iter conservation efforts: save the endangered .iter() and .into_iter()

[joshtriplett]

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/ It looks like you're writing a loop. \
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Every day, more iters are lost, discarded as unwanted, to such hazards
as "concision" and "brevity". Won't someone think of the poor .iter()
and .into_iter(), that future generations may continue to admire them
and their self-documenting properties in their many and varied natural
habitats, and not merely in a zoo of (en)closures?

Make explicit_iter_loop and explicit_into_iter_loop allow-by-default, so
that people can turn them on if they want to enforce that style; avoid
presenting them as the idiomatic Rust style, rather than just a style.

[flip1995]

Also needs to be updated in clippy_lints/src/lib.rs. Running utils/update_lints.py should do this.

[joshtriplett]

@flip1995 Done, thanks.

[joshtriplett]

More serious supporting information: many crates turn this off, including crates like cargo, and clap.

[flip1995]

Oh and the stderr file needs to be updated:

tests/ui/update-references.sh 'target/debug/test_build_base' 'for_loop.rs'

[joshtriplett]

@flip1995 Done.

[joshtriplett]

(The appveyor failure looks spurious.)

[flip1995]

Thanks!

Appveyor error is unrelated: #3118

[Manishearth]

@joshtriplett could you leave the requested comment on #3230 ? This is a minor PR so it doesn't really count, but might as well get the sign off if I can 😄

[joshtriplett]

On October 2, 2018 4:44:13 AM PDT, Manish Goregaokar ***@***.***> wrote: @joshtriplett could you leave the requested comment on #3230 ? This is a minor PR so it doesn't really count, but might as well get the sign off if I can 😄

Done.