<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/97769>97769</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Crash on forwarding a pack to a static member function template of a partial specialization
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    This came up during reduction of #96623.
Code (https://godbolt.org/z/Kjfnfdfns):
```cpp
template <typename>
struct allocator_traits;

template <typename>
struct allocator_traits<int> {   
  template <typename... _Args>
  static void construct(_Args &&...);
};

struct vector {
  void push_back() {
    emplace_back();
  }

  template <typename... _Args>
 void emplace_back(_Args &&...) {
 allocator_traits<int>::construct(_Args{}...);
  }
};
```
Clang 19.0 crash:
```
<source>:5:8: error: partial specialization of 'allocator_traits' does not use any of its template parameters
    5 | struct allocator_traits<int> {   
      |        ^

clang++: /root/llvm-project/clang/lib/Sema/SemaTemplateDeduction.cpp:914:
unsigned int {anonymous}::PackDeductionScope::addPacks(clang::TemplateArgument):
Assertion `!Packs.empty() && "Pack expansion without unexpanded packs?"' failed.

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: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++11 <source>
1.      <eof> parser at end of file
2.      <source>:16:8: instantiating function definition 'vector::emplace_back<>'
 #0 0x0000000003a385c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3a385c8)
 #1 0x0000000003a362bc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3a362bc)
 #2 0x0000000003980688 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007085a0642520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007085a06969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007085a0642476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007085a06287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007085a062871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007085a0639e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000006fea682 clang::Sema::DeduceTemplateArguments(clang::FunctionTemplateDecl*, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::FunctionDecl*&, clang::sema::TemplateDeductionInfo&, bool, bool, clang::QualType, clang::Expr::Classification, llvm::function_ref<bool (llvm::ArrayRef<clang::QualType>)>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6fea682)
#10 0x0000000006da6328 clang::Sema::AddTemplateOverloadCandidate(clang::FunctionTemplateDecl*, clang::DeclAccessPair, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool, bool, clang::CallExpr::ADLCallKind, clang::OverloadCandidateParamOrder, bool) (.constprop.1) SemaOverload.cpp:0:0
#11 0x0000000006da6b2b AddOverloadedCallCandidate(clang::Sema&, clang::DeclAccessPair, clang::TemplateArgumentListInfo*, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool, bool) SemaOverload.cpp:0:0
#12 0x0000000006da6e19 clang::Sema::AddOverloadedCallCandidates(clang::UnresolvedLookupExpr*, llvm::ArrayRef<clang::Expr*>, clang::OverloadCandidateSet&, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6da6e19)
#13 0x0000000006da711e clang::Sema::buildOverloadedCallSet(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::OverloadCandidateSet*, clang::ActionResult<clang::Expr*, true>*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6da711e)
