[clang] Revert "[clang] Reject 'auto' storage class with type specifier in C++" (PR #208436)
via cfe-commits
cfe-commits at lists.llvm.org
Thu Jul 9 04:56:05 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
Reverts llvm/llvm-project#<!-- -->166004.
Breaks stage 2 build, see comments on PR.
---
Patch is 37.17 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/208436.diff
15 Files Affected:
- (modified) clang/docs/ReleaseNotes.md (-2)
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (-2)
- (modified) clang/include/clang/Sema/DeclSpec.h (+2-51)
- (modified) clang/lib/Parse/ParseDecl.cpp (+6-38)
- (modified) clang/lib/Sema/DeclSpec.cpp (-163)
- (modified) clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp (+48-57)
- (modified) clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp (+1-7)
- (modified) clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp (+6-6)
- (modified) clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp (+1-6)
- (modified) clang/test/CXX/dcl/dcl.fct/p17.cpp (+1-1)
- (modified) clang/test/CXX/drs/cwg3xx.cpp (+7-9)
- (modified) clang/test/Parser/c2x-auto.c (-7)
- (modified) clang/test/SemaCXX/auto-cxx0x.cpp (+2-8)
- (modified) clang/test/SemaCXX/class.cpp (+4-5)
- (modified) clang/test/SemaCXX/static-data-member.cpp (+1-6)
``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 61caf2d9ec99e..a573599d76f7d 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -116,8 +116,6 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
as being of type `std::size_t` instead of `int`,
matching the deduction of array sizes from `int(&)[N]`.
This is a breaking change for code that depended on the previously deduced type. (#GH195033)
-- Clang now rejects C++ declarations that combine the `auto` type specifier
- with another type specifier, such as `auto int`.
- Clang now rejects nested local classes defined in a different
block scope than their parent class. (#GH193472)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 45f909fc5452c..15867f69a6718 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2759,8 +2759,6 @@ def err_decltype_auto_invalid : Error<
"'decltype(auto)' not allowed here">;
def err_decltype_auto_cannot_be_combined : Error<
"'decltype(auto)' cannot be combined with other type specifiers">;
-def err_auto_type_specifier : Error<
- "'auto' cannot be combined with a type specifier">;
def err_decltype_auto_function_declarator_not_declaration : Error<
"'decltype(auto)' can only be used as a return type "
"in a function declaration">;
diff --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
index d1abc0e3c21fb..6e7f9cd6e3d38 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -363,10 +363,6 @@ class DeclSpec {
unsigned TypeSpecSat : 1;
LLVM_PREFERRED_TYPE(bool)
unsigned ConstrainedAuto : 1;
- // Track conflicting type specifier when 'auto' is set (for Finish()
- // detection)
- LLVM_PREFERRED_TYPE(TST)
- unsigned ConflictingTypeSpecifier : 7;
// type-qualifiers
LLVM_PREFERRED_TYPE(TQ)
@@ -431,50 +427,10 @@ class DeclSpec {
SourceLocation FS_explicitCloseParenLoc;
SourceLocation FS_forceinlineLoc;
SourceLocation FriendLoc, ModulePrivateLoc, ConstexprLoc;
- SourceLocation TQ_pipeLoc, ConflictingTypeSpecifierLoc;
+ SourceLocation TQ_pipeLoc;
WrittenBuiltinSpecs writtenBS;
void SaveWrittenBuiltinSpecs();
- void setConflictingTypeSpecifier(TST T, SourceLocation Loc) {
- // Store conflicting type specifier for Finish() to detect:
- // - If 'auto' is already set, store the conflicting type (e.g., "auto int")
- // - If 'auto' is being set after another type, store TST_auto
- // (e.g., "int auto").
