fix(cpp): a receiver declared as a class template's member type, like SkipList<Key, Comparator>::Iterator, is that template's member

[colbymchenry]

Summary

This is the follow-up that the #2569 A/B surfaced.

The C++ declarator regex read a declared type as a name plus one template argument list. So SkipList<Key, Comparator>::Iterator iter(&list); couldn't be read whole: the match started at Iterator, and C++ lookup from the calling function found a different class.

• In google/leveldb's skip-list tests, iter.Valid(), Seek() and key() linked to leveldb::Iterator.
• In facebook/rocksdb's skip-list tests, the same calls linked to IteratorBase.
• rocksdb's SkipListRep::Iterator and LookaheadIterator hold an InlineSkipList<const MemTableRep::KeyComparator&>::Iterator iter_; (and prev_). Their iter_.Valid() calls linked to the enclosing iterator's own methods, which the code doesn't call.

What changed:

• Reading the type: CPP_DECLARATOR_TYPE now reads Outer<Args>::Member as one type, so C++ lookup (cppClassWritten) finds the member in the class template. Declarations written with typename, over two lines, through a pointer, and as data members are all covered.

• Library templates: isCppLibraryType counts a member of a library template's specialization as a library type only when it is an iterator. std::vector<int>::iterator is the library's, never a project class named iterator, which is what main linked . calls to. Other members name another type that may be the project's, so their calls go on as before:

  • std::vector<Slice>::value_type;
  • gmock's typename std::tuple_element<N - 1, MatcherTuple>::type matcher.

  The existing test "a std trait or member type names another type, maybe the project's" relies on this rule.

Validation

• New test __tests__/cpp-template-member-types.test.ts (5 tests): 3 reproductions fail on main and pass here. 2 guards pass on both: a member alias BaseHyperClockCache<Table>::Shard*, and std::vector<Slice>::value_type.
• Mutations: switching off each part fails its tests:
  • the member read: the 3 reproductions;
  • the iterator rule: the std::vector<int>::iterator test;
  • the library-member rule: the value_type test and the existing cpp-library-type-receiver test.
• A/B (full index, main vs fix) on google/leveldb, fmtlib/fmt, redis (C control), facebook/rocksdb and protocolbuffers/protobuf. Every changed site was triaged.
  • leveldb: 33 calls in db/skiplist_test.cc moved from leveldb::Iterator::* to leveldb::SkipList::Iterator::*. All are correct.
  • rocksdb: 106 calls moved, all correct:
    • 38 in memtable/skiplist_test.cc moved from IteratorBase to SkipList::Iterator;
    • 38 in memtable/inlineskiplist_test.cc moved from IteratorBase to InlineSkipList::Iterator;
    • 30 in memtable/skiplistrep.cc moved from SkipListRep::Iterator to InlineSkipList::Iterator.
  • fmt, redis, protobuf: byte-identical. A first version without the library-member rule dropped one gmock call in fmt's vendored gtest (the tuple_element<…>::type matcher above). The rule restores it.
  • No edges were added or removed.
• Full suite, including every C/C++ test file: 7,135 passed, 0 failed.

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