feat(format_push_string): give a (possibly incomplete) suggestion

[ada4a]

Resolves https://github.com/rust-lang/rust-clippy/issues/8824

Supersedes https://github.com/rust-lang/rust-clippy/pull/15828 -- I wasn't able to get TyCtxt::in_scope_traits to work, so here's a more basic implementation that just adds a note about the possible need to import std::fmt::Write.

changelog: [format_push_string]: add a suggestion

[rustbot]

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[github-actions[bot]]

Lintcheck changes for 34551be259d4b14af3103d0b61d2ef9d310b9f36

Lint	Added	Removed	Changed
clippy::format_push_string	0	0	29

This comment will be updated if you push new changes

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[ada4a]

@rustbot ready

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.