Treat default values in LangOptions.def in the scope of enums

[sepavloff]

Summary

If an option specified in LangOptions.def is of enum type, its default
value should be a member of that enum, so scope qualifier may always
be added in such cases. It allows to omit the scope qualifiers from
'LangOptions.def', which improves readability.

No functional changes.

[rnk]

I don't think we can do this because GCC 5.1 won't support it.

To confirm, that's still the minimum supported version:
https://llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library

And here's a godbolt example showing the error: https://gcc.godbolt.org/z/fYb58Q

[sepavloff]

Thank you, Reid!

clang/include/clang/Basic/LangOptions.def

 LANGOPT(Digraphs          , 1, 0, "digraphs")
 BENIGN_LANGOPT(HexFloats  , 1, C99, "C99 hexadecimal float constants")
 LANGOPT(CXXOperatorNames  , 1, 0, "C++ operator name keywords")
 LANGOPT(AppleKext         , 1, 0, "Apple kext support")
 BENIGN_LANGOPT(PascalStrings, 1, 0, "Pascal string support")
 LANGOPT(WritableStrings   , 1, 0, "writable string support")
 LANGOPT(ConstStrings      , 1, 0, "const-qualified string support")
 ENUM_LANGOPT(LaxVectorConversions, LaxVectorConversionKind, 2,
-             LaxVectorConversionKind::All, "lax vector conversions")
+             All, "lax vector conversions")
 LANGOPT(ConvergentFunctions, 1, 1, "Assume convergent functions")
 LANGOPT(AltiVec           , 1, 0, "AltiVec-style vector initializers")
 LANGOPT(ZVector           , 1, 0, "System z vector extensions")
 LANGOPT(Exceptions        , 1, 0, "exception handling")
 LANGOPT(ObjCExceptions    , 1, 0, "Objective-C exceptions")
 LANGOPT(CXXExceptions     , 1, 0, "C++ exceptions")
 LANGOPT(DWARFExceptions   , 1, 0, "dwarf exception handling")
 LANGOPT(SjLjExceptions    , 1, 0, "setjmp-longjump exception handling")
ENUM_LANGOPT(ValueVisibilityMode, Visibility, 3, DefaultVisibility,
              "default visibility for functions and variables [-fvisibility]")
 ENUM_LANGOPT(TypeVisibilityMode, Visibility, 3, DefaultVisibility,
              "default visibility for types [-ftype-visibility]")
 LANGOPT(SetVisibilityForExternDecls, 1, 0,
         "apply global symbol visibility to external declarations without an explicit visibility")
 BENIGN_LANGOPT(SemanticInterposition        , 1, 0, "semantic interposition")
 ENUM_LANGOPT(StackProtector, StackProtectorMode, 2, SSPOff,
              "stack protector mode")
-ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, TrivialAutoVarInitKind::Uninitialized,
+ENUM_LANGOPT(TrivialAutoVarInit, TrivialAutoVarInitKind, 2, Uninitialized,
              "trivial automatic variable initialization")
 ENUM_LANGOPT(SignedOverflowBehavior, SignedOverflowBehaviorTy, 2, SOB_Undefined,
              "signed integer overflow handling")
 
 BENIGN_LANGOPT(ArrowDepth, 32, 256,
                "maximum number of operator->s to follow")
 BENIGN_LANGOPT(InstantiationDepth, 32, 1024,
                "maximum template instantiation depth")
 BENIGN_LANGOPT(ConstexprCallDepth, 32, 512,
                "maximum constexpr call depth")
 BENIGN_LANGOPT(ConstexprStepLimit, 32, 1048576,
                "maximum constexpr evaluation steps")
 BENIGN_LANGOPT(EnableNewConstInterp, 1, 0,
                "enable the experimental new constant interpreter")
 BENIGN_LANGOPT(BracketDepth, 32, 256,
                "maximum bracket nesting depth")
 BENIGN_LANGOPT(NumLargeByValueCopy, 32, 0,
         "if non-zero, warn about parameter or return Warn if parameter/return value is larger in bytes than this setting. 0 is no check.")
 VALUE_LANGOPT(MSCompatibilityVersion, 32, 0, "Microsoft Visual C/C++ Version")
-ENUM_LANGOPT(VtorDispMode, MSVtorDispMode, 2, MSVtorDispMode::ForVBaseOverride,
+ENUM_LANGOPT(VtorDispMode, MSVtorDispMode, 2, ForVBaseOverride,
              "How many vtordisps to insert")
 
