tox-poetry-installer/README.md

# tox-poetry-installer

A plugin for [Tox](https://tox.readthedocs.io/en/latest/) that allows test environment
dependencies to be installed using [Poetry](https://python-poetry.org/) from its lockfile.

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

[![ci-status](https://github.com/enpaul/tox-poetry-installer/workflows/CI/badge.svg?event=push)](https://github.com/enpaul/tox-poetry-installer/actions)
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[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

**Documentation**

* [Installation](#installation)
* [Quick Start](#quick-start)
* [Plugin Usage](#reference-and-usage)
* [Reference](#reference)
  * [Configuration Options](#configuration-options)
  * [Command-line Arguments](#command-line-arguments)
  * [Errors](#errors)
  * [Advanced Usage](#advanced-usage)
* [Why would I use this?](#why-would-i-use-this) (What problems does this solve?)
* [Developing](#developing)
* [Contributing](#contributing)
* [Roadmap](#roadmap)
  * [Path to Beta](#path-to-beta)
  * [Path to Stable](#path-to-stable)

Related resources:
* [Poetry Python Project Manager](https://python-poetry.org/)
* [Tox Automation Project](https://tox.readthedocs.io/en/latest/)
* [Other Tox plugins](https://tox.readthedocs.io/en/latest/plugins.html)

Similar projects:
* [Poetry Dev-Dependencies Tox Plugin](https://github.com/sinoroc/tox-poetry-dev-dependencies)
* [Poetry Tox Plugin](https://github.com/tkukushkin/tox-poetry)


## 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-0.5.0 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
```

**Note:** While it is possible to install this plugin using Tox's
[`requires`](https://tox.readthedocs.io/en/latest/config.html#conf-requires)
configuration option, it is not recommended. Dependencies from the `requires` option are
installed using the default Tox installation backend which opens up the
[possibility of transient dependency problems](#why-would-i-use-this) in your automation
environment.


## Quick Start

To add dependencies from the lockfile to a Tox environment, add the option `locked_deps`
to the environment configuration and list names of dependencies (with no version
specifier) under it:

```ini
[testenv]
description = Some very cool tests
locked_deps =
    black
    pylint
    mypy
commands = ...
```

The standard `deps` option can be used in parallel with the `locked_deps` option to
install unlocked dependencies (dependencies not in the lockfile) alongside locked
dependencies:

```ini
[testenv]
description = Some very cool tests
locked_deps =
    black
    pylint
    mypy
deps =
    pytest == 6.1.1
    pytest-cov >= 2.10, <2.11
commands = ...
```

Alternatively, to quickly install all Poetry dev-dependencies to a Tox environment, add the
`install_dev_deps =  true` option to the environment configuration.

**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.


## Reference

### Configuration Options

All options listed below are Tox environment options and can be applied to one or more
environment sections of the `tox.ini` file. They cannot be applied to the global Tox
configuration section.

**NOTE:** Environment settings applied to the main `testenv` environment will be
inherited by child environments (i.e. `testenv:foo`) unless they are explicitly
overridden by the child environment's configuration.

#### `locked_deps`

* **Type:** multi-line list
* **Default:** `[]`

Names of packages in the Poetry lockfile to install to the Tox environment. All
dependencies specified here will be installed to the Tox environment using the details
given by the Poetry lockfile.

#### `require_locked_deps`


* **Type:** boolean
* **Default:** `false`

Whether the environment should allow unlocked dependencies (dependencies not in the
Poetry lockfile) to be installed alongside locked dependencies. If `true` then an error
will be raised if the environment specifies unlocked dependencies to install and the
plugin will block any other plugins from using the
[`tox_testenv_install_deps`](https://tox.readthedocs.io/en/latest/plugins.html#tox.hookspecs.tox_testenv_install_deps)
hook.

#### `install_dev_deps`

* **Type:** boolean
* **Default:** `false`

Whether all Poetry dev-dependencies should be installed to the environment. If `true`
then all dependencies specified in the
[`dev-dependencies` section](https://python-poetry.org/docs/pyproject/#dependencies-and-dev-dependencies)
of `pyproject.toml` will be installed automatically.

### Command-line Arguments

All arguments listed below can be passed to the `tox` command to modify runtime behavior
of the plugin.

#### `--require-poetry`

Indicates that Poetry is expected to be available to Tox and, if it is not, then the Tox
run should fail. If provided and the `poetry` package is not installed to the same
environment as the `tox` package then Tox will fail.

**NOTE:** See [Advanced Usage](installing-alongside-an-existing-poetry-installation)
for more information.

### Errors

If the plugin encounters an error while processing a Tox environment then it will mark
the environment as failed and set the environment status to one of the values below:

**NOTE:** In addition to the reasons noted below, the plugin can encounter errors if the
Poetry lockfile is not up-to-date with `pyproject.toml`. To resynchronize the
lockfile with the `pyproject.toml` run one of
[`poetry update`](https://python-poetry.org/docs/cli/#update) or
[`poetry lock`](https://python-poetry.org/docs/cli/#lock)

#### Poetry Not Installed Error

* **Status value:** `PoetryNotInstalledError`
* **Cause:** Indicates that the `poetry` module could not be imported from the same
  environment as the running `tox` module and the runtime flags specified
  [`--require-poetry`](#--require-poetry).
* **Resolution options:**
  * Install Poetry: ensure that `poetry` is installed to the same environment as `tox`.
  * Skip running the plugin: remove the `--require-poetry` flag from the runtime options.

**NOTE:** See [Advanced Usage](installing-alongside-an-existing-poetry-installation)
for more information.

#### Locked Dependency Version Conflict Error

* **Status value:** `LockedDepVersionConflictError`
* **Cause:** Indicates that a dependency specified in the [`locked_deps`](#locked_deps)
  configuration option in `tox.ini` includes a
  [PEP-508 version specifier](https://www.python.org/dev/peps/pep-0508/#grammar)
  (i.e. `pytest >=6.0, <6.1`).
* **Resolution options:**
  * Use the dependency version from the lockfile: remove any/all version specifiers
    from the item in the `locked_deps` list in `tox.ini`.
  * Do not install the dependency: remove the item from the `locked_deps` list in
    `tox.ini`.

#### Locked Dependency Not Found Error

* **Status value:** `LockedDepNotFoundError`
* **Cause:** Indicates that a dependency specified in the [`locked_deps`](#locked_deps)
  configuration option in `tox.ini` could not be found in the Poetry lockfile.
* **Resolution options:**
  * Add the dependency to the lockfile: run `poetry add <dependency>`;
    see [the Poetry documentation](https://python-poetry.org/docs/cli/#add) for more
    information.
  * Do not install the dependency: remove the item from the `locked_deps` list in
    `tox.ini`.

#### Extra Not Found Error

* **Status value:** `ExtraNotFoundError`
* **Cause:** Indicates that the [`extras`](https://tox.readthedocs.io/en/latest/config.html#conf-extras)
  configuration option specified a setuptools extra that is not configured by Poetry in
  `pyproject.toml`
* **Resolution options:**
  * Configure the extra: add a section for the named extra to the
    [`extras` section of `pyproject.toml`](https://python-poetry.org/docs/pyproject/#extras)
    and optionally assign dependencies to the named extra using the
    [`--optional` dependency setting](https://python-poetry.org/docs/cli/#options_3).
  * Remove the extra: remove the item from the `extras` list in `tox.ini`.

#### Locked Dependencies Required Error

* **Status value:** `LockedDepsRequiredError`
* **Cause:** Indicates that an environment with the [`require_locked_deps`](#require_locked_deps)
  configuration option also specified unlocked dependencies using
  [`deps`](https://tox.readthedocs.io/en/latest/config.html#conf-deps) option in
  `tox.ini`.
* **Resolution options:**
  * Remove all unlocked dependencies: remove the `deps` configuration option in
    `tox.ini`.
  * Allow unlocked dependencies: remove the `require_locked_deps` configuration option
    in `tox.ini` or explicitly set `require_locked_deps = false`.

### Advanced Usage

#### Unsupported Tox configuration options

The `tox.ini` configuration options listed below have no effect on the dependencies
installed by this plugin the Poetry lockfile. Note that these settings will still be
applied by the default Tox installation backend when installing unlocked dependencies
using the built-in `deps` option.

  * [`install_command`](https://tox.readthedocs.io/en/latest/config.html#conf-install_command)
  * [`pip_pre`](https://tox.readthedocs.io/en/latest/config.html#conf-pip_pre)
  * [`download`](https://tox.readthedocs.io/en/latest/config.html#conf-download)
  * [`indexserver`](https://tox.readthedocs.io/en/latest/config.html#conf-indexserver)
  * [`usedevelop`](https://tox.readthedocs.io/en/latest/config.html#conf-indexserver)

All of these options are obsoleted by using the Poetry backend. If a given package
installs successfully using Poetry (using either `poetry add <package>` or
`poetry install`) then the required configuration options are already properly set in
the Poetry configuration and the plugin will automatically use the same settings when
installing the package.

#### Reinstalling locked dependencies to a Tox environment

Updating the `poetry.lock` file will not automatically cause Tox to install the updated
lockfile specifications to the Tox environments that specify them.

The Tox environment(s) with updated locked dependencies must be deleted and recreated
using the [`--recreate`](https://tox.readthedocs.io/en/latest/config.html#cmdoption-tox-r)
runtime flag. Alternatively Tox can be configured to always recreate an environment by
setting the [`recreate`](https://tox.readthedocs.io/en/latest/config.html#conf-recreate)
option in `tox.ini`.

#### Installing Poetry's unsafe dependencies

There are several packages that cannot be installed from the lockfile because they are
excluded by Poetry itself. As a result these packages cannot be installed by this plugin
either as environment dependencies (passed directly to [`locked_deps`](#locked_deps)) or
as transient dependencies (a dependency of a locked dependency).

As of [Poetry-1.1.4](https://github.com/python-poetry/poetry/releases/tag/1.1.4) there
are four packages classified as "unsafe" by Poetry and excluded from the lockfile:

* `setuptools`
* `distribute`
* `pip`
* `wheel`

When one of these packages is encountered by the plugin a warning will be logged and
_**the package will not be installed to the environment**_. If the unsafe package
is required for the environment then it will need to be specified as an unlocked
dependency using the [`deps`](https://github.com/python-poetry/poetry/releases/tag/1.1.4)
configuration option in `tox.ini`, ideally with an exact pinned version.

* The set of packages excluded from the Poetry lockfile can be found at
  [`poetry.puzzle.provider.Provider.UNSAFE_DEPENDENCIES`](https://github.com/python-poetry/poetry/blob/master/poetry/puzzle/provider.py)
* There is an ongoing discussion of Poetry's handling of these packages at
  [python-poetry/poetry#1584](https://github.com/python-poetry/poetry/issues/1584)

#### Installing alongside an existing Poetry installation

The plugin specifies the `poetry` package as an optional dependency to support an
externally managed Poetry installation such as in a container or CI environment. This
gives greater flexibility when using Poetry arguments like `--no-root`, `--no-dev`, or
`--remove-untracked` which can cause Poetry to uninstall itself if Poetry is specified
as a dependency of one of the packages it is managing (like this plugin).

To have the plugin use the externally-managed Poetry package simply do not install the
`poetry` extra when installing this plugin:

```bash
# Installing Poetry as a dependency with the plugin
poetry add tox-poetry-installer[poetry]

# Relying on an externally managed Poetry installation
poetry add tox-poetry-installer
```

Note that Poetry is an optional dependency to support this use case _only_: Poetry must
be installed to the same environment as Tox for the plugin to function. To check that
the local environment has all of the required modules in scope run the below command:

```bash
python -c '\
  import tox;\
  import tox_poetry_installer;\
  from poetry.poetry import Poetry;\
'
```

**NOTE:** To force Tox to fail if Poetry is not installed, run the `tox` command with
the [`--require-poetry`](#--require-poetry) option.


## 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](https://python-poetry.org/) 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](https://tox.readthedocs.io/en/latest/#what-is-tox) is an automation tool
that allows Python developers to run tests suites, perform builds, and automate tasks within
self-contained [Python virtual environments](https://docs.python.org/3/tutorial/venv.html).
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](https://docs.python.org/3/tutorial/venv.html) 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:

```ini
# 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](https://python-poetry.org/docs/faq/#why-are-unbound-version-constraints-a-bad-idea),
  but here it can cause real problems. Poetry will interpret an unbound dependency using
  [the carrot requirement](https://python-poetry.org/docs/dependency-specification/#caret-requirements)
  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:

```ini
# from tox.ini
...

[testenv]
description = Some very cool tests
require_locked_deps = true
locked_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](https://python-poetry.org/docs/#installation).

```bash
# 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](CODE_OF_CONDUCT.md).

The `devel` branch has the latest (potentially unstable) changes. The
[tagged versions](https://github.com/enpaul/tox-poetry-installer/releases) 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](https://github.com/enpaul/tox-poetry-installer/issues/new).
* To report a security concern or code of conduct violation, please contact the project author
  directly at **‌me [at‌] enp dot‎ ‌one**.
* To submit an update, please
  [fork the repository](https://docs.github.com/en/enterprise/2.20/user/github/getting-started-with-github/fork-a-repo)
  and
  [open a pull request](https://github.com/enpaul/tox-poetry-installer/compare).


## 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

- [X] Verify that primary package dependencies (from the `.package` env) are installed
      correctly using the Poetry backend.
- [X] Support the [`extras`](https://tox.readthedocs.io/en/latest/config.html#conf-extras)
      Tox configuration option ([#4](https://github.com/enpaul/tox-poetry-installer/issues/4))
- [X] 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](https://github.com/enpaul/tox-poetry-installer/issues/5))
- [X] Add trivial tests to ensure the project metadata is consistent between the pyproject.toml
      and the module constants.
- [X] Update to use [poetry-core](https://github.com/python-poetry/poetry-core) and
      improve robustness of the Tox and Poetry module imports
      to avoid potentially breaking API changes in upstream packages. ([#2](https://github.com/enpaul/tox-poetry-installer/issues/2))
- [ ] Find and implement a way to mitigate the [UNSAFE_DEPENDENCIES issue](https://github.com/python-poetry/poetry/issues/1584) in Poetry.
      ([#6](https://github.com/enpaul/tox-poetry-installer/issues/6))
- [ ] Fix logging to make proper use of Tox's logging reporter infrastructure ([#3](https://github.com/enpaul/tox-poetry-installer/issues/3))
- [X] Add configuration option for installing all dev-dependencies to a testenv ([#14](https://github.com/enpaul/tox-poetry-installer/issues/14))

### 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
- [X] Add Github Actions based CI
- [ ] Add CI for CPython, PyPy, and Conda
- [ ] Add CI for Linux and Windows