Getting ready for schema based bids-validator

[sappelhoff]

Currently there are two BIDS validator "builds":

1. the "legacy" validator, implemented mainly with custom Java Script
2. the "schema" validator, based on the BIDS schema

We use the legacy validator, but the schema validator will sooner (!) or later replace the legacy validator.

The schema validator will also be more accurate in covering the BIDS specification and might raise errors where the currently used legacy validator remained silent.

We should prepare for a switch, and the potential fixes at mne-bids that this may involve ... or at least be aware of it.

[sappelhoff]

See for example:

• https://github.com/bids-standard/bids-validator/pull/2060

[hoechenberger]

+1 on switching sooner than later

[sappelhoff]

I think the right way would be to add an additional CI run to our suite that uses the schema validator, and then to try and make these tests pass bit by bit.

See also: https://github.com/bids-standard/bids-examples/blob/7c18d6840982518a0251cfeb59fe5c4610099ea1/.github/workflows/validate_datasets.yml#L69-L75

[sappelhoff]

See also:

• NOTICE: Legacy validator to be migrated to bids-standard/legacy-validator bids-standard/legacy-validator#2179

[sappelhoff]

This will also involve updating the contributor documentation:

mne-bids/CONTRIBUTING.md

Lines 63 to 95 in 0042486

	### Install the BIDS validator
	For a complete development setup of `mne-bids`, it is necessary to install the
	[BIDS validator](https://github.com/bids-standard/bids-validator).
	The outputs of `mne-bids` are run through the BIDS validator to check if the conversion
	worked properly and produced datasets conform to the
	[BIDS specification](https://bids-specification.readthedocs.io/en/stable/).
	To install the **stable** version of `bids-validator`, please follow the instructions
	in the [bids-validator README](https://github.com/bids-standard/bids-validator#quickstart).
	You will need the "command line version" of the bids-validator.
	To install the **development** version of `bids-validator`, see the
	[contributor documentation of bids-validator](https://github.com/bids-standard/bids-validator/blob/master/CONTRIBUTING.md#using-the-development-version-of-bids-validator).
	In brief, the most convenient installation can be done using `conda`.
	In your `conda` development environment for `mne-bids` simply call:
	```Shell
	conda install -c conda-forge nodejs
	npm install --global npm@^7
	npm install --global bids-validator
	```
	This would install the **stable** `bids-validator` and make it globally available
	on your system.
	Check your installation by running:
	```Shell
	bids-validator --version
	```