<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/140018>140018</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang crashes with assertion in ResolveSingleFunctionTemplateSpecialization with -std=c++20 since clang 10
        </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>
    It is similar to https://github.com/llvm/llvm-project/issues/138098 but new Stack dump is shown. It only happens with std=c++20 flag.


## Assertion

```
clang++: /root/llvm-project/llvm/include/llvm/Support/Casting.h:578: decltype(auto) llvm::cast(From*) [with To = clang::FunctionTemplateDecl; From = clang::NamedDecl]: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' 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++ -std=c++20 <source>
1.      <source>:16:49: current parser token ';'
2.      <source>:12:1: parsing struct/union/class body 'g_foo_f1<>'
3.      <source>:15:5: parsing function body 'g_foo_f1<>::foo'
4.      <source>:15:5: in compound statement ('{}')
 #0 0x0000000003f98e38 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f98e38)
 #1 0x0000000003f96ac4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f96ac4)
 #2 0x0000000003edb6f8 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007daaf5042520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007daaf50969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007daaf5042476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007daaf50287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007daaf502871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007daaf5039e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000006f6ade4 clang::Sema::ResolveSingleFunctionTemplateSpecialization(clang::OverloadExpr*, bool, clang::DeclAccessPair*, clang::TemplateSpecCandidateSet*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f6ade4)
#10 0x000000000714921f ResolveOverloadForDeduction(clang::Sema&, clang::TemplateParameterList*, clang::Expr*, clang::QualType, bool, clang::TemplateSpecCandidateSet*) SemaTemplateDeduction.cpp:0:0
#11 0x00000000071499c9 AdjustFunctionParmAndArgTypesForDeduction(clang::Sema&, clang::TemplateParameterList*, unsigned int, clang::QualType&, clang::QualType&, clang::Expr::Classification, clang::Expr*, unsigned int&, clang::TemplateSpecCandidateSet*) (.isra.0) SemaTemplateDeduction.cpp:0:0
#12 0x0000000007149cb8 DeduceTemplateArgumentsFromCallArgument(clang::Sema&, clang::TemplateParameterList*, unsigned int, clang::QualType, clang::QualType, clang::Expr::Classification, clang::Expr*, clang::sema::TemplateDeductionInfo&, llvm::SmallVectorImpl<clang::DeducedTemplateArgument>&, llvm::SmallVectorImpl<clang::Sema::OriginalCallArg>&, bool, unsigned int, unsigned int, clang::TemplateSpecCandidateSet*) SemaTemplateDeduction.cpp:0:0
