<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/99858>99858</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clangd crash with auto template parameter pack expansion
        </td>
    </tr>

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

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

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

<pre>
    I have a function with auto template parameter pack and has no reference in current project scope. clangd prints the following trace. I think there needs to be a check for nullptr in there.

```
[~]$ $ pacman -Q --info clang
Name            : clang
Version         : 18.1.8-1
Description     : C language family frontend for LLVM
Architecture    : x86_64
URL             : https://clang.llvm.org/
Licenses        : custom:Apache 2.0 with LLVM Exception
Groups          : None
Provides        : clang-analyzer=18.1.8  clang-tools-extra=18.1.8
Depends On      : llvm-libs  gcc  compiler-rt
Optional Deps   : openmp: OpenMP support in clang with -fopenmp
                  python: for scan-view and git-clang-format [installed]
                  llvm: referenced by some clang headers [installed]
Required By     : doxygen
Optional For    : qt6-tools
Conflicts With  : clang-analyzer  clang-tools-extra
Replaces : clang-analyzer  clang-tools-extra
Installed Size  : 209.03 MiB
Packager        : Evangelos Foutras <foutrelis@archlinux.org>
Build Date      : Sun 30 Jun 2024 11:53:44 AM +03
Install Date    : Sun 14 Jul 2024 12:03:45 AM +03
Install Reason  : Installed as a dependency for another package
Install Script  : No
Validated By    : Signature
```
https://clang.llvm.org/doxygen/SemaTemplateVariadic_8cpp_source.html#:~:text=if%20(Instantiation%2D%3Eis,736

```
 #0 0x00007d1d7bfc4d90 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/usr/lib/libLLVM.so.18.1+0x7c4d90)
 #1 0x00007d1d7bfc1d4d (/usr/lib/libLLVM.so.18.1+0x7c1d4d)
 #2 0x00007d1d7b250ae0 (/usr/lib/libc.so.6+0x3cae0)
 #3 0x00007d1d84e7d57a clang::LocalInstantiationScope::findInstantiationOf(clang::Decl const*) (/usr/lib/libclang-cpp.so.18.1+0x147d57a)
 #4 0x00007d1d84ec8860 clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef<std::pair<llvm::PointerUnion<clang::TemplateTypeParmType const*, clang::NamedDecl*>, clang::SourceLocation>>, clang::MultiLevelTemplateArgumentList const&, bool&, bool&, std::optional<unsigned int>&) (/usr/lib/libclang-cpp.so.18.1+0x14c8860)
 #5 0x00007d1d861a0479 (/usr/lib/libclang-cpp.so.18.1+0x27a0479)
 #6 0x00007d1d84e76ead (/usr/lib/libclang-cpp.so.18.1+0x1476ead)
 #7 0x00007d1d849230f7 (/usr/lib/libclang-cpp.so.18.1+0xf230f7)
 #8 0x00007d1d84923328 clang::Sema::AreConstraintExpressionsEqual(clang::NamedDecl const*, clang::Expr const*, clang::Sema::TemplateCompareNewDeclInfo const&, clang::Expr const*) (/usr/lib/libclang-cpp.so.18.1+0xf23328)
 #9 0x00007d1d84d26035 (/usr/lib/libclang-cpp.so.18.1+0x1326035)