- if (TypeSpecType == TST_auto) {
- ConflictingTypeSpecifier = T;
- ConflictingTypeSpecifierLoc = Loc;
- } else if (T == TST_auto) {
- ConflictingTypeSpecifier = TST_auto;
- ConflictingTypeSpecifierLoc = Loc;
- }
- }
- void setConflictingTypeSpecifier(TST T, SourceLocation Loc,
- SourceLocation NameLoc, ParsedType Rep) {
- setConflictingTypeSpecifier(T, Loc);
- if (TypeSpecType == TST_auto) {
- TypeRep = Rep;
- TSTNameLoc = NameLoc;
- TypeSpecOwned = false;
- }
- }
- void setConflictingTypeSpecifier(TST T, SourceLocation Loc, Expr *Rep) {
- setConflictingTypeSpecifier(T, Loc);
- if (TypeSpecType == TST_auto) {
- ExprRep = Rep;
- TSTNameLoc = Loc;
- TypeSpecOwned = false;
- }
- }
- void setConflictingTypeSpecifier(TST T, SourceLocation Loc,
- SourceLocation NameLoc, Decl *Rep,
- bool Owned) {
- setConflictingTypeSpecifier(T, Loc);
- if (TypeSpecType == TST_auto) {
- DeclRep = Rep;
- TSTNameLoc = NameLoc;
- TypeSpecOwned = Owned && Rep != nullptr;
- }
- }
ObjCDeclSpec *ObjCQualifiers;
@@ -518,15 +474,13 @@ class DeclSpec {
TypeSpecType(TST_unspecified), TypeAltiVecVector(false),
TypeAltiVecPixel(false), TypeAltiVecBool(false), TypeSpecOwned(false),
TypeSpecPipe(false), TypeSpecSat(false), ConstrainedAuto(false),
- ConflictingTypeSpecifier(TST_unspecified),
TypeQualifiers(TQ_unspecified),
OB_state(static_cast<unsigned>(OverflowBehaviorState::Unspecified)),
FS_inline_specified(false), FS_forceinline_specified(false),
FS_virtual_specified(false), FS_noreturn_specified(false),
FriendSpecifiedFirst(false), ConstexprSpecifier(static_cast<unsigned>(
ConstexprSpecKind::Unspecified)),
- Attrs(attrFactory), ConflictingTypeSpecifierLoc(), writtenBS(),
- ObjCQualifiers(nullptr) {}
+ Attrs(attrFactory), writtenBS(), ObjCQualifiers(nullptr) {}
// storage-class-specifier
SCS getStorageClassSpec() const { return (SCS)StorageClassSpec; }
@@ -566,9 +520,6 @@ class DeclSpec {
return static_cast<TypeSpecifierSign>(TypeSpecSign);
}
TST getTypeSpecType() const { return (TST)TypeSpecType; }
- bool hasConflictingTypeSpecifier() const {
- return ConflictingTypeSpecifier != TST_unspecified;
- }
bool isTypeAltiVecVector() const { return TypeAltiVecVector; }
bool isTypeAltiVecPixel() const { return TypeAltiVecPixel; }
bool isTypeAltiVecBool() const { return TypeAltiVecBool; }
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 1b865195f23e5..3f41e7c5c6f0d 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3775,9 +3775,7 @@ void Parser::ParseDeclarationSpecifiers(
// This identifier can only be a typedef name if we haven't already seen
// a type-specifier. Without this check we misparse:
// typedef int X; struct Y { short X; }; as 'short int'.
- // However, if 'auto' is set, we need to check if this identifier is a
- // type name to detect conflicts (e.g., "auto MyInt").
- if (DS.hasTypeSpecifier() && DS.getTypeSpecType() != DeclSpec::TST_auto)
+ if (DS.hasTypeSpecifier())
goto DoneWithDeclSpec;
// If the token is an identifier named "__declspec" and Microsoft
@@ -3862,14 +3860,6 @@ void Parser::ParseDeclarationSpecifiers(
DS.isFriendSpecified()))
goto DoneWithDeclSpec;
- // If 'auto' is set and we're in a template parameter context, the
- // identifier is always the parameter name, not a type specifier, so skip
- // type name lookup to avoid false ambiguity errors.
- if (DS.getTypeSpecType() == DeclSpec::TST_auto &&
- DSContext == DeclSpecContext::DSC_template_param) {
- goto DoneWithDeclSpec;
- }
-
ParsedType TypeRep = Actions.getTypeName(
*Tok.getIdentifierInfo(), Tok.getLocation(), getCurScope(), nullptr,
false, false, nullptr, false, false,
@@ -3877,16 +3867,11 @@ void Parser::ParseDeclarationSpecifiers(
// If this is not a typedef name, don't parse it as part of the declspec,
// it must be an implicit int or an error.
