<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62442>62442</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            "error: pack expansion does not contain any unexpanded parameter packs" for capture, and ice 
        </td>
    </tr>

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

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

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

<pre>
    ```c++
auto f = [](auto) { return [](auto... a) { [](auto...) {}([a]{}...); }; }(0);
```
```
<source>:1:64: error: pack expansion does not contain any unexpanded parameter packs
auto f = [](auto) { return [](auto... a) { [](auto...) {}([a]{}...); }; }(0);
 ~~~~~^
<source>:1:74: note: in instantiation of function template specialization '(anonymous class)::operator()<int>' requested here
auto f = [](auto) { return [](auto... a) { [](auto...) {}([a]{}...); }; }(0);
 ^
```

The capture should qualify `[a]{}...` as an unexpanded parameter pack.

Workaround: discard `a` in the pack expression i.e. `(a, [a]{})...` or `((void)a, [a]{})...` to keep warnings happy.

Possibly related to #48731.

Probably related, this ices:

```c++
int i = [](auto) { return [](auto... a) { return ([a]{}, ..., 0); }; }(0)();
```
```
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 -O3 <source>
1.      <source>:1:75: current parser token ')'
2.      <source>:1:27: instantiating function definition '(anonymous class)::operator()(int)::(anonymous class)::operator()<>'
 #0 0x00005638e846745f llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x356d45f)
 #1 0x00005638e846548c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x356b48c)
 #2 0x00005638e83b6a08 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007f7503454420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
 #4 0x00005638eb429c43 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformLambdaExpr(clang::LambdaExpr*) SemaTemplateInstantiate.cpp:0:0
 #5 0x00005638eb42c372 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
 #6 0x00005638eb433fa5 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCXXFoldExpr(clang::CXXFoldExpr*) SemaTemplateInstantiate.cpp:0:0
 #7 0x00005638eb42c6b2 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
 #8 0x00005638eb42d495 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformInitializer(clang::Expr*, bool) SemaTemplateInstantiate.cpp:0:0
 #9 0x00005638eb42eb87 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#10 0x00005638eb45c9e3 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#11 0x00005638eb461925 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6567925)
#12 0x00005638eb4aa4b0 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x65b04b0)
#13 0x00005638eaac9fa5 clang::Sema::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5bcffa5)
