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Clang crashes on lambda forwarding in template with LocalInstantiationScope::findInstantiationOf assertion since clang 17 with -std=c++20 #139940

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mariete1223 opened this issue May 14, 2025 · 3 comments
Open

Clang crashes on lambda forwarding in template with LocalInstantiationScope::findInstantiationOf assertion since clang 17 with -std=c++20 #139940

mariete1223 opened this issue May 14, 2025 · 3 comments
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@mizvekov
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clang:frontend Language frontend issues, e.g. anything involving "Sema" crash Prefer [crash-on-valid] or [crash-on-invalid] lambda C++11 lambda expressions

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@mariete1223
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The following code causes Clang to crash with an assertion failure during template instantiation.

Assertion

clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateInstantiate.cpp:4558: llvm::PointerUnion<clang::Decl*, llvm::SmallVector<clang::ValueDecl*, 4>*>* clang::LocalInstantiationScope::findInstantiationOf(const clang::Decl*): Assertion `isa<LabelDecl>(D) && "declaration not instantiated in this scope"' failed.

Stack dump

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 -x c++ -std=c++23 <source>
1.	<source>:16:40: current parser token ')'
2.	<source>:12:1: parsing function body 'main'
3.	<source>:12:1: in compound statement ('{}')
4.	<source>:4:16: instantiating function definition 'make_lambda<(lambda at <source>:13:21), int &, std::basic_string<char> &>'
 #0 0x0000000003f95368 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f95368)
 #1 0x0000000003f92ff4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f92ff4)
 #2 0x0000000003ed7c28 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007e7853242520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007e78532969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007e7853242476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007e78532287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007e785322871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007e7853239e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x00000000071cc075 clang::LocalInstantiationScope::findInstantiationOf(clang::Decl const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71cc075)
#10 0x0000000007295038 clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef<std::pair<llvm::PointerUnion<clang::TemplateTypeParmType const*, clang::NamedDecl*>, clang::SourceLocation>>, clang::MultiLevelTemplateArgumentList const&, bool&, bool&, clang::UnsignedOrNone&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7295038)
#11 0x00000000071d5d1a clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExprs(clang::Expr* const*, unsigned int, bool, llvm::SmallVectorImpl<clang::Expr*>&, bool*) SemaTemplateInstantiate.cpp:0:0
#12 0x00000000071e0df9 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#13 0x00000000071d42c8 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#14 0x00000000071e5307 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformType(clang::TypeLocBuilder&, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#15 0x00000000071e42d4 clang::QualType clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformFunctionProtoType<clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformFunctionProtoType(clang::TypeLocBuilder&, clang::FunctionProtoTypeLoc)::'lambda'(clang::FunctionProtoType::ExceptionSpecInfo&, bool&)>(clang::TypeLocBuilder&, clang::FunctionProtoTypeLoc, clang::CXXRecordDecl*, clang::Qualifiers, clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformFunctionProtoType(clang::TypeLocBuilder&, clang::FunctionProtoTypeLoc)::'lambda'(clang::FunctionProtoType::ExceptionSpecInfo&, bool&)) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#16 0x00000000071e56e7 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformType(clang::TypeLocBuilder&, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#17 0x00000000071d2812 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformLambdaExpr(clang::LambdaExpr*) SemaTemplateInstantiate.cpp:0:0
#18 0x00000000071d3ec2 (anonymous namespace)::TemplateInstantiator::TransformLambdaExpr(clang::LambdaExpr*) SemaTemplateInstantiate.cpp:0:0
#19 0x00000000071d444f clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#20 0x00000000071d6475 clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformInitializer(clang::Expr*, bool) (.part.0) SemaTemplateInstantiate.cpp:0:0
#21 0x00000000071d681c clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#22 0x0000000007214bfe clang::TreeTransform<(anonymous namespace)::TemplateInstantiator>::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#23 0x000000000721df24 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x721df24)
#24 0x000000000727d6b7 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x727d6b7)
#25 0x0000000006b5896e void llvm::function_ref<void ()>::callback_fn<clang::Sema::MarkFunctionReferenced(clang::SourceLocation, clang::FunctionDecl*, bool)::'lambda'()>(long) SemaExpr.cpp:0:0
#26 0x0000000007f1f7e1 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7f1f7e1)
#27 0x0000000006b56aaf clang::Sema::MarkFunctionReferenced(clang::SourceLocation, clang::FunctionDecl*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b56aaf)
#28 0x0000000006b5712d MarkExprReferenced(clang::Sema&, clang::SourceLocation, clang::Decl*, clang::Expr*, bool, llvm::DenseMap<clang::VarDecl const*, int, llvm::DenseMapInfo<clang::VarDecl const*, void>, llvm::detail::DenseMapPair<clang::VarDecl const*, int>>&) SemaExpr.cpp:0:0
#29 0x0000000006b47139 clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&, clang::NestedNameSpecifierLoc, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b47139)
#30 0x0000000006f4c43d clang::Sema::FixOverloadedFunctionReference(clang::Expr*, clang::DeclAccessPair, clang::FunctionDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f4c43d)
#31 0x0000000006f8304e FinishOverloadedCallExpr(clang::Sema&, clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, clang::OverloadCandidateSet*, clang::OverloadCandidate**, clang::OverloadingResult, bool) SemaOverload.cpp:0:0
#32 0x0000000006f84130 clang::Sema::BuildOverloadedCallExpr(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f84130)
#33 0x0000000006b7c656 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b7c656)
#34 0x0000000006b7d85e clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef<clang::Expr*>, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b7d85e)
#35 0x000000000669f6dd clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult<clang::Expr*, true>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669f6dd)
#36 0x00000000066980ea clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&, clang::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66980ea)
#37 0x000000000669a287 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669a287)
#38 0x000000000669a319 clang::Parser::ParseAssignmentExpression(clang::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669a319)
#39 0x0000000006650c08 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6650c08)
#40 0x00000000066604f9 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+++0x66604f9)
#41 0x0000000006669197 clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6669197)
#42 0x0000000006669659 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6669659)
#43 0x00000000067273ea clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67273ea)
#44 0x00000000067280dd clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67280dd)
#45 0x000000000672fe03 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x672fe03)
#46 0x00000000067305ca clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67305ca)
#47 0x000000000662a573 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662a573)
#48 0x0000000006660efd 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+++0x6660efd)
#49 0x000000000661e0ae clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661e0ae)
#50 0x000000000661e869 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661e869)
#51 0x000000000662618a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662618a)
#52 0x000000000662712d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662712d)
#53 0x000000000661950a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661950a)
#54 0x000000000493b128 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x493b128)
#55 0x0000000004c31795 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c31795)
#56 0x0000000004bb03ce clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4bb03ce)
#57 0x0000000004d25339 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d25339)
#58 0x0000000000dab05f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdab05f)
#59 0x0000000000da122a ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#60 0x00000000049a2379 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
#61 0x0000000003ed80c4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ed80c4)
#62 0x00000000049a298f 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
#63 0x000000000496475d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x496475d)
#64 0x00000000049657ee 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+++0x49657ee)
#65 0x000000000496dad5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x496dad5)
#66 0x0000000000da6fc8 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda6fc8)
#67 0x0000000000c2c8f4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc2c8f4)
#68 0x00007e7853229d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#69 0x00007e7853229e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#70 0x0000000000da0cd5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda0cd5)