- // However, if 'auto' is already set, we can't have an implicit int.
if (!TypeRep) {
if (TryAnnotateTypeConstraint())
goto DoneWithDeclSpec;
if (Tok.isNot(tok::identifier))
continue;
- // If 'auto' is set, the identifier must be a type name or it's an
- // error. Don't try to parse it as implicit int.
- if (DS.getTypeSpecType() == DeclSpec::TST_auto)
- goto DoneWithDeclSpec;
ParsedAttributes Attrs(AttrFactory);
if (ParseImplicitInt(DS, nullptr, TemplateInfo, AS, DSContext, Attrs)) {
if (!Attrs.empty()) {
@@ -3898,25 +3883,6 @@ void Parser::ParseDeclarationSpecifiers(
goto DoneWithDeclSpec;
}
- // If 'auto' is set and this identifier is a type name, stop parsing
- // declaration specifiers when the next token indicates this is the
- // declarator-id rather than another type specifier.
- if (DS.getTypeSpecType() == DeclSpec::TST_auto && TypeRep) {
- Token Next = NextToken();
- if (Next.isOneOf(tok::equal, tok::l_paren, tok::l_square, tok::amp,
- tok::ampamp, tok::star, tok::coloncolon, tok::comma,
- tok::semi, tok::colon, tok::greater, tok::r_paren,
- tok::arrow)) {
- // This identifier is likely the variable/parameter name, stop parsing
- // decl specifiers. Note: ':' is for range-based for loops:
- // for (auto Arg: x).
- // Note: '>' is for template parameters: template<auto V>
- // Note: ')' is for function/lambda parameters: [](auto c)
- // Note: '->' is for lambda return types: [](auto c) -> int
- goto DoneWithDeclSpec;
- }
- }
-
// Likewise, if this is a context where the identifier could be a template
// name, check whether this is a deduction guide declaration.
CXXScopeSpec SS;
@@ -4171,9 +4137,12 @@ void Parser::ParseDeclarationSpecifiers(
}
};
- if (!getLangOpts().CPlusPlus && MayBeTypeSpecifier()) {
+ if (MayBeTypeSpecifier()) {
isInvalid = DS.SetStorageClassSpec(Actions, DeclSpec::SCS_auto, Loc,
PrevSpec, DiagID, Policy);
+ if (!isInvalid && !getLangOpts().C23)
+ Diag(Tok, diag::ext_auto_storage_class)
+ << FixItHint::CreateRemoval(DS.getStorageClassSpecLoc());
} else
isInvalid = DS.SetTypeSpecType(DeclSpec::TST_auto, Loc, PrevSpec,
DiagID, Policy);
@@ -4731,8 +4700,7 @@ void Parser::ParseDeclarationSpecifiers(
DS.SetRangeEnd(ConsumedEnd.isValid() ? ConsumedEnd : Tok.getLocation());
// If the specifier wasn't legal, issue a diagnostic.
- // Skip diagnostic if 'auto' conflict will be handled in Finish()
- if (isInvalid && !DS.hasConflictingTypeSpecifier()) {
+ if (isInvalid) {
assert(PrevSpec && "Method did not return previous specifier!");
assert(DiagID);
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index 3c882bc3a1003..2add7c6aa3080 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -759,7 +759,6 @@ bool DeclSpec::SetTypeSpecType(TST T, SourceLocation TagKwLoc,
if (TypeSpecType == TST_error)
return false;
if (TypeSpecType != TST_unspecified) {
- setConflictingTypeSpecifier(T, TagKwLoc, TagNameLoc, Rep);
PrevSpec = DeclSpec::getSpecifierName((TST) TypeSpecType, Policy);
DiagID = diag::err_invalid_decl_spec_combination;
return true;
@@ -791,7 +790,6 @@ bool DeclSpec::SetTypeSpecType(TST T, SourceLocation Loc,
if (TypeSpecType == TST_error)
return false;
if (TypeSpecType != TST_unspecified) {
- setConflictingTypeSpecifier(T, Loc, Rep);
PrevSpec = DeclSpec::getSpecifierName((TST) TypeSpecType, Policy);
DiagID = diag::err_invalid_decl_spec_combination;
return true;
@@ -824,7 +822,6 @@ bool DeclSpec::SetTypeSpecType(TST T, SourceLocation TagKwLoc,
if (TypeSpecType == TST_error)
return false;
if (TypeSpecType != TST_unspecified) {
- setConflictingTypeSpecifier(T, TagKwLoc, TagNameLoc, Rep, Owned);
