<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/57632>57632</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] Crash when parsing invalid constrainted type
        </td>
    </tr>

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

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

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

<pre>
    ### Repro

```c++
template<typename, typename>
concept crash = true;

template <typename>
struct forward_declared;

template <typename>
struct forward_declared { };

int main() {
    crash<forward_declared> auto x = 0;
}
```

### Compiler output

```c++
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-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++20 <source>
1.      <source>:11:36: current parser token '='
2.      <source>:10:12: parsing function body 'main'
3.      <source>:10:12: in compound statement ('{}')
 #0 0x00005649ffabbe14 PrintStackTraceSignalHandler(void*) Signals.cpp:0:0
 #1 0x00005649ffab9c7c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x395cc7c)
 #2 0x00005649ff9f7588 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007fe49ca29420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00005649ff9ff517 llvm::FoldingSetBase::InsertNode(llvm::FoldingSetBase::Node*, void*, llvm::FoldingSetBase::FoldingSetInfo const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x38a2517)
 #5 0x0000564a02c0c5cb clang::ASTContext::getAutoTypeInternal(clang::QualType, clang::AutoTypeKeyword, bool, bool, clang::ConceptDecl*, llvm::ArrayRef<clang::TemplateArgument>, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6aaf5cb)
 #6 0x0000564a02c0c71e clang::ASTContext::getAutoType(clang::QualType, clang::AutoTypeKeyword, bool, bool, clang::ConceptDecl*, llvm::ArrayRef<clang::TemplateArgument>) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6aaf71e)
 #7 0x0000564a029ee68d GetDeclSpecTypeForDeclarator((anonymous namespace)::TypeProcessingState&, clang::TypeSourceInfo*&) (.constprop.0) SemaType.cpp:0:0
 #8 0x0000564a029fcaee clang::Sema::GetTypeForDeclarator(clang::Declarator&, clang::Scope*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x689faee)
 #9 0x0000564a02248f9e clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60ebf9e)
#10 0x0000564a02249dd5 clang::Sema::ActOnDeclarator(clang::Scope*, clang::Declarator&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x60ecdd5)
#11 0x0000564a01f31a77 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dd4a77)
#12 0x0000564a01f45a36 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5de8a36)
#13 0x0000564a01f46ce8 clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5de9ce8)
#14 0x0000564a01f47200 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dea200)
#15 0x0000564a01ff06fe clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5e936fe)
#16 0x0000564a01ff0fa3 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5e93fa3)
#17 0x0000564a01ff1ec6 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5e94ec6)
#18 0x0000564a01ff3292 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5e96292)
#19 0x0000564a01f16274 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5db9274)
#20 0x0000564a01f45b7f clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5de8b7f)
#21 0x0000564a01f108b5 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5db38b5)
#22 0x0000564a01f11830 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.0) Parser.cpp:0:0
#23 0x0000564a01f192f1 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dbc2f1)
#24 0x0000564a01f1a70a clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dbd70a)
#25 0x0000564a01f0a0aa clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5dad0aa)
#26 0x0000564a00d213b5 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4bc43b5)
#27 0x0000564a00626011 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x44c9011)
#28 0x0000564a005acb63 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x444fb63)
#29 0x0000564a007091db clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x45ac1db)
#30 0x00005649fd3c8204 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x126b204)
#31 0x00005649fd3c17fb ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#32 0x0000564a00418e99 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#33 0x00005649ff9f7cf7 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x389acf7)
#34 0x0000564a004190cc clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const (.part.0) Job.cpp:0:0
#35 0x0000564a003e4719 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x4287719)
#36 0x0000564a003e510d clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-trunk/bin/clang+++0x428810d)
#37 0x0000564a003ef85c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x429285c)
#38 0x00005649fd3c5f29 clang_main(int, char**) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x1268f29)
#39 0x00007fe49c4d7083 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24083)
#40 0x00005649fd3c140e _start (/opt/compiler-explorer/clang-trunk/bin/clang+++0x126440e)
```

### Expected behaviour

This code should not compile and we should get nice diagnostic.

