Remove unreachable that was reached in modernize-use-nullptr.

[angelgarcia]

Summary

When traversing the parent map, the check assumed that all the nodes would be either Stmt or Decl. After r251101, this is no longer true: there can be TypeLoc and NestedNameSpecifierLoc nodes.

[alexfh]

Looks good with one nit.

test/clang-tidy/modernize-use-nullptr.cpp

191

nit: Merge the lines maybe?

[angelgarcia]

Merge lines.

clang-tidy/modernize/UseNullptrCheck.cpp

while (true) {
 
       const ast_type_traits::DynTypedNode &Parent = Parents[0];
 
       SourceLocation Loc;
       if (const auto *D = Parent.get<Decl>())
         Loc = D->getLocStart();
       else if (const auto *S = Parent.get<Stmt>())
         Loc = S->getLocStart();
-      else
-        llvm_unreachable("Expected to find Decl or Stmt containing ancestor");
 
+      // TypeLoc and NestedNameSpecifierLoc are members of the parent map. Skip
+      // them and keep going up.
+      if (Loc.isValid()) {
         if (!expandsFrom(Loc, MacroLoc)) {
           Result = Parent;
           return true;
         }
+      }
       Start = Parent;
     }
 
     llvm_unreachable("findContainingAncestor");
   }
 
 private:
   SourceManager &SM;

test/clang-tidy/modernize-use-nullptr.cpp

#define ENTRY(X) {X}
   struct A {
     int *Ptr;
   } a[2] = {ENTRY(0), {0}};
   // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: use nullptr
   // CHECK-MESSAGES: :[[@LINE-2]]:24: warning: use nullptr
   // CHECK-FIXES: a[2] = {ENTRY(nullptr), {nullptr}};
 #undef ENTRY
 }
+
+// One of the ancestor of the cast is a NestedNameSpecifierLoc.
+class NoDef;
+char function(NoDef *p);
+#define F(x) (sizeof(function(x)) == 1)
+template<class T, T t>
+class C {};
+C<bool, F(0)> c;
+// CHECK-MESSAGES: :[[@LINE-1]]:11: warning: use nullptr
+// CHECK-FIXES: C<bool, F(nullptr)> c;
+#undef F