[Explicit Modules] Fix detection of a type-checking action in 'ExplicitModuleInterfaceBuilder'

When we run an interface verification tasks with Explicit module builds, we directly invoke a '-explicit-interface-module-build' instance with a '-typecheck-module-from-interface' action. So the builder needs to recognize this as a typechecking invocation. In implicit builds, this gets lowered into a separate compiler sub-instance with a '-typecheck' action, for some reason.

resolves rdar://115565571

Author: artemcm

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -90,6 +90,7 @@ struct ErrorDowngradeConsumerRAII: DiagnosticConsumer {
       for (auto *consumer: allConsumers) {
         consumer->handleDiagnostic(SM, localInfo);
       }
+      Diag.resetHadAnyError();
     }
   }
 };
@@ -215,7 +216,8 @@ std::error_code ExplicitModuleInterfaceBuilder::buildSwiftModuleFromInterface(
   }
   FrontendOptions &FEOpts = Invocation.getFrontendOptions();
   bool isTypeChecking =
-      (FEOpts.RequestedAction == FrontendOptions::ActionType::Typecheck);
+      (FEOpts.RequestedAction == FrontendOptions::ActionType::Typecheck ||
+       FEOpts.RequestedAction == FrontendOptions::ActionType::TypecheckModuleFromInterface);
   const auto &InputInfo = FEOpts.InputsAndOutputs.firstInput();
   StringRef InPath = InputInfo.getFileName();
 

test/ModuleInterface/downgrade-module-verification-error-explicit.swift

@@ -0,0 +1,9 @@
+// RUN: %empty-directory(%t)
+// RUN: echo "// swift-interface-format-version: 1.0" > %t/Main.swiftinterface
+// RUN: echo "// swift-module-flags: -module-name Foo" >> %t/Main.swiftinterface
+// RUN: echo "malfunctioned" >> %t/Main.swiftinterface
+// RUN: %target-swift-frontend -typecheck-module-from-interface %t/Main.swiftinterface -module-name Foo -downgrade-typecheck-interface-error -explicit-interface-module-build &> %t/results.txt
+// RUN: %FileCheck --input-file %t/results.txt %s
+
+// CHECK: warning:
+// CHECK-NOT: error: