Supporting x-tagGroups in join command

[unional]

Describe the problem to be solved

Currently, the join command creates a spec that uses the filename as the x-tagGroups.

This cause all tags are added to the same openapespec group for the following:

# /packages/api-a/open_api/openapespec.yaml
# /packages/api-b/open_api/openapespec.yaml

redocly join packages/api-a/open_api/openapispec.yaml packages/api-b/open_api/openapispec.yaml -o public/openapi.yaml

# or
redocly join packages/*/open_api/*.yaml -o public/openapi.yaml

Describe the solution you'd like

Use info.title of each file as the group name

Describe alternatives you've considered

add a flag to specify which prop to use.

Additional context

[AlexVarchuk]

Seems it is related to @redocly/cli.

[tatomyr]

Thanks for the suggestion @unional!

[tatomyr]

Hey @unional, could you check if using this option covers your case?

[unional]

Hey @unional, could you check if using this option covers your case?

Nope. That changes the tags not the tag groups.

[lornajane]

It's very difficult to pick a prefix solution here that works for everyone - although we do have the option to not create the groups which I think is important. I agree that info.title would be (or should be) a more API-specific group label and would like us to make this change, but we need to take care with special characters in it to create a useful value for the tag groups.

Also we'll need to make it very clear in the changelog that this behaviour is changing - minor version bump at a minimum. I know the join command is still marked experimental but we do see quite a bit of usage!

[unional]

I observe another issue related to this.
Without the x-tagGroups support for the join command, I can' control the order or filter out specific tags from the join doc.

Able to filter out tags are especially important as we can add the next version of API to the documentation during development while they are not exposed in the final doc.

[lornajane]

Thanks for your comment @unional , but in general it's better to open a new issue than to comment on a closed one where additional conversation might not be seen.

For this additional issue, perhaps you can use the filter-out decorator after joining to produce the output of the combined API descriptions without the tagged endpoints? There's more information about the filter-out decorator in the docs: https://redocly.com/docs/cli/decorators/filter-out/