PrevSpec = DeclSpec::getSpecifierName((TST) TypeSpecType, Policy);
DiagID = diag::err_invalid_decl_spec_combination;
return true;
@@ -855,7 +852,6 @@ bool DeclSpec::SetTypeSpecType(TST T, SourceLocation Loc,
if (TypeSpecType == TST_error)
return false;
if (TypeSpecType != TST_unspecified) {
- setConflictingTypeSpecifier(T, Loc);
PrevSpec = DeclSpec::getSpecifierName((TST) TypeSpecType, Policy);
DiagID = diag::err_invalid_decl_spec_combination;
return true;
@@ -1216,164 +1212,6 @@ void DeclSpec::CheckTypeSpec(Sema &S, const PrintingPolicy &Policy) {
<< Hints[4] << Hints[5] << Hints[6] << Hints[7];
}
- // If 'auto' type specifier is combined with another type specifier, we need
- // to handle it based on the language:
- // - In C++11+: Emit error (cannot combine type specifiers)
- // - In C23: Convert 'auto' to storage class (valid)
- // - In OpenCL: Convert 'auto' to storage class, then OpenCL will reject it
- // Handle both cases:
- // - "auto int" (TypeSpecType == TST_auto, ConflictingTypeSpecifier ==
- // TST_int)
- // - "int auto" (TypeSpecType == TST_int, ConflictingTypeSpecifier ==
- // TST_auto)
- if (ConflictingTypeSpecifier != TST_unspecified) {
- // Special case: "auto auto" - duplicate 'auto', emit error
- if (TypeSpecType == TST_auto && ConflictingTypeSpecifier == TST_auto) {
- // Both are 'auto', emit "cannot combine with previous 'auto' declaration
- // specifier" error This matches GCC's "duplicate 'auto'" behavior Note:
- // We keep TypeSpecType = TST_auto (don't set to TST_error) so that later
- // checks in SemaType.cpp can emit "not allowed in function prototype" and
- // "not allowed in function return type" errors as needed.
- const char *PrevSpec = "auto";
- unsigned DiagID = diag::err_invalid_decl_spec_combination;
- S.Diag(ConflictingTypeSpecifierLoc, DiagID) << PrevSpec << PrevSpec;
- // Clear the conflict tracking but keep TypeSpecType = TST_auto
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- } else if ((S.getLangOpts().C23 && !S.getLangOpts().CPlusPlus) ||
- (S.getLangOpts().CPlusPlus && !S.getLangOpts().CPlusPlus11)) {
- // In C23 or C++98, convert 'auto' to storage class specifier
- if (TypeSpecType == TST_auto) {
- // "auto int" case: Convert 'auto' to storage class specifier
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = TSTLoc;
- TypeSpecType = ConflictingTypeSpecifier;
- TSTLoc = ConflictingTypeSpecifierLoc;
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- } else if (ConflictingTypeSpecifier == TST_auto) {
- // "int auto" case: Convert 'auto' to storage class specifier
- // In C23, if 'constexpr' is present, treat 'auto' as a type specifier
- // conflict with 'int' rather than converting it to storage class, so we
- // emit the "cannot combine with previous 'int' declaration specifier"
- // error and mark the type as error to prevent further processing.
- // Otherwise, convert 'auto' to storage class specifier (no type
- // conflict error).
- if (S.getLangOpts().C23 && !S.getLangOpts().CPlusPlus &&
- getConstexprSpecifier() != ConstexprSpecKind::Unspecified) {
- // constexpr int auto: treat as type specifier conflict
- const char *PrevSpec =
- getSpecifierName((TST)TypeSpecType, S.getPrintingPolicy());
- unsigned DiagID = diag::err_invalid_decl_spec_combination;
- S.Diag(ConflictingTypeSpecifierLoc, DiagID) << PrevSpec << "auto";
- TypeSpecType = TST_error;
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- return;
- }
- // int auto (without constexpr): Convert 'auto' to storage class
- // specifier. No type conflict error - auto is treated as storage class,
- // not type specifier.
