[Index] Ignore nullptr decls for indexing

[ahoppen]

Summary

We can end up with a call to indexTopLevelDecl(D) with D == nullptr in non-assert builds e.g. when indexing a module in indexModule and

• ASTReader::GetDecl returns nullptr if Index >= DeclsLoaded.size(), thus returning nullptr

> ModuleDeclIterator::operator* returns nullptr

> we call IndexCtx.indexTopLevelDecl with nullptr

Be resilient and just ignore the nullptr decls during indexing.

clang/lib/Index/IndexDecl.cpp

 bool IndexingContext::indexDeclContext(const DeclContext *DC) {
   for (const auto *I : DC->decls())
     if (!indexDecl(I))
       return false;
   return true;
 }
 
 bool IndexingContext::indexTopLevelDecl(const Decl *D) {
-  if (D->getLocation().isInvalid())
+  if (!D || D->getLocation().isInvalid())
     return true;
 
   if (isa<ObjCMethodDecl>(D))
     return true; // Wait for the objc container.
 
   if (IndexOpts.ShouldTraverseDecl && !IndexOpts.ShouldTraverseDecl(D))
     return true; // skip