[Clang][ICE] crashes when enum class is based on a decltype depending on a static class member

[SchrodingerZhu]

#include <cstdint>
#include <cstddef>
#include <type_traits>

enum Flags : uint64_t
{
    LowMemoryNotification = (1 << 0),
    AlignedAllocation = (1 << 1),
    LazyCommit = (1 << 2),
    NoAllocation = (1 << 3),
    Entropy = (1 << 4),
    Time = (1 << 5),
    CoreDump = (1 << 6),
    WaitOnAddress = (1 << 7),
};

struct A {
    static constexpr uint64_t features = LowMemoryNotification | WaitOnAddress;
    using T = int;
};

struct B {
    static constexpr uint64_t features = 0;
};

template<Flags F, typename T>
static constexpr bool supports = (T::features & F) == F;

struct AA {
    template <class T>
    static auto helper() {
        if constexpr(supports<Flags::WaitOnAddress, T>)
            return typename T::T {};
        else {
            return char{};
        }
    }

    enum class TA : decltype(helper<A>()) {
        A, B, C, D
    };
    enum class TB : decltype(helper<B>()) {
        A, B, C, D
    };
};

Stacktraces:

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.      Program arguments: clang++-20 ice.cc -c
1.      ice.cc:46:6: current parser token ';'
2.      ice.cc:34:1: parsing struct/union/class body 'AA'
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  libLLVM.so.20.0      0x0000794ff9c4d69f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 63
1  libLLVM.so.20.0      0x0000794ff9c4b3b9 llvm::sys::RunSignalHandlers() + 89
2  libLLVM.so.20.0      0x0000794ff9b92757
3  libc.so.6            0x0000794ff8782320
4  libclang-cpp.so.20.0 0x0000795001b42576 clang::ASTContext::getTypeInfoImpl(clang::Type const*) const + 3814
5  libclang-cpp.so.20.0 0x0000795001b4218b clang::ASTContext::getTypeInfoImpl(clang::Type const*) const + 2811
6  libclang-cpp.so.20.0 0x0000795001b65fd5 clang::ASTContext::getIntWidth(clang::QualType) const + 405
7  libclang-cpp.so.20.0 0x000079500259080f clang::Sema::ActOnEnumBody(clang::SourceLocation, clang::SourceRange, clang::Decl*, llvm::ArrayRef<clang::Decl*>, clang::Scope*, clang::ParsedAttributesView const&) + 1327
8  libclang-cpp.so.20.0 0x0000795001a6da4b clang::Parser::ParseEnumBody(clang::SourceLocation, clang::Decl*) + 3883
9  libclang-cpp.so.20.0 0x0000795001a69583 clang::Parser::ParseEnumSpecifier(clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, clang::Parser::DeclSpecContext) + 6547
10 libclang-cpp.so.20.0 0x0000795001a6473f clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) + 9215
11 libclang-cpp.so.20.0 0x0000795001a89b9b clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) + 2347
12 libclang-cpp.so.20.0 0x0000795001a8c54c clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) + 892
13 libclang-cpp.so.20.0 0x0000795001a86884 clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) + 3828
14 libclang-cpp.so.20.0 0x0000795001a8441e clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) + 8190
15 libclang-cpp.so.20.0 0x0000795001a634d5 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) + 4501
16 libclang-cpp.so.20.0 0x0000795001b1f2bc clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 204
17 libclang-cpp.so.20.0 0x0000795001b1efc5 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 565
18 libclang-cpp.so.20.0 0x0000795001b1e184 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 2164
19 libclang-cpp.so.20.0 0x0000795001b1c558 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) + 1576
20 libclang-cpp.so.20.0 0x0000795001a4739e clang::ParseAST(clang::Sema&, bool, bool) + 814
21 libclang-cpp.so.20.0 0x0000795003b9e56c clang::FrontendAction::Execute() + 92
22 libclang-cpp.so.20.0 0x0000795003b10ad4 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 996
23 libclang-cpp.so.20.0 0x0000795003c1d85c clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 700
24 clang++-20           0x00005ead8b4ee1a2 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 5586
25 clang++-20           0x00005ead8b4eb174
26 libclang-cpp.so.20.0 0x000079500379be22
27 libLLVM.so.20.0      0x0000794ff9b924a7 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) + 151
28 libclang-cpp.so.20.0 0x000079500379b6b6 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const + 406
29 libclang-cpp.so.20.0 0x0000795003760be9 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 921
30 libclang-cpp.so.20.0 0x0000795003760e5f clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const + 159
31 libclang-cpp.so.20.0 0x000079500377de60 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) + 352
32 clang++-20           0x00005ead8b4eab9b clang_main(int, char**, llvm::ToolContext const&) + 6699
33 clang++-20           0x00005ead8b4f85e3 main + 131
34 libc.so.6            0x0000794ff87671ca
35 libc.so.6            0x0000794ff876728b __libc_start_main + 139
36 clang++-20           0x00005ead8b4e8d75 _start + 37
clang++-20: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Ubuntu clang version 20.0.0 (++20240827082329+cb9267f05515-1~exp1~20240827082434.375)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-20/bin
clang++-20: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++-20: note: diagnostic msg: /tmp/ice-80506b.cpp
clang++-20: note: diagnostic msg: /tmp/ice-80506b.sh
clang++-20: note: diagnostic msg: 

********************

[SchrodingerZhu]

The code should be rejected

[SchrodingerZhu]

minimized:

#include <cstdint>
#include <cstddef>
#include <type_traits>


struct AA {
    template <size_t X>
    static auto helper() {
        if constexpr(X == 0)
            return int {};
        else {
            return char{};
        }
    }
    enum class TA : decltype(helper<0>()) {
        A, B, C, D
    };
    enum class TB : decltype(helper<1>()) {
        A, B, C, D
    };
};