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = ConflictingTypeSpecifierLoc;
- // TypeSpecType already has the correct type (e.g., TST_int)
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- }
- } else if (S.getLangOpts().OpenCL) {
- // For OpenCL (C or C++), convert 'auto' to storage class specifier first
- // (OpenCL will then reject it via SetStorageClassSpec checks)
- // This must come before the C++11+ check to handle OpenCL C++
- if (TypeSpecType == TST_auto) {
- // "auto int" case: Convert 'auto' to storage class specifier
- // Use SetStorageClassSpec to trigger OpenCL-specific error checking
- const char *PrevSpec = nullptr;
- unsigned DiagID = 0;
- if (SetStorageClassSpec(
- S, SCS_auto, TSTLoc, PrevSpec, DiagID,
- S.getPrintingPolicy())) { // OpenCL rejected it, emit the error
- // with version string
- if (S.getLangOpts().OpenCL && S.getLangOpts().CPlusPlus) {
- S.Diag(TSTLoc, DiagID)
- << S.getLangOpts().getOpenCLVersionString() << PrevSpec << 1;
- } else {
- S.Diag(TSTLoc, DiagID) << PrevSpec;
- }
- TypeSpecType = TST_error;
- } else {
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = TSTLoc;
- TypeSpecType = ConflictingTypeSpecifier;
- TSTLoc = ConflictingTypeSpecifierLoc;
- }
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- } else if (ConflictingTypeSpecifier == TST_auto) {
- // "int auto" case: Convert 'auto' to storage class specifier
- // Use SetStorageClassSpec to trigger OpenCL-specific error checking
- const char *PrevSpec = nullptr;
- unsigned DiagID = 0;
- if (SetStorageClassSpec(S, SCS_auto, ConflictingTypeSpecifierLoc,
- PrevSpec, DiagID, S.getPrintingPolicy())) {
- // OpenCL rejected it, emit the error with version string
- if (S.getLangOpts().OpenCL && S.getLangOpts().CPlusPlus) {
- S.Diag(ConflictingTypeSpecifierLoc, DiagID)
- << S.getLangOpts().getOpenCLVersionString() << PrevSpec << 1;
- } else {
- S.Diag(ConflictingTypeSpecifierLoc, DiagID) << PrevSpec;
- }
- TypeSpecType = TST_error;
- } else {
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = ConflictingTypeSpecifierLoc;
- }
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- }
- } else if (S.getLangOpts().CPlusPlus && S.getLangOpts().CPlusPlus11 &&
- !S.getLangOpts().C23) {
- // In C++11+ (but not C23 or OpenCL), emit error (cannot combine type
- // specifiers)
- if (TypeSpecType == TST_auto) {
- // "auto int" case
- S.Diag(ConflictingTypeSpecifierLoc, diag::err_auto_type_specifier)
- << FixItHint::CreateRemoval(ConflictingTypeSpecifierLoc);
- } else if (ConflictingTypeSpecifier == TST_auto) {
- // "int auto" case
- S.Diag(ConflictingTypeSpecifierLoc, diag::err_auto_type_specifier)
- << FixItHint::CreateRemoval(ConflictingTypeSpecifierLoc);
- }
- // Mark as error to prevent further processing
- TypeSpecType = TST_error;
- } else if (!S.getLangOpts().CPlusPlus) {
- // For C, C23, etc., convert 'auto' to storage class specifier
- // (This is already handled above for C23, but keep for other C dialects)
- // In C, C23, OpenCL, etc., convert 'auto' to storage class specifier
- if (TypeSpecType == TST_auto) {
- // "auto int" case: Convert 'auto' to storage class specifier
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = TSTLoc;
- TypeSpecType = ConflictingTypeSpecifier;
- TSTLoc = ConflictingTypeSpecifierLoc;
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- } else if (ConflictingTypeSpecifier == TST_auto) {
- // "int auto" case: Convert 'auto' to storage class specifier
- StorageClassSpec = SCS_auto;
- StorageClassSpecLoc = ConflictingTypeSpecifierLoc;
- // TypeSpecType already has the correct type (e.g., TST_int)
- // Clear the conflict tracking
- ConflictingTypeSpecifier = TST_unspecified;
- ConflictingTypeSpecifierLoc = SourceLocation();
- }
- }
- }
-
// Validate and finalize AltiVec vector declspec.
if (TypeAltiVecVector) {
// No vector long long without VSX (or ZVector).
@@ -1602,7 +1440,6 @@ voi...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/208436
More information about the cfe-commits
mailing list