Allow two-phase borrows of &mut self in ops

[sapphire-arches]

We need two-phase borrows of ops to be in the initial NLL release since without them lots of existing code will break. Fixes #48129.
CC @pnkfelix and @nikomatsakis

r? @pnkfelix

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @pnkfelix (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[nikomatsakis]

Actually, this lxl revision is still using the MIR borrowck. Can we add a revision that tests the existing borrowck (possibly replacing the existing lxl)? e.g.

// Test that NLL and the older, AST-based checker both accept these constructions:
// revisions: ast nll

#![cfg_attr(nll, feature(nll))]

[nikomatsakis]

(I don't know that we care so much about the MIR-based borrowck without NLL enabled)

[sapphire-arches]

Makes sense, but now I'm really confused about the arguments specified here

rust/src/test/run-pass/borrowck/two-phase-control-flow-split-before-activation.rs

Line 12 in 3ec5a99

//[lxl]compile-flags: -Z borrowck=mir -Z two-phase-borrows

In any case, I've dropped those args now.

[nikomatsakis]

Well, I think that felix was specifically targeting MIR borrowck w/o NLL. But in this case, I don't think we need to, but I think it's important to show that we are preserving the current behavior in terms of what code is accepted.

[nikomatsakis]

@bors r+

[bors]

📌 Commit 7062955 has been approved by nikomatsakis