<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/146506>146506</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang ICEs in SemaTemplateDeduction.cpp since version 4.0
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          mariete1223
      </td>
    </tr>
</table>

<pre>
    
## Assertion

```
clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateDeduction.cpp:868: unsigned int {anonymous}::PackDeductionScope::addPacks(clang::TemplateArgument): Assertion `!Packs.empty() && "Pack expansion without unexpanded packs?"' failed.
```

## Stack dump

```
Stack dump:
0.      Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -x c++ <source>
1.      <source>:10:5: current parser token '{'
2.      <source>:4:1: parsing struct/union/class body 'remove_separators<>'
 #0 0x0000000003f78848 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f78848)
 #1 0x0000000003f764d4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f764d4)
 #2 0x0000000003ebb048 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x0000710809a42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x0000710809a969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x0000710809a42476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x0000710809a287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000710809a2871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x0000710809a39e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x000000000709d351 (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x709d351)
#10 0x000000000709ddb9 DeduceTemplateSpecArguments(clang::Sema&, clang::TemplateParameterList*, clang::QualType, clang::QualType, clang::sema::TemplateDeductionInfo&, bool, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, bool*) SemaTemplateDeduction.cpp:0:0
#11 0x0000000007097ddb DeduceTemplateArgumentsByTypeMatch(clang::Sema&, clang::TemplateParameterList*, clang::QualType, clang::QualType, clang::sema::TemplateDeductionInfo&, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, unsigned int, PartialOrderingKind, bool, bool*) SemaTemplateDeduction.cpp:0:0
#12 0x00000000070a0d05 clang::ClassTemplatePartialSpecializationDecl* getMoreSpecialized<clang::ClassTemplatePartialSpecializationDecl, clang::ClassTemplateDecl>(clang::Sema&, clang::QualType, clang::QualType, clang::ClassTemplatePartialSpecializationDecl*, clang::ClassTemplateDecl*, clang::sema::TemplateDeductionInfo&) SemaTemplateDeduction.cpp:0:0
#13 0x00000000070a1551 clang::Sema::isMoreSpecializedThanPrimary(clang::ClassTemplatePartialSpecializationDecl*, clang::sema::TemplateDeductionInfo&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70a1551)
#14 0x0000000006fe265d void checkTemplatePartialSpecialization<clang::ClassTemplatePartialSpecializationDecl>(clang::Sema&, clang::ClassTemplatePartialSpecializationDecl*) SemaTemplate.cpp:0:0
#15 0x00000000070129d1 clang::Sema::ActOnClassTemplateSpecialization(clang::Scope*, unsigned int, clang::TagUseKind, clang::SourceLocation, clang::SourceLocation, clang::CXXScopeSpec&, clang::TemplateIdAnnotation&, clang::ParsedAttributesView const&, llvm::MutableArrayRef<clang::TemplateParameterList*>, clang::SkipBodyInfo*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70129d1)
#16 0x0000000006696aab clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6696aab)
#17 0x000000000666b4e0 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x666b4e0)
#18 0x0000000006690ba1 clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6690ba1)
#19 0x00000000067470a5 clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67470a5)
#20 0x000000000675492f clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#21 0x0000000006690fed clang::Parser::ParseCXXClassMemberDeclaration(clang::AccessSpecifier, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6690fed)
#22 0x0000000006693161 clang::Parser::ParseCXXClassMemberDeclarationWithPragmas(clang::AccessSpecifier&, clang::ParsedAttributes&, clang::TypeSpecifierType, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6693161)
#23 0x0000000006694fcf clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6694fcf)
#24 0x0000000006697f10 clang::Parser::ParseClassSpecifier(clang::tok::TokenKind, clang::SourceLocation, clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, bool, clang::Parser::DeclSpecContext, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6697f10)
#25 0x000000000666b4e0 clang::Parser::ParseDeclarationSpecifiers(clang::DeclSpec&, clang::Parser::ParsedTemplateInfo&, clang::AccessSpecifier, clang::Parser::DeclSpecContext, clang::Parser::LateParsedAttrList*, clang::ImplicitTypenameContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x666b4e0)
#26 0x0000000006746cbc clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6746cbc)
#27 0x000000000675492f clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#28 0x0000000006754cda clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6754cda)
#29 0x00000000066721b0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66721b0)
#30 0x000000000662f85c clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662f85c)
#31 0x000000000663077d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x663077d)
#32 0x0000000006622aea clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6622aea)
#33 0x000000000492ed48 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x492ed48)
#34 0x0000000004c28c65 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c28c65)
#35 0x0000000004ba5ffe clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ba5ffe)
#36 0x0000000004d1b441 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d1b441)
#37 0x0000000000d8e81f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd8e81f)
#38 0x0000000000d853fa ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#39 0x0000000004995b49 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#40 0x0000000003ebb4e4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ebb4e4)
#41 0x000000000499615f clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#42 0x0000000004957f8d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4957f8d)
#43 0x000000000495901e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x495901e)
#44 0x00000000049614d5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49614d5)
#45 0x0000000000d8accf clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd8accf)
#46 0x0000000000c41924 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc41924)
#47 0x0000710809a29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#48 0x0000710809a29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#49 0x0000000000d84ea5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd84ea5)
```

