Add --extend-select option for selecting rules/formatters

[andre-morise]

Problem

Currently, robocop format --select ... completely replaces the default ENABLED formatters. Users who want to depend on the default formatters and enable one or two extras must either manually list all default formatters, or use the somewhat verbose --configure option, which is not ideal.

A. Example (with select):

[tool.robocop.format]
# Must list all ~20 default formatters just to enable additional formatters
select = [
    "AddMissingEnd",
    "NormalizeSeparators",
    "DiscardEmptySections",
    # ... the rest ...
    # The only ones we actually want to enable
    "AlignKeywordsSection",
    "AlignTestCasesSection"
]

This breaks when robocop's default formatters change.

B. Example (with configure):

select = [
    # defaults
]
configure = [
    "AlignKeywordsSection.enabled=True",
    "AlignTestCasesSection.enabled=True"
]

This would not break when robocop's default formatters change, but is verbose nonetheless.

Proposed Feature

Add --extend-select / extend-select option that augments formatters instead of replacing them.

CLI:

robocop format --extend-select AlignKeywordsSection --extend-select AlignTestCasesSection

TOML:

[tool.robocop.format]
extend-select = [
    "AlignKeywordsSection",
    "AlignTestCasesSection"
]

Behavior

Configuration	Result
extend-select = ["F1"]	All defaults + F1
select = ["F1"] + extend-select = ["F2"]	F1 + F2 (no defaults)
No select or extend-select	All defaults (unchanged)

Benefits

• Reduces configuration verbosity for common use case
• Future-proof: automatically includes new default formatters
• No breaking changes to existing --select behavior
• Follows precedent from Ruff's linter configuration (See extend-select)

Notes

• Custom formatters (via --custom-formatters) should continue to appear last
• --force-order should affect --extend-select same as --select
• When neither --select nor --extend-select is specified, behavior should remain unchanged (all defaults)

[bhirsz]

Thanks for great write up. I agree, we should add it to robocop.

[bhirsz]

For consistency reason we also need to add the same mode to the linter. It also align with other requests, for example with #1517.

[bhirsz]

I started working on this and I have discovered funny situation.. --custom-formatters behaves exactly as --extend-select. It can be used not only to import custom formatters but internal ones as well. You can try to use it now:

[tool.robocop.format]
# Must list all ~20 default formatters just to enable additional formatters
custom_formatters = [
    # The only ones we actually want to enable
    "AlignKeywordsSection",
    "AlignTestCasesSection"
]

Also, custom formatters can be imported with --select as well. The reason behind is that I wanted to add option to either 'only select custom ones or import all default + customs'. As side effect I have implement the extend_select behaviour.

So in the scope of this issue I would simply rename existing option custom_formatters to extend_select and document how it works exactly. My only problem here is versioning, since changing the option names is breaking change requiring major version bump. However there is no downside for us for bumping the major version. I will only need some time to consider if there are any other issues that are potentially breaking changes and should be deployed together in major version.

Can you verify if --custom-formatters works for you in meantime?

[andre-morise]

@bhirsz This solution with the existing --custom-formatters does indeed work in the meantime. Thanks for your work on this!

Given what you've determined regarding the linter and the existing --custom-formatters behavior, would you like the title and description of this issue to be updated in some way, for consistency?

[bhirsz]

Thanks for confirming it.

Yes, I have just updated the title a bit - it should reflect current scope.