Way to properly handle lazy translations/formatting

[last-partizan]

I'm thinking about how to get it right.

Currently our lazy functions just returning str, and I think about changing that to class StrPromise(Promise, str): ...

There's some problems with that, but it's better than plain str, and least disruptive. E.q. we don't need to change much code.

• Return Promise for lazy functions. typeddjango/django-stubs#689 (comment)
• Broaden type annotation for verbose_name(_plural) to accept lazystr. typeddjango/django-stubs#1139 (comment)

It allows us to catch places where we expect StrPromise, but getting str.

class Promise: ...

class StrPromise(Promise, str): ...

def gettext_lazy(v: str) -> StrPromise: ...

v1: StrPromise = StrPromise()
# Error
v2: StrPromise = ""

# Both cases ok
v3: str = ""
v4: str = StrPromise()

@sbdchd what do you think?

[sbdchd]

Good idea!

[last-partizan]

Basic code is merged, I'll test it on a real project and maybe update Readme a little, to add this detail.