alias SwiftNameAlias SwiftNameTest;
+@compatibility_alias SwiftGenericNameAlias SwiftGenericNameTest;
+@compatibility_alias SwiftConstrGenericNameAlias SwiftConstrGenericNameTest;
 
 #pragma clang assume_nonnull end

test/ClangImporter/generic_compatibility_alias.swift

@@ -0,0 +1,23 @@
+// RUN: %empty-directory(%t)
+// RUN: %build-clang-importer-objc-overlays
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk-nosource -I %t) -module-name generic_compat_alias -I %S/Inputs/custom-modules -typecheck -verify %s
+
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+import ObjectiveC
+import Foundation
+import ObjCIRExtras
+
+func foo(_: SwiftConstrGenericNameAlias<String>) {
+// expected-error@-1 {{'SwiftConstrGenericNameAlias' requires that 'String' inherit from 'NSNumber'}}
+// expected-note@-2  {{requirement specified as 'T' : 'NSNumber' [with T = String]}}
+}
+
+func faz(_: SwiftGenericNameAlias<Int>) {
+// expected-error@-1 {{'SwiftGenericNameAlias' requires that 'Int' be a class type}}
+// expected-note@-2  {{requirement specified as 'T' : 'AnyObject' [with T = Int]}}
+}
+
+func bar(_: SwiftGenericNameAlias<NSNumber>) {} // Ok
+func baz<T: AnyObject>(_: SwiftGenericNameAlias<T>) {} // Ok

test/ClangImporter/objc_ir.swift

@@ -336,6 +336,13 @@ func testCompatibilityAliasMangling(obj: SwiftNameAlias) {
   // CHECK: call void @llvm.dbg.declare(metadata %TSo13SwiftNameTestC** {{%.+}}, metadata ![[SWIFT_NAME_ALIAS_VAR:[0-9]+]], metadata !DIExpression())
 }
 
+func testGenericCompatibilityAliasMangling(generic_obj: SwiftGenericNameAlias<NSNumber>) {
+  // CHECK: call void @llvm.dbg.declare(metadata %TSo20SwiftGenericNameTestCySo8NSNumberCG** {{%.+}}, metadata ![[SWIFT_GENERIC_NAME_ALIAS_VAR:[0-9]+]], metadata !DIExpression())
+}
+
+func testConstrGenericCompatibilityAliasMangling(constr_generic_obj: SwiftConstrGenericNameAlias<NSNumber>) {
+  // CHECK: call void @llvm.dbg.declare(metadata %TSo26SwiftConstrGenericNameTestCySo8NSNumberCG** {{%.+}}, metadata ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_VAR:[0-9]+]], metadata !DIExpression())
+}
 
 // CHECK: linkonce_odr hidden {{.*}} @"$SSo1BC3intABSgs5Int32V_tcfcTO"
 // CHECK: load i8*, i8** @"\01L_selector(initWithInt:)"
@@ -347,3 +354,8 @@ func testCompatibilityAliasMangling(obj: SwiftNameAlias) {
 // CHECK: ![[SWIFT_NAME_ALIAS_VAR]] = !DILocalVariable(name: "obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_NAME_ALIAS_TYPE:[0-9]+]])
 // CHECK: ![[SWIFT_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$SSo14SwiftNameAliasaD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})
 
+// CHECK: ![[SWIFT_GENERIC_NAME_ALIAS_VAR]] = !DILocalVariable(name: "generic_obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_GENERIC_NAME_ALIAS_TYPE:[0-9]+]])
+// CHECK: ![[SWIFT_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$SSo21SwiftGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})
+
+// CHECK: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_VAR]] = !DILocalVariable(name: "constr_generic_obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_TYPE:[0-9]+]])
+// CHECK: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$SSo27SwiftConstrGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})