From 5def1a46edac5c389eda2916a227a120e1653128 Mon Sep 17 00:00:00 2001
From: Travis Hathaway <travis.j.hathaway@gmail.com>
Date: Thu, 8 Jun 2023 16:03:38 +0200
Subject: [PATCH] adding the rough draft of the optional dependencies CEP

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+<table>
+    <tr><td> Title </td><td> Optional Dependencies</td>
+    <tr><td> Status </td><td> Draft </td></tr>
+    <tr><td> Author(s) </td><td> Travis Hathaway &lt;travis.j.hathaway@gmail.com&gt;</td></tr>
+    <tr><td> Created </td><td> June 7, 2023</td></tr>
+    <tr><td> Updated </td><td> June 7, 2023</td></tr>
+    <tr><td> Discussion </td><td> NA </td></tr>
+    <tr><td> Implementation </td><td> NA </td></tr>
+</table>
+
+[python-extras]: https://peps.python.org/pep-0508/#extras
+[cargo-features]: https://doc.rust-lang.org/cargo/reference/features.html
+[original-cep]: https://github.com/conda-incubator/ceps/pull/9
+[conda-issue-7502]: https://github.com/conda/conda/issues/7502
+[conda-issue-11053]: https://github.com/conda/conda/issues/11053
+[mamba-issue-245]: https://github.com/mamba-org/boa/issues/245
+
+## Abstract
+
+This CEP proposes a new method for including optional dependencies when installing conda packages.
+Optional dependencies are largely inspired by [Python's "extras"][python-extras] and
+[Cargo's "features"][cargo-features]. When implemented, package builders will have a  way to specify
+dependencies which are not required but if installed would enable different features that are
+not included by default.
+
+## Motivation
+
+Optional dependencies as a feature has been requested for conda compatible package managers for quite
+some time (e.g. [conda-7502][conda-issue-7502], [conda-11053][conda-issue-11053], and [mamba-245][mamba-issue-245]).
+Adding this feature to the conda ecosystem would also give package managers greater flexibility when
+instructing users how to install and use their software. For example, a package could support multiple
+variants by using this methodology. If a package supported either `seaborn` or `matplotlib`,
+users could specify either `seaborn` or `matplotlib` as an optional dependency.
+
+
+## Specification
+
+This section will first show how this works from the end user point of view and then talks about
+how it will work for package builders. Updates to the `repodata.json` format will also be discussed.
+
+### User point of view
+
+When a user goes to install a package, they will specify optional dependencies with the following syntax:
+
+```bash
+# For a single optional dependency
+conda install package_name[optional_a]
+
+# For multiple optional dependencies
+conda install package_name[optional_a,optional_b]
+```
+
+Optional dependencies can also be specified by using the keyword argument syntax:
+
+```bash
+# For a single optional dependency
+conda install package_name[extras=optional_a]
+
+# For multiple optional dependencies
+conda install package_name[extras=optional_a,optional_b]
+```
+
+Later, when running commands like `conda list` the packages will show up as "virtual metapackages", which
+look like the following:
+
+```bash
+conda list
+
+# Name                    Version                   Build  Channel
+package_name              0.1.0                h0c17e10_0  conda-forge
+package_name@optional_a   0.1.0              pyhd8ed1ab_0  conda-forge
+package_name@optional_b   0.1.0              pyhd8ed1ab_0  conda-forge
+```
+
+When a user wants to later remove an optional dependency, they do so by referencing
+these "virtual metapackages":
+
+```bash
+conda remove package_name@optional_a
+```
+
+
+### Packager point of view
+
+**TBD**
+
+
+## Rationale
+
+**TBD**
+
+
+## Backwards compatibility
+
+**TBD**
+
+
+## Sample implementation
+
+**TBD**
+
+
+## FAQ
+
+**TBD**
+
+
+## Resolution
+
+**TBD**
+
+
+## References
+
+- [Python extras][python-extras]
+- [Cargo features][cargo-features]
+- [First CEP for optional dependencies by @wolfv][original-cep]
+- [Conda issue: "Optional groups of dependencies"][conda-issue-7502]
+- [Conda issue: "ENH: More powerful syntax for build variants & optional package-extras"][conda-issue-11053]
+- [Mamba issue: "[recipe-spec] Allow for arbitrary optional dependencies"][mamba-issue-245]
+
+
+## Copyright
+
+All CEPs are explicitly [CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/).