Program

#include <iostream>
using namespace std;
template <typename R, typename... Args >
constexpr auto make_lambda(const R &lambda, Args&&... args)
    -> decltype(lambda(forward<Args>(args)...))
{
    return [lbd = forward<R>(lambda), args = forward<Args>(args)...]() -> decltype(lambda(args...)){

    };
}
int main(int argc, char* argv[])
{
    auto callback = [](int x, const string& y) -> bool {};
    int a{1};
    string b{"test"};
    auto f = make_lambda(callback, a, b);
}

To reproduce:

https://godbolt.org/z/ozx3arr5o
@llvmbot llvmbot added the clang Clang issues not falling into any other category label May 14, 2025
@EugeneZelenko EugeneZelenko added clang:frontend Language frontend issues, e.g. anything involving "Sema" crash Prefer [crash-on-valid] or [crash-on-invalid] lambda C++11 lambda expressions and removed clang Clang issues not falling into any other category labels May 14, 2025
@llvmbot
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llvmbot commented May 14, 2025

@llvm/issue-subscribers-clang-frontend

Author: None (mariete1223)

The following code causes Clang to crash with an assertion failure during template instantiation.

Assertion

clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateInstantiate.cpp:4558: llvm::PointerUnion&lt;clang::Decl*, llvm::SmallVector&lt;clang::ValueDecl*, 4&gt;*&gt;* clang::LocalInstantiationScope::findInstantiationOf(const clang::Decl*): Assertion `isa&lt;LabelDecl&gt;(D) &amp;&amp; "declaration not instantiated in this scope"' failed.