#14 0x0000000006db3865 clang::Sema::BuildOverloadedCallExpr(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6db3865)
#15 0x00000000069b2a08 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x69b2a08)
#16 0x00000000069b4f6c clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x69b4f6c)
#17 0x000000000702d6a0 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#18 0x000000000702131d clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#19 0x000000000705e4bf clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformStmt(clang::Stmt*, clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::StmtDiscardKind) SemaTemplateInstantiate.cpp:0:0
#20 0x000000000705ec74 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#21 0x0000000007066aba clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7066aba)
#22 0x00000000070bf088 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70bf088)
#23 0x00000000070bd39f clang::Sema::PerformPendingInstantiations(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70bd39f)
#24 0x000000000655482f clang::Sema::ActOnEndOfTranslationUnitFragment(clang::Sema::TUFragmentKind) (.part.0) Sema.cpp:0:0
#25 0x000000000655502a clang::Sema::ActOnEndOfTranslationUnit() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x655502a)
#26 0x00000000063cb64a clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63cb64a)
#27 0x00000000063bed6a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x63bed6a)
#28 0x0000000004326808 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4326808)
#29 0x00000000045ad759 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x45ad759)
#30 0x000000000453336e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x453336e)
#31 0x0000000004695bae clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4695bae)
#32 0x0000000000c710c5 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc710c5)
#33 0x0000000000c6a2ea ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#34 0x0000000004369f39 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
#35 0x0000000003980b34 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3980b34)
#36 0x000000000436a52f 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
#37 0x000000000432ffc5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x432ffc5)
#38 0x0000000004330a2d 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+++0x4330a2d)
#39 0x0000000004338435 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4338435)
#40 0x0000000000c6e495 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc6e495)
#41 0x0000000000b46364 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xb46364)
#42 0x00007085a0629d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#43 0x00007085a0629e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#44 0x0000000000c69d9e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc69d9e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWl1z2zaz_jXwDUYaEvy-8IUiWz1p04lP5J5bDUiAMhoQ4AFAx-6vfwcgKRGUlMZ9rc774UkbBwR2n312sbsggbVme0HpLUg-gOTuBnfmSarbe0EY5_ymlOT19vGJaVjhhsKuhaRTTOyhoqSrDJMCyhoCFBVpiqIlCO5AsFpLQiFA-ZMxrQbRCqANQJu9JKXkZinVHqDNHwBtfvm9FjWphQaosNPcYpAG_Z-qbfsRQ5uWY0MhiNbmtaUCNxRE9_1DbVRXGYg5lxU2Uu2MwsxoEH0YxP0TItZMGBDdQ5B9gBD2kyE8J2u5XMLdSu31QSiE2mDDKvgsGYGVFL0WgHI3DwKUApQul0tn-wg2u5sBH7A908pIZYGM0p3YttNPuxJXXwHKASqmzyF0MCs6eX6QDaHVNFHzw1Y5tTPJpwZNgFxk1To8Wp0QY1