Use comments to define message placeholder names

[AndrewIngram]

As we've been rolling out our use of Lingui, one thing that's particularly tedious is having to create a variable binding with a translator-friendly name just for the purposes of use in a string.

There've been a bunch of recent commits to Lingui that improve this in various ways, but I was musing on the possibility of some special comment syntax being supported by the macros to explicitly set the placeholder name, e.g something like:

t`Hello ${/* name */ users[0].firstName}`

I haven't thought through all the implications of this, so it might've already been considered and rejected.

[andrii-bodnar]

There was a similar discussion in #1874.

A great new feature was introduced in v5 that gives translators more context about the placeholders. You may find this useful. See #1965 for more details.

[AndrewIngram]

Checking back in here, we're now running on v5 with the new placeholder metadata enabled; but to be honest, it doesn't help much. We're finding the referenced variables very rarely do the trick in terms of providing a good explanation of what the placeholder means.

We get lots of things like this:

placeholder {0}: FORM_TAB_TO_LABEL[formTab]

It makes me feel like there's still a need to have a way to explicitly define what the placeholder shows up as in the translation string.

[timofei-iatsenko]

The latest proposition was here: #1874 (comment)