[clang][cli] Expose -fno-cxx-modules in cc1

For some use-cases, it might be useful to be able to turn off modules for C++ in `-cc1`. (The feature is implied by `-std=C++20`.)

This patch exposes the `-fno-cxx-modules` option in `-cc1`.

Reviewed By: arphaman

Differential Revision: https://reviews.llvm.org/D106864

Author: jansvoboda11

clang/include/clang/Driver/Options.td

@@ -467,7 +467,6 @@ defvar render_script = LangOpts<"RenderScript">;
 defvar hip = LangOpts<"HIP">;
 defvar gnu_mode = LangOpts<"GNUMode">;
 defvar asm_preprocessor = LangOpts<"AsmPreprocessor">;
-defvar cpp_modules = LangOpts<"CPlusPlusModules">;
 
 defvar std = !strconcat("LangStandard::getLangStandardForKind(", lang_std.KeyPath, ")");
 
@@ -1332,8 +1331,11 @@ defm cxx_exceptions: BoolFOption<"cxx-exceptions",
 defm async_exceptions: BoolFOption<"async-exceptions",
   LangOpts<"EHAsynch">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Enable EH Asynchronous exceptions">, NegFlag<SetFalse>>;
-def fcxx_modules : Flag <["-"], "fcxx-modules">, Group<f_Group>,
-  Flags<[NoXarchOption]>;
+defm cxx_modules : BoolFOption<"cxx-modules",
+  LangOpts<"CPlusPlusModules">, Default<cpp20.KeyPath>,
+  NegFlag<SetFalse, [CC1Option], "Disable">, PosFlag<SetTrue, [], "Enable">,
+  BothFlags<[NoXarchOption], " modules for C++">>,
+  ShouldParseIf<cplusplus.KeyPath>;
 def fdebug_pass_arguments : Flag<["-"], "fdebug-pass-arguments">, Group<f_Group>;
 def fdebug_pass_structure : Flag<["-"], "fdebug-pass-structure">, Group<f_Group>;
 def fdepfile_entry : Joined<["-"], "fdepfile-entry=">,
@@ -2154,7 +2156,7 @@ def fmodules_ts : Flag <["-"], "fmodules-ts">, Group<f_Group>,
   Flags<[CC1Option]>, HelpText<"Enable support for the C++ Modules TS">,
   MarshallingInfoFlag<LangOpts<"ModulesTS">>;
 defm modules : BoolFOption<"modules",
-  LangOpts<"Modules">, Default<!strconcat(fmodules_ts.KeyPath, "||", cpp_modules.KeyPath)>,
+  LangOpts<"Modules">, Default<!strconcat(fmodules_ts.KeyPath, "||", fcxx_modules.KeyPath)>,
   PosFlag<SetTrue, [CC1Option], "Enable the 'modules' language feature">,
   NegFlag<SetFalse>, BothFlags<[NoXarchOption, CoreOption]>>;
 def fmodule_maps : Flag <["-"], "fmodule-maps">, Flags<[CoreOption]>, Alias<fimplicit_module_maps>;
@@ -2213,8 +2215,6 @@ def fno_diagnostics_color : Flag<["-"], "fno-diagnostics-color">, Group<f_Group>
   Flags<[CoreOption, NoXarchOption]>;
 def fno_common : Flag<["-"], "fno-common">, Group<f_Group>, Flags<[CC1Option]>,
     HelpText<"Compile common globals like normal definitions">;
-def fno_cxx_modules : Flag <["-"], "fno-cxx-modules">, Group<f_Group>,
-  Flags<[NoXarchOption]>;
 defm digraphs : BoolFOption<"digraphs",
   LangOpts<"Digraphs">, Default<std#".hasDigraphs()">,
   PosFlag<SetTrue, [], "Enable alternative token representations '<:', ':>', '<%', '%>', '%:', '%:%:' (default)">,
@@ -5298,7 +5298,7 @@ def fmodules_local_submodule_visibility :
   HelpText<"Enforce name visibility rules across submodules of the same "
            "top-level module.">,
   MarshallingInfoFlag<LangOpts<"ModulesLocalVisibility">>,
-  ImpliedByAnyOf<[fmodules_ts.KeyPath, cpp_modules.KeyPath]>;
+  ImpliedByAnyOf<[fmodules_ts.KeyPath, fcxx_modules.KeyPath]>;
 def fmodules_codegen :
   Flag<["-"], "fmodules-codegen">,
   HelpText<"Generate code for uses of this module that assumes an explicit "

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3150,8 +3150,6 @@ void CompilerInvocation::setLangDefaults(LangOptions &Opts, InputKind IK,
   Opts.HexFloats = Std.hasHexFloats();
   Opts.ImplicitInt = Std.hasImplicitInt();
 
-  Opts.CPlusPlusModules = Opts.CPlusPlus20;
-
   // Set OpenCL Version.
   Opts.OpenCL = Std.isOpenCL();
   if (LangStd == LangStandard::lang_opencl10)

clang/test/Modules/cxx20-disable.cpp

@@ -0,0 +1,10 @@
+// RUN: rm -rf %t && mkdir %t
+// RUN: %clang_cc1 -x objective-c++ -std=c++20                  -I %t %s -verify=enabled
+// RUN: %clang_cc1 -x objective-c++ -std=c++20 -fno-cxx-modules -I %t %s -verify=disabled
+
+// enabled-no-diagnostics
+
+// The spelling of these errors is misleading.
+// The important thing is Clang rejected C++20 modules syntax.
+export module Foo; // disabled-error{{expected template}}
+                   // disabled-error@-1{{unknown type name 'module'}}