<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/113762>113762</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang] Assertion `(!Unexpanded.empty() || LambdaReferencingOuterPacks) && "Unable to find unexpanded parameter packs"' failed. at clang::Sema::ActOnFinishFullExpr
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          yijan4845
      </td>
    </tr>
</table>

<pre>
    **This testcase is generated by a fuzzer.**

Compiler Explorer: [https://godbolt.org/z/6c5b51jGW](https://godbolt.org/z/6c5b51jGW)

This invalid code will crash on Clang Assertion Trunk.
```cpp
template<typename T> using Int = int;
template<typename ...Ts> void Pack() {
 Int<Ts>({});
}
template void Pack<>();
```

It seems that this goes back to clang-12. The compiler gets the same assertion fail with [113598](https://github.com/llvm/llvm-project/issues/113598) but in the different function.

Stack dump:
```
clang++: /root/llvm-project/clang/lib/Sema/SemaTemplateVariadic.cpp:473: bool clang::Sema::DiagnoseUnexpandedParameterPack(clang::Expr*, clang::Sema::UnexpandedParameterPackContext): Assertion `(!Unexpanded.empty() || LambdaReferencingOuterPacks) && "Unable to find unexpanded parameter packs"' failed.
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-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 <source>
1.      <source>:4:1: current parser token '}'
2.      <source>:2:38: parsing function body 'Pack'
3.      <source>:2:38: in compound statement ('{}')
 #0 0x0000000003bd9c18 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bd9c18)
 #1 0x0000000003bd78dc llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3bd78dc)
 #2 0x0000000003b24f68 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x000075d3e9842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x000075d3e98969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x000075d3e9842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x000075d3e98287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x000075d3e982871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x000075d3e9839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x00000000074f36fc (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x74f36fc)
#10 0x0000000006ddbbfe clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ddbbfe)
#11 0x00000000071851ee clang::Sema::ActOnExprStmt(clang::ActionResult<clang::Expr*, true>, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71851ee)
#12 0x00000000067aee44 clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67aee44)
#13 0x00000000067a511c clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67a511c)
#14 0x00000000067a6030 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 32u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67a6030)
#15 0x00000000067a6f05 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67a6f05)
#16 0x00000000067a865a clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67a865a)