Stack dump

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 -x c++ -std=c++23 &lt;source&gt;
1.	&lt;source&gt;:16:40: current parser token ')'
2.	&lt;source&gt;:12:1: parsing function body 'main'
3.	&lt;source&gt;:12:1: in compound statement ('{}')
4.	&lt;source&gt;:4:16: instantiating function definition 'make_lambda&lt;(lambda at &lt;source&gt;:13:21), int &amp;, std::basic_string&lt;char&gt; &amp;&gt;'
 #<!-- -->0 0x0000000003f95368 llvm::sys::PrintStackTrace(llvm::raw_ostream&amp;, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f95368)
 #<!-- -->1 0x0000000003f92ff4 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3f92ff4)
 #<!-- -->2 0x0000000003ed7c28 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #<!-- -->3 0x00007e7853242520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #<!-- -->4 0x00007e78532969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #<!-- -->5 0x00007e7853242476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #<!-- -->6 0x00007e78532287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #<!-- -->7 0x00007e785322871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #<!-- -->8 0x00007e7853239e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #<!-- -->9 0x00000000071cc075 clang::LocalInstantiationScope::findInstantiationOf(clang::Decl const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x71cc075)
#<!-- -->10 0x0000000007295038 clang::Sema::CheckParameterPacksForExpansion(clang::SourceLocation, clang::SourceRange, llvm::ArrayRef&lt;std::pair&lt;llvm::PointerUnion&lt;clang::TemplateTypeParmType const*, clang::NamedDecl*&gt;, clang::SourceLocation&gt;&gt;, clang::MultiLevelTemplateArgumentList const&amp;, bool&amp;, bool&amp;, clang::UnsignedOrNone&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7295038)
#<!-- -->11 0x00000000071d5d1a clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExprs(clang::Expr* const*, unsigned int, bool, llvm::SmallVectorImpl&lt;clang::Expr*&gt;&amp;, bool*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->12 0x00000000071e0df9 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCallExpr(clang::CallExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->13 0x00000000071d42c8 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->14 0x00000000071e5307 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeLocBuilder&amp;, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#<!-- -->15 0x00000000071e42d4 clang::QualType clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformFunctionProtoType&lt;clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformFunctionProtoType(clang::TypeLocBuilder&amp;, clang::FunctionProtoTypeLoc)::'lambda'(clang::FunctionProtoType::ExceptionSpecInfo&amp;, bool&amp;)&gt;(clang::TypeLocBuilder&amp;, clang::FunctionProtoTypeLoc, clang::CXXRecordDecl*, clang::Qualifiers, clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformFunctionProtoType(clang::TypeLocBuilder&amp;, clang::FunctionProtoTypeLoc)::'lambda'(clang::FunctionProtoType::ExceptionSpecInfo&amp;, bool&amp;)) (.constprop.0) SemaTemplateInstantiate.cpp:0:0
#<!-- -->16 0x00000000071e56e7 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformType(clang::TypeLocBuilder&amp;, clang::TypeLoc) SemaTemplateInstantiate.cpp:0:0
#<!-- -->17 0x00000000071d2812 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformLambdaExpr(clang::LambdaExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->18 0x00000000071d3ec2 (anonymous namespace)::TemplateInstantiator::TransformLambdaExpr(clang::LambdaExpr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->19 0x00000000071d444f clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformExpr(clang::Expr*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->20 0x00000000071d6475 clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformInitializer(clang::Expr*, bool) (.part.0) SemaTemplateInstantiate.cpp:0:0
#<!-- -->21 0x00000000071d681c clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformReturnStmt(clang::ReturnStmt*) SemaTemplateInstantiate.cpp:0:0
#<!-- -->22 0x0000000007214bfe clang::TreeTransform&lt;(anonymous namespace)::TemplateInstantiator&gt;::TransformCompoundStmt(clang::CompoundStmt*, bool) SemaTemplateInstantiate.cpp:0:0
#<!-- -->23 0x000000000721df24 clang::Sema::SubstStmt(clang::Stmt*, clang::MultiLevelTemplateArgumentList const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x721df24)
#<!-- -->24 0x000000000727d6b7 clang::Sema::InstantiateFunctionDefinition(clang::SourceLocation, clang::FunctionDecl*, bool, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x727d6b7)
