Give many `impl Iterator` return types an ExactSizeIterator bound

[oli-obk]

E.g. in https://github.com/rust-lang/miri/pull/1083/files?utf8=%E2%9C%93&diff=unified&w=1#r352037361 we had to use weird code to check that the iterator is the same length as a slice.

After changing the fn args_iter function to have an ExactSizeIterator bound, we should undo the hack

This issue has been assigned to @hashedone via this comment.

[osa1]

What do you mean by "many"? Is this about grepping impl Iterator returns in std and replacing them with impl ExactSizeIterator whenever possible? I'd like to give this a try but not sure what exactly this is asking.

[oli-obk]

Ah, not libstd, just in the compiler. But yea, you got the right idea, grep for it, see if it can be ExactSizeIterator, if not leave it

[hashedone]

Hi, this looks pretty easy and I would actually try to get involved into rustc - could I take this one as starting point for incoming weekend?

[osa1]

@hashedone Go for it. Just search for impl Iterator returns in the compiler source code and replace them with impl ExactSizeIterator whenever possible.

[hashedone]

@rustbot claim