tox-poetry-installer/README.md

tox-poetry-installer

A plugin for Tox that allows test environment dependencies to be installed using Poetry from its lockfile.

⚠️ This project is alpha software and should not be used in production environments ⚠️

Documentation

• Installation
• Quick Start
• Usage Examples
• Known Drawbacks and Problems
• Why would I use this? (What problems does this solve?)
• Developing
• Contributing
• Roadmap
  • Path to Beta
  • Path to Stable

Related resources:

• Poetry Python Project Manager
• Tox Automation Project
• Poetry Dev-Dependencies Tox Plugin
• Poetry Tox Plugin
• Other Tox plugins

Installation

Add the plugin as a development dependency of a Poetry project:

~ $: poetry add tox-poetry-installer --dev

Confirm that the plugin is installed, and Tox recognizes it, by checking the Tox version:

~ $: poetry run tox --version
3.20.0 imported from .venv/lib64/python3.8/site-packages/tox/__init__.py
registered plugins:
    tox-poetry-installer-0.2.2 at .venv/lib64/python3.8/site-packages/tox_poetry_installer.py

If using Pip, ensure that the plugin is installed to the same environment as Tox:

# Calling the virtualenv's 'pip' binary directly will cause pip to install to that virtualenv
~ $: /path/to/my/automation/virtualenv/bin/pip install tox
~ $: /path/to/my/automation/virtualenv/bin/pip install tox-poetry-installer

Quick Start

To require a Tox environment install all it's dependencies from the Poetry lockfile, add the require_locked_deps = true option to the environment configuration and remove all version specifiers from the dependency list. The versions to install will be taken from the lockfile directly:

[testenv]
description = Run the tests
require_locked_deps = true
deps =
    pytest
    pytest-cov
    black
    pylint
    mypy
commands = ...

To require specific dependencies be installed from the Poetry lockfile, and let the rest be installed using the default Tox installation backend, add the suffix @poetry to the dependencies. In the example below the pytest, pytest-cov, and black dependencies will be installed from the lockfile while pylint and mypy will be installed using the versions specified here:

[testenv]
description = Run the tests
require_locked_deps = true
deps =
    pytest@poetry
    pytest-cov@poetry
    black@poetry
    pylint >=2.5.0
    mypy == 0.770
commands = ...

Note: Regardless of the settings outlined above, all dependencies of the project package (the one Tox is testing) will always be installed from the lockfile.

Usage Examples

After installing the plugin to a project your Tox automation is already benefiting from the lockfile: when Tox installs your project package to one of your environments, all the dependencies of your project package will be installed using the versions specified in the lockfile. This happens automatically and requires no configuration changes.

But what about the rest of your Tox environment dependencies?

Let's use an example tox.ini file, below, that defines two environments: the main testenv for running the project tests and testenv:check for running some other helpful tools:

[tox]
envlist = py37, static
isolated_build = true

[testenv]
description = Run the tests
deps =
    pytest == 5.3.0
commands = ...

[testenv:check]
description = Static formatting and quality enforcement
deps =
    pylint >=2.4.4,<2.6.0
    mypy == 0.770
    black --pre
commands = ...

Let's focus on the testenv:check environment first. In this project there's no reason that any of these tools should be a different version than what a human developer is using when installing from the lockfile. We can require that these dependencies be installed from the lockfile by adding the option require_locked_deps = true to the environment config, but this will cause an error:

[testenv:check]
description = Static formatting and quality enforcement
require_locked_deps = true
deps =
    pylint >=2.4.4,<2.6.0
    mypy == 0.770
    black --pre
commands = ...

Running Tox using this config gives us this error:

tox_poetry_installer.LockedDepVersionConflictError: Locked dependency 'pylint >=2.4.4,<2.6.0' cannot include version specifier

This is because we told the Tox environment to require all dependencies be locked, but then also specified a specific version constraint for Pylint. With the require_locked_deps = true setting Tox expects all dependencies to take their version from the lockfile, so when it gets conflicting information it errors. We can fix this by simply removing all version specifiers from the environment dependency list:

[testenv:check]
description = Static formatting and quality enforcement
require_locked_deps = true
deps =
    pylint
    mypy
    black
commands = ...

Now all the dependencies will be installed from the lockfile. If Poetry updates the lockfile with a new version then that updated version will be automatically installed when the Tox environment is recreated.

