<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91677>91677</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Crash on missing `template` disambiguator after C++20-allowed missing `typename` disambiguator
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang,
            crash-on-invalid
      </td>
    </tr>

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

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

<pre>
    https://godbolt.org/z/shvqo8jhY
```
template <typename> struct t1 {
  template <typename>
  struct t2 {};
};

template <typename T>
t1<T>::t2<T> f1();

void f2() {
  f1<bool>();
}
```

```
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-16.0.0/bin/clang++ -gdwarf-4 -g -o /app/output.s -mllvm --x86-asm-syntax=intel -S --gcc-toolchain=/opt/compiler-explorer/gcc-12.2.0 -fcolor-diagnostics -fno-crash-diagnostics -std=c++20 <source>
1.      <eof> parser at end of file
2.      <source>:9:6: LLVM IR generation of declaration 'f2'
3.      <source>:9:6: Generating code for declaration 'f2'
 #0 0x0000569be3cb48df llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x3ba18df)
 #1 0x0000569be3cb290c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x3b9f90c)
 #2 0x0000569be3c05518 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007599e2a42520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x0000569be357cac5 llvm::FunctionType::get(llvm::Type*, llvm::ArrayRef<llvm::Type*>, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x3469ac5)
 #5 0x0000569be4449873 clang::CodeGen::CodeGenTypes::GetFunctionType(clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4336873)
 #6 0x0000569be423c394 clang::CodeGen::CodeGenTypes::ConvertFunctionTypeInternal(clang::QualType) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4129394)
 #7 0x0000569be423d7f8 clang::CodeGen::CodeGenTypes::ConvertType(clang::QualType) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x412a7f8)
 #8 0x0000569be41fd6bf clang::CodeGen::CodeGenModule::GetAddrOfFunction(clang::GlobalDecl, llvm::Type*, bool, bool, clang::CodeGen::ForDefinition_t) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40ea6bf)
 #9 0x0000569be44a558c EmitFunctionDeclPointer(clang::CodeGen::CodeGenModule&, clang::GlobalDecl) CGExpr.cpp:0:0
#10 0x0000569be44b405a EmitDirectCallee(clang::CodeGen::CodeGenFunction&, clang::GlobalDecl) CGExpr.cpp:0:0
#11 0x0000569be44cd525 clang::CodeGen::CodeGenFunction::EmitCallee(clang::Expr const*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x43ba525)
#12 0x0000569be44cd94a clang::CodeGen::CodeGenFunction::EmitCallExpr(clang::CallExpr const*, clang::CodeGen::ReturnValueSlot) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x43ba94a)
#13 0x0000569be4516727 (anonymous namespace)::ScalarExprEmitter::VisitCallExpr(clang::CallExpr const*) CGExprScalar.cpp:0:0
#14 0x0000569be450b5e0 (anonymous namespace)::ScalarExprEmitter::Visit(clang::Expr*) CGExprScalar.cpp:0:0
