[clang] Crash on invalid template deduction guide

[aeubanks]

$ cat /tmp/a.ii

namespace a {
template <class> struct pair;
}
template <class _T2> pair() -> pair<_T2>;

$ clang++ "-cc1" "-triple" "x86_64-unknown-linux-gnu"  "-x" "c++" a.ii -fsyntax-only
a.ii:4:22: error: no template named 'pair'; did you mean 'a::pair'?
    4 | template <class _T2> pair() -> pair<_T2>;
      |                      ^~~~
      |                      a::pair
a.ii:2:25: note: 'a::pair' declared here
    2 | template <class> struct pair;
      |                         ^
a.ii:4:32: error: no template named 'pair'; did you mean 'a::pair'?
    4 | template <class _T2> pair() -> pair<_T2>;
      |                                ^~~~
      |                                a::pair
a.ii:2:25: note: 'a::pair' declared here
    2 | template <class> struct pair;
      |                         ^
a.ii:4:22: error: deduction guide must be declared in the same scope as template 'a::pair'
    4 | template <class _T2> pair() -> pair<_T2>;
      |                      ^
a.ii:2:25: note: template is declared here
    2 | template <class> struct pair;
      |                         ^

clang++: ../../clang/lib/Sema/SemaDeclCXX.cpp:11468: bool clang::Sema::CheckDeductionGuideDeclarator(Declarator &, QualType &, StorageClass &): Assertion `Qualifiers && "expected QualifiedTemplate"' failed.

[shafik]

Looks like a clang trunk regression: https://godbolt.org/z/bh7q8Pd5n

CC @hokein

Backtrace:

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 -std=c++20 <source>
1.	<source>:4:41: current parser token ';'
 #0 0x0000000003b258d8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b258d8)
 #1 0x0000000003b2359c llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3b2359c)
 #2 0x0000000003a6c198 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x00007cbf7c842520 (/lib/x86_64-linux-gnu/libc.so.6+0x42520)
 #4 0x00007cbf7c8969fc pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x969fc)
 #5 0x00007cbf7c842476 gsignal (/lib/x86_64-linux-gnu/libc.so.6+0x42476)
 #6 0x00007cbf7c8287f3 abort (/lib/x86_64-linux-gnu/libc.so.6+0x287f3)
 #7 0x00007cbf7c82871b (/lib/x86_64-linux-gnu/libc.so.6+0x2871b)
 #8 0x00007cbf7c839e96 (/lib/x86_64-linux-gnu/libc.so.6+0x39e96)
 #9 0x0000000006a1abf2 clang::Sema::CheckDeductionGuideDeclarator(clang::Declarator&, clang::QualType&, clang::StorageClass&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6a1abf2)
#10 0x000000000697e500 clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef<clang::TemplateParameterList*>, bool&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x697e500)
#11 0x0000000006981470 clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6981470)
#12 0x00000000070c15c1 clang::Sema::ActOnTemplateDeclarator(clang::Scope*, llvm::MutableArrayRef<clang::TemplateParameterList*>, clang::Declarator&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70c15c1)
#13 0x00000000065e714d clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65e714d)
#14 0x00000000065f696b 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+++0x65f696b)
#15 0x00000000066bf0c6 clang::Parser::ParseDeclarationAfterTemplate(clang::DeclaratorContext, clang::Parser::ParsedTemplateInfo&, clang::ParsingDeclRAIIObject&, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66bf0c6)
#16 0x00000000066cc704 clang::Parser::ParseTemplateDeclarationOrSpecialization(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::AccessSpecifier) (.part.0) ParseTemplate.cpp:0:0
#17 0x00000000066cca1a clang::Parser::ParseDeclarationStartingWithTemplate(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x66cca1a)
#18 0x00000000065ff903 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65ff903)
#19 0x00000000065bc741 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65bc741)
#20 0x00000000065bd5cd clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65bd5cd)
#21 0x00000000065b0bba clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x65b0bba)
#22 0x0000000004470d68 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4470d68)
#23 0x0000000004702ca9 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4702ca9)
#24 0x000000000468655e clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x468655e)
#25 0x00000000047ec0ce clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x47ec0ce)
#26 0x0000000000cb996f cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcb996f)
#27 0x0000000000cb2bba ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) driver.cpp:0:0
#28 0x00000000044b4189 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
#29 0x0000000003a6c644 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x3a6c644)
#30 0x00000000044b477f 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
#31 0x000000000447a6c5 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x447a6c5)
#32 0x000000000447b12d 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+++0x447b12d)
#33 0x0000000004482d75 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4482d75)
#34 0x0000000000cb6d65 clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcb6d65)
#35 0x0000000000b89614 main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xb89614)
#36 0x00007cbf7c829d90 (/lib/x86_64-linux-gnu/libc.so.6+0x29d90)
#37 0x00007cbf7c829e40 __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e40)
#38 0x0000000000cb266e _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcb266e)
clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation)
Compiler returned: 134

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Arthur Eubanks (aeubanks)

$ cat /tmp/a.ii

namespace a {
template <class> struct pair;
}
template <class _T2> pair() -> pair<_T2>;

$ clang++ "-cc1" "-triple" "x86_64-unknown-linux-gnu"  "-x" "c++" a.ii -fsyntax-only
a.ii:4:22: error: no template named 'pair'; did you mean 'a::pair'?
    4 | template <class _T2> pair() -> pair<_T2>;
      |                      ^~~~
      |                      a::pair
a.ii:2:25: note: 'a::pair' declared here
    2 | template <class> struct pair;
      |                         ^
a.ii:4:32: error: no template named 'pair'; did you mean 'a::pair'?
    4 | template <class _T2> pair() -> pair<_T2>;
      |                                ^~~~
      |                                a::pair
a.ii:2:25: note: 'a::pair' declared here
    2 | template <class> struct pair;
      |                         ^
a.ii:4:22: error: deduction guide must be declared in the same scope as template 'a::pair'
    4 | template <class _T2> pair() -> pair<_T2>;
      |                      ^
a.ii:2:25: note: template is declared here
    2 | template <class> struct pair;
      |                         ^

clang++: ../../clang/lib/Sema/SemaDeclCXX.cpp:11468: bool clang::Sema::CheckDeductionGuideDeclarator(Declarator &, QualType &, StorageClass &): Assertion `Qualifiers && "expected QualifiedTemplate"' failed.