Document specs::Channel (#3077)

* Add CondaURL doc

* Add specs::Channel documentation

* Document Version and VersionSpec

* Shortcut redirect

docs/source/api/specs.rst

@@ -0,0 +1,302 @@
+Describing Conda Objects
+========================
+
+The ``libmambapy.specs`` submodule contains object to *describe* abstraction in the Conda ecosystem.
+They are purely functional and do not have any observable impact on the user system.
+For instance ``libmambapy.specs.Channel`` is used to describe a channel but does not download any file.
+
+CondaURL
+--------
+The ``CondaURL`` is a rich URL object that has additional capabilities for dealing with tokens,
+platforms, and packages.
+
+To parse a string into a ``CondaURL``, use ``CondaURL.parse`` as follows:
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   url = specs.CondaURL.parse(
+       "https://conda.anaconda.org/t/someprivatetoken/conda-forge/linux-64/x264-1%21164.3095-h166bdaf_2.tar.bz2"
+   )
+   assert url.host() == "conda.anaconda.org"
+   assert url.package() == "x264-1!164.3095-h166bdaf_2.tar.bz2"
+   assert url.package(decode=False) == "x264-1%21164.3095-h166bdaf_2.tar.bz2"
+
+The ``CondaURL.parse`` method assumes that the URL is properly
+`percent encoded <https://en.wikipedia.org/wiki/Percent-encoding>`_.
+For instance, here the character ``!`` in the file name ``x264-1!164.3095-h166bdaf_2.tar.bz2`` had
+to be replaced with ``%21``.
+The getter functions, such as ``CondaURL.package`` automatically decoded it for us, but we can
+specify ``decode=False`` to keep the raw representation.
+The setters follow the same logic, as described bellow.
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   url = specs.CondaURL()
+   url.set_host("mamba.pm")
+   url.set_user("my%20name", encode=False)
+   url.set_password("n&#4d!3gfsd")
+
+   assert url.user() == "my name"
+   assert url.user(decode=False) == "my%20name"
+   assert url.password() == "n&#4d!3gfsd"
+   assert url.password(decode=False) == "n%26%234d%213gfsd"
+
+Path manipulation is handled automatically, either with ``CondaURL.append_path`` or the ``/``
+operator.
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   url1 = specs.CondaURL.parse("mamba.pm")
+   url2 = url / "/t/xy-12345678-1234/conda-forge/linux-64"
+
+   assert url1.path() == "/"
+   assert url2.path() == "/t/xy-12345678-1234/conda-forge/linux-64"
+   assert url2.path_without_token() == "/conda-forge/linux-64"
+
+You can always assume that the paths returned will start with a leading ``/``.
+As always, encoding and decoding options are available.
+
+.. note::
+
+   Contrary to ``pathlib.Path``, the ``/`` operator will always append, even when the sub-path
+   starts with a ``/``.
+
+The function ``CondaURL.str`` can be used to get a raw representation of the string.
+By default, it will hide all credentials
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   url = specs.CondaURL.parse("mamba.pm/conda-forge")
+   url.set_user("[email protected]")
+   url.set_password("private")
+   url.set_token("xy-12345678-1234")
+
+   assert url.str() == "https://user%40mail.com:*****@mamba.pm/t/*****"
+   assert (
+       url.str(credentials="Show")
+       == "https://user%40mail.com:[email protected]/t/xy-12345678-1234"
+   )
+   assert url.str(credentials="Remove") == "https://mamba.pm/"
+
+Similarily the ``CondaURL.pretty_str`` returns a more user-friendly string, but that may not be
+parsed back.
+
+
+ChannelSpec
+-----------
+A ``ChannelSpec`` is a lightweight object to represent a channel string, as in passed in the CLI
+or configuration.
+It does minimal parsing and can detect the type of ressource (an unresolved name, a URL, a file)
+and the platform filters.
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   cs = specs.ChannelSpec.parse("https://conda.anaconda.org/conda-forge/linux-64")
+
+   assert cs.location == "https://conda.anaconda.org/conda-forge"
+   assert cs.platform_filters == {"linux-64"}
