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fix "bivariant wf" bug in the NLL subtyping code #54105

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nikomatsakis opened this issue Sep 10, 2018 · 8 comments
Open

fix "bivariant wf" bug in the NLL subtyping code #54105

nikomatsakis opened this issue Sep 10, 2018 · 8 comments
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@nikomatsakis
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A-NLL Area: Non-lexical lifetimes (NLL) A-traits Area: Trait system C-bug Category: This is a bug. NLL-sound Working towards the "invalid code does not compile" goal P-medium Medium priority T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@nikomatsakis
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#53873 generalized the NLL subtyping code to handle subtyping and the like, but I think it is vulnerable to a similar flaw as the one from #41677. I didn't want to block that PR so I am filing this issue to follow-up.
@nikomatsakis nikomatsakis self-assigned this Sep 10, 2018
@nikomatsakis nikomatsakis added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. NLL-sound Working towards the "invalid code does not compile" goal labels Sep 10, 2018
@nikomatsakis nikomatsakis added this to the Edition 2018 RC 2 milestone Sep 10, 2018
nikomatsakis added a commit to nikomatsakis/rust that referenced this issue Sep 10, 2018
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add link to rust-lang#54105
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@nikomatsakis nikomatsakis mentioned this issue Sep 10, 2018
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bors added a commit that referenced this issue Sep 11, 2018
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Auto merge of #53873 - nikomatsakis:nll-universe-subtyping-and-patter…
2f1547c 
…n-ascription, r=pnkfelix

support ascription for patterns in NLL

This implements the strategy outlined in [this comment](#47184 (comment)):

- We first extend the NLL subtyping code so it can handle inference variables and subtyping.
- Then we extend HAIR patterns with type ascription.
- Then we treat the type `T` in `let pat: T = ...` as an ascription.

Before landing, a few things:

- [x] Fix the WF rule bug (filed a FIXME #54105)
- [x] Fix an ICE I encountered locally around bound regions, or else file a follow-up
- [x] More tests probably =)

r? @pnkfelix
@nikomatsakis nikomatsakis mentioned this issue Oct 2, 2018
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@nikomatsakis nikomatsakis added the A-NLL Area: Non-lexical lifetimes (NLL) label Oct 4, 2018
@pnkfelix pnkfelix self-assigned this Oct 9, 2018
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pnkfelix commented Oct 9, 2018

assigning self to this to try to help offload work from @nikomatsakis

@nikomatsakis
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I have yet to come up with a way to exercise this bug. I tried e.g. this example but we do catch it.

@nikomatsakis
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nikomatsakis commented Oct 18, 2018 •
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I'm demoting this to Release. I still think there is probably a bug here but since we don't even know how to reproduce it, it doesn't seem like an RC2 blocker.

@nikomatsakis nikomatsakis removed this from the Rust 2018 Release milestone Nov 13, 2018
@nikomatsakis nikomatsakis added the A-traits Area: Trait system label Nov 13, 2018
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Tagging as A-traits too because @scalexm is expanding this code as part of their work on the trait system unification code, and we may wind up fixing it then. Still need to come up with a test case.

Removing from the Rust 2018 milestone.

@nikomatsakis nikomatsakis self-assigned this Nov 28, 2018
@pnkfelix pnkfelix mentioned this issue Jan 21, 2019
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@pnkfelix
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NLL triage. This needs prioritization. I'm inclined to go with P-medium.

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nominating for discussion at NLL meeting tonight. Namely, I'm seeking a volunteer to look for a test case.

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pnkfelix commented Feb 27, 2019 •
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removing I-nominated tag. We discussed briefly at the NLL meeting but I think I didn't make the bait here attractive enough.

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pnkfelix commented Mar 6, 2019

NLL-triage. Marking P-medium.

@pnkfelix pnkfelix added the P-medium Medium priority label Mar 6, 2019
@jonas-schievink jonas-schievink added the C-bug Category: This is a bug. label Jan 13, 2020
@lcnr lcnr mentioned this issue May 2, 2020
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@lcnr lcnr mentioned this issue Jun 8, 2022
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A-NLL Area: Non-lexical lifetimes (NLL) A-traits Area: Trait system C-bug Category: This is a bug. NLL-sound Working towards the "invalid code does not compile" goal P-medium Medium priority T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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mir relate: we don't need needs_wf lcnr/rust
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@nikomatsakis @pnkfelix @jonas-schievink