fix(cpp): a call on a data member of the caller's class reaches its type's method, wherever the class is declared

[colbymchenry]

Summary

C++ receiver inference reads back through the call's file, then the header of the same name (foo.cc → foo.h). A data member of the calling method's class declared anywhere else was never read, and calls on it were guessed by the receiver's name.

facebook/rocksdb declares DBImpl in db_impl.h, while its methods live in db_impl_write.cc, db_impl_compaction_flush.cc, db_impl_open.cc and more. On main before #2532 (c19f0284), 684 of the 686 calls on x_ receivers in those files were name guesses at 0.65/0.7 (versions_->GetColumnFamilySet() at 0.7), and 385 more were unresolved.

Follows #2532 (merged as 79cd737b), which this was built and measured on.

What changed (name-matcher.ts)

• Member lookup at the caller's boundary. Where the backward scan leaves the calling function, the name is looked up as a data member of the function's class before anything outside it, as C++ does: block scopes, then the class and its bases, then namespaces. This is cppCallersMember:

  • the class's own declaration lines, wherever the class is declared (cppDataMemberIn, memoized per declaration and name);
  • of several classes sharing a qualified name, the declaration in the caller's own translation unit (fix(cpp): a call a method makes with no receiver links to its class's own or inherited method #2479's cppScopeDeclarations);
  • then the classes it derives from, through their base edges, skipping a base that depends on the template's parameters (a bare name isn't looked up there);
  • a gtest TEST_F(Fixture, …) / TEST_P body is a method of a class derived from its fixture, so db_ there is the fixture's member (cppTestFixture).

  An earlier function's local of the same name, which the old scan reached first, no longer wins over the member.

• Same record, same rules. The member goes into the declaration record as the caller's own, with its class as the lookup site (declared). So fix(cpp): a call on a declared pointer, value or reference reaches the class its type names, not a namesake #2493's lookup, the library-type gate, fix(cpp): a -> call on a smart pointer or optional reaches the type it holds #2440's held-type path (std::unique_ptr<VersionSet> versions_) and fix(cpp): a call on an auto variable or a chained call reaches the class C++ finds, not a namesake #2532's chains all apply.

• What stays as before:

  • a member of a template parameter's type (TComparator cmp_);
  • a member of an alias of one (using Shard = typename ClockCache::Shard;, or protobuf's using MapFieldBase = std::conditional_t<kIsMutable, …>, which made isCppTemplateDependentType count std traits too);
  • a name the scan saw an unreadable declaration of in the function (auto mutex_ = Make();).

• Reading members correctly:

  • Only declarations outside parentheses count, and not a name an argument list follows. Method declarations have no nodes, so their parameters are in the class's lines: rocksdb's DB::CreateColumnFamilies(…, std::vector<…>* column_families) read as a member of DBImpl.
  • Block comments are followed across lines. cppCodeOf takes a code line that starts with a dereference (*first_key, scratch);) for a comment, which left the paren depth open for the rest of the class.
  • String literals are blanked.

• cppExpressionType's own member fallback (from fix(cpp): a range-based for loop over auto elements has the element type of its range #2492, for loop ranges) is now redundant and was removed.

Validation

Site-keyed edge diffs (diff-sites.mjs) against #2532's tip (978709dc; main's 79cd737b has the same tree), both arms built the same way, kernel included:

repo	removed	added	retargeted	metadata-only
google/leveldb	7	40	51	48
fmtlib/fmt	10	37	36	46
facebook/rocksdb	695	2,454	7,303	5,519
protocolbuffers/protobuf	266	162	405	753

Against c19f0284, main before #2532 (both PRs together): leveldb −7 / +75 / 51 / 48, fmt −13 / +143 / 47 / 81, rocksdb −897 / +5,510 / 8,060 / 6,035, protobuf −435 / +637 / 423 / 824. Nodes and files are identical.