#17 0x00000000066bc1e3 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66bc1e3)
#18 0x00000000066f089d clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f089d)
#19 0x00000000067ba056 clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67ba056)
#20 0x00000000067c791c clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#21 0x00000000067c7c3a clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67c7c3a)
#22 0x00000000066f8e43 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66f8e43)
#23 0x00000000066b7ec7 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66b7ec7)
#24 0x00000000066b8d6d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66b8d6d)
#25 0x00000000066ab28a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66ab28a)
#26 0x0000000004550478 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4550478)
#27 0x000000000480c359 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x480c359)
#28 0x000000000478ae4e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x478ae4e)
#29 0x00000000048f1bee clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x48f1bee)
#30 0x0000000000ce2d9f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xce2d9f)
#31 0x0000000000cdaa6a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#32 0x0000000004594119 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
#33 0x0000000003b25414 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b25414)
#34 0x000000000459470f 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
#35 0x000000000455a08d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x455a08d)
#36 0x000000000455b17d 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+++0x455b17d)
#37 0x0000000004562aa5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4562aa5)
#38 0x0000000000cdfc39 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcdfc39)
#39 0x0000000000badfd4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xbadfd4)
#40 0x000075d3e9829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#41 0x000075d3e9829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#42 0x0000000000cda51e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcda51e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWt9T4zgS_mvMiyopW_79wEMIZI8trqCA3X1MyXI70Y4j-SSZgfnrryQ7xDJJgDkytVU3xZBgS62vv_7UalsiSrEVBzj34gsvvjwjrV4Lef7C_iY8yqL4rBDly7mHZx6ePa6ZQhqUpkQBYgqtgIMkGkpUvCCCqvbHD5DTrrHnX3p-_3suNg2rQaKr56YWEqQXzpAXX6y1bpQXzjy88PBiJcpC1Hoq5MrDix8eXiQ0LuLg79_-8uJLD2cfb47z4fAWN-NPpGYloqIE9J3VNaKSqDUSHM1rwldophRIzQRHj7Ll36a9hcTvfmjTdFc0bJqaaPDCuX5pgJMNoEcvvEKtYnyFrrlGXniJGNdeeHG4y3Q6fVSm25NgJboj9JuHMw_nyEv7XsaUF85tK3MvvfDSS-Pa1qz507E_sBXO-17D9ltfhuRca6QANgrpNdFIG6pWAhQqCP2GtEDUkDMJ8BQ9rgHRbSRXoE0XQMo4Q165qwir0Xem1ya-QRDGebY3eEyv22JKxcbDi7p-2n5MGin-Bqo9vGBKtaA8vOit4BwVrUaM22FLVlUggWtUtZyaoadDrx60gV-2m8YMuc9765eHL8yPUSNeSCH0Wxh9u0XNCg8vHmBD-o_HnvQ_iWSkZHRqFBLOojQ09goh6o47AyCc2Y