[Index] Prevent canonical decl becoming nullptr

[krasimir]

Summary

This patch prevents getCanonicalDecl returning nullptr in case it finds
a canonical TemplateDeclaration with no attached TemplatedDecl.
Found by running the indexer over a version of the standard library deep inside
a template metaprogramming mess.

[vsk]

Do you have a test case?

[krasimir]

I've figured out a test case for this:

template <template <typename> class A> class B { typedef A<int> A_int; };

The real-world problem comes from ptr_traits.h.

[krasimir]

@vsk: could you help me turning this into a test case?

[vsk]

Take a look at the tests in clang/test/Index/Core. You should be able to write a test which uses c-index-test to dump the symbols in this source.

[krasimir]

• Add an Index test case

[krasimir]

@vsk: thank you!

[vsk]

LGTM, thank you! (Let me know if you need someone to commit this for you.)

lib/Index/IndexingContext.cpp

for (;; Parent = cast<Decl>(Parent->getDeclContext())) {
     }
     return Parent;
   }
 }
 
 static const Decl *getCanonicalDecl(const Decl *D) {
   D = D->getCanonicalDecl();
   if (auto TD = dyn_cast<TemplateDecl>(D)) {
-    D = TD->getTemplatedDecl();
+    if (auto TTD = TD->getTemplatedDecl()) {
+      D = TTD;
       assert(D->isCanonicalDecl());
     }
+  }
 
   return D;
 }
 
 static bool shouldReportOccurrenceForSystemDeclOnlyMode(
     bool IsRef, SymbolRoleSet Roles, ArrayRef<SymbolRelation> Relations) {
   if (!IsRef)
     return true;

test/Index/Core/no-templated-canonical-decl.cpp

+// RUN: c-index-test core -print-source-symbols -include-locals -- %s | FileCheck %s
+
+template <template <typename> class A> class B { typedef A<int> A_int; };
+// CHECK: [[@LINE-1]]:46 | class(Gen)/C++ | B | c:@ST>1#t>1#T@B | <no-cgname> | Def | rel: 0