+   assert cs.type == specs.ChannelSpec.Type.URL
+
+Dynamic platforms (as in not known by Mamba) can only be detected with the ``[]`` syntax.
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   cs = specs.ChannelSpec.parse("conda-forge[prius-avx42]")
+
+   assert cs.location == "conda-forge"
+   assert cs.platform_filters == {"prius-avx42"}
+   assert cs.type == specs.ChannelSpec.Type.Name
+
+
+Channel
+-------
+The ``Channel`` are represented by a ``CondaURL`` and a set of platform filters.
+A display name is also available, but is not considered a stable identifiaction form of the
+channel, since it depends on the many configuration parameters, such as the channel alias.
+
+We construct a ``Channel`` by *resolving* a ``ChannelSpec``.
+All parameters that influence this resolution must be provided explicitly
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   cs = specs.ChannelSpec.parse("conda-forge[prius-avx42]")
+   chan, *_ = specs.Channel.resolve(
+       spec=cs,
+       channel_alias="https://repo.mamba.pm"
+       # ...
+   )
+
+   assert chan.url.str() == "https://repo.mamba.pm/conda-forge"
+   assert cs.platforms == {"prius-avx42"}
+   assert chan.display_name == "conda-forge[prius-avx42]"
+
+There are no hard-coded names:
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   cs = specs.ChannelSpec.parse("defaults")
+   chan, *_ = specs.Channel.resolve(
+       spec=cs,
+       channel_alias="https://repo.mamba.pm"
+       # ...
+   )
+
+   assert chan.url.str() == "https://repo.mamba.pm/defaults"
+
+You may have noticed that ``Channel.resolve`` returns multiple channels.
+This is because of custom multichannel, a single name can return mutliple channels.
+
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   chan_main, *_ = specs.Channel.resolve(
+       spec=specs.ChannelSpec.parse("pkgs/main"),
+       # ...
+   )
+   chan_r, *_ = specs.Channel.resolve(
+       spec=specs.ChannelSpec.parse("pkgs/r"),
+       # ...
+   )
+
+   defaults = specs.Channel.resolve(
+       spec=specs.ChannelSpec.parse("defaults"),
+       custom_multichannels=specs.Channel.MultiChannelMap(
+           {"defaults": [chan_main, chan_r]}
+       ),
+       # ...
+   )
+
+   assert defaults == [chan_main, chan_r]
+
+.. note::
+
+   Creating ``Channel`` objects this way, while highly customizable, can be very verbose.
+   In practice, one can create a ``ChannelContext`` with ``ChannelContext.make_simple`` or
+   ``ChannelContext.make_conda_compatible`` to compute and hold all these parameters from a
+   ``Context`` (itself getting its values from all the configuration sources).
+   ``ChannelContext.make_channel`` can then directly construct a ``Channel`` from a string.
+
+
+Version
+-------
+In the conda ecosystem, a version is an epoch and a pair of arbitrary length sequences of arbitrary
+length sequences of string and integer pairs.
+Let's unpack this with an example.
+The version ``1.2.3`` is the outer sequence, it can actually contain as many elements as needed
+so ``1.2.3.4.5.6.7`` is also a valid version.
+For alpha version, we sometimes see something like ``1.0.0alpha1``.
+That's the inner sequence of pairs, for the last part ``[(0, "alpha"), (1, "")]``.
+There can also be any number, such as in ``1.0.0alpha1dev3``.
+We can specify another *"local"* version, that we can separate with a ``+``, as in ``1.9.0+2.0.0``,
+but that is not widely used.
+Finally, there is also an epoch, similar to `PEP440 <https://peps.python.org/pep-0440/>`_, to
+accomodate for change in the versioning scheme.
+For instance, in ``1!2.0.3``, the epoch is ``1``.
+
+To sum up, a version like ``7!1.2a3.5b4dev+1.3.0``, can be parsed as:
+
+- **epoch**: ``7``,
+- **version**: ``[[(1, "")], [(2, "a"), (3, "")], [(5, "b"), (4, "dev")]]``
+- **local version**: ``[[(1, "")], [(3, "")], [(0, "")]]``
+
+Finally, all versions are considered equal to the same version with any number of trailing zeros,