### Compiler explorer

https://godbolt.org/z/1W8cM36on
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJztWt1y27wRfRr5BiMN_38ufEHLdpqvSe1GnvZSA4KgxIYiWBB05Dx9FwApEbQkOym_TGZaDyVTAAicPbvYXRBIWfZyPXNcfaEvtOZsZt3OrKT7Dix9kZlzIy9VKuiuLrGgM3cpXmpa4R2dOUt0uHfvdDvCKkJrgQjHzRbN3FskeAvVN8Mh-s7QsLe-hwYeIALljH_DPFtnlJSY02yCLtAsvIHP7airohJoh4tq5kQzJ5aNdDmCPyUGDPEazR3CrWBor2S0jl1C9yaNBrcH2pdsVxcl5Yi1om7F2wp4_HSXrO5Q06a7QiCM0naDOK0ZFwhgbIWom5kLA9zDtSnEtk0XhO3gR1k-9__moOp_USLgZ9E0LW3gBuEqQ0VFyjajSGxpp7kUk6-CY6K0XHNpJIQ2DZDYsJbrYvkkbhpGClBEhnhboYbwohYLDXkloBOUtbtaIlNFFlTFj5xtON4hzDftjlZCAkcAhdUSGemYmdN9XTJOuSwrcbWZg1arr_ArlbrSZZohNN9koJ587sEdmjPZGa5r2aVid9Gg-U4SgObzfRTMcbObNy-VwHtQHqiflmi-groNIXPBWEm20hzc24uYZOOmwnWzZQLNc8KgYp4VeFOxRhQEhswrNldsmsWNAPO57ZTrWNKCO057-7UlS0axm9g2fLmBpIq0nANtqMa8AQsS7CutQORQIQ51F86pLiz55cgu5KNFtUF5WxFRsAql4BVkH3oidJ24lzspKiSJYS3YQSPABqQykZpGoZxFoYLjxN10ArO3kLW34M8PvDjPcZpS20OPHFSgbOVJGtyq2FS4_AsYVyl5jp5Zkc2cRE5NXdUsSC0tylKfQ9_2qO-YhAQp4wfjc5PmpdE3y5Liqq0fKt0bjNBWDdyCBZdMWlSsRfh5c4TL2ruxTwCBIb5jQIzz0I8itJQW8oUS9kz5y1h4YEYCMtosGVjsXpxmwe2GCHPqxQQ7sQcWtl5z2ggAv-adfu7LIoVvmAzrwJuXRdXu55uq1RW12HKKs0XDFpaSxfagF0MSbyRJ7tvhgOx7VmZgXisqbnBDddnHCoxV_I1l4Duiy011o0T6mIP2l290fyz7WOUMDLNqgLpgMnVG2AEZDRL8IwnYcohFfJIi_aCClKyeOl3p3xsqEogZTxCuPkIx19Y3eODvLS5lrZR22E_30F_pyzfGM1mbgpca_h-0XuoIfAuR6hVxCef45QvNYU4PnnjqYmnS-WM50Q99x5rKSUgMMM6BI4PEYExiaNN3kvj7kjc1acCJQVpokBZTGkQZ-kAV7lVNiRT4nvFbla1gmPkKSIQrVr3sWNsgmS41tQrvcScHPPKog7ycRtKdq-lj0CMbrVQwkJNMMdTPsIWSGNKEWjoN8NV0h2Xz024qMgXICaaG1uXT-g6kOiXNoO2wfAx4RVhNu-gxiTKiOAeohjJiQxbHi_L4jCzar5-T44jVEOGVeEeL_NwKnJb0smE-wsM7Cu7mUyE9YtIZ6CRsWDQFYQ9syChsjdiIs8w_zUZCxEP135ExmRgEUBpi2EMx7Ny1cRgOgTyq3Gtw3yODZCrJge0j0qTKEiF4kbZCZtzvNd1XI2S9RkcB7uxTMGe-QAW0L8SEc8DPMg_YMOhyTLo8H4Njf4uuD5y1tUnIo