Make non-local-def lint Allow by default

[wesleywiser]

Updates the non-local-def lint to be Allow by default. The lint currently triggers undesirably in a few places and we'd like to see that updated (or at least fully investigated) before this ships to stable Rust.

cc #124396
cc #124557
cc #124534
cc #120363

cc @Urgau as discussed in the T-compiler triage meeting today 🙂

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[wesleywiser]

Nominating for beta-backport so it can ride the 1.79 release train with #122747 which marked it Allow by default.

[wesleywiser]

@bors rollup=never

When this lint was changed to Warn by default, it triggered a perf regression. Thus, this PR will likely trigger a perf improvement.

[Urgau]

Should this PR be beta only? Since all the issues pointed are either already fixed or not an issue at all.

#124396 (fixed, backported on 1.79), #124534 (fixed, waited on backport), #124557 (not an FP, closed).

[wesleywiser]

Ah, I didn't realize #124396 had been fixed. Then yeah I will retarget this to the beta branch.

[fmease]

Should this PR be closed then (I don't know if you can retarget a PR)?

[apiraino]

Beta backport accepted as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle.

@rustbot label +beta-accepted

[cuviper]

Then yeah I will retarget this to the beta branch.

I've opened #125183 for other backports -- @wesleywiser do you want to add yours there?
(In a brief attempt, I found that this commit is not a clean cherry-pick to beta.)

[cuviper]

Oh, the conflict is that beta doesn't have the rustdoc test from #124568. I'll just skip that for backport.

And since this PR wasn't formally approved yet, I'll switch to my compiler-contributor hat to say r=me. :)

[fmease]

#124950 (comment):

And since this PR wasn't formally approved yet, I'll switch to my compiler-contributor hat to say r=me. :)

Right, sorry about that. I hereby formally approve this PR after the fact ;) Got confused by the backporting story.

[fmease]

Thanks @wesleywiser for the fix!

Closing this PR then since it got successfully backported to beta in #125183 and since nightly doesn't need be patched.
Feel free to reopen if I misunderstood the situation ^^'.