<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/123854>123854</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Clang] Crash when mangling lambda with requires clause
        </td>
    </tr>

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

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

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

<pre>
    The following C++20 code causes a crash since Clang 18:
```c++
template <class T>
constexpr auto f() {
    return [] () requires requires (T x) { x; } {};
}

int main() {
    f<int>()();
}
```

See https://compiler-explorer.com/z/z475c49eW.

Assertion:
```console
clang++: /root/llvm-project/clang/lib/AST/ItaniumMangle.cpp:5919:
void {anonymous}::CXXNameMangler::mangleFunctionParam(const clang::ParmVarDecl*):
Assertion `parmDepth < FunctionTypeDepth.getDepth()' failed.
```

<details>

<summary>Stack dump</summary>

```console
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 -std=c++20 <source>
1.      <eof> parser at end of file
2.      <source>:6:5: LLVM IR generation of declaration 'main'
3.      <source>:6:5: Generating code for declaration 'main'
4.      <source>:3:12: Mangling declaration 'f()::(anonymous class)::operator()'
 #0 0x0000000003cb5ea8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3cb5ea8)
 #1 0x0000000003cb3bb4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3cb3bb4)
 #2 0x0000000003c00088 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x0000757fbf442520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x0000757fbf4969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x0000757fbf442476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x0000757fbf4287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x0000757fbf42871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x0000757fbf439e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000007a9ca8d (anonymous namespace)::CXXNameMangler::mangleFunctionParam(clang::ParmVarDecl const*) ItaniumMangle.cpp:0:0
#10 0x0000000007a9fd15 (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool)::'lambda0'(clang::NamedDecl const*)::operator()(clang::NamedDecl const*) const (.isra.0) ItaniumMangle.cpp:0:0
#11 0x0000000007a9869f (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool) ItaniumMangle.cpp:0:0
#12 0x0000000007aa8eba (anonymous namespace)::CXXNameMangler::mangleRequirement(clang::SourceLocation, clang::concepts::Requirement const*) ItaniumMangle.cpp:0:0
#13 0x0000000007a99405 (anonymous namespace)::CXXNameMangler::mangleExpression(clang::Expr const*, unsigned int, bool) ItaniumMangle.cpp:0:0
#14 0x0000000007a9cfdb (anonymous namespace)::CXXNameMangler::mangleBareFunctionType(clang::FunctionProtoType const*, bool, clang::FunctionDecl const*) ItaniumMangle.cpp:0:0
#15 0x0000000007a9e4e0 (anonymous namespace)::CXXNameMangler::mangleFunctionEncoding(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#16 0x0000000007a9f5c7 (anonymous namespace)::CXXNameMangler::mangle(clang::GlobalDecl) ItaniumMangle.cpp:0:0
#17 0x0000000007aa1e04 (anonymous namespace)::ItaniumMangleContextImpl::mangleCXXName(clang::GlobalDecl, llvm::raw_ostream&) ItaniumMangle.cpp:0:0
#18 0x0000000007ac663b clang::MangleContext::mangleName(clang::GlobalDecl, llvm::raw_ostream&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7ac663b)
#19 0x00000000041f1c24 getMangledNameImpl(clang::CodeGen::CodeGenModule&, clang::GlobalDecl, clang::NamedDecl const*, bool) CodeGenModule.cpp:0:0
#20 0x00000000042045dd clang::CodeGen::CodeGenModule::getMangledName(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42045dd)
#21 0x000000000423e701 clang::CodeGen::CodeGenModule::GetAddrOfFunction(clang::GlobalDecl, llvm::Type*, bool, bool, clang::CodeGen::ForDefinition_t) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x423e701)
#22 0x000000000403b703 clang::CodeGen::CodeGenFunction::EmitCXXMemberOrOperatorMemberCallExpr(clang::CallExpr const*, clang::CXXMethodDecl const*, clang::CodeGen::ReturnValueSlot, bool, clang::NestedNameSpecifier*, bool, clang::Expr const*, llvm::CallBase**) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x403b703)
