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[NLL] Possible proptest-arbitrary-0.2.2 regression #53789

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lqd opened this issue Aug 29, 2018 · 4 comments
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[NLL] Possible proptest-arbitrary-0.2.2 regression #53789

lqd opened this issue Aug 29, 2018 · 4 comments
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A-NLL Area: Non-lexical lifetimes (NLL) NLL-complete Working towards the "valid code works" goal
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Edition 2018 RC 2

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lqd commented Aug 29, 2018

Filing for investigation.

The recent crater run found an interesting case in proptest-arbitrary 0.2.2, which used to compile with AST borrowck.

Crater logs.

There are 2 reproductions:

  • the first collates the necessary parts from proptest-arbitrary and proptest and reproduces faithfully the messages from the crater run. Playground.
  • the second is a bit more minimal, while still being accepted by AST borrowck. It is however, in an effort to simplify the code, partially automatically reduced to focus on only one of these two identical errors. Playground.
@lqd lqd added the A-NLL Area: Non-lexical lifetimes (NLL) label Aug 29, 2018
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I believe this is likely a duplicate of #53121

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lqd commented Aug 29, 2018

@nikomatsakis they might be sharing the same cause, but lacking the specific conditions that only fail with --crate-type lib in #53121

@nikomatsakis nikomatsakis added this to the Edition 2018 RC 2 milestone Sep 11, 2018
@nikomatsakis nikomatsakis added the NLL-complete Working towards the "valid code works" goal label Sep 11, 2018
@nikomatsakis nikomatsakis self-assigned this Sep 11, 2018
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Adding to the RC 2 milestone. Hopefully a dup of #53121. Assigning to myself as I am investigating both of them now.

@nikomatsakis nikomatsakis mentioned this issue Sep 11, 2018
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@nikomatsakis nikomatsakis mentioned this issue Sep 21, 2018
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Fix in #54453

bors added a commit that referenced this issue Sep 26, 2018
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Auto merge of #54453 - nikomatsakis:nll-issue-53121-shred-outlives, r…
c7df1f5 
…=pnkfelix

rework how we handle outlives relationships

When we encounter an outlives relationship involving a projection, we use to over-constrain in some cases with region constraints. We also used to evaluate whether the where-clauses in the environment might apply **before** running inference.

We now avoid doing both of those things:

- If there are where-clauses in the environment that might be useful, we add no constraints.
- After inference is done, we check if we wound up inferring values compatible with the where-clause, and make use of them if so.

I realize now that this PR includes some meandering commits and refactorings from when I expected to go in a different direction. If desired, I could try to remove some of those.

Fixes #53121
Fixes #53789

r? @pnkfelix
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