#13 0x0000000007166f7c clang::Sema::DeduceAutoType(clang::TypeLoc, clang::Expr*, clang::QualType&, clang::sema::TemplateDeductionInfo&, bool, bool, clang::TemplateSpecCandidateSet*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7166f7c)
#14 0x0000000006fd32dc clang::Sema::DeduceFunctionTypeFromReturnExpr(clang::FunctionDecl*, clang::SourceLocation, clang::Expr*, clang::AutoType const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6fd32dc)
#15 0x0000000006fd567d clang::Sema::BuildReturnStmt(clang::SourceLocation, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6fd567d)
#16 0x0000000006fd6377 clang::Sema::ActOnReturnStmt(clang::SourceLocation, clang::Expr*, clang::Scope*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6fd6377)
#17 0x0000000006730417 clang::Parser::ParseReturnStatement() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6730417)
#18 0x00000000067336bd clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67336bd)
#19 0x0000000006734d3d clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6734d3d)
#20 0x000000000673ca63 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x673ca63)
#21 0x000000000673d22a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x673d22a)
#22 0x0000000006646140 clang::Parser::ParseLexedMethodDef(clang::Parser::LexedMethod&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6646140)
#23 0x0000000006645e2d clang::Parser::ParseLexedMethodDefs(clang::Parser::ParsingClass&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6645e2d)
#24 0x0000000006699ef6 clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation, clang::SourceLocation, clang::ParsedAttributes&, unsigned int, clang::Decl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6699ef6)
#25 0x000000000669cce0 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+++0x669cce0)
#26 0x000000000666f790 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+++0x666f790)
#27 0x00000000067489fc clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67489fc)
#28 0x000000000675659f clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#29 0x000000000675694a clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x675694a)
#30 0x00000000066764a0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66764a0)
#31 0x0000000006632e9c clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6632e9c)
#32 0x0000000006633d8d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6633d8d)
#33 0x000000000662615a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662615a)
#34 0x0000000004942fd8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4942fd8)
#35 0x0000000004c39725 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c39725)
#36 0x0000000004bb834e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4bb834e)
#37 0x0000000004d2d289 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d2d289)
#38 0x0000000000daba2f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdaba2f)
#39 0x0000000000da1bfa ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#40 0x00000000049aa2c9 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
#41 0x0000000003edbb94 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3edbb94)
#42 0x00000000049aa8df 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
#43 0x000000000496c6ad clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x496c6ad)
#44 0x000000000496d73e 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+++0x496d73e)
#45 0x0000000004975a25 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4975a25)
#46 0x0000000000da7998 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda7998)
#47 0x0000000000c2d064 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc2d064)
#48 0x00007daaf5029d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#49 0x00007daaf5029e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#50 0x0000000000da16a5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda16a5)
```

## Program

```
#include <iostream>
using namespace std;
template <typename... Funcs>
struct g_foo_f1;
template <typename Func>
struct g_foo_f1<Func>
{
    static Func foo()
    {}
};
template <>
struct g_foo_f1<>
{
    static constexpr auto foo()
    {
        return foo<decltype(g_foo_f1<int>::foo)>;
    }
};
```

## To reproduce quickly:

https://godbolt.org/z/3Tsxa5cPT


</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzkW1tz4ygW_jXkhbJLQrIuD3lQnMlsZnu2s53U7Ly5ECCHiQwaQGlnfv0WSLIuvnTcE3dt1aZycQQcvvOdw-GAAGvN14Kxa7C4AYvbK1ybZ6muN1hxZpiPUHCVS_p2fW8g11DzDS-xgkbCZ2MqDYIMoDuA7tbcPNf5nMgNQHdl-dr9mVVK_sGIAeiOa10zDdCdHyRemsC8NlCwr_DRYPICab2pXA_P8quYw3sDpSjf4DOuKiY0_MrNM9SGguCWAHQD0A3yYFHi9Rx4WfuNAoACmGnNlOFStE8jr_32MlJisW5agyCDAN0pKc0-0hY_F6SsKesfPNZVJZWtscTacLGeP4MgW8SJlUYZKc1bxQBKcG0kQCl0zYIMBBnB2gCU3CnLT2bLwOLG6fQkIQhuYQPN1b2rBbH4n9imKrFht4yUILiBtvG07r_whlFXYXFrQeyUhyDyuMYgWD5JEPwEUPIbLl2_KAIoggAhhylYPr015bYQq3W9YcJAWUAuiNxU2PC8ZLBRzAcIARTDAvOS0fmE3d4EvUX3bTAoC2yZNwde-qDkWuHNrn_dmkdWlmyLg5dMzdi2KqViyj6zHMxwp66eGVWLF4Duci664sbScLamX7EqZiGcreFMWrm4qqz02lS1mWs421hLwdlsm0QzrDcz_SYM3oLglgvDSjgrhJy9MpVLzWw5nD3C2WxNyMxIWZJnzAUIbk_itZW1wJV-lgbOCiJLqWaU47WQ2nCimz6Iwvp5_HgLSafH1P1BsNSyVoRZA3qZb5kcPQsyPwJBFqaWTlIrZU1bYaWZHcEvTECAYhDc2N9ehg61R_aXbW6bcbGG2qjaDZJa2DHmqNYa2hhhpa1XhZSrwgfB0rmVFRwcErywI2couGjd_pgo5--FlI3M8KRMLqA1gqwFhdpgw5xTOyePQXwD4lv7AaXAs24WeNDbet1XUKQJC5LB4NVvuvnwoLgwzoGfFCZ2pPeVFP66ktoohjduiC0hF6YZcMkHeTJAN962hdeD9yfgI0zCQ-CXJcOirj6LR74WNhYktXChn8JS2i4uAdWC6aGiEVRG86hI4NL6_BdG5CtTbw22f2BBS9tj0nI4qrOUwrCtmZPKhhDP_TTyg1Z-TDEuFl6IFnaUOKVKngN0t02iVRTOSi7q7Wwt6qaAzLWcRw6ya9IDDscC0ygtCKzMs2KYrl54WZ4n3bXvpS-mcMM4gmvtKDgXdhhHveBoLBglcRFAnEtlzhPrGvZi4z2xfn62QD_vBSZjgUHK0