[llvm-bugs] [Bug 38671] New: "destructor cannot be declared as a template" leads to segfault in Sema::LookupSpecialMember

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38671

            Bug ID: 38671
           Summary: "destructor cannot be declared as a template" leads to
                    segfault in Sema::LookupSpecialMember
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: arthur.j.odwyer at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

cat >test.cc <<EOF
struct S {
    template<class> ~S();
};
struct T : S {
    ~T() = default;
};
EOF
clang++ -std=c++11 -c test.cc

segfaults.

Partial stack trace:
4  libsystem_platform.dylib 0x000000000a876600 _sigtramp + 2173608176
5  clang-8                  0x000000010992decd
clang::Sema::CheckCompletedCXXClass(clang::CXXRecordDecl*) + 10061
6  clang-8                  0x0000000109934e91
clang::Sema::ActOnFinishCXXMemberSpecification(clang::Scope*,
clang::SourceLocation, clang::Decl*, clang::SourceLocation,
clang::SourceLocation, clang::ParsedAttributesView const&) + 465
7  clang-8                  0x000000010953692c
clang::Parser::ParseCXXMemberSpecification(clang::SourceLocation,
clang::SourceLocation, clang::Parser::ParsedAttributesWithRange&, unsigned int,
clang::Decl*) + 1980

What's happening here is that when we emit err_destructor_template, we produce
a CXXRecordDecl with no destructor (because the destructor the user wrote was
invalid). Therefore, in Sema::LookupSpecialMember, `DD = RD->getDestructor()`
is nullptr; and then the call to `DD->isDeleted()` blows up.

I'm not sure what the appropriate fix is, but I think it would involve doing a
better fixup to `RD->getDestructor()` all the way back where we emit
err_destructor_template.

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