pygettext: Extend support for specifying custom keywords

Feature or enhancement

Proposal:

pygettext already allows specifying custom keywords in a limited fashion. For example, specifying --keyword=foo will
look for functions named foo in addition to the default keywords (gettext, etc..).

However, the CLI currently only allows specifying single-argument functions (i.e. gettext('foo')). It is not possible to add
keywords that take msgid_plural or msgctxt or both.

Both xgettext and babel support this with a simple keywordspec syntax that defines the function name and argument positions of msgid, msgid_plural and msgctxt.

For example, --keyword:foo:1c,2 defines a pgettext-like function where the msgctxt is the first argument and msgid is the second argument, e.g. foo('context', 'message').

It is also possible to use t to only match functions with that exact number of arguments. For example, foo:1,1t only matches foo('bar') but not foo('bar', 'baz').

I propose to support this in pygettext as well. For that we will need to:

• Support the keyword spec syntax when specifying keywords. I suggest skipping the t specifier for now.
• Support specifying multiple --keyword arguments with the same function name (this will require some internal changes, as those are stored in a dictionary with the function name as the key).
• Support the t specifier.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-130463
• gh-130709
• gh-131380