#10 0x00007d1d84d2644a clang::Sema::CheckOverload(clang::Scope*, clang::FunctionDecl*, clang::LookupResult const&, clang::NamedDecl*&, bool) (/usr/lib/libclang-cpp.so.18.1+0x132644a)
#11 0x00007d1d849810da clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&, bool, bool) (/usr/lib/libclang-cpp.so.18.1+0xf810da)
#12 0x00007d1d8498744c clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef<clang::TemplateParameterList*>, bool&) (/usr/lib/libclang-cpp.so.18.1+0xf8744c)
#13 0x00007d1d849987a5 clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) (/usr/lib/libclang-cpp.so.18.1+0xf987a5)
#14 0x00007d1d849a400b clang::Sema::ActOnStartOfFunctionDef(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>, clang::Sema::SkipBodyInfo*, clang::Sema::FnBodyKind) (/usr/lib/libclang-cpp.so.18.1+0xfa400b)
#15 0x00007d1d8406276f clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/usr/lib/libclang-cpp.so.18.1+0x66276f)
#16 0x00007d1d84064265 clang::Parser::ParseSingleDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo const&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/usr/lib/libclang-cpp.so.18.1+0x664265)
#17 0x00007d1d84064afa clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/usr/lib/libclang-cpp.so.18.1+0x664afa)
#18 0x00007d1d84065056 clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/usr/lib/libclang-cpp.so.18.1+0x665056)
#19 0x00007d1d83fd997b clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/usr/lib/libclang-cpp.so.18.1+0x5d997b)
#20 0x00007d1d8406544b clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/usr/lib/libclang-cpp.so.18.1+0x66544b)
#21 0x00007d1d83fb7f8f clang::Parser::ParseInnerNamespace(llvm::SmallVector<clang::Parser::InnerNamespaceInfo, 4u> const&, unsigned int, clang::SourceLocation&, clang::ParsedAttributes&, clang::BalancedDelimiterTracker&) (/usr/lib/libclang-cpp.so.18.1+0x5b7f8f)
#22 0x00007d1d83fb90e9 clang::Parser::ParseNamespace(clang::DeclaratorContext, clang::SourceLocation&, clang::SourceLocation) (/usr/lib/libclang-cpp.so.18.1+0x5b90e9)
#23 0x00007d1d83fd9b2c clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/usr/lib/libclang-cpp.so.18.1+0x5d9b2c)
#24 0x00007d1d8406544b clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/usr/lib/libclang-cpp.so.18.1+0x66544b)
#25 0x00007d1d84065fdb clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/usr/lib/libclang-cpp.so.18.1+0x665fdb)
#26 0x00007d1d83f89ec0 clang::ParseAST(clang::Sema&, bool, bool) (/usr/lib/libclang-cpp.so.18.1+0x589ec0)
#27 0x00007d1d85a1a7c1 clang::FrontendAction::Execute() (/usr/lib/libclang-cpp.so.18.1+0x201a7c1)
#28 0x0000605d7e700e44 (/usr/bin/clangd+0x57ae44)
#29 0x0000605d7e6fc63c (/usr/bin/clangd+0x57663c)
#30 0x0000605d7e754c59 (/usr/bin/clangd+0x5cec59)
#31 0x00007d1d7b2a6ded (/usr/lib/libc.so.6+0x92ded)
