Add flag to hide experimental ClangImporter diagnostics behind

Author: Nuri Amari

include/swift/Basic/LangOptions.h

@@ -314,6 +314,9 @@ namespace swift {
     /// Enable experimental flow-sensitive concurrent captures.
     bool EnableExperimentalFlowSensitiveConcurrentCaptures = false;
 
+    /// Enable experimental ClangImporter diagnostics.
+    bool EnableExperimentalClangImporterDiagnostics = false;
+
     /// Enable inference of Sendable conformances for public types.
     bool EnableInferPublicSendable = false;
 

include/swift/Option/FrontendOptions.td

@@ -267,6 +267,10 @@ def enable_experimental_flow_sensitive_concurrent_captures :
   Flag<["-"], "enable-experimental-flow-sensitive-concurrent-captures">,
   HelpText<"Enable flow-sensitive concurrent captures">;
 
+def enable_experimental_clang_importer_diagnostics :
+  Flag<["-"], "enable-experimental-clang-importer-diagnostics">,
+  HelpText<"Enable experimental ClangImporter diagnostics">;
+
 def enable_resilience : Flag<["-"], "enable-resilience">,
      HelpText<"Deprecated, use -enable-library-evolution instead">;
 }

lib/Frontend/CompilerInvocation.cpp

@@ -450,6 +450,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.EnableExperimentalFlowSensitiveConcurrentCaptures |=
     Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures);
 
+  Opts.EnableExperimentalClangImporterDiagnostics |=
+      Args.hasArg(OPT_enable_experimental_clang_importer_diagnostics);
+
   Opts.DisableImplicitConcurrencyModuleImport |=
     Args.hasArg(OPT_disable_implicit_concurrency_module_import);