[ModuleInterface] Fix silencing errors mode in swiftinterface rebuild

Make sure we disable forwarding diagnostics from the underlying instance
when building a swiftinterface in silencing errors mode.

Author: xymus

include/swift/AST/ModuleLoader.h

@@ -173,6 +173,7 @@ struct InterfaceSubContextDelegate {
                                                    StringRef interfacePath,
                                                    StringRef outputPath,
                                                    SourceLoc diagLoc,
+                                                   bool silenceErrors,
     llvm::function_ref<std::error_code(SubCompilerInstanceInfo&)> action) = 0;
 
   virtual ~InterfaceSubContextDelegate() = default;

include/swift/Frontend/ModuleInterfaceLoader.h

@@ -523,6 +523,7 @@ struct InterfaceSubContextDelegateImpl: InterfaceSubContextDelegate {
                                            StringRef interfacePath,
                                            StringRef outputPath,
                                            SourceLoc diagLoc,
+                                           bool silenceErrors,
     llvm::function_ref<std::error_code(SubCompilerInstanceInfo&)> action) override;
 
   ~InterfaceSubContextDelegateImpl() = default;

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -330,6 +330,7 @@ bool ImplicitModuleInterfaceBuilder::buildSwiftModuleInternal(
 
     SubError = (bool)subASTDelegate.runInSubCompilerInstance(
         moduleName, interfacePath, OutPath, diagnosticLoc,
+        silenceInterfaceDiagnostics,
         [&](SubCompilerInstanceInfo &info) {
           auto EBuilder = ExplicitModuleInterfaceBuilder(
               *info.Instance, rebuildDiags, sourceMgr, moduleCachePath, backupInterfaceDir,

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1724,7 +1724,8 @@ InterfaceSubContextDelegateImpl::runInSubContext(StringRef moduleName,
                                                  SourceLoc diagLoc,
     llvm::function_ref<std::error_code(ASTContext&, ModuleDecl*, ArrayRef<StringRef>,
                             ArrayRef<StringRef>, StringRef)> action) {
-  return runInSubCompilerInstance(moduleName, interfacePath, outputPath, diagLoc,
+  return runInSubCompilerInstance(moduleName, interfacePath, outputPath,
+                                  diagLoc, /*silenceErrors=*/false,
                                   [&](SubCompilerInstanceInfo &info){
     return action(info.Instance->getASTContext(),
                   info.Instance->getMainModule(),
@@ -1739,6 +1740,7 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
                                                           StringRef interfacePath,
                                                           StringRef outputPath,
                                                           SourceLoc diagLoc,
+                                                          bool silenceErrors,
                   llvm::function_ref<std::error_code(SubCompilerInstanceInfo&)> action) {
   // We are about to mess up the compiler invocation by using the compiler
   // arguments in the textual interface file. So copy to use a new compiler
@@ -1833,7 +1835,8 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
   subInstance.getSourceMgr().setFileSystem(SM.getFileSystem());
 
   ForwardingDiagnosticConsumer FDC(*Diags);
-  subInstance.addDiagnosticConsumer(&FDC);
+  if (!silenceErrors)
+    subInstance.addDiagnosticConsumer(&FDC);
   std::string InstanceSetupError;
   if (subInstance.setup(subInvocation, InstanceSetupError)) {
     return std::make_error_code(std::errc::not_supported);

test/Index/index_system_modules_swiftinterfaces.swift

@@ -55,9 +55,9 @@
 // RUN:     2>&1 | %FileCheck -check-prefix=BROKEN-BUILD %s
 
 /// We don't expect so see the swiftinterface error for indexing
-// BROKEN-BUILD: indexing system module {{.*}} skipping
 // BROKEN-BUILD-NOT: error
 // BROKEN-BUILD-NOT: breaking_the_swifinterface
+// BROKEN-BUILD: indexing system module {{.*}} skipping
 
 /// We don't expect SystemModule to be indexed with a broken swiftinterface
 // RUN: c-index-test core -print-unit %t/idx | %FileCheck -check-prefix=BROKEN-UNIT %s