Dart: calls to private members across part files are dropped since 1.6 #2466

Summary

Since 1.6, a Dart call to a private (_-prefixed) member defined in another file of the same library — the library file and its part files — no longer produces a calls edge. Dart privacy is per library, not per file, so these calls are legal and common: any library split into part files calls its own private helpers across those files. They disappear from callers / impact.

On a ~1,400-file Flutter app that splits its large libraries into part files, cross-file calls edges onto Dart private members went from 552 on 1.5.0 to 9 on 1.6.2. The overall edge count only dropped ~4% (1.6 also removed many wrong name-matched edges), so the loss is easy to miss.

Reproduction

// lib/greeter.dart
part 'greeter_format.dart';
part 'greeter_shout.dart';
part 'src/_greeter_whisper.dart';

class Greeter with _Formatting, _Shouting, _Whispering {
  String greet(String name) => _format(name); // library file -> private member in a part
  String hello() => _local();                 // same-file control
  String _local() => 'hi';
}

void _trace(String s) => print(s);

// lib/greeter_format.dart
part of 'greeter.dart';

mixin _Formatting {
  String _format(String name) {
    _trace(name); // part -> private top-level function in the library file
    return 'Hello, $name';
  }
}

// lib/greeter_shout.dart
part of 'greeter.dart';

mixin _Shouting on _Formatting {
  String shout(String name) => _format(name).toUpperCase(); // part -> sibling part
}

// lib/src/_greeter_whisper.dart
part of '../greeter.dart';

mixin _Whispering on _Formatting {
  String whisper(String name) => _format(name).toLowerCase(); // part in a subdirectory -> sibling part
}

npx @colbymchenry/codegraph@1.6.2 init -y .
sqlite3 .codegraph/codegraph.db "SELECT s.qualified_name, t.qualified_name FROM edges e
  JOIN nodes s ON s.id = e.source JOIN nodes t ON t.id = e.target WHERE e.kind = 'calls'"

Root cause

isVisibleAcrossFiles (src/resolution/name-matcher.ts) puts dart in PRIVATE_IS_FILE_LOCAL:

if (PRIVATE_IS_FILE_LOCAL.has(lang)) return candidate.visibility !== 'private';

and the Dart extractor marks every _-prefixed name private (src/extraction/languages/dart.ts). That holds for Kotlin / Java / C#, but in Dart a private name is visible across the whole library: the defining file plus every file its part directives name. It is the same shape as #2164 (the file-local rule dropping legal calls), here for Dart.

Still present on main @ b635dd467 (line 2805).

Suggested fix

main already has inSameDartLibrary (src/resolution/dart-libraries.ts, from #2391), so this may be a single line ahead of the PRIVATE_IS_FILE_LOCAL check:

if (lang === 'dart' && candidate.visibility === 'private')
  return inSameDartLibrary(ref.filePath, candidate.filePath, context);

I have not built main. I verified the equivalent change on 1.6.2: since 1.6.2 has no inSameDartLibrary, the check there resolves each file's part of target and compares libraries. Results:

• The reproduction above: 5 of 5 edges.
• The 1,400-file app: cross-file private calls edges went from 9 to 482. Compared with stock 1.6.2, 477 edges were added and 4 removed. A sample of the added edges were all real calls between parts of the same library; the 4 removed were wrong matches across two test files.