[Frontend] Always emit generated ObjectiveC header when allowing errors

Resolves rdar://75754282

Author: bnbarham

lib/AST/Decl.cpp

@@ -6808,8 +6808,8 @@ const ParamDecl *swift::getParameterAt(const ValueDecl *source,
 Type AbstractFunctionDecl::getMethodInterfaceType() const {
   assert(getDeclContext()->isTypeContext());
   auto Ty = getInterfaceType();
-  if (Ty->hasError())
-    return ErrorType::get(getASTContext());
+  if (Ty->is<ErrorType>())
+    return Ty;
   return Ty->castTo<AnyFunctionType>()->getResult();
 }
 

lib/FrontendTool/FrontendTool.cpp

@@ -989,11 +989,12 @@ static void performEndOfPipelineActions(CompilerInstance &Instance) {
   if (!ctx.hadError()) {
     emitLoadedModuleTraceForAllPrimariesIfNeeded(
         Instance.getMainModule(), Instance.getDependencyTracker(), opts);
-    
-    emitAnyWholeModulePostTypeCheckSupplementaryOutputs(Instance);
 
     dumpAPIIfNeeded(Instance);
   }
+  if (!ctx.hadError() || opts.AllowModuleWithCompilerErrors) {
+    emitAnyWholeModulePostTypeCheckSupplementaryOutputs(Instance);
+  }
 
   // Verify reference dependencies of the current compilation job. Note this
   // must be run *before* verifying diagnostics so that the former can be tested

lib/PrintAsObjC/DeclAndTypePrinter.cpp

@@ -1597,6 +1597,10 @@ class DeclAndTypePrinter::Implementation
     os << " */";
   }
 
+  void visitErrorType(ErrorType *Ty, Optional<OptionalTypeKind> optionalKind) {
+    os << "/* error */id";
+  }
+
   bool isClangPointerType(const clang::TypeDecl *clangTypeDecl) const {
     ASTContext &ctx = getASTContext();
     auto &clangASTContext = ctx.getClangModuleLoader()->getClangASTContext();

test/PrintAsObjC/error.swift

@@ -0,0 +1,60 @@
+// RUN: %empty-directory(%t)
+// RdsagUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) %s -typecheck -emit-objc-header-path %t/error.h
+// RUadsgN: %FileCheck %s < %t/error.h
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-module-path %t/error.swiftmodule -emit-objc-header-path %t/error.h -experimental-allow-module-with-compiler-errors %s
+// RUN: %FileCheck %s < %t/error.h
+// RUN: %check-in-clang %t/error.h
+
+// REQUIRES: objc_interop
+
+import Foundation
+
+@objc class ErrorClass: NSObject {
+// CHECK: @interface ErrorClass
+  @objc let member: Int
+  // CHECK: @property {{.*}} NSInteger member;
+  @objc let invalidMember: undefined
+  // TODO: Not output on invalid type
+
+  @objc func method() {}
+  // CHECK: - (void)method;
+
+  @objc func methodParams(a: Int, b: Int) {}
+  // CHECK: - (void)methodParamsWithA:(NSInteger)a b:(NSInteger)b;
+
+  @objc class func classMethod() {}
+  // CHECK: + (void)classMethod;
+
+  @objc(objcMethod)
+  func renamedMethod() {}
+  // CHECK: - (void)objcMethod;
+
+  @objc func invalidBody() {
+  // CHECK: - (void)invalidBody;
+    undefined
+  }
+
+  @objc func invalidRet() -> undefined {}
+  // CHECK: - (/* error */id)invalidRet
+
+  @objc func invalidParams(a: undefined) {}
+  // TODO: Not output with invalid parameters
+
+  @objc(invalid::)
+  func invalidRenamedMethod() {}
+  // CHECK: - (void)invalidRenamedMethod;
+
+  @objc @undefined func invalidAttribute() {}
+  // CHECK: - (void)invalidAttribute;
+
+  @objc undefined func invalidModifier() {}
+  // TODO: Not output with invalid modifier
+
+  @objc @available
+  func invalidAvailability() {}
+  // CHECK: - (void)invalidAvailability;
+}
+
+@objc class InvalidParent: undefined {}
+// CHECK: @interface InvalidParent