85Lez_2Wr4jY31UOCG_wfcrl6D81ydGlK5em9gvYZBGQJDBoDtiMCA0usjgqgBrGJrdOdM6TdSYhpOGdJHIMy1ORNWLlL6lnMkoj4FRg3JvRHnoWNZ75_hvQvYvog4DMwZ1vkldbgU5vWyt_frwgY89peEcj8FttcNl-Q9KpHM0AttK7HrLcZ1WhbO3fad86H26OekPflw3E3FPYxeoNbgPxtzn2P0J7n8XsqcjCngwiApHRNmUXA5Ky-5txoGwG5a9ALp-JTQRUA9wGECjEVDXiZ2LQO-71zZjoCOXdDm4advQedaUBhsAekO82BTPDpzQe5d4tzQvIEy8creDLOHPy54-6dy5m9l98jyZT01jYGFIk2ONc6g0zP-fQ13KoYAgg8FR0m5bUeq_yeADH5jb6fcy7wsBFzlPiFxZy7oiL6SQk9mRC0IaLIxycduO3HenNQYZZ-feD3Ixto7TXCxqzIV-d6ARvn5zIKUb5cl27OT2Renu9lqlZ5O3n5NoMv0REMDQ3ygthZWnhS9K-MTqT_SZltrlD0V7qPG_W_ooRkH94DjUS4MTIf24SP_MsrakH3dyo-n4Umgy4TOQzRB-lFha2MKvhU9WT6O3BRKvufyYNGZnOAMcBlAjC7Myx3ZNX7NkGf1Aq0RNJl10t6cEDKwr6nYbJ4DnpcRzR07AyH2swAks25gm91y6_io7gW9KZB6JYWADmZHsWD4maeCaxOmxPkKExhWhp7k7L8p09ul5Xg7gDPRGLmOFVmxnxjv_DudRiOdDkIwuCTmdS_GAUgA1RG3uu2UuiRwLMjBir7t979MvubeY94lS0u0JmGXD_ZlpwNtOkAI2A7w9Am-HeYp6npf2k5rop9cy4LfKk5IoG8l48XwmzLhGELU8O6JxrIQdvH7tN0_XXPGlavXk0VulcBGAIrfS13llumA9dmcMSxvsYYerbDwPT-rlWPhQy-FxaRSuII5Vm86za62pHWdZt16T_V7tJMOV4qYg60Y170gyGsuCteC4kBv0unrUHQgnrVuvGbt62SQ5OuDksBmiH5k5YYl3aYbV1nDPFUjabb3-wdLTCnHHe6ckH-44ntoh1TVf2mqFc1q-GHxe1t1km4YxBpiGNXsjw4otQtD_tGGMkr-zFmCkBpZLvRBWlueYUxrDr2JbT6fhjEcPygbnFogXmiZGAjLlDqDnRCHIaphRMCLDt63sR8kAppvzTECtXPQaTFxysgfl17iQeldHF95PXmchfx6FETBkUBiOKMwj_-xMvB3cGyH-RGw_R_0vpHCiTMKJHeDEIC0aBWM_d7pJ2OcSPWjlNZJpc4MIRjPg9OmYPu7iwXIictF6XRapdGDgUxSqd5x5IfK0S6DGcTzoZDiKN06fbM-iSPc_lWQedHkc8_LZwbs9LELlibuUbvFzwVo-bPe0LRqwiYyiZsvaMkMVE6hDpo7sfTvUbKhAVUEoOp5PW7xxXPEg2aDZ6PAhy1JWigXjIOL9d_jY_4zIZzdg1RW9tgNYiwRO7HtX2bWbxW6Mr0QhSno982-Wihf_Vp93Qt-2tDqcVCuqZ1wWnbVD7KkkAfLk51XLy-ufP__oh4HrXG2vwT3kGCzey7GDaZ57LiVxHtAo9x0_9p2rEqe0bCRMQHhVXDuW41ixFdmRF9vegkZ-mML8CGCl5bg0moFCwfbKhRxYknHFrxWGtN00UFmCb22OlbhRZ9Bo3z9uxZbx6z8-4-8t_1rQbwX5fqVAXyvE_wFK7mKZ">