Now let's look at the testenv environment. Let's make the same changes to the testenv environment that we made to testenv:check above; remove the PyTest version and add require_locked_deps = true. Then imagine that we want to add the Requests library to the test environment: we can add requests as a dependency of the test environment, but this will cause an error:

[testenv]
description = Run the tests
require_locked_deps = true
deps =
    pytest
    requests
commands = ...

Running Tox with this config gives us this error:

tox_poetry_installer.LockedDepNotFoundError: No version of locked dependency 'requests' found in the project lockfile

This is because requests is not in our lockfile yet. Tox will refuse to install a dependency that isn't in the lockfile to an an environment that specifies require_locked_deps = true. We can fix this by running poetry add requests --dev to add it to the lockfile.

Now let's combine dependencies from the lockfile with dependencies that are specified in-line in the Tox environment configuration. This isn't generally recommended, but it is a valid use case and fully supported by this plugin. Let's modify the testenv configuration to install PyTest from the lockfile but then install an older version of the Requests library.

The first thing to do is remove the require_locked_deps = true setting so that we can install Requests as an unlocked dependency. Then we can add our version specifier to the requests entry in the dependency list:

[testenv]
description = Run the tests
deps =
    pytest
    requests >=2.2.0,<2.10.0
commands = ...

However we still want pytest to be installed from the lockfile, so the final step is to tell Tox to install it from the lockfile by adding the suffix @poetry to the pytest entry in the dependency list:

[testenv]
description = Run the tests
deps =
    pytest@poetry
    requests >=2.2.0,<2.10.0
commands = ...

Now when the testenv environment is created it will install PyTest (and all of its dependencies) from the lockfile while it will install Requests (and all of its dependencies) using the default Tox installation backend.

Known Drawbacks and Problems

• The following tox.ini configuration options have no effect on the dependencies installed from the Poetry lockfile (note that they will still affect unlocked dependencies):

  • install_command
  • pip_pre
  • downloadcache (deprecated)
  • download
  • indexserver
  • usedevelop

• Tox environments automatically inherit their settings from the main testenv environment. This means that if the require_locked_deps = true is specified for the testenv environment then all environments will also require locked dependencies. This can be overwritten by explicitly specifying require_locked_deps = false on child environments where unlocked dependencies are needed.

• There are a handful of packages that cannot be installed from the lockfile, whether as specific dependencies or as transient dependencies (dependencies of dependencies). This is due to an ongoing discussion in the Poetry project; the list of dependencies that cannot be installed from the lockfile can be found here. This plugin will skip these dependencies entirely, but log a warning when they are encountered.

Why would I use this?

Introduction

The lockfile is a file generated by a package manager for a project that records what dependencies are installed, the versions of those dependencies, and any additional metadata that the package manager needs to recreate the local project environment. This allows developers to have confidence that a bug they are encountering that may be caused by one of their dependencies will be reproducible on another device. In addition, installing a project environment from a lockfile gives confidence that automated systems running tests or performing builds are using the same environment as a developer.

Poetry is a project dependency manager for Python projects, and so it creates and manages a lockfile so that its users can benefit from all the features described above. Tox is an automation tool that allows Python developers to run tests suites, perform builds, and automate tasks within self-contained Python virtual environments. To make these environments useful Tox supports installing dependencies in each environment. However, since these environments are created on the fly and Tox does not maintain a lockfile, there can be subtle differences between the dependencies a developer is using and the dependencies Tox uses.

This is where this plugin comes into play.

By default Tox uses Pip to install the PEP-508 compliant dependencies to a test environment. This plugin extends the default Tox dependency installation behavior to support installing dependencies using a Poetry-based installation method that makes use of the dependency metadata from Poetry's lockfile.

The Problem

Environment dependencies for a Tox environment are usually specified in PEP-508 format, like the below example:

# from tox.ini
...

[testenv]
description = Some very cool tests
deps =
    foo == 1.2.3
    bar >=1.3,<2.0
    baz

...

Let's assume these dependencies are also useful during development, so they can be added to the Poetry environment using this command:

poetry add --dev \
   foo==1.2.3 \
   bar>=1.3,<2.0 \
   baz

However there is a potential problem that could arise from each of these environment dependencies that would only appear in the Tox environment and not in the Poetry environment in use by a developer:

• The foo dependency is pinned to a specific version: let's imagine a security vulnerability is discovered in foo and the maintainers release version 1.2.4 to fix it. A developer can run poetry remove foo and then poetry add foo^1.2 to get the new version, but the Tox environment is left unchanged. The development environment, as defined by the lockfile, is now patched against the vulnerability but the Tox environment is not.