#14 0x00005638eb3acfa9 clang::Sema::DeduceReturnType(clang::FunctionDecl*, clang::SourceLocation, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x64b2fa9)
#15 0x00005638eae848d7 clang::Sema::DiagnoseUseOfDecl(clang::NamedDecl*, llvm::ArrayRef<clang::SourceLocation>, clang::ObjCInterfaceDecl const*, bool, bool, clang::ObjCInterfaceDecl*, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5f8a8d7)
#16 0x00005638eb1f678e CreateFunctionRefExpr(clang::Sema&, clang::FunctionDecl*, clang::NamedDecl*, clang::Expr const*, bool, clang::SourceLocation, clang::DeclarationNameLoc const&) SemaOverload.cpp:0:0
#17 0x00005638eb23c0b8 clang::Sema::BuildCallToObjectOfClassType(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x63420b8)
#18 0x00005638eaee1b45 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5fe7b45)
#19 0x00005638eaf02d3b clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x6008d3b)
#20 0x00005638ea9e313a clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ae913a)
#21 0x00005638ea9daba7 clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ae0ba7)
#22 0x00005638ea9ddd7e clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, clang::Parser::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ae3d7e)
#23 0x00005638ea9ddf7d clang::Parser::ParseAssignmentExpression(clang::Parser::TypeCastState) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ae3f7d)
#24 0x00005638ea99b39c clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5aa139c)
#25 0x00005638ea9af046 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5ab5046)
#26 0x00005638ea9779b7 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a7d9b7)
#27 0x00005638ea978b0f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (.part.0) Parser.cpp:0:0
#28 0x00005638ea980594 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a86594)
#29 0x00005638ea981b4d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a87b4d)
#30 0x00005638ea9820e4 clang::Parser::ParseFirstTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a880e4)
#31 0x00005638ea970e9a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x5a76e9a)
#32 0x00005638e95c7f25 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x46cdf25)
#33 0x00005638e8eb5cd1 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3fbbcd1)
#34 0x00005638e8e38e13 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x3f3ee13)
#35 0x00005638e8f96183 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0x409c183)
#36 0x00005638e5d6739c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-trunk/bin/clang+++0xe6d39c)
