Author: Osama Abdelkader
Date: 2026-07-09T11:00:08+02:00
New Revision: d7ccd02c9c78b6576ca2caa3f4d2435ebda50744

URL: 
https://github.com/llvm/llvm-project/commit/d7ccd02c9c78b6576ca2caa3f4d2435ebda50744
DIFF: 
https://github.com/llvm/llvm-project/commit/d7ccd02c9c78b6576ca2caa3f4d2435ebda50744.diff

LOG: [clang] Reject 'auto' storage class with type specifier in C++ (#166004)

Fixes #164273

---------

Signed-off-by: Osama Abdelkader <[email protected]>

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.md
    clang/include/clang/Basic/DiagnosticSemaKinds.td
    clang/include/clang/Sema/DeclSpec.h
    clang/lib/Parse/ParseDecl.cpp
    clang/lib/Sema/DeclSpec.cpp
    clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp
    clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp
    
clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp
    clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp
    clang/test/CXX/dcl/dcl.fct/p17.cpp
    clang/test/CXX/drs/cwg3xx.cpp
    clang/test/Parser/c2x-auto.c
    clang/test/SemaCXX/auto-cxx0x.cpp
    clang/test/SemaCXX/class.cpp
    clang/test/SemaCXX/static-data-member.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index a573599d76f7d..61caf2d9ec99e 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -116,6 +116,8 @@ 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 
diff erent
   block scope than their parent class. (#GH193472)
 

diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td 
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 15867f69a6718..45f909fc5452c 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2759,6 +2759,8 @@ 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 6e7f9cd6e3d38..d1abc0e3c21fb 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -363,6 +363,10 @@ 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)
@@ -427,10 +431,50 @@ class DeclSpec {
   SourceLocation FS_explicitCloseParenLoc;
   SourceLocation FS_forceinlineLoc;
   SourceLocation FriendLoc, ModulePrivateLoc, ConstexprLoc;
-  SourceLocation TQ_pipeLoc;
+  SourceLocation TQ_pipeLoc, ConflictingTypeSpecifierLoc;
 
   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;
 
@@ -474,13 +518,15 @@ 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), writtenBS(), ObjCQualifiers(nullptr) {}
+        Attrs(attrFactory), ConflictingTypeSpecifierLoc(), writtenBS(),
+        ObjCQualifiers(nullptr) {}
 
   // storage-class-specifier
   SCS getStorageClassSpec() const { return (SCS)StorageClassSpec; }
@@ -520,6 +566,9 @@ 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 3f41e7c5c6f0d..1b865195f23e5 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3775,7 +3775,9 @@ 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'.
-      if (DS.hasTypeSpecifier())
+      // 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)
         goto DoneWithDeclSpec;
 
       // If the token is an identifier named "__declspec" and Microsoft
@@ -3860,6 +3862,14 @@ 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,
@@ -3867,11 +3877,16 @@ 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()) {
@@ -3883,6 +3898,25 @@ 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;
@@ -4137,12 +4171,9 @@ void Parser::ParseDeclarationSpecifiers(
           }
         };
 
-        if (MayBeTypeSpecifier()) {
+        if (!getLangOpts().CPlusPlus && 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);
@@ -4700,7 +4731,8 @@ void Parser::ParseDeclarationSpecifiers(
     DS.SetRangeEnd(ConsumedEnd.isValid() ? ConsumedEnd : Tok.getLocation());
 
     // If the specifier wasn't legal, issue a diagnostic.
-    if (isInvalid) {
+    // Skip diagnostic if 'auto' conflict will be handled in Finish()
+    if (isInvalid && !DS.hasConflictingTypeSpecifier()) {
       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 2add7c6aa3080..3c882bc3a1003 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -759,6 +759,7 @@ 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;
@@ -790,6 +791,7 @@ 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;
@@ -822,6 +824,7 @@ 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;
@@ -852,6 +855,7 @@ 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;
@@ -1212,6 +1216,164 @@ 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).
@@ -1440,6 +1602,7 @@ void DeclSpec::CheckTypeSpec(Sema &S, const 
PrintingPolicy &Policy) {
       S.getLangOpts().getHLSLVersion() < LangOptions::HLSL_202y &&
       TypeSpecType == TST_auto)
     S.Diag(TSTLoc, diag::ext_hlsl_auto_type_specifier) << /*HLSL*/ 1;
+  // Emit warning for 'auto' storage class in pre-C++11 dialects
   if (S.getLangOpts().CPlusPlus && !S.getLangOpts().CPlusPlus11 &&
       StorageClassSpec == SCS_auto)
     S.Diag(StorageClassSpecLoc, diag::warn_auto_storage_class)