#23 0x000000000403bd13 clang::CodeGen::CodeGenFunction::EmitCXXOperatorMemberCallExpr(clang::CXXOperatorCallExpr const*, clang::CXXMethodDecl const*, clang::CodeGen::ReturnValueSlot, llvm::CallBase**) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x403bd13)
#24 0x0000000004019246 clang::CodeGen::CodeGenFunction::EmitCallExpr(clang::CallExpr const*, clang::CodeGen::ReturnValueSlot, llvm::CallBase**) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4019246)
#25 0x0000000004087814 (anonymous namespace)::ScalarExprEmitter::VisitCallExpr(clang::CallExpr const*) CGExprScalar.cpp:0:0
#26 0x000000000407b6d0 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#27 0x0000000004088aca (anonymous namespace)::ScalarExprEmitter::VisitExprWithCleanups(clang::ExprWithCleanups*) CGExprScalar.cpp:0:0
#28 0x000000000407c2b7 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::ScalarExprEmitter, llvm::Value*>::Visit(clang::Stmt*) CGExprScalar.cpp:0:0
#29 0x000000000408148c clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x408148c)
#30 0x0000000003ff2ffe clang::CodeGen::CodeGenFunction::EmitAnyExpr(clang::Expr const*, clang::CodeGen::AggValueSlot, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ff2ffe)
#31 0x00000000040175fd clang::CodeGen::CodeGenFunction::EmitIgnoredExpr(clang::Expr const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x40175fd)
#32 0x0000000004155e2e clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4155e2e)
#33 0x000000000415dbdc clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x415dbdc)
#34 0x00000000041c2f7c clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41c2f7c)
#35 0x00000000041d5ffe clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x41d5ffe)
#36 0x000000000423ebda clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x423ebda)
#37 0x0000000004239e65 clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4239e65)
#38 0x000000000423a24b clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x423a24b)
#39 0x0000000004244573 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (.part.0) CodeGenModule.cpp:0:0
#40 0x0000000004646386 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) ModuleBuilder.cpp:0:0
#41 0x0000000004636ea4 clang::BackendConsumer::HandleTopLevelDecl(clang::DeclGroupRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4636ea4)
#42 0x000000000667de74 clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x667de74)
#43 0x0000000004643fd8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4643fd8)
#44 0x000000000490a755 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x490a755)
#45 0x000000000488d0ce clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x488d0ce)
#46 0x00000000049f7dae clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49f7dae)
#47 0x0000000000cf4ccf cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcf4ccf)
#48 0x0000000000cec79a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#49 0x000000000468a949 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
#50 0x0000000003c00534 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3c00534)
#51 0x000000000468af3f 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
#52 0x000000000464dd0d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x464dd0d)
#53 0x000000000464ed8e 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+++0x464ed8e)
#54 0x0000000004656895 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4656895)
#55 0x0000000000cf1b03 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcf1b03)
#56 0x0000000000bbcc44 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbbcc44)
#57 0x0000757fbf429d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#58 0x0000757fbf429e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#59 0x0000000000cec245 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcec245)
```