ug8ga5JLzAdOlhURJiycDhdPrINbj59YVqWr-yRi3XJpjPuY8UIxyX_C7s8AiUDEZ9fmSolpj9tK-Wm8iXMpSzt30EtOyVnhDCtHzDv6g3Khz0tsaCc2n-YGUn88AHZMtLwZUPHKPDFfpgiv4AtNZ2id1LdMlqTfSocm02sO6DaA1Z4wwxTn7g2-wwM-Bs8_XeNyyeXaxyk9SRtKbSA-qypxTyJE1Ztf6p2SlKY0T9qbTpXeMBqkwmaqbWFoz-ShF3YdcHtiPpTgcdLHJFthLfJfMFJ67bH-B4DOAb9CMcAJXOuFZ575zCOpoyTPIGuAeuaZ13uZ_PcJS7L7sEP4fs9j89nevBU70LPHl_3opCtSv28_bjBZfkbI0aq-01VgmA5Ci-WOTqlzmVc58jp4-Fnxddc4LIlvpfUjcIpiydY_aBRGox9JoqKmBwO5g0dWW1kY7Whv9gnnyQ5M_pM_et91uu4Oj9yfXCgb9nqA304nhhpgOhJLncz4lvF7Hj8wkytRMNacmCt6page3w-uuT8kzxjmHRGhEQKfSF2Wv17dhYTdhZRTA-zc1PzkjZkPJrNNDS9U92Lze4OeK9WNFErCuL4sFoZMZ_F31Vr2IRIO4ouZDyrR69lPNIyDrzQH2n54Na7g8-dnu2ysN36-GiYDZAeZjKBGUQ5PQlzB_CzsqMLK0d_VhimMmMUz2vD9GgJOgj1kzDvbOqMhMK6j-2nuqe2UbvU-sawnlq_aT8EebC3aY1L2MCy3NsgndggpMH32OB_hfRLEGYp2RGGvAlhBEfBSQWW7a7LjrgbSd8ASi4V8hpIPWB_ApgihE8C7iawKeDJWu6Ik498pYl5F3Jkq0iv5iidjqIw8kPvJLhPbMvor8w8S3rLirF-w8qDehdSpQHbqxJMVFkwdHpMjlXRx3V5aDYWXa5-MWUs3F6ZcZoVpSkrotPj5ffff2WbnCm35dAvKN49_54sPBKIT6TuO1-_AFeOjZ6rxYQrQthpH3aGbHlikzzUyJc2z5YvTPyTC3oOT1ZrK_g9EbpL5Adp_zB9dXs-A5AHFwNDqV3fh6P-D5ooG_Z724wzR7uWSE_bZjA77pTX-2H0YiR_P7ld4Gs2D1qyD29Z2fUzJ9zY9YnAG7aTegGDOMp7g0yS3DBJC_Jeg7iUsWN03ya2llTfZug9lmlDrhX7Jbu__5w3L1Sn1aaD8V3p4WkXuMCc60juTTBJ4BfRIi1OcjV8f9ua4rM6tbX8LWtcirZ5hZVp9vNGwPf3ZFA6JSENT-dXw8BgsDJcrP_DzfP3ueN3EXABz3Bq7zxj_PowiuIoxO-Olj_aA75d44csNBqSegrHeXsUIJaejm8_bQ1TApdHqfwIKgbhrJm5LsOF07bnYpLcBwFNTmfET7L6xF5Z2SRvo5dVFf6zZg9GTbePSfmzknX1hRUHF6b9ztCvktYlu99UUhm3RrpUBuLU7EmYLAtQ5C_2A032-HT05cB4L_YCgB2kHvAo9Q_TEBU0GQJeSsp-ZiJrXiG1e2eM1IZl3VulC8BsgfQwR1l3SII0RovR4SNlA4-gB3BeCGGDoUc4yj3DPE-CkI2JbPq8F9pgQdhhLo-rdBH_bXH2WowStpAiipJ0vG_q8PbKvMpDa789ZS8Sglp8PfpRruNRnGNUQEL81Qbz8fZXphR-c2FkSZ6x6rftbVhZwvEztISvktPLKNGg7HVIJzr4eYFhR_vSf3Jx4fBGXveibE-hybs1K6OdqLt6zrmo4q9M7adPoTcOEhgjkjpKBkK7c1Ar5Vh1pc3Q252CIrgsc0xeVoUYB_am49Z1lv5SbjZY0OkoPmg9d7jMPpOV7R1bAgbkGMXFup0uGtPuGqxWZLv1_eafHGtOVtpVbykcVbYPVkZhbnRXPBGHy9IOhWY7tS23VQavTpz7NIS7JgDFJd7kFLtTXR1VKOnONf0i8wPG8KenkfJ0eHDq0JmjpuRLLR5xwcq3EZen7XaB01UN4p3Dh2jqXAkdLVD-75xjsrY57AXBmLWIRJgeZc1ZDe_NjB2Vo9A9aWgrDILE8kQfw6rZKJ0ZKPaxWYJTu3elSTIT0Thg55Lyi8z1cUZ-kfknrs2IkVOxeOcBFebW-PtblydJbN3kh1BpyeqpHCdcabzA44RrCPt28HmUIBzIDI6Z4AdSeYFs1dHTkxdN5vA4TdukustEOvAulGRtIPj2DP3huYdF1uMeZX8eQdSLQmgRf3THjei-48mJSpTS9MwTsK5JLzCdCmShB1cr22alDVZmNVDr3V2wwRughTdN1CK8gI3wj7eTFd52ffDqQnsTYf_eAkBBex8E2jHTHfV2J-9rd4Bd4A3TFSasma5ugJeZdpvLNjHtrvF8Pod3tSC6aducp4f9Yfdj7VyjI22WfRmIrQAIoTv4zolrBt25-e7QOISwPQRvq9_ud3mslyM9uIHFtpWCuDbyYF_NJ_ul3OkLVylYDu7MDLrhzUm2JquywprM92YnbwT8sB2fJFSsUpLWhME_a05eyjcQtDeFJleXJM1laeZSrQG6-wugu-BJb_GCPDw11a_odUDTIMVX7NqPwxilizBIr56v0ziNCy9ZUL_wY4-mHkOMxnFehLHHChxd8WvkoYW38BdevPCCdE4ThEiOwzRnrMCLHIQe22Bezm3Isgiu3C2paz_0PD-5KnHOSu2uZiHUOjMCi9srde2uLOX1WoPQK7k2uhdhuCnZ9dJWh-5GCWvvT-3GCeQCnnECumm9d_9Ec0HatAD63lWtyuu_cSms0fj1Gv03AAD__yaL0zs">