Can't find package when using `--package` without a `py.typed` file

[AAriam]

Crash Report

This is similar to #17048:

When an installed package does not contain a py.typed file, trying to type-check it with mypy --package returns a Can't find package error.

To Reproduce

1. Create a package:

.
├── src/
│   └── test_package/
│       └── __init__.py
└── pyproject.toml

with pyproject.toml:

[project]
name = "test_package"
version = "0.0.0"

[build-system]
requires = ["setuptools >= 72.1.0"]
build-backend = "setuptools.build_meta"

[tool.setuptools.packages.find]
where = ["src"]

2. Install the package: pip install .
3. Run mypy: mypy --package test_package

Your Environment

• Mypy version used: mypy 1.13.0 (compiled: yes)
• Mypy command-line flags: --package
• Python version used: 3.13.0
• Operating system and version: macOS 13.7

[brianschubert]

Hi AAriam, this is expected behavior. Mypy requires a py.typed marker file in order to use type information shipped with an installed package. After #17908 (which should land with v1.14), you should see a slightly more informative error message:

Package 'test_package' cannot be type checked due to missing py.typed marker. See https://mypy.readthedocs.io/en/stable/installed_packages.html for more details

See Creating PEP 561 compatible packages from the mypy docs and Packaging Type Information from PEP 561 for more details.