Should `format_collect` be warn by default?

[smoelius]

Description

format_collect suggests to replace format! with write!.

A downside of this suggestion is that it replaces a infallible function with a fallible one (i.e., write! returns a Result, whereas format! does not).

format_push_string has a similar downside, and it was moved to restriction for this reason.

Should the same standard apply to format_collect? Or is something about its situation different?

cc: @y21, @Centri3

[y21]

Yeah, we were discussing the category a bit on the PR and centri3 suggested pedantic I think. I wasn't aware of that lint. I do kinda agree now that warn by default might be a bit too strong and maybe this should be in restriction, seeing that format_push_string is also and the arguments given.
It's a bit unfortunate that write! on a string, an operation that can't fail, returns a Result, thus requiring an unnecessary let _ = or .unwrap(), but it makes sense given that the macro goes through the generic std::fmt::Write machinery.

[smoelius]

Rereading my post, though, I didn't mean to suggest that format_collect should be restriction.

I too think pedantic could make sense.

(EDIT: And similarly for format_push_string.)

[y21]

Right, so I think format_collect and format_push_string should probably be in the same category, since they're basically checking for the same kind of pattern but in different places. So there's two options, then:

1. Move format_collect to restriction and leave format_push_string where it is
2. Move format_collect and format_push_string to pedantic

I personally think 2) is better (I haven't found a strong argument as to why it should be restriction specifically), but I created a poll on zulip for this:
https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/.60format_collect.60.20category