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[clang] Accept empty enum in MSVC compatible C #159981

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Merged
yronglin merged 15 commits into from
Nov 5, 2025
Merged

[clang] Accept empty enum in MSVC compatible C #159981

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77fc06c
[clang] Accept empty enum in MSVC compatible C
yicuixi Sep 21, 2025
191eacf
Fix test
yicuixi Sep 21, 2025
e153bf2
Merge branch 'main' into ms-ext
yicuixi Sep 24, 2025
c106aaa
address comments
yicuixi Sep 24, 2025
6bb40da
correct format
yicuixi Sep 26, 2025
d9ab0fe
Merge branch 'main' into ms-ext
yicuixi Sep 28, 2025
f573438
Merge branch 'main' into ms-ext
yicuixi Sep 28, 2025
b1cbba5
Update clang/docs/ReleaseNotes.rst
yicuixi Sep 30, 2025
4dfd0fd
Merge branch 'main' into ms-ext
yicuixi Oct 19, 2025
259e58d
[clang] Add CodeGen test to check the ABI compatibility
yicuixi Oct 20, 2025
394ae9c
Fix test
yicuixi Oct 22, 2025
5db9747
Update clang/docs/LanguageExtensions.rst
yicuixi Oct 28, 2025
475b498
Update clang/docs/LanguageExtensions.rst
yicuixi Oct 28, 2025
a1232cd
Merge branch 'main' into ms-ext
yicuixi Oct 28, 2025
e515d11
Merge branch 'main' into ms-ext
yicuixi Oct 30, 2025
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1 change: 1 addition & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -380,6 +380,7 @@ Bug Fixes in This Version
a function without arguments caused us to try to access a non-existent argument.
(#GH159080)
- Fixed a failed assertion with empty filename arguments in ``__has_embed``. (#GH159898)
- Accept empty enum in MSVC-compatible C. (#GH114402)

Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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4 changes: 3 additions & 1 deletion clang/include/clang/Basic/DiagnosticGroups.td
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Expand Up @@ -1435,6 +1435,7 @@ def MicrosoftDrectveSection : DiagGroup<"microsoft-drectve-section">;
def MicrosoftInclude : DiagGroup<"microsoft-include">;
def MicrosoftCppMacro : DiagGroup<"microsoft-cpp-macro">;
def MicrosoftFixedEnum : DiagGroup<"microsoft-fixed-enum">;
def MicrosoftEmptyEnum : DiagGroup<"microsoft-empty-enum">;
def MicrosoftSealed : DiagGroup<"microsoft-sealed">;
def MicrosoftAbstract : DiagGroup<"microsoft-abstract">;
def MicrosoftUnqualifiedFriend : DiagGroup<"microsoft-unqualified-friend">;
Expand Down Expand Up @@ -1488,7 +1489,8 @@ def Microsoft : DiagGroup<"microsoft",
MicrosoftConstInit, MicrosoftVoidPseudoDtor, MicrosoftAnonTag,
MicrosoftCommentPaste, MicrosoftEndOfFile,
MicrosoftInitFromPredefined, MicrosoftStringLiteralFromPredefined,
MicrosoftInconsistentDllImport, MicrosoftInlineOnNonFunction]>;
MicrosoftInconsistentDllImport, MicrosoftInlineOnNonFunction,
MicrosoftEmptyEnum]>;

def ClangClPch : DiagGroup<"clang-cl-pch">;

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3 changes: 3 additions & 0 deletions clang/include/clang/Basic/DiagnosticParseKinds.td
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Expand Up @@ -116,6 +116,9 @@ def err_enumerator_unnamed_no_def : Error<
def ext_ms_c_enum_fixed_underlying_type : Extension<
"enumeration types with a fixed underlying type are a Microsoft extension">,
InGroup<MicrosoftFixedEnum>;
def ext_ms_c_empty_enum_type : Extension<
"empty enumeration types are a Microsoft extension">,
InGroup<MicrosoftEmptyEnum>;
def ext_c23_enum_fixed_underlying_type : Extension<
"enumeration types with a fixed underlying type are a C23 extension">,
InGroup<C23>;
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9 changes: 7 additions & 2 deletions clang/lib/Parse/ParseDecl.cpp
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Expand Up @@ -5360,8 +5360,13 @@ void Parser::ParseEnumBody(SourceLocation StartLoc, Decl *EnumDecl,
T.consumeOpen();

// C does not allow an empty enumerator-list, C++ does [dcl.enum].
if (Tok.is(tok::r_brace) && !getLangOpts().CPlusPlus)
Diag(Tok, diag::err_empty_enum);
if (Tok.is(tok::r_brace) && !getLangOpts().CPlusPlus) {
if (getLangOpts().MicrosoftExt)
Diag(T.getOpenLocation(), diag::ext_ms_c_empty_enum_type)
<< SourceRange(T.getOpenLocation(), Tok.getLocation());
else
Diag(Tok, diag::err_empty_enum);
}

SmallVector<Decl *, 32> EnumConstantDecls;
SmallVector<SuppressAccessChecks, 32> EnumAvailabilityDiags;
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6 changes: 6 additions & 0 deletions clang/test/Parser/ms-empty-enum.c
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@@ -0,0 +1,6 @@
// RUN: %clang_cc1 %s -fsyntax-only -Wmicrosoft -verify -fms-extensions

typedef enum tag1 { } A; // expected-warning {{empty enumeration types are a Microsoft extension}}
typedef enum tag2 { } B; // expected-warning {{empty enumeration types are a Microsoft extension}}
typedef enum : unsigned { } C; // expected-warning {{enumeration types with a fixed underlying type are a Microsoft extension}}\
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@erichkeane erichkeane Sep 29, 2025

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This shouldn't warn 2x, the 'with a fixed underlying type' version is sufficient.

Also, isn't this a C23 extension, not a microsoft extension (or at least, as well)? See: ext_c23_enum_fixed_underlying_type.

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@yicuixi yicuixi Sep 30, 2025

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Thanks for the review!

Also, isn't this a C23 extension, not a microsoft extension (or at least, as well)? See: ext_c23_enum_fixed_underlying_type.

In microsoft-extension mode, it's ext_ms_c_enum_fixed_underlying_type but not ext_ms_c_enum_fixed_underlying_type.

This shouldn't warn 2x, the 'with a fixed underlying type' version is sufficient.

Should we suppress the 2nd empty enumeration types are a Microsoft extension warning? Seems they are 2 different issue.

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@erichkeane erichkeane Sep 30, 2025

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I'm a little confused here as to the order of warnings/what we should do. I suspect @AaronBallman and I need to spend some time figuring out/discussing what we're looking for.

I'm not sure about the suppressing the 2nd warning, there is perhaps a 'we should do both' kinda thing since one might be disabled, but it also looks silly.

Ping this in another ~week and a half, and Aaron and I can discuss it (he should be back by then!).

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@AaronBallman AaronBallman Oct 8, 2025

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I think emitting two diagnostics is fine (one for the underlying type and one for the empty enum) because they are separate extensions. But I think it's a bit odd that we claim the underlying type is a Microsoft extension rather than a C23 extension -- that seems to be a preexisting issue which could be handled in a separate PR: https://godbolt.org/z/sMhGoE3qq

// expected-warning {{empty enumeration types are a Microsoft extension}}