#<!-- -->25 0x0000000006b5896e void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::Sema::MarkFunctionReferenced(clang::SourceLocation, clang::FunctionDecl*, bool)::'lambda'()&gt;(long) SemaExpr.cpp:0:0
#<!-- -->26 0x0000000007f1f7e1 clang::StackExhaustionHandler::runWithSufficientStackSpace(clang::SourceLocation, llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7f1f7e1)
#<!-- -->27 0x0000000006b56aaf clang::Sema::MarkFunctionReferenced(clang::SourceLocation, clang::FunctionDecl*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b56aaf)
#<!-- -->28 0x0000000006b5712d MarkExprReferenced(clang::Sema&amp;, clang::SourceLocation, clang::Decl*, clang::Expr*, bool, llvm::DenseMap&lt;clang::VarDecl const*, int, llvm::DenseMapInfo&lt;clang::VarDecl const*, void&gt;, llvm::detail::DenseMapPair&lt;clang::VarDecl const*, int&gt;&gt;&amp;) SemaExpr.cpp:0:0
#<!-- -->29 0x0000000006b47139 clang::Sema::BuildDeclRefExpr(clang::ValueDecl*, clang::QualType, clang::ExprValueKind, clang::DeclarationNameInfo const&amp;, clang::NestedNameSpecifierLoc, clang::NamedDecl*, clang::SourceLocation, clang::TemplateArgumentListInfo const*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b47139)
#<!-- -->30 0x0000000006f4c43d clang::Sema::FixOverloadedFunctionReference(clang::Expr*, clang::DeclAccessPair, clang::FunctionDecl*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f4c43d)
#<!-- -->31 0x0000000006f8304e FinishOverloadedCallExpr(clang::Sema&amp;, clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, clang::OverloadCandidateSet*, clang::OverloadCandidate**, clang::OverloadingResult, bool) SemaOverload.cpp:0:0
#<!-- -->32 0x0000000006f84130 clang::Sema::BuildOverloadedCallExpr(clang::Scope*, clang::Expr*, clang::UnresolvedLookupExpr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6f84130)
#<!-- -->33 0x0000000006b7c656 clang::Sema::BuildCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b7c656)
#<!-- -->34 0x0000000006b7d85e clang::Sema::ActOnCallExpr(clang::Scope*, clang::Expr*, clang::SourceLocation, llvm::MutableArrayRef&lt;clang::Expr*&gt;, clang::SourceLocation, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6b7d85e)
#<!-- -->35 0x000000000669f6dd clang::Parser::ParsePostfixExpressionSuffix(clang::ActionResult&lt;clang::Expr*, true&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669f6dd)
#<!-- -->36 0x00000000066980ea clang::Parser::ParseCastExpression(clang::CastParseKind, bool, bool&amp;, clang::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66980ea)
#<!-- -->37 0x000000000669a287 clang::Parser::ParseCastExpression(clang::CastParseKind, bool, clang::TypeCastState, bool, bool*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669a287)
#<!-- -->38 0x000000000669a319 clang::Parser::ParseAssignmentExpression(clang::TypeCastState) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x669a319)
#<!-- -->39 0x0000000006650c08 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6650c08)
#<!-- -->40 0x00000000066604f9 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&amp;, clang::DeclaratorContext, clang::ParsedAttributes&amp;, clang::Parser::ParsedTemplateInfo&amp;, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66604f9)
#<!-- -->41 0x0000000006669197 clang::Parser::ParseSimpleDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, bool, clang::Parser::ForRangeInit*, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6669197)
#<!-- -->42 0x0000000006669659 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&amp;, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6669659)
#<!-- -->43 0x00000000067273ea clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector&lt;clang::Stmt*, 24u&gt;&amp;, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67273ea)
#<!-- -->44 0x00000000067280dd clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector&lt;clang::Stmt*, 24u&gt;&amp;, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67280dd)
#<!-- -->45 0x000000000672fe03 clang::Parser::ParseCompoundStatementBody(bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x672fe03)
#<!-- -->46 0x00000000067305ca clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x67305ca)
#<!-- -->47 0x000000000662a573 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&amp;, clang::Parser::ParsedTemplateInfo const&amp;, clang::Parser::LateParsedAttrList*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662a573)