#15 0x0000569be450da97 clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x43faa97)
#16 0x0000569be44aebb6 clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x439bbb6)
#17 0x0000569be44cbce9 clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x43b8ce9)
#18 0x0000569be4135593 clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4022593)
#19 0x0000569be413b7aa clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40287aa)
#20 0x0000569be419b08d clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x408808d)
#21 0x0000569be41a62a6 clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40932a6)
#22 0x0000569be41fd88a clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40ea88a)
#23 0x0000569be41fa015 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40e7015)
#24 0x0000569be41fa503 clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x40e7503)
#25 0x0000569be4201ff9 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#26 0x0000569be4fa6d01 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#27 0x0000569be4f9973d clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4e8673d)
#28 0x0000569be61c9a74 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x60b6a74)
#29 0x0000569be4fa4865 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4e91865)
#30 0x0000569be4880671 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x476d671)
#31 0x0000569be4804993 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x46f1993)
#32 0x0000569be4964b3b clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x4851b3b)
#33 0x0000569be148d41c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x137a41c)
#34 0x0000569be1488bdc ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#35 0x0000569be4665ce9 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
#36 0x0000569be3c05977 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x3af2977)
#37 0x0000569be4665f1c 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
#38 0x0000569be462e3fc clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x451b3fc)
#39 0x0000569be462eded clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x451bded)
#40 0x0000569be463923c clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x452623c)
#41 0x0000569be148b523 clang_main(int, char**) (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x1378523)
#42 0x00007599e2a29d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#43 0x00007599e2a29e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#44 0x0000569be1484d1e _start (/opt/compiler-explorer/clang-16.0.0/bin/clang+++0x1371d1e)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWlFvpDgS_jXkxaIFNhj8kIdOZzo3q1nt3GQ0p3tqGdsQdozNGZNJ7tefDE26TbqT6V32dNJJu5pg7PL3lT9XVdvQrqsrJcR1kN4E6e0V7e2DNtf8RyFp_b0WV4Xmz9cP1rZdgNYB3AZwW2leaGlX2lQB3P47gNvu4fFfOv_94Z9BdBtE6wBH-_-GRyuaVlIrQIA29rkVijYiQB9AZ03PLLAxCLKbsSsAZzpPr6cxcBiT3QZoP9L7--y04OuLLRsHaDM8onWA1hbuH0EZBzAPIJmZe9Q1ByUc3x0jLp2hQmvpbM1GZrcnPXKy8fOnD-v7D6Dri6a2gIKir4ARrTYWWA1mS1Dbh75YMd0EcCvl4_RP2Br9u2A2gNu663rRBXALqOKgVkz2XAD7IAAztHsABWXfraFMBHADWiNao5noOsFBp3szNruRtOs0q6kVHJhegY6ZurWrEfK9pew74H3TOmRDU7QKIvLZ6MrQBlBT9Y1Q1gEHAdzq1iFjumlrKUwonlqpjTCuTVJVhTFeRasogNuiVlNjAG8CeAPCiv-gpgwTEFYg1M4abVtns7dtb1cdCBvnARCGTzkOadeE3bOy9ClAt7WyQoLwHoRhxVhotZbsgdYqQLdvgnKdY7iCqwiEJdNSm5DXtFK6szXrQFgqHQ7O9Js7ywN0y0bgMHL627t00l7snBSgjdClU1xLTScMoBYIxYEuQVlLMfaE-54HA2hNArTGzqOfPn37FXz8AiqhhKG21soN5oJJun8MYOYkm43G0FvG7vZGVAWY5gKU2rxhCgQQRSB6iqIoSjEpBGJFkvMSDGIcdlT33I1_fDa1soNUvo56yw-dDP2x0501gjYBxE5ztbLDBnM76U8IJoA30RMqaJzz0m3JF9TxDDUkETuFeiMFVX37m7qvK0VlAPNeDbGSA6ndLIthJCWJmIcR-hijNI1zsHFK-yKYfhTmeQT1N6q4dFPle695fTZaWfFkV6x12zMa_n-ZAu2nyFJCBKQJTJ1SB0KyLgK4fcrxDiehrFX_FFaqH1-wVadXeAA-DPFgJx7sNGOUpUeu3faKOSl9fW7F2FIJ66lheAPXTgaHxrUx9PmLKAO0ed3ThdwNGKLvYguSYEJZ6jFLj5klSULyDIFx4CgWzcWdUN6Dg7jX0p2wHnmYnx17N3X8qEoNmFadHTbGQuQShHCeIY8c9shBxBBJLiC30epRGI_gR2WFGTfNkZ2_91SO9JciE0OCSOKRyWZkeFbml5N5vUp_BXialbkHPvfAxyXHRfke-F8176V40dmac_NbOS2Gz-FO6oLKW8Gkv8OOtt24kw7_npt8q82tKGtVu1l2y0XsJBIUF37EJv7mo2maM_ChqV8k5xh91i7Lm7e2luevMdmccQ4Bm7sPT615HTpdAol8PEUSpXTAc1sbweyGSine3OPjw2GN_jiU2IfCeArT9wTzMu_Q6HCfQuzmnMLPesHwU9AUHmKr4wDnHEhC_xgHh3nm933rEZPzmv4ibG_UNyp7cS_1gppGBSUJ9Ugjj3Qa4wxmbjaqtHpudN8B93Ola4d6iYz47hmV1Dg6jrAT-9D8re4uoD_paTR2WlWJDy4qUhH9GXCvlfXTUNIZFE5Jdrk4DuDeFPnChUSCSkpJ5q07nsUyURT4cj5r9fwTZM6ZXVfVkcgXJ02KosAe6Wy2wwsmyOWkP1ZKG8HfJb7crs2ZIB6RWX5GaUreLQNPqNE2sy3hWrylO1n9Hg1YW3tE2RXBi-VfCFOCPNZkxrrI6B8J0Lppda-44_qP2j7o3t4z_boYPvQ6qn7fL0h8US_njTyjXuSGfvaPSRHl_HJvTC03mj-_qYXFmOR5lHOPiV88xBRDemEs2p8ZCPfy50rNQ9HzZoj6y38GRQRB6kUpCOfFd56_K_Pj4tst60j7UJdOFfLPOWdsH2S87NoLmue-itGMLI3idwvH02T_d0hmUexVljCZk0yjd8P1aZLnqS0IP428uAv92gdGcVm-mzbn8L_q9pN4FHuwxyTGlmkBVi011uEjwLN0siqDfhVTUsyj-L0CcW_WxQttPjatHJvHI6y3Yd4Z3bcuB0ICRlg3fS25OF0zQr_cKAnJkBehbyj7LhTfaNX1zVSoXopjmVUXOc6QH5W9GgPHjNDMO435TE0n1vdfZ1lDNHSWKRct63BUYJolHlIyU0GS41MxZH2c-p4E661YT4cTC3qSxDn2tr9_Pp3keYSz-Bjf1mhlheInAC4KLcMcZ7EHzU-9eZSQeSE5TvZRdZYqJk577zyXJVMlLmPiV4T--XRCcFKgAngV-QD0wOJRM_oa9CuWS-aDPI0LVHiwvaQXJzlPYgYYi3cNdTby01X3A52V2hvgt8ENeNQ1XxJ9jDKaxMxDn8zQ5wVnYPL0Jv46bPcjDvcNlfKbYC_h9gSVQSbc1I9nYuns4Bvj1P10G65CDxOV-3JnZwaHDW-ni9D97SqjUhaUfd-Vyv8hM869l8Mm3uimoYrP9-LJhRmu2Vybbt3sVHoXBPfW1Koaen7Yr9rLgN2OPT3F8fhQ0K5mu27ovveR19k17Kyhte2m1zNzVEonb22O3rsuRycKgzJGzw9DAphJ2hScBjA7uArm083SL7o4vR54fjNEsuxoKU7d_-wPt3p1T0shnz13vr10i92o0BKSzDsImZ3TY5yWbi_-HwtjVoWdVYB_BoGhQOV5xw0rRl-lt8mbXjSeDXQdvF_gP9d17VUhR9wWCOkuopd-UCRzb3DBL_XGL7rozrviF118qjv_MOKtIPuy-i2t3cIPN7M_7729RP5KH3LhVZyJXydhRCA6q6jbo7-9LH8ivZ_z_X_Rh0sVEynEEHnKS-JZOi5SuC_hpnJiQj0EjvXC5UGeQq8mS6B_oQ8JJxde6A9DPJtoblMkEdjt3LBdZ6mxA9VLZxGJP8u8sEl4LMBofzF3xTwWh0mnD6-u-DXiBBF6Ja7jLE4hSVFGrh6uBYljBhnmuEyLPON5EcdcIIa5yDnC2VV9DSOYRGlEIExxTFYc4ZSjHMYwynmGkyCJRENruXI6X2lTXQ0fZF2TGGfZlaSFkN3w0R2Ee7gwgBv3NHxQpFVYq0cqXVkJg_T2ylwP33cVfdUFSSTrznYH07a2UlwPyR9oBZq662pVgQBH00dwAY4ArzvaFHXVu5QEaGmFAZvpK6XQJasfgnuDp-_v5oOveiPnHwVe8EXa4IP_BAAA___bawbo">