diff  --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp 
b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp
index 723a79628116c..3a3f752a9e93b 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.stc/p2.cpp
@@ -1,66 +1,75 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++98 %s
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=cxx98 -std=c++98 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=cxx11 -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=cxx17 -std=c++17 %s
 
 // The auto or register specifiers can be applied only to names of objects
 // declared in a block (6.3) or to function parameters (8.4).
 
-auto int ao; // expected-error {{illegal storage class on file-scoped 
variable}}
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
+auto int ao;
+// cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+// cxx17-error@-2 {{'auto' cannot be combined with a type specifier}}
+// cxx98-error@-3 {{illegal storage class on file-scoped variable}}
 
-auto void af(); // expected-error {{illegal storage class on function}}
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
+auto void af();
+// cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+// cxx17-error@-2 {{'auto' cannot be combined with a type specifier}}
+// cxx98-error@-3 {{illegal storage class on function}}
 
-register int ro; // expected-error {{illegal storage class on file-scoped 
variable}}
-#if __cplusplus >= 201703L
-// expected-error@-2 {{ISO C++17 does not allow 'register' storage class 
specifier}}
-#elif __cplusplus >= 201103L
-// expected-warning@-4 {{'register' storage class specifier is deprecated}}
-#endif
+register int ro;
+// cxx98-error@-1 {{illegal storage class on file-scoped variable}}
+// cxx11-error@-2 {{illegal storage class on file-scoped variable}}
+// cxx11-warning@-3 {{'register' storage class specifier is deprecated and 
incompatible with C++17}}
+// cxx17-error@-4 {{illegal storage class on file-scoped variable}}
+// cxx17-error@-5 {{ISO C++17 does not allow 'register' storage class 
specifier}}
 
-register void rf(); // expected-error {{illegal storage class on function}}
+register void rf();
+// cxx98-error@-1 {{illegal storage class on function}}
+// cxx11-error@-2 {{illegal storage class on function}}
+// cxx17-error@-3 {{illegal storage class on function}}
 
 struct S {
-  auto int ao; // expected-error {{storage class specified for a member 
declaration}}
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
-  auto void af(); // expected-error {{storage class specified for a member 
declaration}}
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
+  auto int ao;
+  // cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+  // cxx17-error@-2 {{'auto' cannot be combined with a type specifier}}
+  // cxx98-error@-3 {{storage class specified for a member declaration}}
+  auto void af();
+  // cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+  // cxx17-error@-2 {{'auto' cannot be combined with a type specifier}}
+  // cxx98-error@-3 {{storage class specified for a member declaration}}
 
-  register int ro; // expected-error {{storage class specified for a member 
declaration}}
-  register void rf(); // expected-error {{storage class specified for a member 
declaration}}
+  register int ro;
+  // cxx98-error@-1 {{storage class specified for a member declaration}}
+  // cxx11-error@-2 {{storage class specified for a member declaration}}
+  // cxx17-error@-3 {{storage class specified for a member declaration}}
+  register void rf();
+  // cxx98-error@-1 {{storage class specified for a member declaration}}
+  // cxx11-error@-2 {{storage class specified for a member declaration}}
+  // cxx17-error@-3 {{storage class specified for a member declaration}}
 };
 