722yUjKy4U_MHhuSG8hPKOSLIBDbJXwaDb1XMj7Xya7zd2wMhccA3P2gZ_NlC28d5oItj1m8Km0S-v2pt76RzdkE1RknuwDFPGV7dtb1jZVjjxcII8jP_gpKjByKRivETtq1XUbOGgpuuGPZxadUDZR-ru5mr2cIVUW2yYRgQV7QpJaITUxuDP6wURXiLGad2WYLXSTXQjaC0JBUNmI6GRgoJSUCIlWtldNj2JUoIym9Vky5GikjV6elBW_tTz8zspVpJsEJGrdgNcq15SorES6ifNBLbpr5fV5HXeqIk2ScfDi4LxneqMOtFkVX4nsppEaLJCE2HskqYx1lvdtHqq0GRjuECTyXOWTIjaTNQL1-TZCy8Z11CjScXF5AlkIRSY-2jygCaTFaUTLURN14RxL7w8itc0Vpw0ai00mlRU1EJOyk7KmlHVjWGZdi574bynN7zqCAsMYc7lcBZ54SwwnNFW2kndEKlAIi2-AUceTm3mSzsDeI8B7IWzMDMWTE-Th7dpAZkFzJjoJldvIzxqg3Gb6ETLS6Q00WBiiuwcSbdpOH1dZJCHQx_5z_72X1iUOQ0yZHVqp6l6Ud2XO8m4tip67KSY7RpJ8n0plJZANnaGze0aYudb9kVa8vCF_9zDc_AHI_xpVtJ9-Oc1EN42t_yBrTipPZy13BYQJaqFGeUUaA0YBy120eKoSjI0N9q7ByqeQL508P5FeFmbQbOeSadNnyT7vO3b_69DhP0QaVyGkGcRjrHfu9atBM9ZskyiSc14-zxZ8ba7QadKTBML3HZxYEeuzTzJK4oavZZAyuU3U5J8agDb3xkgHoOO0gStlOXis-CjNHFsJ65tnKVViEhhsvWnLNuOjuX0jeWg-LTNoHBsZq7NMIc8-ZxN28WxmQ9Vl0ZVmFT0q9Xem90VsDgMnNySlGVRVLC_GphRfcsXjDO1XrR13RUPHygnbBK8EZQYiOamqV7efn753O6dcbx1MlEaZHEAx7w1Hj3ojXb9nNnUfw-qrU0JvZ8BLVub-U_nXw_f8c_JXUlKAKJo6N-dXfkG3zsP-0XIdfNN29JQsSv-vjxeHVzHn3DkTxwE9Kg_r77cykugNZFWdbNKg5xpLVnRalPGDRbGhw2p6z-BaiHdYHaBt8EMcWtjmYy0_Q5FR-fBeJ50_Ycg9442bnGKMBiWnTBEozAkfuj_RBj-KbyfgjNDicNZPOas8uOjPsz7ovCVuwtRmkenU6XHDpKDORlhzpKYHMW86OvgMeZBHxP_A2p3FENFAydTtHHE8TR1PE0KGkD4IU8voWKc9WoedWB8tVW7kB9R7fYp_5pXAlHBlT7e64Zo2GWBG6b0ifTcEeIwlrmMVX6Wl0e9M1T8JkXbHCTqoQH61uEdhfsn9AcT5UGi37b_UGru7S2EvCd8BdecnYx8y61Dfu5OzIL4cfIu-cPFb0vA27n5LtWfIHIQ2_vZ9fVt0b09eY_vDy10TosZpaCU0Q-rmCH5BEnDkjyMAnZr5ZSm-TvVyJatQTRupUVNavaDvM0i7wXkVMxNGyL11CxgyAH-9vHV8BCMeaDh8WVi4P-DJlIzvvqL6fXPifKnODiBPqzbjj7wKEVmEB1fVNza6Jfq4P0Wv6Rw6khyWAxHS3MKNH3nGUaD5KQ-yOZXsPFm2TrRumu8deiIRnRkZXJ83X0UzQ08Qd0VXkMebhvynxbu9Kjgfl2o76HaW27vnor_Lcq2hutNI6S2Nd-JJlfnpsODW08npMDZ26Qze3h0Xe62VJJf8bqhg-RgdurpKI79KM2GmOeihN-Ady8Utq8QgLYa-kv9xsnXIu2BOEidejjKfBrG-RDpQpo8xMs9UE8EssPggHRK0CjNCETg0tkNe82VJpzCfkYPe3USLfc4HUdyl-0qKNzXUD3knT9Pr1k4O-bvSZJSj2_ogLsj4VPAZV4hSoPlhjD3MX8mJXmxiWVO10Run3Jm_bsx9xqe203m0_jRoXTcCFw3SkISgrbkz4NHmyn2v7O43jT1Xp9srtl1MTb6NXzwhJejUrInkHvrK3cHIorzKAjybvd9Z3e7A7WUllt7d7sjf9U1oaSuC0K_LSvuJvxu7F5D82AuNhvCy_Gk3htDpft2ojGjE8PBgB8tGV_1y0gX4NcOyyV9fg6C7o-CKEaXyjbvWXQamwtLLQnTant7ZI7UtZkT3cuj_r5pMtuleCuijnPbxcNpbfee7f7aliqcbfeWfhfF_niEox2hOAqiQSj27ft0d-5b_kAqqF8cOo-H7hSbXBaxo_xoLLHUr9D_s0RGT0EHtRCPlnTiZ-VB4mzsyJsVc8umk8xHHU2DQ6-EjjSdOcXOwLcvLiCM246gxqVOEaSf5uV3UajDpPwuihumtEPKsdT8qoOGMCMBu0v7cR57sfwSNg1ZDptuORYnmJD4EPLLwXencNhTMRyKwi9k8wTlrKXH4S8bLewVDftydluhbPHbtDLrk8L7y_ZX1yQWmQPdqQ39gpRVGSED-qvH7kwPx4780WZ5XuafPJdguzg2g7FNiHy0XJpuS6WJ1MuBcx8eBSJ3FDyu5OIAUGf_62NmjL-OPrwdzhBIKewJVHsdVf0TBqL9jOgOqXWHGOGZ6e7IaBBGBmarAE2ekBZIASA2KPvz0VlXCbqVHMycNJ1HhxDPyvOwzMOcnMF5kOI8jwMc4LP1eRUkGOMspYHRVpUngZ9TnOCo9Muo8OkZO8c-jgIfJ0Hk-34-jWOchmVCSZ6SqqLUi3zYEFZPzVyZCrk6s0fjzoMgTBN8VpMCamXP-2K8TQ5bEuw5vbm5YU9yCT7pz83ubox7mGrpxw8TJuzFl2fy3J7LK9qV8iK_ZkqrHRDNdG2PGndW4st_3tlERPSHD1ectbI-_58OtpqAPJ3j_wYAAP__D_r_kw">