dmdzNepninFI2hMoQdx2IPw2IZwEph_XQaUsM_o7WWnapojyIB0SoH0QpSpaSyv7RYGYY51C2tGObsD3wM9OzEIJRBIqmGQhrYaQqxeLVTmdFHUluscEMNVfronwSCbA3fGHz2xy4bfkByP3VjZRkA6IP9E60gQBslpQFow_lzs2iV_J1apjfDvA1nJUCbLW3w8NfjAPhu3N1LuwujVRHGBzY74TIGgUwYiw4LKV4b2WnnGuvUB1x9PUjYVrKl_TgmxD7SAOU9Ajc66lypfddQYabJYKU1VY586z0UuuVL2rTmdQx5F3YQIGSfQfrSYqHtgm_MPMnOwE64MUIJbJ3yaAMQsl6rMeOULKcEPny6X23voe7KhhmIYdnZTNdKZaCRcJbPmHnqymUlm4HgU56Z1h3VAG0gFpavineEQvNE-wCFdgMZhSsK0Bq2irZKVlRrSuAQoGjtVmKtZcWwoQSqTkBdKdaaAfjWWLtJ17QH1oIlCIoHJfcKNxAPtOohImTrIkA2LeNULehLy6WiaoyKBR4p1wujOvEVoE3JxDFobHDBxZ58w6pexHCxhwtp5eK2tdI703ZmqeGisVzAxeIlTxdYNwv9Kgx-AdEdE4ZyuNjCxWJfVQsjJa-eMBMguvsuPDtZC9zqJ2ngoq4kl2pBGN4LqQ2rNFzUQi4csf6wNgREd1UPPQyht_8dYaElDERrKmu75VqsNFUQG0gFsXu5Zpz2M9Ewc5pAwnTMIExog4Vh2NgSWXeir5CE1kywPoxR1ufyPva9TBqtrTyUDXsdoCiAwUsw_kQ4ypMqhy7U3Gr9qocNp5gwLhAe-2jKj5MU_raT2iiKG7dX1nbf9jsnf6dwAOhD8DLAs7v3gD-c4U9RWZ3Dv-YUi679LLZsLzAHKD8kGS6tlmugtWA8tMhDW-RBmudwbePpC63kM1WvPbz_wYJwqzQfmPTmrKUw9MUMiTNw_x1URIOKLMgTHKQxSlAwmNbn4pc83aXxgjPRvSz2ousfVEstl6kD7pZ4sGNfZpEWdQVb86QoJruvjPO3KXDrPQXJHHScpXCvHRdvBR9nqSc79WWjPKsjiEubcN8k2S30JGcnksPyzTLD0pOZ-zKjghbp22S6JZ7MYhp1aU1xmiM4KY-uOrvfXEml83I5q6abIekcK3nFAVrZff-dmvuJafNR1HKYedyiK6Xw6xdag2g9WX7_0io71aYrT-6o_aA1nU3QB2tOWo1ev1tQSsmnf08E_G-H-eNrS2fDDtGQS-yRpmaVa9p8a8aMvFPOIiseesnyvLkHndbeov__eyekwfOH0LDZ00v_KcFphPLzobEiZOTz8zNVXGKyxoIwgg39K_FhR1eV7UUeMFN_U_CcIN9ScyEgzgTGGnN-jILV3Sc78AsT5M-0PNje_LMiVB0lO_cu3eGkVbJdhnbI0j2uPk3v1mHh3GElKuGKkHEVJRbUBc_0bfh8w_xre-JHSEFzUmhYXIziC0zNktxvQlEt-TMln6T82rWjIVe1-f23fM-Ft-WjGVlZGNLzZJUd4zO6HGIvpNzZ62R3T-h6K6m_dgaXnL6R263rlj_JY07-U-Ln6FYua32huuPmvFa0hkZ1fZJeXcdd1hueu2LfXWWUp8l5d304dVcP_Br--i71V3XmBMQ8U7y7OxzbnjsSzx1FiXBwoWA6d7yDE_5z6e3Z8-hNZ_TGdVpdyOSV-Sz-jem9Bp2WLY_ObEpnFiCS4sCr7orSR4WFrqVqQLQGKD-8a4MCN1S37rBf-M3Ax8NLCKkO71kPcs475Ti6Gov6qTh6vr7nMzPCKCRXN-PUhL8Kv_DhJzQu66vD35pmXqrdyMk57R2VWw13TFdYkb4tfhtRKJgTVWXx9cNVNq3sBDklzH-ymvekP2xW6JuVprjE55Patiu1-VHP_dpxwz7RZ8rPNen9ByHXXr57qhlsmKYahHwjyzrILxTGCV_Hw_z4-nJm-PdS6cmbgEuHuCvY78zz7I9m9pOoqM_b_0CVjbsHKggT-yMbVjFA-fUwW0geZr-3TJI4Rxcwu2p7L8jn2u0b7tD-JpjZKLzvP6mcHDT7bfbbOGPMCPbY22JllsG4kc7vmmQGLgnQhV1zEdzhA877Ftoei8ek37dEVZnGHtgH975_8vujbN3W7YN3yt3nFv9_Rx-M8tsNO_EnJbvWNSL3p8f4Ix-_StJx-rFppTJb494CXCMLDGZ6PGQ-DyUl6SkPq-3jxfcS1-45e0geZq-7iCOU5n5Lv5aE_kRFfzwcOwFadYYOQ1eJsgGIh9RrJOIEkyzx3nNslBSGCnIG6pVA9himIP0vSnESRVFK4ayqWrV94qvoeUYvW3WVWB5weoZ4ZTtOi6TE1G_lHeSjPc-HOjXvIjx7r9L9D_g8A7ySHFRZGFQJrKpw12Ar48JL6Sesxt7hcLjxxtDa3dG4jh09Ss-MyDcjxYhiOJK_Dh9dppgYs20w5__nPoF-bFp-1qbUP-hZGcNXNa9vIoo9U3W2PkWxnzbSoo6K_vLKxa8B7ul4UWa8noI5L3H1dVcLP-H3uocYWodr2TRYkPmmPutD9znajsnWaseWgwk_RjGxH8pI7-DDgt2uenkJw-H9H9as2mk3fWDRm2wHjpdJ3OOZuMOdk8nz4eXZmOJdEPWcuyUAZRw3JcEAZUeqUD5-pf1Zluf9kcy_rZZRPHHFuS-o_ZMvndjimvJXj87vu-4Kn4t7xF7kp7MQw4nfn_3XhcisebwYC9mspNd1lVwkzvkOn1TMkU0vmc8W2gmThLH-jo7p1NXsrf_BtnduIKzZXkDNWp0owIi8lZefZakvk_KzLGenz2mePU3NhzhoMVPDlbQ38DgEy9_BpiPLY7OYsZnH0cUou5v87jUOZzqGS174G9m8Qjvr6JnyFwezwk7jYuBv7FBG_C6trE4-FV0q2-_dkzhkHnSvNwzKOI3SGFrQ7627F-3pRrNrJwUp3njDxy3xZEZzmTQO4G5nl-20wcrsJsb9sBYa-1rimcMLUlDYy39_n1nhB-3Tx9N7uG4c1sMJA1bDjujvbboLnpC-MBtdhMIwii3MTlO4eIZGQk0pZJO2v5hdBr4htxEpogLf0NswQ0GIcpRHN0-3NS1SFOd5EtAwiPMYxRiXdVTWZYnqIsU37BYFKA6yIEYhiuNoGadlmOMySVAdVDSkIA5ogxlf2t2wlGp_426C3hZZlhY3HJeUa3fhHiFBv0H3ECAEkrsbdevukJbdXoM44EwbfZRimOH01jVLUApYS_UNK8LEHmJ3udWajceL5w1tSqqOtxAPl5Fl7aafu-N80yl--9evufb2Pd-ifwQAAP__yEvKpQ">