Removed, every group read:

• rocksdb (695): calls on members of library types whose name guesses reached project classes:

  • result_map_.find (std::unordered_map) → toku::omt::find (104);
  • saved_value_.capacity (std::string) → autovector (102);
  • cf_name_.c_str → gtest's FilePath (78);
  • compaction_queue_.empty (std::deque), std::set / std::optional / std::thread / std::mutex / std::counting_semaphore / std::array members, smart pointers' own get / reset.

  Plus edits_.size() (10). Main's 0.9 there came from another class's autovector member above the method, while this class's own std::vector<VersionEdit> edits_ is declared below it.

• protobuf (266):

  • members of descriptor classes whose accessors the index doesn't hold (const Descriptor* descriptor_, enum_, foo_file_), fix(cpp): a call on a declared pointer, value or reference reaches the class its type names, not a namesake #2493's policy;
  • library-type members;
  • members of generated messages the index doesn't hold, which get no edge just as a declared local of those types already gets none on main.

• fmt (10) and leveldb (7): std::vector / std::string members, in fmt's vendored gtest and in leveldb's DBIter.

Retargeted, every group read, all wrong→right:

• rocksdb:
  • 4,309 gtest bodies' db_->… (ModelDB at 0.65 → DB at 0.9);
  • 251 + 124 + 104 iterator members (→ IteratorBase, InternalIteratorBase, CompactionIterator), and 80 MemTableRep::Iterator → IteratorBase (auto it = db_->NewIterator(…) in gtest bodies, the original namesake);
  • 264 write_batch_ → WriteBatchWithIndex;
  • 368 TransactionDB / StackableDB, 299 env_ → SpecialEnv's EnvWrapper;
  • the wrapper classes in env.h / file_system.h, each with its own target_ (0.9→0.9: the old scan took the nearest target_ above, another wrapper's);
  • ShortenedIndexBuilder, CompactionProxy, ThreadStatusUpdater and so on.
• protobuf: 340 Java generators' context_->… → compiler::java::Context (137 of them a 0.9 namesake hpb_generator::Context); TextFormat::FieldValuePrinter, GzipOutputStream::sub_stream_, ParserImpl::error_collector_.
• leveldb: IteratorWrapper::iter_ → Iterator, MemTableIterator::iter_ → SkipList::Iterator, db_ → DB.

Added: calls on typed members, and chains through them (db_->CompactRange(…).PermitUncheckedError()).

Metadata-only: the same target, now at 0.9.

The A/B rounds also caught three mistakes before this version: parameters read as members, the comment guess, and an alias check that stopped at a mid-name alias (MemTable::Table::Iterator). Each now has a test.

Tests: __tests__/cpp-member-receiver.test.ts, 10 cases:

• 4 fail on fix(cpp): a call on an auto variable or a chained call reaches the class C++ finds, not a namesake #2532's code: the rocksdb reproduction; a member below an inline method plus one a base declares; a gtest fixture member; the class's own member, not a nested class's.
• 6 guard behavior that must not change: the caller's translation unit's class; a dependent base; an unreadable local; a method's parameter or a method; a member of a template parameter's type; an alias of one.
• 14 mutations, one per guard or branch, each fail a test.
• Full suite: 6,973 passed, 0 failed, 80 skipped.

CPU (rocksdb, full index, process CPU time, interleaved; main c19f0284 vs this branch on top of #2532): main 151.3 / 154.6 / 153.1 s vs 147.1 / 141.0 / 140.6 s. The member lookup is memoized per caller and name, and per class declaration; no measurable cost.

Not in this PR

• A local declared T* const name = … isn't read by the declarator pattern. That's older than this change: rocksdb's Iterator* const iter = iter_guard.get();.
• Bare calls in a gtest body to the fixture's methods (auto iter = NewIterator(…)) still go through the name strategies. Most of the 111 remaining rocksdb MemTableRep::Iterator edges come from these; the other 42 are memtable.cc's own, and right. There were 342 before fix(cpp): a call on an auto variable or a chained call reaches the class C++ finds, not a namesake #2532 and 181 after it.

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