#32 0x00007d1d7b32a0dc (/usr/lib/libc.so.6+0x1160dc)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWl1z4rjS_jXOjQrKlr_gggtC4H2zJ9nkhNnZyykht0EbIXkkOQN7sb_9lGQ-LAeYYTd19lRtaiZxotajfh61uiULojVbCoBRkN4G6d0Nqc1KqhFZleTV3CxksR3doxV5A0RQWQtqmBToGzMrRGojkYF1xYkBVBFF1mBAoYrQV0REgVZEIyGRghIUCAqICURrpUAYVCn5G1CDNJUV9BHlRCwLVCkmjEZmBaiUnMtvTCyRUYRCH90js2Li1TYqQAKg0MhItLCO0RXQV1RKhUTNeWWUHcoZ9oPwLgjHu-9ZuPvX_Jre_hGkdwFOkP1fEbomAvX-jXo9JkrZONWY_kzWgFpfQTxuN38Gpa0u7eZo0I_6g17UWNyBpopVZm9lLSbIItRkCagka8a3qFRSGBCFo_Lw8Pmx6TxWdMUMUFMr2HfeDLIvWdK0__LygLrerYypdBCPAzwL8Mz52uf8bd2Xamn_5jo-MApCg_Zo1drIdRCPxxWhK0C4Hzbzbf1B0w0Fx6IB-D8l60r7I_8sBTStz0q-saIDbz3pEUH49ndQQXzX6IR2DUZKrnuwMYoc2vYKViAKjZ7EEcwS6nG20AgtKUWIynXFOKieMk2nJ-cr4egOnJu2k6xArCv79FSBeHxGuq4qqYwLT-tEQ7dX7gwdEHr3VW3NSgoLYydLUyJ6bwy-uchfMtNr-JRSrYlBQXrLhDaEcyhsyJ3BtHws4mHJFGixRVquYefZCkgBSp_Ge4GvNVNQoNvtQaFCbrZLEB01ZlLtDb6arBG9MZlIUXJGjUa_WhFOTNmpmdoNX3FCQV_T535PAs3Z79AMh8NhP4zRI7vdRRGhr2QJqh1F0zcilsClRjNZG0XsoJPSPgJnOkhCouiKM1FvXLzH0wbqtma8QHc2Xx2g5rVAcYh-qgXCIU5QFAXxOI2DeJwkaPyIAnwbxp63B4B99yhBP9V81x0H8Th03dMz3V-AaJsGbPejAEQjggoX5CDo1kUVEdJmMZdSyRJ8mLlLKPs1t0tEhLOCmEMMOA_ZUhCbOk4mwe_kiX384Nkc1uTTLtt_JoqRgtEvA1pVX7SsFYX-yqx5gC3zP4J4bGBjgviOlQFOcRjggXNbGEZc9sApvgtwGk-ZDvAkj7MLeRoFOA5RuAnDMMyLqMgXJU2KYbhfLkE81lvdPDzbCjI3hL5-smUjwIOjkSLfvkhtFJB1gLMATxATJsBDFOBBgGe1VgGecbZovtt019eyb3OQncRN7gYN8PDoVdTxKiqS4ofRrLGHhj00nIYEwtNo1EJlDiemBHyn4hbMIIG8SHOyK1ZOhgdJCfdmY26LcNNYMlF4bU9lgAet3ndAOaJSaBPg8VnxmuVOq8rjHCXOGc_bxPeWDgZZ2PbWhl3zNLFF_nm_zbBZQc-kmm4qIrQLqbabcxeTlmoTbhP0rvHFphDbcoyQsVJk-wJlEE-0KZq_VYSpIJ4cjZ4lEwbUL8ICx5MW7n55fNpW8EzU2v5saeX5YHcUhRXTNsXTkx4e3I-n700ea27YA7wB3w87Vst6DcI8MG32w7owX0jJ3z8eGMpdWQjiSS3cbrBwK8MOmV09xW4GvSlO21OcRSRM8qswce66eJhZJ8gzIGdW3tlQtF08zNzDHOI4LPNrMEvXw4McdCFjPDgd3WMFEztlijBhpptKgbZRradfa8L92D6EzrnYst3PtR1H3IfNRK4rouBn-GYx793OtxU853GvmsTScffEGXriFDgL4_SqOYxdlwOmTchhFzNJyIV08vQGiksbB17ycPnwnXSz3fFnv2r91gcpX-vqBXTNzTkBvUXfXpDXrbHY0fJ4R36gDaKwuMS7TYWoXY78UAk8en-KZulIeCxxh2WeJPTMcqLmSXRZSvVDJNvm3Rm0bRN7SNucWFs23zeZ266iH9LnWFYea0MWHFol6ERlOZQ_m-OPleOQ1a8U2OrnCezvHYbDQU7S0wL_PxEFh7-q7EfQv46zo-Rx9ncgQ5KE4eJCUM0NUeapPMZW-fdRP5PZ56-supXF9nQUHu1mwlr9i4niWhWdSJ6KXpFPwgznWdke9Zkobc_7h-eWgEyw9xnIGjGxvLQY32EWe7UuVbF2r4dGWQ3F2JiDtNeJkTmunhhZR4wEZ-lFx-dMLI-riUkxLg2oPZv3O_BGkUMi-iBVdnK_jO_vnxa_AT1h1t1XnxTXickWtQH93mJMKWg9r4CykoG6WmyrpSd23hWblOSiHns5WnI_KecQ4ez3E8Xwe4r_D4hCSr9SDjqipGGaXRSlJYbLcEwsf2Vm9edC8O8XxPL1BPE2m3FZDIf54kcF-W-T_75Fd4xrc1bq-LcFwmE3YpLkskDTjQElCD8r1EcQbaUlGwx_JjtbIh7TyA-FRV4OLpeqeyFA2b27rrrvlOZrwvlnoLY-eXW7DeL3b6ryBCV1EE-9dOydvj86qG4JJ4La4wdna2ariyL0FdT1-8bUKeZJijuSDkMYXpS0reYHrq1u-5W8rNser7ibNRaY_qOzxgJ7Bwac_GOyRneDm5bFZaafZOVezzVn5TbFp4p8reHZdFKGNXQXau4QMD0xf4ed-6Msag7360oqMzeuPl-7ijPHwKOY-dE-GAIN31Eczz91DjzWq7982k_daJ473sYuJRHJaeS9jNjdlo5p85K0eUUFtHbblSvHx6HD9xzYb6KyMC1yyMMQksTDXDCxvzQpGhY5gSTxQIYeSFbSLKbfA8my2Ftmh-uPnSdpQtPhd0Ao0NRLZp3bCkyyAs69Mz3eLwxxAYUH419TxJiEBf0uTBRlYdHitL_huSlGcTGMh-QGRlGOoyyJ0yi-WY0ikqUxSRIKNIYSIhIVSQq0zPMyikmR3LARDnES5hhHYTSI4_4gXYSU5oNokYW4zNMgCWFNGD9cZ90wrWsYDYeDdHDDyQK4dp96wFjAN-QaA4yD9O5GjdzN8qJe6iAJOdNGH1EMMxxGjdSIKqJXP_B5CNhfU9zUio_8S7clM6t60adybWWzW4vmR2_3IYkAz5xzOsCzxvm3Ef5PAAAA___vriwm">