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzUWktz2zjW_TX0BiUVCfC58EKW7f5SX3qcij3VvXOBwKWEDgWwATCRZzG_fQqkHgRFa5xuuaeTciwKz3vOPbi4gEmNESsJcB0kN0Fye0Vbu1b6Ghi1m1ZflYq_XAdp2P-wAN-4n_A2CBe0tQpVKCC3qO8b4NyVBbhAQXaDNNhWS79uPp8jum8wrtmVB5krC5Ib6mq7731lQG6Qq9x94DzsC3tzDkZOfyVLo1rNICB3AVlEAVmkcUAWCLRW2j00lH1BsG2oNEJJxBUYJJVFTElLhURUvqBWdg04cNRQTTdgQXcdzd-SEvRv9y9I7l7lIOs4kMqC-xQSCWkslVZQ60hQFapaybpnC5umphaQaYAJWot_9W0CnDl7pZIvG9UaxGpqTGfFIiAL1YCmVmlnvitbCmnd9DhDGn5vwVjgaA0a_p4EHrkbyan7_bQGxGhjWw3IrFVbc_R7S2tRvSDXcjxbGiJqEJWvy2g-HP0Xpb9QrVrJnW-4MIxq7gambiQhkV3DQbUaTCdbMYd5NznOaYCXyDMiwMXODqV3jQKcf1WCB7g419wq9AWgQd-olkKuDFrTpnnxrP2kjBFl_YI0OJVw1yfAJM4zEvkNtSrpoKGb1q6FQYKBcaIZtJ0OPEJaJP6ERvYNRoJwhnSiWKLwVWXsZPymmBPOg7D4pNVK0w2ietVuQFoHEQX4XjU2wPdMbRpRg57BtqmVBu3KaipXM6tb-SXA96WQ-7KeAzRb8W9UV7MYzVZo5li-p03jhmxt09q5QbNNXX_doNlsm6czajYz8yIt3QbkVkgLNZo9otlsxdjMKlWzNRUyILdnbXKNjaSNWSuLZhVTtdIzLuhKKmMFM2hWSTVjmpq1X2wsD8jtzn04RLMHgrw41DHlFFJMhafEscVarUFat1YMaGTVF9iFncL97kbAr4yAsz6wHaKaXB1DGodKSPH9UQznLortK78n-vWhbx9cMAlRuA3DMExSkkMep1mcVMg5r-9vXkz_8EkLaR8tZV-eNGUQ4PzYSNNvz8pYDXQT4NTJt7euE_ifEFqAb8ItSVIeJ5Wz_mB0NDI6iXM2ZfSyBirb5kE-ipWkdYDzVnbJBke1crNczMQyzplnIvZMJGVKwxwtnTw_A1NfQb_0Nv0flbx2M-086rdZKmlha-esaQKyCLv_hynIboqsypKQxEkc4xA9P2swVml41nYHrhZlgO-3efqcxrNayHY7W8m2r2jsWgPlc6PmYYclcqN4SOIhkjLGBYsJ6inoSH7SAE-aSlMpvXEKG6pR0g2YphPMTpFPu138w2FFuOznbj_WbpyPdFNyerdtHDODyYblC0fXI2zo6ZAwzVgygsJIht8dyimIP2p-6ptPSEWTdzd_-euv96rmpyi8iu8Hk419kZY_ki_ykfk8Lt7fFx_cXuESX3gNxRKVStXfjaYYoYEyz94dzecuC3q0G-uDGZZ_n2Pc1hD6UBJWwPuHq6XaNC5PPgXj1_wxDzlYkQ8rjQrs6c0NtntqS2NPDRkYMCj9ua2t-Ahfod5bstiliR-F6Y6exnZ7-mV2yjRJswInh_3FIcM-MkrjMpxGNiDpfpdB3R4SqBHaLgv7qBjt6zzQx86s9nwy_rwU6DKMy9ADTYagKWXFKJQfQetW_iLs-rGtKsEE7JKwx16k5yEfM6J9wvmsoQrI0h240D4lvLsUzqRkVUV95_rJA6GsosU0zlvgLYN-7T-9NCNwEy47C_2i_otLXNHCw-VlEhTyOOfZK7j6wwj808BD1Zs_BPYPugE-QHX02UJr-vK589frUJ33PCoeyt-WH6QFXVEGbtz9Gp6U-bmOo2h1EYVUOc155jHpJzVRlWY5oKWGwSL_DNXpxt0x3J823qyTMdmjHXSSqrcGFTcs1V2Nm-ajYl70dOY-fAVdK8qnI7yfEGHCwjKfltRNK2q-pHX9pB7K34DZh2rpTn2ny-aRKVc0BfYtq-goxp9bS8sapjW5H-5EjOMRL7QeSYzDMvdUlPvrEaIyfiWeHsibkNTfi63XjHiPPSqpICtjP3Z7SSGtQsxJOc3pgtkH-QNzeiFdhmHOSTnkEHvZKC2ARIQOTfjU3SgNnj8pYyuxvTtcqHYb_9YndbELi6at7TQReImsbuGSuzuFIiLUQxf56DgtaXYW3ZIae4Tmgxo2du267_8vJD_V_DjqD7u6IOi6P1pq4bTrxbydUAhL6u1lGI_44DyD9-Xjf08C4Rl4JJAxCVXGz5Kw6P4A6M4cb6FiBO1yOKqMezhiH0dRkoKdxTHIABaVBb3_rvRC8oW1WpStBeNDOzY6L-vumR-Pi5UapBev9rpX-jOVK_gghb2o22lECubR5WfEBa3COP2vdP2kVduc-lrIlat9bICd4jsytrsdncLv8T0eYbwpjLehv4TBMgnj1GMw9RnMsqI8H00dEw96cBTu8vf-ovu7CHlbi7NeWTAGxrg6UQlHw6V4ynhR-lE2G_GUl2H11oXp0TV5c_AubI0VNs3WvKHazkP3rccweVDAfq5b5GFSxGfx3217WQx4-GswX0oDeZoUsaeBYsRBVMbnN5kn1XTXXKcn8IeG_t7CJ6v9TOoQnrpk824iihzS358Vb2v4sGmU3m9LF7sxS2ielbG3M5FRUpnjEM4L4F5oY39gBvIQPPeTUeKZhVCcptWLx6dXrwze5QxFsxQKL0P2_wxYJCyr_GvbpeLwE8g-od-n8MBaC7ui7pLuIubFKeOVf_dKvFwthzJhPPKuU7TbYiWfsO-ClpGqLBmPPMti3zKSQ0R84vq5-jthBtPcvQ7lcvokFQGIiGe9lwzlVZFGOfFPnp2dRxBfD8nI-I8HHsjLBdU4LFiU-1Z7CUjC06zLeFn0vKFujHz6bnJNBxdnuwO4V4aXqH_D52LGQ8q99HP_1ssVvya8IAW9gusozXFGwozkV-vrMs4jFkZZlBNIoyqOCyd1IGVYJFWS4StxjUNMwhgXYRThKJ_HRR7mjEGKSRTTggdxCBsq6rkjYa706koY08J1iuMYX9W0hNp0bzBiLOEb6ioDjIPk9kpfuz6zsl2ZIA5rYaw5jmKFreE6wPhSrwFijCql92-FOfKp5EgwQFetrq_X1jbd2xH4PsD3K2HXbTlnahPg-869_ces0eo3YM5HHRIT4PsO6X8CAAD__7dDqd4">