Regression tests for Rustup breakage tracking issue #3913

[flip1995]

cc #3913

Tests for the tracking issue. This commits can be cherry-picked for fixing these issues.

[flip1995]

Failures: https://travis-ci.com/rust-lang/rust-clippy/jobs/191751335#L1226-L1538

Closing this PR to keep the queue clean. This can be reopened to rerun Travis.

[flip1995]

lets see if #4082 has fixed the identity conversion bug

[flip1995]

Yes identity conversion is fixed!
https://travis-ci.com/rust-lang/rust-clippy/jobs/199515830#L1474-L1476

failures:
    [ui] ui/explicit_iter_loop_no_sugg.rs
    [ui] ui/into_iter_on_array_in_for_loop.rs

[flip1995]

I think 19e852c is also fixed.

[flip1995]

Nice everything is fixed. The tests for this already exist in

rust-clippy/tests/ui/into_iter_on_ref.rs

Line 13 in bd39cea

for _ in [1, 2, 3].into_iter() {} //~ ERROR equivalent to .iter()

rust-clippy/tests/ui/into_iter_on_ref.stderr

Lines 1 to 6 in bd39cea

	error: this .into_iter() call is equivalent to .iter() and will not move the array
	--> $DIR/into_iter_on_ref.rs:13:24
	|
	LL | for _ in [1, 2, 3].into_iter() {} //~ ERROR equivalent to .iter()
	| ^^^^^^^^^ help: call directly: `iter`
	|

and

rust-clippy/tests/ui/for_loop.rs

Line 107 in bd39cea

for _v in vec.iter() {}

rust-clippy/tests/ui/for_loop.stderr

Lines 65 to 71 in bd39cea

	error: it is more concise to loop over references to containers instead of using explicit iteration methods
	--> $DIR/for_loop.rs:107:15
	|
	LL | for _v in vec.iter() {}
	| ^^^^^^^^^^ help: to write this more concisely, try: `&vec`
	|
	= note: `-D clippy::explicit-iter-loop` implied by `-D warnings`