## Program

```
template <class...>
struct remove_separators;
template <int T>
struct remove_separators<>
{
    template <class...>
    struct helper;
    template <class Sep>
    struct helper<Sep>
    {
 static constexpr bool value = false;
    };
}
```


## To quickly reproduce:

https://godbolt.org/z/55G4Y59cv
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsW1tz4yj2_zTkhbJLQveHPChOe_6Zf3d1tpOd7X1yIYRsNjJoAKWd-fRbINm6-BInE09N1XZXOrEFnMvvXDgIwEqxJaf0GgQ3ILi9wrVeCXm9xpJRTV2EvKtM5C_XwEkB8gDyYKoUlZoJbh45KQid9sdJSYn5EqAb8-OlEKC5FEIDNC_L5_WkkuI_lGy_AjTXQpQKoHk7bF6yDKD5A13j9s8jXVcl1vSW5jUxLKekqoCXxmFs6Nfcyp5DxjUE0Q3mgr-sRa1AdAu8FHjpPSZPu8EPRFS0eY7z3DQpgOKGuX26ZZfKZb2mXAOUGDY7haHRErl25JSuK_0CUAxQAgEKAQohQMi0QbqpMFdmwA-mV6LWsOb2WU5zWFm-3hwgBFAEC8xKmk9HQHZoP2hDMa_X1T7cvTbPtDlT4CT3UiwlXkPcKqFaS4jKIE_EumIllRO6qUohqdzCP8FbLdVEy5o_ATTPGO-sY4wKJ8v8B5bFxIeTJZwIQxdXlaFe66rWUwUna2NcOJls4nCC1XqiXrjGG-DdMq5pCScFF5NnKjOhqGmHkwc4mSwJmRhvICvMOPBuT8prOiuOK7USGk4KIkohJznDSy6UZkQ1PIjEajV8vIGk1QN4MyVqSSjwPgEndQ1wg2de6jrASwMDHqmlpFzDCktFJdTiiXIIUASiG_PbSdGB4b4hYUabUYwvodKyts5fcxM7FleloAkuQ0zStXimC0UrLLEWUgFvZihZBhAgz4HOxtn-84oojv0Y2kCyvqteVOvyknFtPeNRYkIBirtOEv9YCKUlxWvrsjMTOY0Dxx_kIgDdOJtWPBM_jfDuSPjQz_1Dws9KinldfeUPbMlxCVC8i_FSGBaXENUI04mKBqLSLHP8GM6MM32jRDxT-dLI9n-Y56XhGLcYDvrMBNd0o9t85dj_DX2vpR-5Tuwk2EcBclqlmvy3icNF6E9KxuvNZMnrpoFMlZiGVmQ7pBPYHxJMwqQgsNIrSXG-eGJl-TbqdnxHPRiL60chXCoLwVvF9qOwIxwOCaM4KjyIMyH128jagR3ZaI-sm72ZoJt1BOMhQS-hSfg2gnZIRzDpO1jkJLkXuB_t1S3ZhqmJP2fMNM8SaGdGup31HipK0t2kMZgYmynZJowD0-U9lnhNNZWfmdIApaNu_6hx-fhS0fMeK8NqQH43f9_xQrRSZEKU5m-XQh7WuCx_o0QLebeuSuDNekQbRfO9-d3k1x691ITxqbpjG8cGUXeEaJTn2QjRHZo3L0bTL1iT1d8c2I8CtF-ame_3WGqGy68yp5Lx5f8znvft-A780RB_7ORO0Nd3ZqbXHpKGvXFxhkv2BzZEbykxTOGS6i9C0l0jzYfKnktpdpS9bTfYvG77txn1bCVflW6vyzn-cr61vJG13CBw4RgM-4mpkTEeV5jfS7bG8mUI4HuVP0-zD8_IVucuI_t9RMKCojDI4bNgOSQrSp5O6vUu_zzP_94A6tD6B4weDI3uoiQ_YvSU6K98wHqk8FByu5Br7DpONP00ipf_VHSbavrjbZ3-WZCW9vmNs-_fLXMj3fG8fZennAvdEhj3ujfLiDzVWrKs1lT9xugPSAQ3KX6Ug7_UGmclTaXEL99oMTT70VnCGHqo0hOrbkT-0nh3ehHvtsbtvDsceHeYhBhneyDI3mdrfGv0gtmqutdZi6dWZbP0eqtBjb8etteeELsJrTcj9vqnhNCBkN0EdoTqlne7HHjFEy6TeVr0O9tEQ9uEmU-dk7AYLcyqlAm-U35UIV4U5PeD2_b83IRJC_bhasoUOYwwbWZZjtd0R_UCBrGQdwaJR8HiZNg9HSzfv9t4-ULXGZU98wyNcgaUY-_7U6a7b151GHm-pXd3X7Pmdd8lEk6LUofhYFUVRn7k4OBcp04LTeVWtX2_bl7IvO5lfwKicbdxQnttDjkjjD7eBA3IOxMgZ2iCwE9QcRKrfgHamuKrPDXxv2aNS8E2rbDUUxOxcCD4fs2D3HEsFzT_GcuvxnJB886R0AhDzw3fmQ__xfTqXuLlGqtX4Hy7q5iJYkfgwNqsVyd_PGAGkg4wbwSYX5DTkTf7_r3BqlWAHKqy310lH8HuRKl-UawMGh1W_girqHBPVz8_K9MLVqYG_c42wc_K9G9VmaJwVFWFJCM_q6oLV1UG5M4E0c-qykPxGASS47MTg8ZSM740tcD73PFdAFzAM6zanWcMlzxhhNzs7Gz5V3vA6z3GPC5TDFiQdhAON9XDEBVxcDq_fdpoKjkuj0L5EVD00lkzc10GC6tth8Vo5eI5UXR65fIoqs_0mZZN8dYH4WuFf6_pvZbjXSNS_iJFXdl3mZ8O-MDuhfAXkdclvVtXQuoHbSP2MhWIVbMDYbT0QAjT_USTPjwefZU-3NG6hNWMSJ3Ag9LfTxDN_Xjwxlrk9BfKU9LsG5hHnzaU1Jq2j7YnmD5UzFaQTsxB1e0TFJNw8HpmLk3i4fkBOS8kYSNDJ-Gg9vQzHBQFHQLZ8LzjSmNO6GEsj6t0Ef9t5ey0GBRsfu5mvj9YOrfydso8i0Nrvz1lL5KCWvk66Qe1jpPHNHYLSIi7WGNDoHeSqb8lssJyu3-y2_wYPEMzu7F2GSUaKTsd4pEOgVdguIV95j7avBCf3GffU2i0LWRotBN1b-Mogblkz1Tul0_DIyd-kgSZnzR7jR3RoubWURfSompbm9BrDrQBLyW4LDNMnhbFaAeyYdy6zsydifUa83wcxQetp3TbT1SGOzYA9MDRkvFlO100pt0NWCzIZuO6zZcMK0YWynZvIRx0Ng8WWmKm1bZ5RA6XpQkFIXvtpks6Op_QAG6HABSVeJ2ZmizqoELx9qjaryLbN4bvjA-Y-bR_Fu7QMbKm5VvNH3BBy5cBlqftdoEDc43EO4f33ZFzhW4wWKD8zznHaG1z2AvQELUgKuL8KGrWanhvZtxCOUjdo4Gmw2B3-byu6aCc6Sn2sVWCVbtzpVExEySOS98Kyq8iU8cR-VVkn5nSR_bb93PxzgMqzIzx919dngSxdZO_BEoDVgflsOBKQtfPg2Ni3_Y-DwqEA5XBMRP8hVBeoFq18HTgBaM5HJPt-_RtJbIV3qaStE0Er8_QH157GMk6uQfVn0N8N0E-NBJ_NOOGdMd4fOo2yZM3Hmq2QzqC8Zgg9R24WJgxC6Wx1IueWmezoH6PRTIysk9xABviH28nQ7xlffCaR3trY_-Oh27fWMGm4lJqOp02lxaaCwXwwMWBm9E4xjV8fG3QrOkAIjMaQgiPczatLaEVLSsTskcHwQdaHR01GzS2rJXGmpEmbOimkjZxwmdc1obqLSxwqWjH0d71ubGS3x6Ad4fwo4C_14w8lS9Q0kqKvG7WcLbPSuvKXkFAc4DmS5FnotRTIZcAzf8AaB4Ev_j_DhLyfJVfe3niJfiKXrtR4Hph5PjoanWNfNfN_TDzMw-RzA0pLrysyD0SFp6TI_eKXSMHBU7kuK4TOL47TSiJI5q4AS48z3dz4Dt0jVk5NWnE8L5iStX02vXDwAmvSpzRUtlrWgi1DoZAcHslr-3tqqxeKuA7JVNadSQ00yW9npnu8G72SUHGj5_ZhIpxQuEzlfbykj91rmpZXo_AYXpVZ1Mi1t1FrtH1Liu3Amjeiv58jf4bAAD__4ZG7G8">