Add .cfg/.ini params parser

[percevalw]

Hi,

Following #7122, this PR adds support for .ini / .cfg files (INI format).
While we don't assume that nested sections of INI files follow the same convention as TOML (i.e., [section.nested]), we still parse them as nested dictionaries because it should not affect non-nested configurations and it allows more complex overrides on files that do present nesting (àla spaCy config.cfg files).

Documentation PR: iterative/dvc.org#5060

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here:

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (3e4e143) 90.61% compared to head (945c69c) 90.64%.

Files	Patch %	Lines
dvc/utils/serialize/_ini.py	97.56%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10175      +/-   ##
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+ Coverage   90.61%   90.64%   +0.02%     
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  Files         499      501       +2     
  Lines       37880    37992     +112     
  Branches     5505     5414      -91     
==========================================
+ Hits        34326    34436     +110     
  Misses       2912     2912              
- Partials      642      644       +2     

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[skshetry]

@percevalw, thank you for taking the time to create the pull request.

Unfortunately, I'm leaning towards declining this PR as it will be difficult for us to maintain as the configuration parsing scope increases. This is because:

1. There is no single standard ini format.
2. There is no support for native types, so we'll have to do a custom parsing. This makes it tricky to modify.
3. Comments are not preserved on the update.
4. Given the support for TOML, YAML, JSON, Python, and Hydra, there's less demand for .ini files. And I expect it to decline further in the future.

We are a small team, and we have struggled to maintain all the implemented params formats, especially in the case of Python parsing, which has been left unmaintained for an extended period.

Given that, I'm hesitant to introduce one more format, particularly one with a scope that may potentially increase over time at this time.

[percevalw]

Hi, thank you for your review. I understand the difficulty of maintaining a very specific feature like this one.

Would you be open in this case to considering a third party serialization ecosystem, using entry points for example?
I believe such a mechanism would have a lower impact on the maintenance of dvc, and could accommodate for custom requirements.

For instance, having in a "my-custom-dvc-ini-serializer" package a pyproject.toml field looking like the following:

[project.entry-points."dvc_serializers"]
"cfg" = "my_custom_dvc_ini_serializer"

with my_custom_dvc_ini_serializer/__init__.py containing the changes suggested in this PR, and having dvc look for such entry points when running dvc/utils/serialize/__init__.py to update its dictionaries.
This could look like :

... # content of serialize/__init__.py

import sys
from importlib.metadata import entry_points

for ep in entry_points(group='dvc_serializers'):
    ext = ep.load()
    PARSERS.update(ext.PARSERS)
    LOADERS.update(ext.LOADERS)
    MODIFIERS.update(ext.MODIFIERS)
    DUMPERS.update(ext.DUMPERS)

[skshetry]

@percevalw, unfortunately, we cannot provide a stable API/hook for the config API. The PARSERS/LOADERS, et al. are utilities meant for internal usage and were not designed thinking about extensibility. They are not in a very good state either.

While I do understand your use case, we don't see the demand or interests in #7122. There has been discussion about providing an API in #6506 before, and reusing the current utilities might lock us in when we come to improve parameters' workflow in the future.

[skshetry]

Closing as stale.