Frame out the env spec cep

cep-??.md

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+<table>
+<tr><td> Title </td><td> Environment yaml specification </td>
+<tr><td> Status </td><td> Draft </td></tr>
+<!-- <tr><td> Status </td><td> Draft | Proposed | Accepted | Rejected | Deferred | Implemented </td></tr> -->
+<tr><td> Author(s) </td>
+    <td>
+      Eric Dill
+      Marius van Niekerk
+      Jaime Rodríguez-Guerra
+      Albert DeFusco
+    </td>
+</tr>
+<tr><td> Created </td><td> March 28, 2023</td></tr>
+<tr><td> Updated </td><td> NA </td></tr>
+<tr><td> Discussion </td><td> NA </td></tr>
+<tr><td> Implementation </td><td> NA </td></tr>
+</table>
+
+## Abstract
+
+This CEP aims to formalize the current state of the environment.yaml specification.
+It notably does not attempt to address any proposed changes to the specification.
+That is currently being discussed elsewhere.
+
+## Motivation
+
+There are a number of existing projects that can accept the env.yml format as input.
+Each project that wants to use the env.yml spec has to implement their own parser.
+This is a problem because it means that there are multiple implementations of the same specification.
+This makes it difficult to evolve the specification because right now it is implicitly defined as however `conda-env` handles the env.yml file.
+This CEP aims to formalize the specification so that it can be used as a reference for other projects, including `conda-env`.
+There are [existing docs](https://conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html) that defines how a user should create an environment.yml file.
+From what I can tell this is the only formal specification for this file.
+It is the objective of this CEP to formalize the existing specification so that other projects can standardize on what they expect as input.
+Evolutions to this spec are expected and welcome, but are out of the scope for the initial proposal.
+
+Issues found in the wild that result from env.yaml not having a published spec:
+- [vscode issue #280](https://github.com/microsoft/vscode-python/issues/280)
+
+## Specification
+
+There are four keys that the conda env spec expects:
+
+`name`, `str`, specifying the name of the conda env that will be created.
+
+`channels`, `list`, specifying the channels that the solver should find and pull packages from
+
+`dependencies`, `list`, specifying the top-level dependencies that the solver should start with
+- `dependencies` also has an optional dict with the `pip` key that expects a `list` as its value. This key tells the solver to also include the listed dependencies to pull from pypi
+- Each non-pip `dependencies` entry must follow the form expected by the current [MatchSpec](https://github.com/conda/conda/blob/a8e441e3c0e80b0d4e1595579f7d9eaad2b0fb2b/conda/models/match_spec.py#L92) implementation. Some examples of currently supported dependency specs (at least at the time of this CEP):
+```
+Examples:
+    >>> str(MatchSpec(name='foo', build='py2*', channel='conda-forge'))
+    'conda-forge::foo[build=py2*]'
+    >>> str(MatchSpec('foo 1.0 py27_0'))
+    'foo==1.0=py27_0'
+    >>> str(MatchSpec('foo=1.0=py27_0'))
+    'foo==1.0=py27_0'
+    >>> str(MatchSpec('conda-forge::foo[version=1.0.*]'))
+    'conda-forge::foo=1.0'
+    >>> str(MatchSpec('conda-forge/linux-64::foo>=1.0'))
+    "conda-forge/linux-64::foo[version='>=1.0']"
+    >>> str(MatchSpec('*/linux-64::foo>=1.0'))
+    "foo[subdir=linux-64,version='>=1.0']"
+```
+
+`prefix`, `str`, the full path to the environment. It's not clear to me how `name` and `prefix` interact.
+
+`variables`, `dict`, {`str`: `str`} format of environment variables to set/unset when the environment is activated/deactivated.
+
+jsonschema version of the current spec:
+
+```json
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "object",
+  "properties": {
+    "name": {"type": "string"},
+    "prefix": {"type": "string"},
+    "channels": {
+      "type": "array",
+      "items": {"type": "string"}
+    },
+    "dependencies": {
+      "type": "array",
+      "items": {
+        "anyOf": [
+          {"type": "string"},
+          {"$ref": "#/definitions/pip"}
+        ]
+      }
+    },
+    "variables": {
+      "type": "object",
+      "additionalProperties": {"type": "string"}
+    }
+  },
+  "definitions": {
+    "pip": {
+        "type": "object",
+        "additionalProperties": {
+            "type": "array",
+            "required": ["pip"],
+            "properties": {
+                "pip": {"type": "array"}
+            }
+        }
+    }
+  }
+}
+```
+
+## Other sections
+
+Other relevant sections of the proposal.  Common sections include:
+
+    * Specification -- The technical details of the proposed change.
+    * Motivation -- Why the proposed change is needed.
+    * Rationale -- Why particular decisions were made in the proposal.
+    * Backwards Compatibility -- Will the proposed change break existing
+      packages or workflows.
+    * Alternatives -- Any alternatives considered during the design.
+    * Sample Implementation -- Links to prototype or a sample implementation of
+      the proposed change.
+    * FAQ -- Frequently asked questions (and answers to them).
+    * Resolution -- A short summary of the decision made by the community.
+    * Reference -- Any references used in the design of the CEP.
+
+## Copyright
+
+All CEPs are explicitly [CC0 1.0 Universal](https://creativecommons.org/publicdomain/zero/1.0/).

env-specs/env1.yml

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+name: stats
+dependencies:
+  - numpy
+  - pandas

env-specs/env2.yml

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+name: stats2
+channels:
+  - javascript
+dependencies:
+  - python=3.9
+  - bokeh=2.4.2
+  - conda-forge::numpy=1.21.*
+  - nodejs=16.13.*
+  - flask
+  - pip
+  - pip:
+    - Flask-Testing

env-specs/env3.yml

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+name: env-name
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - python=3.7
+  - codecov
+prefix: /Users/username/anaconda3/envs/env-name

env-specs/env4.yml

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+name: env-name
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - python=3.7
+  - codecov
+variables:
+  VAR1: valueA
+  VAR2: valueB

env-specs/schema.json

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+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "type": "object",
+    "properties": {
+        "name": {
+            "type": "string"
+        },
+        "prefix": {
+            "type": "string"
+        },
+        "channels": {
+            "type": "array",
+            "items": {
+                "type": "string"
+            }
+        },
+        "dependencies": {
+            "type": "array",
+            "items": {
+                "anyOf": [
+                    {
+                        "type": "string"
+                    },
+                    {
+                        "$ref": "#/definitions/pip"
+                    }
+                ]
+            }
+        },
+        "variables": {
+            "type": "object",
+            "additionalProperties": {
+                "type": "string"
+            }
+        }
+    },
+    "definitions": {
+        "pip": {
+            "type": "object",
+            "additionalProperties": {
+                "type": "array",
+                "required": [
+                    "pip"
+                ],
+                "properties": {
+                    "pip": {
+                        "type": "array"
+                    }
+                }
+            }
+        }
+    }
+}