+so ``1.2``, ``1.2.0``, and ``1.2.0.0`` are all considered equal.
+
+.. warning::
+
+   The flexibility of conda versions (arguably too flexible) is meant to accomodate differences
+   in various ecosystems.
+   Library authors should stick to well defined version schemes such as
+   `semantic versioning <https://semver.org/>`_,
+   `calendar versioning <https://calver.org/>`_, or
+   `PEP440 <https://peps.python.org/pep-0440/>`_.
+
+A ``Version`` can be created by parsing a string with ``Version.parse``.
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   v = specs.Version.parse("7!1.2a3.5b4dev+1.3.0")
+
+
+The most useful operations on versions is to compare them.
+All comparison operators are available:
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   assert specs.Version.parse("1.2.0") == specs.Version.parse("1.2.0.0")
+   assert specs.Version.parse("1.2.0") < specs.Version.parse("1.3")
+   assert specs.Version.parse("2!4.0.0") >= specs.Version.parse("1.8")
+
+
+VersionSpec
+-----------
+A version spec is a way to describe a set of versions.
+We have the following primitives:
+
+- ``*`` matches all versions (unrestricted).
+- ``==`` for **equal** states matches versions equal to the given one (a singleton).
+  For instance ``==1.2.4`` matches ``1.2.4`` only, and not ``1.2.4.1`` or ``1.2``.
+  Note that since ``1.2.4.0`` is the same as ``1.2.4``, this is also matched.
+- ``!=`` for ``not equal`` is the opposite, it matches all but the given version.
+  For instance ``=!1.2.4`` matches ``1.2.5`` and ``1!1.2.4`` but not ``1.2.4``.
+- ``>`` for **greater** matches versions stricly greater than the current one, for instance
+  ``>1.2.4`` matches ``2.0.0``, ``1!1.0.0``, but not ``1.1.0`` or ``1.2.4``.
+- ``>=`` for **greater or equal**.
+- ``<`` for **less**.
+- ``<-`` for **less or equal**.
+- ``=`` for **starts with** matches versions that start with the same non zero parts of the version.
+  For instance ``=1.7`` matches ``1.7.8``, and ``1.7.0alpha1`` (beware since this is smaller
+  than ``1.7.0``).
+  This spec can equivalently be written ``1.7`` (bare), ``1.7.*``, or ``=1.7.*``.
+- ``=!``  with ``.*`` for **not starts with** matches all versions but the one that starts with
+  the non zero parts specified.
+  For instance ``!=1.7.*`` matches ``1.8.3`` but not ``1.7.2``.
+- ``~=`` for **compatible with** matches versions that are greater or equal and starting with the
+  all but the last parts specified, including zeros.
+  For instance `~=2.0` matches ``2.0.0``, ``2.1.3``, but not ``3.0.1`` or ``2.0.0alpha``.
+
+All version spec can be combine using a boolean grammar where ``|`` means **or** and ``,`` means
+**and**.
+For instance, ``(>2.1.0,<3.0)|==2.0.1`` means:
+
+- Either
+   - equal to ``2.0.1``,
+   - or, both
+     - greater that ``2.1.0``
+     - and less than ``3.0``.
+
+To create a ``VersionSpec`` from a string, we parse it with ``VersionSpec.parse``.
+To check if a given version matches a version spec, we use ``VersionSpec.contains``.
+
+
+.. code:: python
+
+   import libmambapy.specs as specs
+
+   vs = specs.VersionSpec.parse("(>2.1.0,<3.0)|==2.0.1")
+
+   assert vs.contains(specs.Version.parse("2.4.0"))
+   assert vs.contains(specs.Version.parse("2.0.1"))
+   assert not vs.contains(specs.Version.parse("3.0.1"))

docs/source/index.rst

@@ -51,11 +51,12 @@ You can try Mamba now by visiting the installation for
    advanced_usage/package_resolution
 
 .. toctree::
-   :caption: API reference
+   :caption: API USAGE
    :maxdepth: 2
    :hidden:
 
    python_api
+   api/specs
 
 .. toctree::
    :caption: developer zone

docs/source/python_api.rst

@@ -135,4 +135,4 @@ Here is an example usage of ``libmambapy``:
             t = libmambapy.Transaction(api_solver, package_cache)
             return t
 
-.. _boa: https://www.github.com/mamba-org/boa/blob/main/boa/core/solver.py
+.. _boa: https://github.com/mamba-org/boa/blob/main/boa/core/solver.py