</details>
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzkW29z26j2_jTKG8YZCf1_kReOU-fXnXa702S6fedBgGz9KoEuoNS5n_4OIFtCceI4G3f3zt3ZdGxJHJ7n4XDOASMkZbVmlF558bUX31ygTm24uPqM1pQpdC8o3fBO0ouCk8er-w0FJa9r_rNia7Dw4LUHr6EPMCcUYNRJKgECWCC5AbJimIJFjdgaBJkXzj1_7iW-_R_bpp4_V7Rpa6Qo8MIFrpGU4N4LP3j-HHMmFd22AqBOcVB6MPNgDrxUtwIAAEFVJxiwuEF_W9B_dZWgcvjgwewebPumYOuF18BLb4yd9MYLtTX9wdf4KqZAgyr2pK_SCxcVUxqZudX_O269o2Yt3VEKNkq1UhOHSw8uMW_aqqZiRrdtzQUVl5g3Hlz-W_9FaYyjnP55aVvPpaRCVZxNZeNM8ppqdbSuvYjhHHhwKThXHlzW9UMzawX_f4r11_65ZV0VHlzO7-49uPyoEKu65jNi65pe4rb1wnmcB7nt7IFXRDNHjLPHhnfSyDT3wvni-_ffUUNtO2GvNebLsmNYw_0DCdR4MDNjB2zf5rE_kGi-IXFDce3BuZHO4Qm8xG-RaG5oqzbaFcDO5P1jS83VyzVV5sNuBFJQoqqm5PKp-l64IFShqpbWl-wl2TUNEo9e-OFOIfwDkK5pvXDhweVwp3_4qeD-pefnfwi-FqgBSKy7hjIle-15qw6N8E7_GdrxlDMlOvbDg8tCe9lyNIxgtiY_kShnEZitwYxru6httfVOtZ26lGDW6NEFs9k2S2ZINjP5yBTaeuFNxRStwaxkfPZARcEl1ffB7A7MZmuMZ4rzGm-0Z4c3L-LVD0uGWrnhCsxKzGsuZqRCa8alqrC0fZgZ7l6WinjhDd6HBK037wSmVtRAy-eFC8pLL_wAWiQkFQApQBkBvARlZVSG_WND03CeaPfUQn_69O0z-PgVrCmjAhm34SUgFNeo_-rB1E7f1PPn4Uu2bnsbbG2DV8nF85aiA5ZCL5wHUJsy80EbmrQvd0FibmJAtp9QwMS5_S3eaiRc7P1axxwPhj7wt_7uvxAXMUUZ0A5gm8lH2c8tUTFlPPpeIEw9mA0PCfRzxaUSVE_LxIMLoKOYDm26s3fxWw9e-9sensZvwQcT8GFRRIfAL2qKWNd-YXfVmqHag1nHTEIioOa6i3NA1WAGqNCF6vt-loGF9vCvFPMHKh4ttv9DjOi4B7NeQ-eZBWeKblUfTn3zZ-2Hvf00TsuijCIY6-lhSNmovM2SVRLN6op129madfYGvpT8MjGQTZMBcOQazJO8xKBVG0ERWf2o6vo066b9YD2ewo3SBKylkeBU2FGaDIYT1zDM0jIEqOBCnWbWNBzMpk_MBsXJBoNiMJi5BsOc5slpBk2TwWA-drAU5RhlBDgBgaGGytZM3vzkXHswywKTgm2uBYcS_s5D9Vz1JwBLEsRvB_hh2woqpa5eHHT6-gjWAuxnuplPC1BwXo8CZlqjpiDI1xHRMaT7JVOSh2Pp0Wb2syZ7WUmBLv3X6BVM9MqSvPz79DoKF7pwUUYL9Ha4X21hrcsfF--dyY6fODYZUAMc3cScYdqqPuqPbJzkqOFE-Dzy_0ZHPQo3mk78khRvh3uNBB1XxS7ofVgQXHF922FgETsjsmtwcrSIJ6xoRP2_Hs4-MMxJpTP1mNVtzQtU22XDcWTJNI7FOH07sr-CJJ1MuYD60TEkjs2-nPjYtPUYU4_2eWgL8Hzxdxx25sLGSRIWY59xsI1x_RVQ71zf9bBt-tWknPQbBWWAYQTWVFkyREM3MjvwF5zQW8qcL5856bRbJJOZ5FI9knGG6OFYfToY0MnKEfSjmBDwOojmkkvxJW9-5xHose5HAAYuk5CmfnAKk1uq5oSIL-UuWLzO1WyQdOLfgTjodL7k