apint fails to compile on beta

[Mark-Simulacrum]

apint fails to compile (https://crater-reports.s3.amazonaws.com/beta-1.31-1/beta-2018-10-30/reg/apint-0.2.0/log.txt) on beta. Note that the crate must be compiled in test mode.

Nov 03 02:59:10.198 INFO kablam!    Compiling apint v0.2.0 (/source)
Nov 03 02:59:13.651 INFO kablam! error[E0597]: borrowed value does not live long enough
Nov 03 02:59:13.651 INFO kablam!    --> src/apint/constructors.rs:429:11
Nov 03 02:59:13.651 INFO kablam!     |
Nov 03 02:59:13.651 INFO kablam! 429 |               .chain([
Nov 03 02:59:13.651 INFO kablam!     |  ____________________^
Nov 03 02:59:13.651 INFO kablam! 430 | |                 u8::max_value(),
Nov 03 02:59:13.651 INFO kablam! 431 | |                 10,
Nov 03 02:59:13.651 INFO kablam! 432 | |                 42,
Nov 03 02:59:13.651 INFO kablam! 433 | |                 99,
Nov 03 02:59:13.651 INFO kablam! 434 | |                 123
Nov 03 02:59:13.651 INFO kablam! 435 | |             ].into_iter()
Nov 03 02:59:13.651 INFO kablam!     | |_____________^ temporary value does not live long enough
Nov 03 02:59:13.651 INFO kablam! 436 |                .map(|v| *v))
Nov 03 02:59:13.651 INFO kablam! 437 |       }
Nov 03 02:59:13.651 INFO kablam!     |       - temporary value only lives until here
Nov 03 02:59:13.651 INFO kablam!     |
Nov 03 02:59:13.651 INFO kablam!     = note: borrowed value must be valid for the static lifetime...
Nov 03 02:59:13.651 INFO kablam! 
Nov 03 02:59:13.657 INFO kablam! error[E0597]: borrowed value does not live long enough
Nov 03 02:59:13.657 INFO kablam!    --> src/apint/constructors.rs:480:11
Nov 03 02:59:13.657 INFO kablam!     |
Nov 03 02:59:13.657 INFO kablam! 480 |               .chain([
Nov 03 02:59:13.657 INFO kablam!     |  ____________________^
Nov 03 02:59:13.657 INFO kablam! 481 | |                 u16::max_value(),
Nov 03 02:59:13.657 INFO kablam! 482 | |                 500,
Nov 03 02:59:13.657 INFO kablam! 483 | |                 1000,
Nov 03 02:59:13.657 INFO kablam! ...   |
Nov 03 02:59:13.657 INFO kablam! 486 | |                 42_000
Nov 03 02:59:13.657 INFO kablam! 487 | |             ].into_iter().map(|v| *v))
Nov 03 02:59:13.657 INFO kablam!     | |_____________^ temporary value does not live long enough
Nov 03 02:59:13.657 INFO kablam! 488 |       }
Nov 03 02:59:13.657 INFO kablam!     |       - temporary value only lives until here
Nov 03 02:59:13.657 INFO kablam!     |
Nov 03 02:59:13.657 INFO kablam!     = note: borrowed value must be valid for the static lifetime...
Nov 03 02:59:13.657 INFO kablam! 
Nov 03 02:59:13.658 INFO kablam! error[E0597]: borrowed value does not live long enough
Nov 03 02:59:13.658 INFO kablam!    --> src/apint/constructors.rs:513:11
Nov 03 02:59:13.658 INFO kablam!     |
Nov 03 02:59:13.658 INFO kablam! 513 |               .chain([
Nov 03 02:59:13.658 INFO kablam!     |  ____________________^
Nov 03 02:59:13.658 INFO kablam! 514 | |                 u32::max_value(),
Nov 03 02:59:13.658 INFO kablam! 515 | |                 1_000_000,
Nov 03 02:59:13.658 INFO kablam! 516 | |                 999_999_999,
Nov 03 02:59:13.658 INFO kablam! 517 | |                 1_234_567_890
Nov 03 02:59:13.658 INFO kablam! 518 | |             ].into_iter().map(|v| *v))
Nov 03 02:59:13.658 INFO kablam!     | |_____________^ temporary value does not live long enough
Nov 03 02:59:13.658 INFO kablam! 519 |       }
Nov 03 02:59:13.658 INFO kablam!     |       - temporary value only lives until here
Nov 03 02:59:13.659 INFO kablam!     |
Nov 03 02:59:13.659 INFO kablam!     = note: borrowed value must be valid for the static lifetime...
Nov 03 02:59:13.659 INFO kablam! 
Nov 03 02:59:13.663 INFO kablam! error[E0597]: borrowed value does not live long enough
Nov 03 02:59:13.663 INFO kablam!    --> src/apint/constructors.rs:544:11
Nov 03 02:59:13.663 INFO kablam!     |
Nov 03 02:59:13.663 INFO kablam! 544 |               .chain([
Nov 03 02:59:13.663 INFO kablam!     |  ____________________^
Nov 03 02:59:13.663 INFO kablam! 545 | |                 u64::max_value(),
Nov 03 02:59:13.663 INFO kablam! 546 | |                 1_000_000_000_000,
Nov 03 02:59:13.663 INFO kablam! 547 | |                 999_999_999_999_999_999,
Nov 03 02:59:13.663 INFO kablam! 548 | |                 0x0123_4567_89AB_CDEF
Nov 03 02:59:13.663 INFO kablam! 549 | |             ].into_iter().map(|v| *v))
Nov 03 02:59:13.663 INFO kablam!     | |_____________^ temporary value does not live long enough
Nov 03 02:59:13.663 INFO kablam! 550 |       }
Nov 03 02:59:13.664 INFO kablam!     |       - temporary value only lives until here
Nov 03 02:59:13.664 INFO kablam!     |
Nov 03 02:59:13.664 INFO kablam!     = note: borrowed value must be valid for the static lifetime...
Nov 03 02:59:13.664 INFO kablam! 
Nov 03 02:59:13.671 INFO kablam! error[E0597]: borrowed value does not live long enough
Nov 03 02:59:13.671 INFO kablam!    --> src/apint/constructors.rs:575:11
Nov 03 02:59:13.671 INFO kablam!     |
Nov 03 02:59:13.671 INFO kablam! 575 |               .chain([
Nov 03 02:59:13.671 INFO kablam!     |  ____________________^
Nov 03 02:59:13.671 INFO kablam! 576 | |                 u128::max_value(),
Nov 03 02:59:13.671 INFO kablam! 577 | |                 1_000_000_000_000_000_000_000_000,
Nov 03 02:59:13.671 INFO kablam! 578 | |                 999_999_999_999_999_999_999_999_999,
Nov 03 02:59:13.671 INFO kablam! 579 | |                 0x0123_4567_89AB_CDEF_FEDC_BA98_7654_3210
Nov 03 02:59:13.671 INFO kablam! 580 | |             ].into_iter().map(|v| *v))
Nov 03 02:59:13.671 INFO kablam!     | |_____________^ temporary value does not live long enough
Nov 03 02:59:13.672 INFO kablam! 581 |       }
Nov 03 02:59:13.672 INFO kablam!     |       - temporary value only lives until here
Nov 03 02:59:13.672 INFO kablam!     |
Nov 03 02:59:13.672 INFO kablam!     = note: borrowed value must be valid for the static lifetime...
Nov 03 02:59:13.672 INFO kablam! 
Nov 03 02:59:14.105 INFO kablam! error: aborting due to 5 previous errors

