<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/138657>138657</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang crash (ICE) on partial specialization with template<int N, int... Args> for template<auto V> since clang 18
        </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>
    Clang crashes with an internal compiler error (ICE) when attempting to partially specialize a class template template<auto V> using a function-style syntax like template<int N, int... Args> class meta<N(Args...)>. The syntax appears invalid but instead of producing a diagnostic, Clang segfaults inside CallExpr::getCallReturnType. This occurs at compile time, even without instantiation.

## Assertion

```
clang++: /root/llvm-project/llvm/tools/clang/include/clang/AST/Type.h:8839: const T* clang::Type::castAs() const [with T = clang::FunctionType]: Assertion `isa<T>(CanonicalType)' 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.      <eof> parser at end of file
 #0 0x0000000003f70b58 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f70b58)
 #1 0x0000000003f6e7e4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f6e7e4)
 #2 0x0000000003eb36a8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fa969642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007fa9696969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007fa969642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007fa9696287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007fa96962871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007fa969639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x000000000782b06f clang::CallExpr::getCallReturnType(clang::ASTContext const&) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x782b06f)
#10 0x000000000783a92b ClassifyInternal(clang::ASTContext&, clang::Expr const*) ExprClassification.cpp:0:0
#11 0x000000000783bb44 clang::Expr::ClassifyImpl(clang::ASTContext&, clang::SourceLocation*) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x783bb44)
#12 0x000000000711017b clang::Sema::DeduceAutoType(clang::TypeLoc, clang::Expr*, clang::QualType&, clang::sema::TemplateDeductionInfo&, bool, bool, clang::TemplateSpecCandidateSet*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x711017b)
#13 0x0000000007026319 clang::Sema::CheckTemplateArgument(clang::NonTypeTemplateParmDecl*, clang::QualType, clang::Expr*, clang::TemplateArgument&, clang::TemplateArgument&, bool, clang::Sema::CheckTemplateArgumentKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7026319)
#14 0x000000000702b501 clang::Sema::CheckTemplateArgument(clang::NamedDecl*, clang::TemplateArgumentLoc&, clang::NamedDecl*, clang::SourceLocation, clang::SourceLocation, unsigned int, clang::Sema::CheckTemplateArgumentInfo&, clang::Sema::CheckTemplateArgumentKind) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x702b501)
#15 0x000000000702c761 clang::Sema::CheckTemplateArgumentList(clang::TemplateDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo&, clang::DefaultArguments const&, bool, clang::Sema::CheckTemplateArgumentInfo&, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x702c761)
#16 0x0000000007037335 clang::Sema::CheckTemplateIdType(clang::TemplateName, clang::SourceLocation, clang::TemplateArgumentListInfo&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7037335)
#17 0x0000000007039062 clang::Sema::ActOnTagTemplateIdType(clang::TagUseKind, clang::TypeSpecifierType, clang::SourceLocation, clang::CXXScopeSpec&, clang::SourceLocation, clang::OpaquePtr<clang::TemplateName>, clang::SourceLocation, clang::SourceLocation, llvm::MutableArrayRef<clang::ParsedTemplateArgument>, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7039062)
#18 0x0000000006655613 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+++0x6655613)
#19 0x000000000662ad10 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+++0x662ad10)
#20 0x00000000066f5cfc clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f5cfc)
#21 0x000000000670389f clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#22 0x0000000006703c4a clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6703c4a)
#23 0x0000000006631a10 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6631a10)
#24 0x00000000065ee70c clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65ee70c)
#25 0x00000000065ef5fd clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65ef5fd)
#26 0x00000000065e19da clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65e19da)
#27 0x0000000004912908 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4912908)
#28 0x0000000004c05bb5 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c05bb5)
#29 0x0000000004b851be clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4b851be)
#30 0x0000000004cf9a09 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4cf9a09)
#31 0x0000000000da625f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda625f)
#32 0x0000000000d9c42a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#33 0x00000000049791b9 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
#34 0x0000000003eb3b44 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3eb3b44)
#35 0x00000000049797cf 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
#36 0x000000000493bc1d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x493bc1d)
#37 0x000000000493ccae 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+++0x493ccae)
#38 0x0000000004944b05 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4944b05)
#39 0x0000000000da21c8 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda21c8)
#40 0x0000000000c27864 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc27864)
#41 0x00007fa969629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#42 0x00007fa969629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#43 0x0000000000d9bed5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9bed5)
```