 void foo(auto int ap, register int rp) {
-#if __cplusplus >= 201703L
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-// expected-error@-3 {{ISO C++17 does not allow 'register' storage class 
specifier}}
-#elif __cplusplus >= 201103L
-// expected-warning@-5 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-// expected-warning@-6 {{'register' storage class specifier is deprecated}}
-#endif
+  // cxx17-error@-1 {{'auto' cannot be combined with a type specifier}}
+  // cxx17-error@-2 {{ISO C++17 does not allow 'register' storage class 
specifier}}
+  // cxx11-error@-3 {{'auto' cannot be combined with a type specifier}}
+  // cxx11-warning@-4 {{'register' storage class specifier is deprecated and 
incompatible with C++17}}
   auto int abo;
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
-  auto void abf(); // expected-error {{illegal storage class on function}}
-#if __cplusplus >= 201103L // C++11 or later
-// expected-warning@-2 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
-#endif
+  // cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+  // cxx17-error@-2 {{'auto' cannot be combined with a type specifier}}
+  auto void abf();
+  // cxx11-error@-1 {{'auto' cannot be combined with a type specifier}}
+  // cxx11-warning@-2 {{empty parentheses interpreted as a function 
declaration}}
+  // cxx11-note@-3 {{replace parentheses with an initializer to declare a 
variable}}
+  // cxx17-error@-4 {{'auto' cannot be combined with a type specifier}}
+  // cxx17-warning@-5 {{empty parentheses interpreted as a function 
declaration}}
+  // cxx17-note@-6 {{replace parentheses with an initializer to declare a 
variable}}
+  // cxx98-error@-7 {{illegal storage class on function}}
 
   register int rbo;
-#if __cplusplus >= 201703L
-// expected-error@-2 {{ISO C++17 does not allow 'register' storage class 
specifier}}
-#elif __cplusplus >= 201103L
-// expected-warning@-4 {{'register' storage class specifier is deprecated}}
-#endif
+  // cxx17-error@-1 {{ISO C++17 does not allow 'register' storage class 
specifier}}
+  // cxx11-warning@-2 {{'register' storage class specifier is deprecated and 
incompatible with C++17}}
 
-  register void rbf(); // expected-error {{illegal storage class on function}}
+  register void rbf();
+  // cxx98-error@-1 {{illegal storage class on function}}
+  // cxx11-error@-2 {{illegal storage class on function}}
+  // cxx17-error@-3 {{illegal storage class on function}}
 }

diff  --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp 
b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp
index e8f12156a4242..880014d591706 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-1y.cpp
@@ -56,7 +56,13 @@ namespace p3_example {
   auto x = 5;
   const auto *v = &x, u = 6;
   static auto y = 0.0;
-  auto int r;  // expected-warning {{storage class}} expected-error 
{{file-scope}}
+  auto int r;
+#if __cplusplus >= 201103L
+  // expected-error@-2 {{'auto' cannot be combined with a type specifier}}
+#else
+  // expected-warning@-4 {{storage class}}
+  // expected-error@-5 {{file-scope}}
+#endif
 
   static_assert(is_same<decltype(x), int>(), "");
   static_assert(is_same<decltype(v), const int*>(), "");

diff  --git 
a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp
 
b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp
index a590f8eb77005..7577a789eb1c0 100644
--- 
a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp
+++ 
b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3-generic-lambda-1y.cpp
@@ -62,11 +62,11 @@ int main()
   {
     auto l = [](auto (*)(auto)) { }; //expected-error{{'auto' not allowed}} 
expected-warning {{'auto' parameters are a C++20 extension}}
     //FIXME: These diagnostics might need some work.
-    auto l2 = [](char auto::*pm) { };       // expected-error {{cannot combine 
with previous 'char' declaration specifier}} \
-                                               expected-error{{'pm' does not 
point into a class}}
-    auto l3 = [](char (auto::*pmf)()) { };  // expected-error{{'auto' not 
allowed}}\
-                                               expected-error{{'pmf' does not 
point into a class}}\
-                                               expected-error{{function cannot 
return function type 'char ()'}} \
-                                               expected-warning {{'auto' 
parameters are a C++20 extension}}
+    auto l2 = [](char auto::*pm) { };  //expected-error{{'auto' cannot be 
combined with a type specifier}}\
+                                         expected-error{{'pm' does not point 
into a class}}
+    auto l3 = [](char (auto::*pmf)()) { };  //expected-error{{'auto' not 
allowed}}\
+                                              expected-error{{'pmf' does not 
point into a class}}\
+                                              expected-error{{function cannot 
return function type 'char ()'}} \
+                                              expected-warning {{'auto' 
parameters are a C++20 extension}}
   }
 }

