Remove lifetime bounds in higher-ranked lifetimes

[RalfJung]

Those bounds are ignored by the compiler, and will trigger an error once rust-lang/rust#48326 lands. According to crater, this is the only crate using these bounds. This patch should make the crate work on nightly again.

However, I have been unable to compile the crate even with nightly 2018-02-25, which does not include the change mentioned above. So, I couldn't compile-test this PR.

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This change is 

[Rhuagh]

Thanks!

Bors r+

[Rhuagh]

We'll see if it builds on CI :)

[bors]

Build succeeded

• continuous-integration/travis-ci/push

[Rhuagh]

Looks like it works there atleast

[RalfJung]

The build failure was caused by rust-lang/rust#48551. That's fixed, but my branch where I develop rust-lang/rust#48326 does not include the fix yet, so I can't test whether this will keep working when my patch lands. However, these are all the occurrences of higher-ranked lifetime bounds that crater found.

Thanks for merging so quickly. :) Please release a new minor version of the create before the patch hits stable (which will take ~9 weeks).

[Rhuagh]

We will probably release a new major version before that (we have some breaking changes).

[RalfJung]

AFAIK a new minor version with the fix would be necessary for reverse dependencies that will just do cargo update -- they won't get the new major version automatically, so they would fail to build.

[Rhuagh]

True, I'll get that out tonight.

[RalfJung]

I compiled rustc with my patch merged into master, and can confirm that this can build current rhusics master (while it fails on the version without my patch, as expected).

So, looking good :)

[Rhuagh]

The breaking changes had not been merged to master yet, so this was easier than I thought it would :) Anyways, new minors have been released.