4oaWFat0L6tzrJR6-oM4TnaO_LBI_fCYOHsdbL5qKrX4_v0zbQoqvogvfQ1kvy9QXeuENnHv_qrjmOP72pza8Kfe-xyyr2Y37huqO3pXc_WM2L9Tqaw_3rUUV2WlJXwuQz0BOAytxn-NpB3e-TmGyQ7EMEzhdJhI8LZhetXwDI_9kpH6xcKSYCRs5Aob5DBK3iDs29z8n6SLYT7oEru6ZGkWHC0h7jCqkdCMtSZqV898q-QJCuVgcasvWWMHElPiIkuLhPhjVe9Uo0yXXBjJwoXZHNS3ECGrlldMQ4OL0-k4Y2KGSkM2G3I7npNFiWpeySqd6J0hfHSV9JLe-uqfldr0O1zy6RrDvfsajNlEeQyL9L9f-XyifBBl-PQIMEA-sprb1V_vPoEN8P0EnuzfliUsS3o6rTl7fAWn58zO1-sDKfn991Qtu4F7MAnqaVwerV2fcv-4ZlxQcpT_OYKxRjzwcYu0II4pfMNY2ikxnSTPlDhzIdDjV1ra30V3DeZKjZiHH85B3tIbyIcT8qQgb5ifC960vGNEU9aRj3fqDvPpNsb4qR3P5DWVu-vp5xBF0x5EccuWAMMyfYMouyvXnDy-6BlnIGQgD4TceiMg8cnhqv9Njeqbr1uhDeu5F6PY4nb34EdW8pFbnEEVw3tQJZkuXQuCTlm66kG27If9tt368nUa2ev7jHueFWlB0MA5nXDOaRK_jfM_katmM3DNJlwRjIq3cf2lGywG58DCraBgFMXp0cXplMU9bz_RB9pjHnMZTm2Y30laJJT9neTIDlbk7mAlURJmydH9WGvTLn6H7U_74-vLGG8F71qdMWEOLKbrrqoJPVBzRm6BkoQJRdFYsWuEf1BGFpzJrtnV9aeCeO9htzD3wx45VUmSpISm0eTUjaTmzI-TWWiDJkn1TGVhD2kAHE4cIixJdsBP5-MsuaW4U3S-2_c7i64GyADTze25j9LYCYBLwZmijBzAeSaEFsOA0E3WWUZ8PEnWts-PTCrEMD2s5fOUzpNcLc6BhZtc8zIliLobgAbvQOZh_-PitGZ0yJ4ndVh8A3onTfq4jDAuAcbBqj9BeLiU36BJ_b4A7jW4AA-8IuchYVEOHDKXA8VpjsBO9kVwb-LCiMldg-r6G8X72HyAUDLZhee87n8xcio3IqqHg6HZTWZJhvIoN5KMjJZ9MbUSRlV7ZrE_btVvSWBU1wXCP1Ylc5dQtuPedRbBgjcNYmQ6iw-O3n43hbe6d6QFGImjRMXW5skP_dDuG6xWeLsNAvulQLLCK2ke7yV0HtYXVkqgSsnd7Yk5VNd6KnAxuq8fGW1wDKcbbJP9gQp7nqKXCma7Y1a_8eLpYMT-9HBUHI7PcR06AtXvpnbsDpW0fnS0fHncznHYyyDeO3wcTJ2rDEvwv-wck5LusBfASd4mxCfPqmZGDT3JjDspndA9aagfcFb9r3t07pQzI2LvXCVo2oMrTYsZSjJ6qii_8UI-r8hvvPhUSXcf5KVYvPeAFlWiP7F-goi9m_wSKbVYg5RuwZXESZbHz8G-GX12CoQDlcFzQ_ALpTxDtWrkGcSLJ3VIUOx-QN5VIjvwJpTMn-w0Ppeh37320MgG3E715xcFxlFk3r54746t6aHj6YnRnOQnHsg1TQaD2dQgjXywWuk2K6mQUKsRrVd3QaNRF_m0UINRDKzxdx8nY7zv-sl7FR5cDq9WXJCrkORhji7oVZCGaeyHWRJcbK6yMM3KIE6iHJU5SsMs8n0_zrPQDwmOInxRXUEfxn4AAz0gkX-ZB0lSln4O4zzz8yDyIp82qKovtZ9ecrG-qKTs6FUAwyyOLmpU0Fqal5Yg7BlAL765EFfmDZiiW0sv8utKKjmYUJWqzZtO5rUkL76xZ7jBzw1loNmd47dlEvhZqc3wGhGuUSfpRSfqK_e9nnWlNl3Rv8xjJtWTl3AMcunBZQ_-4Qr-JwAA__9h8FfS">