diff  --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp 
b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp
index 440c78201293b..8d7765523461c 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.spec.auto/p3.cpp
@@ -42,7 +42,12 @@ void p3example() {
   static auto y = 0.0;
   // In C++98: 'auto' storage class specifier is redundant and incompatible 
with C++0x
   // In C++0x: 'auto' storage class specifier is not permitted in C++0x, and 
will not be supported in future releases
-  auto int r; // expected-warning {{'auto' storage class specifier}}
+  auto int r;
+#if __cplusplus >= 201103L
+  // expected-error@-2 {{'auto' cannot be combined with a type specifier}}
+#else
+  // expected-warning@-4 {{'auto' storage class specifier}}
+#endif
 
   same<__typeof(x), int> xHasTypeInt;
   same<__typeof(v), const int*> vHasTypeConstIntPtr;

diff  --git a/clang/test/CXX/dcl/dcl.fct/p17.cpp 
b/clang/test/CXX/dcl/dcl.fct/p17.cpp
index d837d0900d5b9..971edc7bf26eb 100644
--- a/clang/test/CXX/dcl/dcl.fct/p17.cpp
+++ b/clang/test/CXX/dcl/dcl.fct/p17.cpp
@@ -135,7 +135,7 @@ void undefined(Foo auto); // expected-error {{unknown type 
name 'Foo'}}
 
 struct AStruct {};
 
-void a_struct(AStruct auto); // expected-error {{cannot combine with previous 
'type-name' declaration specifier}}
+void a_struct(AStruct auto); // expected-error {{'auto' cannot be combined 
with a type specifier}}
 }
 
 #if __cplusplus >= 202002L

diff  --git a/clang/test/CXX/drs/cwg3xx.cpp b/clang/test/CXX/drs/cwg3xx.cpp
index 10bf57e422f33..05db04255780b 100644
--- a/clang/test/CXX/drs/cwg3xx.cpp
+++ b/clang/test/CXX/drs/cwg3xx.cpp
@@ -1704,14 +1704,16 @@ namespace cwg395 { // cwg395: 3.0
 
 namespace cwg396 { // cwg396: 3.0
   void f() {
-    auto int a();
-    // since-cxx11-error@-1 {{'auto' storage class specifier is not permitted 
in C++11, and will not be supported in future releases}}
-    // expected-error@-2 {{illegal storage class on function}}
+    auto int a(); // #cwg396-a
+    // cxx98-error@#cwg396-a {{illegal storage class on function}}
+    // since-cxx11-error@#cwg396-a {{'auto' cannot be combined with a type 
specifier}}
+    // since-cxx11-warning@#cwg396-a {{empty parentheses interpreted as a 
function declaration}}
+    // since-cxx11-note@#cwg396-a {{replace parentheses with an initializer to 
declare a variable}}
     int (i); // #cwg396-i
-    auto int (i);
-    // since-cxx11-error@-1 {{'auto' storage class specifier is not permitted 
in C++11, and will not be supported in future releases}}
-    // expected-error@-2 {{redefinition of 'i'}}
-    //   expected-note@#cwg396-i {{previous definition is here}}
+    auto int (i); // #cwg396-auto-i
+    // cxx98-error@#cwg396-auto-i {{redefinition of 'i'}}
+    // cxx98-note@#cwg396-i {{previous definition is here}}
+    // since-cxx11-error@#cwg396-auto-i {{'auto' cannot be combined with a 
type specifier}}
   }
 } // namespace cwg396
 

diff  --git a/clang/test/Parser/c2x-auto.c b/clang/test/Parser/c2x-auto.c
index dc0e1f34dabdc..145e6f8b08b09 100644
--- a/clang/test/Parser/c2x-auto.c
+++ b/clang/test/Parser/c2x-auto.c
@@ -167,6 +167,13 @@ void t1() {
   int auto d2 = 0;
 }
 
