[index] Return when DC is null in handleReference

[MaskRay]

Summary

DC may sometimes be NULL and getContainerInfo(DC, Container) will fail.

See https://github.com/jacobdufault/cquery/issues/192 for the full story.

https://github.com/nlohmann/json/blob/develop/test/src/unit-constructor1.cpp and many other files in that project's test/src/ direcotory cannot be indexed because

https://github.com/llvm-mirror/clang/blob/master/tools/libclang/CXIndexDataConsumer.cpp#L203

c++
    handleReference(ND, Loc, Cursor,
                    dyn_cast_or_null<NamedDecl>(ASTNode.Parent),
                    ASTNode.ContainerDC, ASTNode.OrigE, Kind);

dyn_cast_or_null<NamedDecl>(ASTNode.Parent) is somehow a null pointer and in https://github.com/llvm-mirror/clang/blob/master/tools/libclang/CXIndexDataConsumer.cpp#L935

c++
  ContainerInfo Container;
  getContainerInfo(DC, Container);

The null DC is casted ContInfo.cursor = getCursor(cast<Decl>(DC)); and SIGSEGV.

https://github.com/llvm-mirror/clang/blob/master/tools/libclang/CXIndexDataConsumer.cpp#L203

handleReference(ND, Loc, Cursor,
                dyn_cast_or_null<NamedDecl>(ASTNode.Parent),
                ASTNode.ContainerDC, ASTNode.OrigE, Kind);

#0  0x00007fa31b51a4b0 in clang::Decl::castFromDeclContext(clang::DeclContext const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#1  0x00007fa31b4a202a in clang::cxindex::CXIndexDataConsumer::handleReference(clang::NamedDecl const*, clang::SourceLocation, CXCursor, clang::NamedDecl const*, clang::DeclContext const*, clang::Expr const*, CXIdxEntityRefKind) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#2  0x00007fa31b4a1871 in clang::cxindex::CXIndexDataConsumer::handleDeclOccurence(clang::Decl const*, unsigned int, llvm::ArrayRef<clang::index::SymbolRelation>, clang::FileID, unsigned int, clang::index::IndexDataConsumer::ASTNodeInfo) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#3  0x00007fa31b77a9a5 in clang::index::IndexingContext::handleDeclOccurrence(clang::Decl const*, clang::SourceLocation, bool, clang::Decl const*, unsigned int, llvm::ArrayRef<clang::index::SymbolRelation>, clang::Expr const*, clang::Decl const*, clang::DeclContext const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#4  0x00007fa31b77acc6 in clang::index::IndexingContext::handleReference(clang::NamedDecl const*, clang::SourceLocation, clang::NamedDecl const*, clang::DeclContext const*, unsigned int, llvm::ArrayRef<clang::index::SymbolRelation>, clang::Expr const*, clang::Decl const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#5  0x00007fa31b7798e0 in (anonymous namespace)::IndexingDeclVisitor::handleTemplateArgumentLoc(clang::TemplateArgumentLoc const&, clang::NamedDecl const*, clang::DeclContext const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#6  0x00007fa31b7797f9 in (anonymous namespace)::IndexingDeclVisitor::VisitTemplateDecl(clang::TemplateDecl const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#7  0x00007fa31b7774d9 in clang::index::IndexingContext::indexDecl(clang::Decl const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#8  0x00007fa31b777709 in clang::declvisitor::Base<clang::declvisitor::make_const_ptr, (anonymous namespace)::IndexingDeclVisitor, bool>::Visit () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#9  0x00007fa31b7774d9 in clang::index::IndexingContext::indexDecl(clang::Decl const*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#10 0x00007fa31b6cf5ba in clang::ASTUnit::visitLocalTopLevelDecls(void*, bool (*)(void*, clang::Decl const*)) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#11 0x00007fa31b77241a in clang::index::indexASTUnit(clang::ASTUnit&, std::shared_ptr<clang::index::IndexDataConsumer>, clang::index::IndexingOptions) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#12 0x00007fa31b4b11ed in clang_indexTranslationUnit::$_1::operator()() const () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#13 0x00007fa31c804980 in llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#14 0x00007fa31c804a34 in RunSafelyOnThread_Dispatch(void*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#15 0x00007fa31c84bcba in ExecuteOnThread_Dispatch(void*) () from /home/maskray/Dev/Util/cquery/build/debug/bin/../lib/clang+llvm-5.0.1-x86_64-linux-gnu-ubuntu-14.04/lib/libclang.so.5
#16 0x00007fa31ecbc494 in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#17 0x00007fa31a4d3a8f in clone () from /lib/x86_64-linux-gnu/libc.so.6

[MaskRay]

DC -> Parent

[MaskRay]

DC -> Parent

[MaskRay]

Sorry for changing this back and forth. But I do not have a powerful workstation and have to reverse engineer this.