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

```c++ #include <cstdint> #include <cstddef> #include <type_traits>

enum Flags : uint64_t
{
LowMemoryNotification = (1 << 0),
AlignedAllocation = (1 << 1),
LazyCommit = (1 << 2),
NoAllocation = (1 << 3),
Entropy = (1 << 4),
Time = (1 << 5),
CoreDump = (1 << 6),
WaitOnAddress = (1 << 7),
};

struct A {
static constexpr uint64_t features = LowMemoryNotification | WaitOnAddress;
using T = int;
};

struct B {
static constexpr uint64_t features = 0;
};

template<Flags F, typename T>
static constexpr bool supports = (T::features & F) == F;

struct AA {
template <class T>
static auto helper() {
if constexpr(supports<Flags::WaitOnAddress, T>)
return typename T::T {};
else {
return char{};
}
}

enum class TA : decltype(helper<A>()) {
    A, B, C, D
};
enum class TB : decltype(helper<B>()) {
    A, B, C, D
};

};

Stacktraces:

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0. Program arguments: clang++-20 ice.cc -c

1.  ice.cc:46:6: current parser token ';'
   

2.  ice.cc:34:1: parsing struct/union/class body 'AA'
   

Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var LLVM_SYMBOLIZER_PATH to point to it):
0 libLLVM.so.20.0 0x0000794ff9c4d69f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 63
1 libLLVM.so.20.0 0x0000794ff9c4b3b9 llvm::sys::RunSignalHandlers() + 89
2 libLLVM.so.20.0 0x0000794ff9b92757
3 libc.so.6 0x0000794ff8782320
4 libclang-cpp.so.20.0 0x0000795001b42576 clang::ASTContext::getTypeInfoImpl(clang::Type const*) const + 3814
5 libclang-cpp.so.20.0 0x0000795001b4218b clang::ASTContext::getTypeInfoImpl(clang::Type const*) const + 2811
6 libclang-cpp.so.20.0 0x0000795001b65fd5 clang::ASTContext::getIntWidth(clang::QualType) const + 405
7 libclang-cpp.so.20.0 0x000079500259080f clang::Sema::ActOnEnumBody(clang::SourceLocation, clang::SourceRange, clang::Decl*, llvm::ArrayRef<clang::Decl*>, clang::Scope*, clang::ParsedAttributesView const&) + 1327
8 libclang-cpp.so.20.0 0x0000795001a6da4b clang::Parser::ParseEnumBody(clang::SourceLocation, clang::Decl*) + 3883
9 libclang-cpp.so.20.0 0x0000795001a69583 clang::Parser::ParseEnumSpecifier(clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo const&, clang::AccessSpecifier, clang::Parser::DeclSpecContext) + 6547
10 libclang-cpp.so.20.0 0x0000795001a6473f clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) + 9215
11 libclang-cpp.so.20.0 0x0000795001a89b9b clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) + 2347
12 libclang-cpp.so.20.0 0x0000795001a8c54c clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) + 892
13 libclang-cpp.so.20.0 0x0000795001a86884 clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) + 3828
14 libclang-cpp.so.20.0 0x0000795001a8441e clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) + 8190
15 libclang-cpp.so.20.0 0x0000795001a634d5 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) + 4501
16 libclang-cpp.so.20.0 0x0000795001b1f2bc clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) + 204
17 libclang-cpp.so.20.0 0x0000795001b1efc5 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) + 565
18 libclang-cpp.so.20.0 0x0000795001b1e184 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) + 2164
19 libclang-cpp.so.20.0 0x0000795001b1c558 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) + 1576
20 libclang-cpp.so.20.0 0x0000795001a4739e clang::ParseAST(clang::Sema&, bool, bool) + 814
21 libclang-cpp.so.20.0 0x0000795003b9e56c clang::FrontendAction::Execute() + 92
22 libclang-cpp.so.20.0 0x0000795003b10ad4 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 996
23 libclang-cpp.so.20.0 0x0000795003c1d85c clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 700
24 clang++-20 0x00005ead8b4ee1a2 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 5586
25 clang++-20 0x00005ead8b4eb174
26 libclang-cpp.so.20.0 0x000079500379be22
27 libLLVM.so.20.0 0x0000794ff9b924a7 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) + 151
28 libclang-cpp.so.20.0 0x000079500379b6b6 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>, bool) const + 406
29 libclang-cpp.so.20.0 0x0000795003760be9 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const + 921
30 libclang-cpp.so.20.0 0x0000795003760e5f clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const + 159
31 libclang-cpp.so.20.0 0x000079500377de60 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) + 352
32 clang++-20 0x00005ead8b4eab9b clang_main(int, char**, llvm::ToolContext const&) + 6699
33 clang++-20 0x00005ead8b4f85e3 main + 131
34 libc.so.6 0x0000794ff87671ca
35 libc.so.6 0x0000794ff876728b __libc_start_main + 139
36 clang++-20 0x00005ead8b4e8d75 _start + 37
clang++-20: error: clang frontend command failed with exit code 139 (use -v to see invocation)
Ubuntu clang version 20.0.0 (++20240827082329+cb9267f05515-1exp120240827082434.375)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-20/bin
clang++-20: note: diagnostic msg:

---

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang++-20: note: diagnostic msg: /tmp/ice-80506b.cpp
clang++-20: note: diagnostic msg: /tmp/ice-80506b.sh
clang++-20: note: diagnostic msg:

---

</details>

[Sirraide]

Godbolt: https://godbolt.org/z/Yczq84osq

The crash seems to be a regression that appeared in 18. Before 18, we reject this, and so does GCC, though MSVC and EDG accept this.

[shafik]

@Fznamznon git bisect reports this commit as the cause 20a0567