+void typedef_type_specifiers(void) {
+  typedef int MyInt;
+
+  auto MyInt a = 0;
+  MyInt auto b = 0;
+}
+
 void t2() {
   auto long long a1 = 0;
   long auto long a2 = 0;

diff  --git a/clang/test/SemaCXX/auto-cxx0x.cpp 
b/clang/test/SemaCXX/auto-cxx0x.cpp
index f429bebb9941a..00ede3358b6b4 100644
--- a/clang/test/SemaCXX/auto-cxx0x.cpp
+++ b/clang/test/SemaCXX/auto-cxx0x.cpp
@@ -1,8 +1,14 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
 // RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++1y
 void f() {
-  auto int a; // expected-warning {{'auto' storage class specifier is not 
permitted in C++11, and will not be supported in future releases}}
-  int auto b; // expected-error {{cannot combine with previous 'int' 
declaration specifier}}
+  auto int a; // expected-error {{'auto' cannot be combined with a type 
specifier}}
+  int auto b; // expected-error {{'auto' cannot be combined with a type 
specifier}}
+  unsigned auto int x; // expected-error {{'auto' cannot be combined with a 
type specifier}} expected-error-re {{'{{.*}}' cannot be signed or unsigned}}
+  signed auto int s; // expected-error {{'auto' cannot be combined with a type 
specifier}} expected-error-re {{'{{.*}}' cannot be signed or unsigned}}
+  auto double y; // expected-error {{'auto' cannot be combined with a type 
specifier}}
+  auto float z; // expected-error {{'auto' cannot be combined with a type 
specifier}}
+  long auto int l; // expected-error {{'auto' cannot be combined with a type 
specifier}} expected-error-re {{'long {{.*}}' is invalid}}
+  auto int arr[10]; // expected-error {{'auto' cannot be combined with a type 
specifier}}
 }
 
 typedef auto PR25449(); // expected-error {{'auto' not allowed in typedef}}

diff  --git a/clang/test/SemaCXX/class.cpp b/clang/test/SemaCXX/class.cpp
index f1e02d5158aac..71c71a1acc807 100644
--- a/clang/test/SemaCXX/class.cpp
+++ b/clang/test/SemaCXX/class.cpp
@@ -2,11 +2,12 @@
 // RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx98 -Wc++11-compat %s 
-std=c++98
 class C {
 public:
-  auto int errx; // expected-error {{storage class specified for a member 
declaration}}
-#if __cplusplus <= 199711L
-  // expected-warning@-2 {{'auto' storage class specifier is redundant}}
+  auto int errx;
+#if __cplusplus >= 201103L
+  // expected-error@-2 {{'auto' cannot be combined with a type specifier}}
 #else
-  // expected-warning@-4 {{'auto' storage class specifier is not permitted in 
C++11, and will not be supported in future releases}}
+  // expected-error@-4 {{storage class specified for a member declaration}}
+  // expected-warning@-5 {{'auto' storage class specifier is redundant}}
 #endif
   register int erry; // expected-error {{storage class specified for a member 
declaration}}
   extern int errz; // expected-error {{storage class specified for a member 
declaration}}

diff  --git a/clang/test/SemaCXX/static-data-member.cpp 
b/clang/test/SemaCXX/static-data-member.cpp
index fb63da9b40099..2dbcae1745e5b 100644
--- a/clang/test/SemaCXX/static-data-member.cpp
+++ b/clang/test/SemaCXX/static-data-member.cpp
@@ -13,7 +13,12 @@ double ABC::a = 1.0;
 extern double ABC::b = 1.0; // expected-error {{static data member definition 
cannot specify a storage class}}
 static double ABC::c = 1.0;  // expected-error {{'static' can only be 
specified inside the class definition}}
 __private_extern__ double ABC::d = 1.0; // expected-error {{static data member 
definition cannot specify a storage class}}
-auto double ABC::e = 1.0; // expected-error {{static data member definition 
cannot specify a storage class}}
+auto double ABC::e = 1.0;
+#if __cplusplus >= 201103L
+// expected-error@-2 {{'auto' cannot be combined with a type specifier}}
+#else
+// expected-error@-4 {{static data member definition cannot specify a storage 
class}}
+#endif
 #if __cplusplus < 201703L
 register double ABC::f = 1.0; // expected-error {{static data member 
definition cannot specify a storage class}}
 #endif


        
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