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

[jansvoboda11]

Summary

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.

[jansvoboda11]

clang/test/Modules/cxx20-disable.cpp

3

I'm not sure how to best test this. Checking the error messages is not that useful, since they don't make the intent here any clearer:

<path>/llvm-project/clang/test/Modules/cxx20-disable.cpp:4:8: error: expected template
export module Foo;
       ^
<path>/llvm-project/clang/test/Modules/cxx20-disable.cpp:4:8: error: unknown type name 'module'
2 errors generated.

[arphaman]

clang/test/Modules/cxx20-disable.cpp

3

You could still check the errors with -verify but add a comment that expressed the intent of why these errors are verified. Also it might make sense to add an inverse test case that doesn't use the -fno-cxx-modules flag, where this will just work.

[jansvoboda11]

Add negative test, check error messages.

clang/test/Modules/cxx20-disable.cpp

3

Addressed in the latest revision.

[arphaman]

Thanks, LGTM

clang/include/clang/Driver/Options.td

 defvar c2x = LangOpts<"C2x">;
 defvar lang_std = LangOpts<"LangStd">;
 defvar open_cl = LangOpts<"OpenCL">;
 defvar cuda = LangOpts<"CUDA">;
 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, ")");
 
 /////////
 // Options
 
 // The internal option ID must be a valid C++ identifier and results in a
 // clang::driver::options::OPT_XX enum constant for XX.
def fcrash_diagnostics_dir : Joined<["-"], "fcrash-diagnostics-dir=">,
   HelpText<"Put crash-report files in <dir>">, MetaVarName<"<dir>">;
 def fcreate_profile : Flag<["-"], "fcreate-profile">, Group<f_Group>;
 defm cxx_exceptions: BoolFOption<"cxx-exceptions",
   LangOpts<"CXXExceptions">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Enable C++ exceptions">, NegFlag<SetFalse>>;
 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=">,
     Group<f_clang_Group>, Flags<[CC1Option]>;
 def fdiagnostics_fixit_info : Flag<["-"], "fdiagnostics-fixit-info">, Group<f_clang_Group>;
 def fno_diagnostics_fixit_info : Flag<["-"], "fno-diagnostics-fixit-info">, Group<f_Group>,
   Flags<[CC1Option]>, HelpText<"Do not include fixit information in diagnostics">,
   MarshallingInfoNegativeFlag<DiagnosticOpts<"ShowFixits">>;

 def fimplicit_module_maps : Flag <["-"], "fimplicit-module-maps">, Group<f_Group>,
   Flags<[NoXarchOption, CC1Option, CoreOption]>,
   HelpText<"Implicitly search the file system for module map files.">,
   MarshallingInfoFlag<HeaderSearchOpts<"ImplicitModuleMaps">>;
 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>;
 def fmodule_name_EQ : Joined<["-"], "fmodule-name=">, Group<f_Group>,
   Flags<[NoXarchOption,CC1Option,CoreOption]>, MetaVarName<"<name>">,
   HelpText<"Specify the name of the module to build">,
   MarshallingInfoString<LangOpts<"ModuleName">>;
 def fmodule_implementation_of : Separate<["-"], "fmodule-implementation-of">,

 def fno_builtin : Flag<["-"], "fno-builtin">, Group<f_Group>, Flags<[CC1Option, CoreOption]>,
   HelpText<"Disable implicit builtin knowledge of functions">;
 def fno_builtin_ : Joined<["-"], "fno-builtin-">, Group<f_Group>, Flags<[CC1Option, CoreOption]>,
   HelpText<"Disable implicit builtin knowledge of a specific function">;
 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)">,
   NegFlag<SetFalse, [], "Disallow alternative token representations '<:', ':>', '<%', '%>', '%:', '%:%:'">,
   BothFlags<[CC1Option]>>;
 def fno_eliminate_unused_debug_symbols : Flag<["-"], "fno-eliminate-unused-debug-symbols">, Group<f_Group>;
 def fno_inline_functions : Flag<["-"], "fno-inline-functions">, Group<f_clang_Group>, Flags<[CC1Option]>;
 def fno_inline : Flag<["-"], "fno-inline">, Group<f_clang_Group>, Flags<[CC1Option]>;
def fmodules_embed_all_files : Joined<["-"], "fmodules-embed-all-files">,
   MarshallingInfoFlag<FrontendOpts<"ModulesEmbedAllFiles">>;
 // FIXME: We only need this in C++ modules / Modules TS if we might textually
 // enter a different module (eg, when building a header unit).
 def fmodules_local_submodule_visibility :
   Flag<["-"], "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 "
            "object file will be built for the module">,
   MarshallingInfoFlag<LangOpts<"ModulesCodegen">>;
 def fmodules_debuginfo :
   Flag<["-"], "fmodules-debuginfo">,
   HelpText<"Generate debug info for types in an object file built from this "

clang/lib/Frontend/CompilerInvocation.cpp

#endif
   Opts.CPlusPlus17 = Std.isCPlusPlus17();
   Opts.CPlusPlus20 = Std.isCPlusPlus20();
   Opts.CPlusPlus2b = Std.isCPlusPlus2b();
   Opts.GNUMode = Std.isGNUMode();
   Opts.GNUCVersion = 0;
   Opts.HexFloats = Std.hasHexFloats();
   Opts.ImplicitInt = Std.hasImplicitInt();
 
-  Opts.CPlusPlusModules = Opts.CPlusPlus20;
-
   // Set OpenCL Version.
   Opts.OpenCL = Std.isOpenCL();
   if (LangStd == LangStandard::lang_opencl10)
     Opts.OpenCLVersion = 100;
   else if (LangStd == LangStandard::lang_opencl11)
     Opts.OpenCLVersion = 110;
   else if (LangStd == LangStandard::lang_opencl12)
     Opts.OpenCLVersion = 120;

clang/test/Modules/cxx20-disable.cpp

+// 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'}}