 LANGOPT(ApplePragmaPack, 1, 0, "Apple gcc-compatible #pragma pack handling")
 
 LANGOPT(RetainCommentsFromSystemHeaders, 1, 0, "retain documentation comments from system headers in the AST")
 
 LANGOPT(SanitizeAddressFieldPadding, 2, 0, "controls how aggressive is ASan "
                                            "field padding (0: none, 1:least "
LANGOPT(XRayAlwaysEmitTypedEvents, 1, 0,
         "controls whether to always emit intrinsic calls to "
         "__xray_typedevent(...) builtin.")
 
 LANGOPT(ForceEmitVTables, 1, 0, "whether to emit all vtables")
 
 BENIGN_LANGOPT(AllowEditorPlaceholders, 1, 0,
                "allow editor placeholders in source")
 
-ENUM_LANGOPT(ClangABICompat, ClangABI, 4, ClangABI::Latest,
+ENUM_LANGOPT(ClangABICompat, ClangABI, 4, Latest,
              "version of Clang that we should attempt to be ABI-compatible "
              "with")
 
 COMPATIBLE_VALUE_LANGOPT(FunctionAlignment, 5, 0, "Default alignment for functions")
 
 LANGOPT(FixedPoint, 1, 0, "fixed point types")
 LANGOPT(PaddingOnUnsignedFixedPoint, 1, 0,
         "unsigned fixed point types having one extra padding bit")
 
 LANGOPT(RegisterStaticDestructors, 1, 1, "Register C++ static destructors")
 
 COMPATIBLE_VALUE_LANGOPT(MaxTokens, 32, 0, "Max number of tokens per TU or 0")
 
-ENUM_LANGOPT(SignReturnAddressScope, SignReturnAddressScopeKind, 2, SignReturnAddressScopeKind::None,
+ENUM_LANGOPT(SignReturnAddressScope, SignReturnAddressScopeKind, 2, None,
              "Scope of return address signing")
-ENUM_LANGOPT(SignReturnAddressKey, SignReturnAddressKeyKind, 1, SignReturnAddressKeyKind::AKey,
+ENUM_LANGOPT(SignReturnAddressKey, SignReturnAddressKeyKind, 1, AKey,
              "Key used for return address signing")
 LANGOPT(BranchTargetEnforcement, 1, 0, "Branch-target enforcement enabled")
 
 #undef LANGOPT
 #undef COMPATIBLE_LANGOPT
 #undef BENIGN_LANGOPT
 #undef ENUM_LANGOPT
 #undef COMPATIBLE_ENUM_LANGOPT
 #undef BENIGN_ENUM_LANGOPT
 #undef VALUE_LANGOPT
 #undef COMPATIBLE_VALUE_LANGOPT
 #undef BENIGN_VALUE_LANGOPT

clang/lib/Basic/LangOptions.cpp

 //===- LangOptions.cpp - C Language Family Language Options ---------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file defines the LangOptions class.
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Basic/LangOptions.h"
 
 using namespace clang;
 
 LangOptions::LangOptions() {
 #define LANGOPT(Name, Bits, Default, Description) Name = Default;
-#define ENUM_LANGOPT(Name, Type, Bits, Default, Description) set##Name(Default);
+#define ENUM_LANGOPT(Name, Type, Bits, Default, Description) \
+  set##Name(Type::Default);
 #include "clang/Basic/LangOptions.def"
 }
 
 void LangOptions::resetNonModularOptions() {
 #define LANGOPT(Name, Bits, Default, Description)
 #define BENIGN_LANGOPT(Name, Bits, Default, Description) Name = Default;
 #define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description) \
-  Name = Default;
+  Name = static_cast<unsigned>(Type::Default);
 #include "clang/Basic/LangOptions.def"
 
   // These options do not affect AST generation.
   SanitizerBlacklistFiles.clear();
   XRayAlwaysInstrumentFiles.clear();
   XRayNeverInstrumentFiles.clear();
 
   CurrentModule.clear();