[Mark-Simulacrum]

cc @Robbepop -- I believe this is your crate, though it seems plausible this is a bug in the compiler

[Mark-Simulacrum]

cc @rust-lang/compiler -- beta/stable regression, would be good to proactively triage before meeting if possible

[eddyb]

@oli-obk Could this be promotion-related?

[oli-obk]

Yea. The call to into_iter on arrays does not actually do what it advertises, it derefs to a slice and then does into_iter. We stopped allowing const fns in promoteds #53851. max_value is still marked as promotable, so that shouldn't be the issue. I'll investigate later today when I get back to a PC

[Robbepop]

@Mark-Simulacrum yeah that's my crate thanks for linking!

I have already stumbled upon this CI error but couldn't yet find time to wrap my head around it.
Though I thought it was a bug in a former version of the borrow checker that now got fixed.

Yea. The call to into_iter on arrays does not actually do what it advertises, it derefs to a slice and then does into_iter. We stopped allowing const fns in promoteds #53851. max_value is still marked as promotable, so that shouldn't be the issue. I'll investigate later today when I get back to a PC

So if I understood correctly simply using a vec![..] instead of plain [..] would solve that issue?
Maybe we should reiterate on this design for into_iter on arrays if that's the case. :D

[oli-obk]

minimal repro

    let x: &'static _ = &u8::max_value();

Though I thought it was a bug in a former version of the borrow checker that now got fixed.

Nope, it's a new bug that I was sure we had regression tests against.

[pnkfelix]

This was injected between rustc 1.31.0-nightly (5597ee8 2018-10-03) and rustc 1.31.0-nightly (8c4ad4e 2018-10-04)

Log of bors commits in that time in the details block

% git log 5597ee8..8c4ad4e --author bors --format=oneline
8c4ad4e Auto merge of #54649 - nikomatsakis:universes-refactor-1, r=scalexm
a57f1c9 Auto merge of #54666 - matthewjasper:mir-function-spans, r=pnkfelix
5de5281 Auto merge of #54784 - Manishearth:clippyup, r=oli-obk
5472b07 Auto merge of #54809 - pietroalbini:rollup, r=pietroalbini
8a0e5cb Auto merge of #54638 - christianpoveda:master, r=kennytm
088fc73 Auto merge of #53851 - oli-obk:local_promotion, r=eddyb
c67ea54 Auto merge of #54624 - arielb1:evaluate-outlives, r=nikomatsakis
d078728 Auto merge of #54447 - KiChjang:issue-54331, r=nikomatsakis
4bf883b Auto merge of #54391 - davidtwco:issue-54230, r=petrochenkov

[pnkfelix]

Hmm I wonder if this could somehow be a consequence fo #54447 ...?

• update: probably not, since this afflicts both AST-borrowck and MIR-borrowck.

[oli-obk]

Full diff: 5597ee8...8c4ad4e

#53851 (limiting promotability of const fns) also fell in there.

[oli-obk]

I even added unit tests, but never any for promoting functions from the libstd.

rust/src/librustc/ty/constness.rs

Line 88 in 0ee045e

fn is_promotable_const_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {

will only work if a function call is promoted in the same crate where the rustc_promotable function is declared.

I think the solution is to make the const qualifier eagerly call is_promotable_const_fn while a function is qualified to cache the result (in the query engine), so that the query is never evaluated in the perspective of another crate (and add an assert!(def_id.is_local())) to is_promotable_const_fn to safeguard against messing this up