Borrowed types are Copy so their methods should take self

[sffc]

For example, TimeZoneIdMapperWithFastCanonicalizationBorrowed.

Is there a Clippy warning for this? @Manishearth

[Manishearth]

Can't find a clippy warning.

[sffc]

If there's no clippy warning, then I think we have no real choice except to make this a best-effort kind of thing.

[sffc]

rust-lang/rust-clippy#12078

[Manishearth]

We should just enable trivially_copy_pass_by_ref. It has a decent threshold set: it warns for types that are of the size usize * 2, which is roughly the threshold where pass by value matters.

We'd need to enable the avoid-breaking-exported-api setting to be allowed to use this

[Manishearth]

2.0: Manish to audit

[sffc]

In general, audit that things that are usize * 2 are using copy self, and likewise that things bigger than usize * 2 should maybe be using &self. (both directions)