• The bar dependency specifies a dynamic range: a dynamic range allows a range of versions to be installed, but the lockfile will have an exact version specified so that the Poetry environment is reproducible; this allows versions to be updated with poetry update rather than with the remove and add commands used above. If the maintainers of bar release version 1.6.0 then the Tox environment will install it because it is valid for the specified version range. Meanwhile the Poetry environment will continue to install the version from the lockfile until poetry update bar explicitly updates it. The development environment is now has a different version of bar than the Tox environment.

• The baz dependency is unpinned: unpinned dependencies are generally a bad idea, but here it can cause real problems. Poetry will interpret an unbound dependency using the carrot requirement but Pip (via Tox) will interpret it as a wildcard. If the latest version of baz is 1.0.0 then poetry add baz will result in a constraint of baz>=1.0.0,<2.0.0 while the Tox environment will have a constraint of baz==*. The Tox environment can now install an incompatible version of baz and any errors that causes cannot be replicated using poetry update.

All of these problems can apply not only to the dependencies specified for a Tox environment, but also to the dependencies of those dependencies, those dependencies' dependencies, and so on.

The Solution

This plugin allows dependencies specified in Tox environment take their version directly from the Poetry lockfile without needing an independent version to be specified in the Tox environment configuration. The modified version of the example environment given below appears less stable than the one presented above because it does not specify any versions for its dependencies:

# from tox.ini
...

[testenv]
description = Some very cool tests
require_locked_deps = true
deps =
    foo
    bar
    baz

...

However with the tox-poetry-installer plugin installed the require_locked_deps = true setting means that Tox will install these dependencies from the Poetry lockfile so that the version installed to the Tox environment exactly matches the version Poetry is managing. When poetry update updates the lockfile with new versions of these dependencies, Tox will automatically install these new versions without needing any changes to the configuration.

Developing

This project requires a developer to have Poetry version 1.0+ installed on their workstation, see the installation instructions here.

# Clone the repository...
# ...over HTTPS
git clone https://github.com/enpaul/tox-poetry-installer.git
# ...over SSH
git clone git@github.com:enpaul/tox-poetry-installer.git

# Create a the local project virtual environment and install dependencies
cd tox-poetry-installer
poetry install

# Install pre-commit hooks
poetry run pre-commit install

# Run tests and static analysis
poetry run tox

Contributing

All project contributors and participants are expected to adhere to the Contributor Covenant Code of Conduct, Version 2.

The devel branch has the latest (potentially unstable) changes. The tagged versions correspond to the releases on PyPI.

• To report a bug, request a feature, or ask for assistance, please open an issue on the Github repository.
• To report a security concern or code of conduct violation, please contact the project author directly at ethan dot paul at enp dot one.
• To submit an update, please fork the repository and open a pull request.

Roadmap

This project is under active development and is classified as alpha software, not yet ready for usage in production environments.

• Beta classification will be assigned when the initial feature set is finalized
• Stable classification will be assigned when the test suite covers an acceptable number of use cases

Path to Beta

• Verify that primary package dependencies (from the .package env) are installed correctly using the Poetry backend.
• Support the extras Tox configuration option (#4)
• Add per-environment Tox configuration option to fall back to default installation backend.
• Add warnings when an unsupported Tox configuration option is detected while using the Poetry backend. (#5)
• Add trivial tests to ensure the project metadata is consistent between the pyproject.toml and the module constants.
• Update to use poetry-core and improve robustness of the Tox and Poetry module imports to avoid potentially breaking API changes in upstream packages. (#2)
• Find and implement a way to mitigate the UNSAFE_DEPENDENCIES issue in Poetry. (#6)
• Fix logging to make proper use of Tox's logging reporter infrastructure

Path to Stable

Everything in Beta plus...

• Add tests for each feature version of Tox between 2.3 and 3.20
• Add tests for Python-3.6, 3.7, and 3.8
• Add Github Actions based CI
• Add CI for CPython, PyPy, and Conda
• Add CI for Linux and Windows