## Program

```
#include <iostream>
using namespace std;
template <auto V>
class meta {};
template<int N, int... Args>
class meta<N(Args...)> {}
```

## To reproduce

It happens in version 18, 19, 20 and current 

All versions compiled: https://gcc.godbolt.org/z/aa3PxYePK
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzkWk1T5DjS_jXioqgKW_4-cHAXzbzM9EzzNuzs7ImQZblKi0vySjIN8-s3JNnlD0wBvdTERmwH3W3sVOrJJ1OplJ1YKbbllJ6D6BOILs5wq3dCnu-xZFRTH6HgrBDl0_mmxnwLicRqRxX8zvQOYg4Z11RyXEMi9g2rqYRUSiEhQOnV5jNAGfy-oxxirem-0YxvoRawwVIzXNdPUDWUMFyzPynEkNRYKWgEa6zp4QIEG9xqAX8HwWfYKqMDw6rlRDPBV0o_1RSqJ67xI6zZ_WQc4xr-BtDGwFyv1zCXW2W0uJn2VGMQbH4DKDUP1us1QBkIPq_h7e6gEjcNxVJBxh9wzUpYtBoyrjTFJRQVbKQoW-IwlQxvuVCaETOl40vRbYXbWhsFipUUbnBdf35sJAhyEORbqs2Nb1S3kt8-NdTMzRQUhLRSQax7XqFme2rU0gfKLfuiA4K5ZthQsQZebn5QAFAAc6WoNLe7u7HX_Xg5McgA-mR-ghwCdCmF0ABd1vXDftVI8U9K-l8ButRC1Aqgy27YJeOkbks6upPf3AJ0aeHvQJCnaZAZxURwpeEtQDl0ktZkI-auCFY6VwClJkycMIg-2ci6hSC4GI-67PxtR0cXRv3BQghijynjylsQfAYo3WAuOCO4ttIoAyiBFWY1LdczKga-bjQm97Bs981zwkbPAvPMWwMvu5ZiK_EeYrlt95Rr1XEpGsNdvxxW9LGphaSyp2uFe9hqpWXL7wG6LBgf2DRugatt-R3LahXC1RauhNGLm8Zob3XT6rWCq71xD1ytHtN4hdV-5eIVBBdmSdZwVXGxeqCyEIqa53B1A1erLSEr40-yw4yD4OIoXiOsOG7UTmi4qoiohVwNQa7cHDYjTG8_QtLZAYKNEq0k1DjGy31DHAg2VFRmGTZYKipNlFNuV1PFago8Q2PgQe_R6_8EVeIVUQptRNp4UE_KXVxLxrV10K3EhAKUDkISf78TSkuK9wDFXR4wwWZj7kM8BdAn77GDZyLNgfen4GOa0HAJ_KammLfNV37DthzXAKUtt9m4hLUwU5wAqgUzQEUTqLQIYpzCjfHpN0rEA5VPDtv_YV7WZsa043AisxFc00e9Jo1ZIp796_QHnf6kwlmcxSGKkNcZVbMCoMvHNL6Lw1XNePu42vLWPSBrJdaxhWyHDIDDqcIszioCG72TFJd396yu36fdjh-0R3O4YRLDrbIUvBd2mMSD4niqGKVJFUBcCKnfp9YOHNQmz9T6xbsV-sWgMJ0qDDKaxe9TaIcMCrNxgCUpKry4Gmf2VzZEgNKRcH5z24Wa2zDssj5sHh-7VDqszhKzqL2pJQHOUGG2eaVY9XTVFUIv4e0S0OiZMbq3IjdWmBudOkbclj5dTwaEPwNRFGE419onlw7ZvnkHqhubrr8IB6BDdiJ-LfiB30kqSnzf85NiAo3usbu6oGVLaN5q8TxEzJ0vgiyQbY2Z3P3_tq8R5jSow1y3XTlp5zR2XfFKdAMKIerx_2MY3bCbhpIN5iUrzS-09_VHc-nYGrgMJlx6KA78bJnLzY6S-x5t3hUzU0p_c3VXL3SN5f6CkvoYn28g__mccye8ILHA9ivm_MJ4eQrWHa8D6-GM9SLy_B9nHe9puczzfKCN9zl7R8bPF_krDw9Fid3630P8aK38N3jL-GPwVjTzFkni93jrC1Mzjw2p4t2kLylfJu-C2gNlL6hGG-GPLI0Xs9lJ0pQjeXBBPHVBkARB9AbwV-VC3u-embD_MOZPwIC1cWAgmTGQeTFaZiAn-iu_xdujJODt3xR1C2gzP3WbrYhVjMqFFH2Uos0ff9wQ4RS8XjFMHn5t8L9aeq0lCDYvOcuc2f-T9DQcrH5tNS5qmkuJn77RajrntTltls9y7quznyIGjJeHGEjHMRDHURT7AZwjl6NrW9od3DkNAS3uO47FPeULoXCUXZO6lt38DMSByuU8lRNCJyAXs9NYaz_3oTZ9LlnmWktWtJqq06zPjv3BN9nUNwiXvneUFmMFlpbbg_Fq6qKTkvzj5HaSX1yJ15Htdrn5XmbOFIwwbTIJx3t60HoCh1jKDw5B3tQhVUQq8laH5JWmsmf0uU-MlJCvM_QWzxgZxrdG7bf86upr4V6qvpY8FwNiHvXHQ-AELrAkDy6YnEHjxAvSrDrK1bgw6lzxVd707_4709_jjVPRtm6w1GsTbXAC_PlBHKE5CSTEb04MGkvN-PbvTO9-LBx_iICPjwxn9hAZwXRxBj5-e7b8qyPgdYnFdyEfvrgsSQOFkzNkHFGaeMfz2-dH9-bpRSo_gopROnM710m4cNYOXEQzLqqoKo8nGtF8oQ-0diew9PVC1Aj-JEXb2HLx87Gz6q-ibGt6tW-E1DfartiTrCln5kBCPCPBz8rnicZ-gkvnuJfOdacAbCANgCdHmjDzUealk-OEKOlPlOf2bVr_hoiSVtPulvsi-MEwOyADzEnVHRIvKorJ2fNSmsTDywWcJ0LoMAwIJ7VnWKSRX9ApkW7OK_sZmNBlLl826STx2-E8WDH9kheSKsNeNn07aPEOxjwcEm56zNiTpKAO34B-Uut4JY5RVEFC_Ls9NgpGXxvHp84dHr3a706Yk3toAx8EK09jhEM52ICmNmQkRBj2tG_8W5sXRpbc7HFd_06JFtJ-PFgyKJ6evI2OpS8zpWQPVD4vn4JgmiSSzC8yS8lIad_kcSctq_apW3oGghUhuK4LTO7vKj5N7G7iLnQ2_kbs95iX81W86D2lOznRmNmxIWBEjpaMb7vtwrn2MODujjw--r77pcCKkTtlxTsKJ8Lmxp2WmGnVP56pw3VtloKQo-dGJJ-9pXOE2yEAJTXeFyYdJwNVKO0_J_8sigVnhPOPwEU4_l699KnXPfnW8htc0fppwuVxv53go7ZDPAR8NA-uhEwOKP9zwTE72yxHQTxlLSiIX77ImvUafrYz9lROUvdsoBGYvLV-m2g-KWdO9FGyM3sIpVkxExCC6XtJ-VkU6mVGfhbFF6b0hJFjufgQAQ1m0jW5vYfELkz-EioNWQOV04IrC8PCi16CfTG6nhQIC5XBSy74C6k8QbVq6RnIy2Z1CPJJV1T3lUgP3qaSvEsEr-_QH157GGQH3OGk-vMIStI4hAbxR0_sVA8T-7POmKzM3tl4ZIcMCtFcIQ09eHdnxtwpjaW-G5n15iloOJoimBVqBS0j6JR_uJ-s8m7qxY7IrsHxeTskQEHXAwrNmuk77GyHn-vP5XhPVYMJddvVJ-Dlh7becTuva0btWnEhSD6B5GIq_nIT72TsUhtvr-8l-24FlNT171L34ErDHW4ayhVkHD5QqZjg0E_N5H5m_kUetBmglZJyDd2wvK57YdX365q8AndaN7bTD126dsr1VpSFqPVayC1Al38CdIlxcP34D3r9y1l5HpRZkOEzeu4nYRwhP_bTs905CfyCVGkWJzSLyqD0Uj9N_TgNqqysfITO2DnyUORFXuylURAk68CvQhKmOKwQLpPYA6FH95jVa5MNzNxnTKmWnvtBGkfJWY0LWivb_41QFycIRBdn8tx2BBftVoHQq5nSalChma7puCt81PMteN_jPXR425zs-sbf0KFdCbncAK4YJ90GDP30rJX1-YxmpndtsSZiP7QwzxqbrfUKoMuOgIdz9O8AAAD__6nnj_E">