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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang crashes while checking constraints of a concept parameter pack that is missing an ellipsis"
href="https://bugs.llvm.org/show_bug.cgi?id=47043">47043</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Clang crashes while checking constraints of a concept parameter pack that is missing an ellipsis
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++2a
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ezra@ezisland.org
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>The clang frontend will crash if a user accidentally omits the ellipsis when
attempting to expand a parameter pack inside of a concept's parameter list. In
the reproduction steps below, the parameter pack T is written without the
ellipses in the second line (Foo<T>). When both Foo and Bar are concepts, this
causes clang to crash instead of emitting the usual diagnostic. This issue
appears could be a duplicate of two previously reported bugs #45770 and #45699.
$ uname -a
Linux 4.19.0-9-amd64 #1 SMP Debian 4.19.118-2+deb10u1 (2020-06-07) x86_64
GNU/Linux
$ clang++-12 -v
Debian clang version 12.0.0-++20200715052739+d6e79e3dd6d-1~exp1
$ cat foo.cpp
template<typename... T> concept Foo = true;
template<typename... T> concept Bar = Foo<T>; // vs Foo<T...>
static_assert(Bar<int, int, int>);
$ clang++-12 -std=c++20 foo.cpp
#0 0x00007fb7c2fd374f llvm::sys::PrintStackTrace(llvm::raw_ostream&)
(/usr/lib/x86_64-linux-gnu/libLLVM-12.so.1+0xb0f74f)
#1 0x00007fb7c2fd1ab0 llvm::sys::RunSignalHandlers()
(/usr/lib/x86_64-linux-gnu/libLLVM-12.so.1+0xb0dab0)
#2 0x00007fb7c2fd3c25 (/usr/lib/x86_64-linux-gnu/libLLVM-12.so.1+0xb0fc25)
#3 0x00007fb7c9edb140 __restore_rt
(/lib/x86_64-linux-gnu/libpthread.so.0+0x14140)
#4 0x00007fb7c7ebaf7b (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xc83f7b)
#5 0x00007fb7c7e9404a (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xc5d04a)
#6 0x00007fb7c7e96551 (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xc5f551)
#7 0x00007fb7c7e920a9 clang::Expr::EvaluateAsRValue(clang::Expr::EvalResult&,
clang::ASTContext const&, bool) const
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xc5b0a9)
#8 0x00007fb7c830ab8c (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x10d3b8c)
#9 0x00007fb7c8305a32
clang::Sema::CheckConstraintSatisfaction(clang::NamedDecl const*,
llvm::ArrayRef<clang::Expr const*>, llvm::ArrayRef<clang::TemplateArgument>,
clang::SourceRange, clang::ConstraintSatisfaction&)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x10cea32)
#10 0x00007fb7c87416a1 clang::Sema::CheckConceptTemplateId(clang::CXXScopeSpec
const&, clang::SourceLocation, clang::DeclarationNameInfo const&,
clang::NamedDecl*, clang::ConceptDecl*, clang::TemplateArgumentListInfo const*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x150a6a1)
#11 0x00007fb7c8741997 clang::Sema::BuildTemplateIdExpr(clang::CXXScopeSpec
const&, clang::SourceLocation, clang::LookupResult&, bool,
clang::TemplateArgumentListInfo const*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x150a997)
#12 0x00007fb7c846c3be clang::Sema::ActOnIdExpression(clang::Scope*,
clang::CXXScopeSpec&, clang::SourceLocation, clang::UnqualifiedId&, bool, bool,
clang::CorrectionCandidateCallback*, bool, clang::Token*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x12353be)
#13 0x00007fb7c7c57122
clang::Parser::tryParseCXXIdExpression(clang::CXXScopeSpec&, bool,
clang::Token&) (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa20122)
#14 0x00007fb7c7c581ca clang::Parser::ParseCXXIdExpression(bool)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa211ca)
#15 0x00007fb7c7c47e5e
clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&,
clang::Parser::TypeCastState, bool, bool*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa10e5e)
#16 0x00007fb7c7c4b5aa
clang::Parser::ParseCastExpression(clang::Parser::CastParseKind, bool, bool&,
clang::Parser::TypeCastState, bool, bool*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa145aa)
#17 0x00007fb7c7c46d36
clang::Parser::ParseConstantExpressionInExprEvalContext(clang::Parser::TypeCastState)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa0fd36)
#18 0x00007fb7c7c34f3e
clang::Parser::ParseStaticAssertDeclaration(clang::SourceLocation&)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x9fdf3e)
#19 0x00007fb7c7c1bf2a
clang::Parser::ParseDeclaration(clang::DeclaratorContext,
clang::SourceLocation&, clang::Parser::ParsedAttributesWithRange&,
clang::SourceLocation*) (/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x9e4f2a)
#20 0x00007fb7c7cac94f
clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&,
clang::ParsingDeclSpec*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa7594f)
#21 0x00007fb7c7cab75b
clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0xa7475b)
#22 0x00007fb7c7c0e17d clang::ParseAST(clang::Sema&, bool, bool)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x9d717d)
#23 0x00007fb7c91d75f8 clang::FrontendAction::Execute()
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x1fa05f8)
#24 0x00007fb7c918d8c1
clang::CompilerInstance::ExecuteAction(clang::FrontendAction&)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x1f568c1)
#25 0x00007fb7c923cf40
clang::ExecuteCompilerInvocation(clang::CompilerInstance*)
(/usr/lib/x86_64-linux-gnu/libclang-cpp.so.12+0x2005f40)
#26 0x00000000004131bf cc1_main(llvm::ArrayRef<char const*>, char const*,
void*) (/usr/lib/llvm-12/bin/clang+0x4131bf)
#27 0x00000000004115fe (/usr/lib/llvm-12/bin/clang+0x4115fe)
#28 0x000000000041140a main (/usr/lib/llvm-12/bin/clang+0x41140a)
#29 0x00007fb7c1ff8cca __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x26cca)
#30 0x000000000040e89a _start (/usr/lib/llvm-12/bin/clang+0x40e89a)</pre>
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