[ci] [docs] readthedocs configuration options are deprecated

[jameslamb]

Description

This project uses readthedocs to build and host its documentation at https://lightgbm.readthedocs.io/en/latest/.

The way those docs are built is configured here:

LightGBM/.readthedocs.yaml

Lines 1 to 14 in 4aaeb22

	version: 2
	formats:
	- pdf
	python:
	version: 3
	install:
	- requirements: docs/requirements.txt
	sphinx:
	builder: html
	configuration: docs/conf.py
	fail_on_warning: true
	submodules:
	include: all
	recursive: true

According to the documentation for that service, some of the configuration options used in this project's .readthedocs.yaml are deprecated.

python.version (link)

This option is now deprecated and replaced by build.tools.python. See python.version (legacy) for the description of this option.

According to https://docs.readthedocs.io/en/stable/config-file/v2.html#python-version-legacy, using version: 3 is also deprecated.

Make sure to use quotes (") to make it a string. We previously supported using numbers here, but that approach is deprecated.

Additional Comments

These deprecated configuration should be removed, so that documentation builds don't break when those features are removed in future changes to the readthedocs service.

Given the discussion in #4948, I think this should be accomplished by switching the project's readthedocs builds to use mamba, as documented at "Making builds faster with mamba" (RTD docs link).

[jameslamb]

Linking some relevant discussions showing support for mamba on RTD added a few months ago.

• Build: use new Docker images from design document readthedocs/readthedocs.org#8453
• Mamba usage to improve performance (memory & speed) readthedocs/readthedocs.org#7239

[akshitadixit]

Hi @jameslamb is this available to work on?

[jameslamb]

Thanks for your interest @akshitadixit ! But no, #4957 (linked above) is already addressing this.

[github-actions]

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