Namespace packages supported by default?

I notice in the changelog that 0.990 adds support for namespace packages by default.

I've been using mypy on namespace packages (jaraco, svg, backports, and others) for some time now (https://github.com/jaraco/skeleton/commit/7455f2f25310b2d778a648e45d32033ccc790946).

With the release of mypy 0.990, however, tests have started failing across all projects with namespace packages:

error: Source file found twice under different module names: "collections" and "jaraco.collections"

The change log indicates that 0.990 adds support for namespace packages by default. Annoyingly, this change has had the opposite effect for my projects. I find that I can restore functionality by adding explicit_package_bases = True to the config file (or equivalent command line). It's slightly annoying to have to add this configuration to all of my projects just to support some projects with namespace packages.

Is it possible that explicit package bases will become default in the future?

mypy 0.990 の changelog と explicit_package_bases 設定の挙動を確認します。jaraco や backports のような namespace package プロジェクトで重複モジュールエラーを再現し、その後、期待されるデフォルトの挙動を判断します。デフォルトの挙動が決定され、影響を受ける namespace package のシナリオが正常に動作するか、明確に文書化されていれば完了です。