#<!-- -->48 0x0000000006660efd clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&amp;, clang::DeclaratorContext, clang::ParsedAttributes&amp;, clang::Parser::ParsedTemplateInfo&amp;, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6660efd)
#<!-- -->49 0x000000000661e0ae clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec&amp;, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661e0ae)
#<!-- -->50 0x000000000661e869 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661e869)
#<!-- -->51 0x000000000662618a clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&amp;, clang::ParsedAttributes&amp;, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662618a)
#<!-- -->52 0x000000000662712d clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&lt;clang::DeclGroupRef&gt;&amp;, clang::Sema::ModuleImportState&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x662712d)
#<!-- -->53 0x000000000661950a clang::ParseAST(clang::Sema&amp;, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x661950a)
#<!-- -->54 0x000000000493b128 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x493b128)
#<!-- -->55 0x0000000004c31795 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4c31795)
#<!-- -->56 0x0000000004bb03ce clang::CompilerInstance::ExecuteAction(clang::FrontendAction&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4bb03ce)
#<!-- -->57 0x0000000004d25339 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4d25339)
#<!-- -->58 0x0000000000dab05f cc1_main(llvm::ArrayRef&lt;char const*&gt;, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xdab05f)
#<!-- -->59 0x0000000000da122a ExecuteCC1Tool(llvm::SmallVectorImpl&lt;char const*&gt;&amp;, llvm::ToolContext const&amp;) driver.cpp:0:0
#<!-- -->60 0x00000000049a2379 void llvm::function_ref&lt;void ()&gt;::callback_fn&lt;clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const::'lambda'()&gt;(long) Job.cpp:0:0
#<!-- -->61 0x0000000003ed80c4 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref&lt;void ()&gt;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3ed80c4)
#<!-- -->62 0x00000000049a298f clang::driver::CC1Command::Execute(llvm::ArrayRef&lt;std::optional&lt;llvm::StringRef&gt;&gt;, std::__cxx11::basic_string&lt;char, std::char_traits&lt;char&gt;, std::allocator&lt;char&gt;&gt;*, bool*) const (.part.0) Job.cpp:0:0
#<!-- -->63 0x000000000496475d clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&amp;, clang::driver::Command const*&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x496475d)
#<!-- -->64 0x00000000049657ee clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x49657ee)
#<!-- -->65 0x000000000496dad5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&amp;, llvm::SmallVectorImpl&lt;std::pair&lt;int, clang::driver::Command const*&gt;&gt;&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x496dad5)
#<!-- -->66 0x0000000000da6fc8 clang_main(int, char**, llvm::ToolContext const&amp;) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda6fc8)
#<!-- -->67 0x0000000000c2c8f4 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xc2c8f4)
#<!-- -->68 0x00007e7853229d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#<!-- -->69 0x00007e7853229e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#<!-- -->70 0x0000000000da0cd5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xda0cd5)

Program

#include &lt;iostream&gt;
using namespace std;
template &lt;typename R, typename... Args &gt;
constexpr auto make_lambda(const R &amp;lambda, Args&amp;&amp;... args)
    -&gt; decltype(lambda(forward&lt;Args&gt;(args)...))
{
    return [lbd = forward&lt;R&gt;(lambda), args = forward&lt;Args&gt;(args)...]() -&gt; decltype(lambda(args...)){

    };
}
int main(int argc, char* argv[])
{
    auto callback = [](int x, const string&amp; y) -&gt; bool {};
    int a{1};
    string b{"test"};
    auto f = make_lambda(callback, a, b);
}

To reproduce:

https://godbolt.org/z/ozx3arr5o

@cor3ntin
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@mizvekov @zyn0217

@mizvekov
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This will at some point be fixed by #107942

@mizvekov mizvekov self-assigned this May 14, 2025
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@mizvekov mizvekov

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clang:frontend Language frontend issues, e.g. anything involving "Sema" crash Prefer [crash-on-valid] or [crash-on-invalid] lambda C++11 lambda expressions
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@mizvekov @cor3ntin @EugeneZelenko @llvmbot @mariete1223