feat: Create features and environments from extras

docs/advanced/pyproject_toml.md

@@ -103,6 +103,49 @@ matplotlib = "*"
 This would result in the conda dependencies being installed and the pypi dependencies being ignored.
 As pixi takes the conda dependencies over the pypi dependencies.
 
+## Optional dependencies
+If your python project includes groups of optional dependencies, pixi will automatically interpret them as [pixi features](../configuration.md#the-feature-table) of the same name with the associated `pypi-dependencies`.
+
+You can add them to pixi environments manually, or use `pixi init` to setup the project, which will create one environment per feature. Self-references to other groups of optional dependencies are also handled.
+
+For instance, imagine you have a project folder with a `pyproject.toml` file similar to:
+```toml
+[project]
+name = "my_project"
+dependencies = ["package1"]
+
+[project.optional-dependencies]
+test = ["pytest"]
+all = ["package2","my_project[test]"]
+```
+
+Running `pixi init` in that project folder will transform the `pyproject.toml` file into:
+```toml
+[project]
+name = "my_project"
+dependencies = ["package1"]
+
+[project.optional-dependencies]
+test = ["pytest"]
+all = ["package2","my_project[test]"]
+
+[tool.pixi.project]
+channels = ["conda-forge"]
+platforms = ["linux-64"] # if executed on linux
+
+[tool.pixi.environments]
+default = {features = [], solve-group = "default"}
+test = {features = ["test"], solve-group = "default"}
+all = {features = ["all", "test"], solve-group = "default"}
+```
+In this example, three environments will be created by pixi:
+
+ - **default** with 'package1' as pypi dependency
+ - **test** with 'package1' and 'pytest' as pypi dependencies
+ - **all** with 'package1', 'package2' and 'pytest' as pypi dependencies
+
+All environments will be solved together, as indicated by the common `solve-group`, and added to the lock file. You can edit the `[tool.pixi.environments]` section manually to adapt it to your use case (e.g. if you do not need a particular environment).
+
 ## Example
 As the `pyproject.toml` file supports the full pixi spec with `[tool.pixi]` prepended an example would look like this:
 ```toml title="pyproject.toml"

examples/flask-hello-world-pyproject/.gitattributes

@@ -0,0 +1,2 @@
+# GitHub syntax highlighting
+pixi.lock linguist-language=YAML

examples/flask-hello-world-pyproject/.gitignore

@@ -1 +1,3 @@
+# pixi environments
+.pixi
 *.egg-info

examples/flask-hello-world-pyproject/pyproject.toml

@@ -4,7 +4,10 @@ version = "0.1.0"
 description = "Example how to get started with flask in a pixi environment."
 readme = "README.md"
 requires-python = ">=3.11"
-dependencies = ["flask==2.*", "pytest"]
+dependencies = ["flask==2.*"]
+
+[project.optional-dependencies]
+test = ["pytest"]
 
 [build-system]
 requires = ["setuptools", "wheel"]
@@ -17,6 +20,12 @@ platforms = ["linux-64", "osx-arm64", "osx-64", "win-64"]
 [tool.pixi.pypi-dependencies]
 flask-hello-world-pyproject = { path = ".", editable = true }
 
+[tool.pixi.environments]
+default = { features = [], solve-group = "default" }
+test = { features = ["test"], solve-group = "default" }
+
 [tool.pixi.tasks]
 start = "python -m flask --app flask_hello_world_pyproject.app:app run --port=5050"
+
+[tool.pixi.feature.test.tasks]
 test = "pytest -v tests/*"