[MaskRay]

HighCommander4 narrowed it down https://github.com/jacobdufault/cquery/issues/219#issuecomment-354903152 to a much simpler reproduce:

c++
template <typename>
struct actor;

template <template <typename> class Actor = actor>
struct terminal;

This may trigger null pointer dereference of DC (because it calls cast). If the default template argument is removed, the crash goes away.

[MaskRay]

Ping

[sammccall]

Sorry, I was hoping @akyrtzi would see this.
I don't know enough about the code to know whether DC==null is an indicator of some other problem, but if this is crashing today then let's not block on that.

[akyrtzi]

Could you add a test case for this change ? See examples in test/Index/Core.
Also for the test case code: template <template <typename> class Actor = actor>, is the actor reference in this code reported ?
See the test examples on how to print out and test how the source symbols are indexed.

[MaskRay]

@akyrtzi When I run c-index-test core -print-source-symbols -- a.cc on

template <typename>
struct actor;

template <template <typename> class Actor = actor>
struct terminal;

the issue disappears. It emerges only when clang_indexTranslationUnit is called with interactions of other things.

[MaskRay]

rebase

[akyrtzi]

Ah, sorry I mislead you. To test this try using c-index-test -index-file /path/to/file, see other examples in test/Index, e.g. test/Index/index-file.cpp

[MaskRay]

In D41575#970412, @akyrtzi wrote:

Ah, sorry I mislead you. To test this try using c-index-test -index-file /path/to/file, see other examples in test/Index, e.g. test/Index/index-file.cpp

Thanks for the command. It is really helpful. I have re-run cquery with or without the !DC patch (on git-svn HEAD) and see no libclang crash. I guess the real issue was in somewhere else and in these weeks it has been fixed. The !DC check patch was useful then.

zsh
% cat a.cc
template <typename>
struct actor;

template <template <typename> class Actor = actor>
struct terminal;

# Arch Linux extra/clang 5.0.1-1
% c-index-test -index-file a.cc
[startedTranslationUnit]
[enteredMainFile]: a.cc
[indexEntityReference]: kind: c++-class-template | name: actor | USR: c:@ST>1#T@actor | lang: C++ | cursor: TypeRef=actor<type-parameter-0-0>:2:8 | loc: 2:8 | <parent>:: <<NULL>> | container: [TU] | refkind: direct
libclang: crash detected during indexing source file: {
  'source_filename' : '(null)'
  'command_line_args' : ['clang', 'a.cc'],
  'unsaved_files' : [],
  'options' : 1,
}
Failure (no details available)


# llvm+clang git-svn HEAD
% ~/Dev/llvm/release/bin/c-index-test -index-file a.cc
# no failure

% ~/Dev/llvm/release/bin/c-index-test -index-file test/src/unit-cbor.cpp -Isrc -Itest/thirdparty/catch -std=c++11 -resource-dir ~/Dev/llvm/release/lib/clang/7.0.0
# no failure

tools/libclang/CXIndexDataConsumer.cpp

bool CXIndexDataConsumer::handleReference(const NamedDecl *D, SourceLocation Loc,
                                       CXCursor Cursor,
                                       const NamedDecl *Parent,
                                       const DeclContext *DC,
                                       const Expr *E,
                                       CXIdxEntityRefKind Kind) {
   if (!CB.indexEntityReference)
     return false;
 
-  if (!D)
+  if (!D || !Parent)
     return false;
   if (Loc.isInvalid())
     return false;
   if (!shouldIndexFunctionLocalSymbols() && isFunctionLocalDecl(D))
     return false;
   if (isNotFromSourceFile(D->getLocation()))
     return false;
   if (D->isImplicit() && shouldIgnoreIfImplicit(D))