fix(flutter): recover path dependency locations from pubspec.yaml

[pawelchcki]

Problem

flutter pub deps --json reports path dependencies as source: "path" but omits the description that carries their location:

{"name": "my_local_pkg", "source": "path", "kind": "direct", ...}

The package_config generator resolves path_value to "" for these, and the if path_value: guard then skips add_package entirely — so the package is silently dropped. Any workspace using a path dependency (a vendored package, a monorepo with several local packages, generated API clients kept in-tree) builds without it and fails later on unresolved imports, with nothing pointing at the cause.

Fix

Recover the location from the pubspec that declares the dependency, and use it only as a fallback when the JSON has no path of its own — so nothing changes for the cases that already work.

Applied at all three sites that resolve a path dependency: both copies of the package_config generator and the pubspec.lock synthesis.

Note on the parsing

The lookup is a small indentation-aware scan rather than a YAML parse. These scripts run with whatever bare python3 is on the host and cannot assume PyYAML is available. It only has to handle the shape pub itself requires:

dependencies:
  my_local_pkg:
    path: ../my_local_pkg

Happy to swap it for something stricter if you would rather take a dependency here.

Testing

Exercised against a real app with three path dependencies (two generated API clients and a vendored package). Before: all three missing from package_config.json and the build fails on unresolved imports. After: all three resolve, and a full web build, test suite and analyze run pass.

Marked draft — tell me how you would like the parsing handled and I will adjust before marking ready.