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regression 1.49: failing to infer generic param when not explicitly stated #79905

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@rylev

Logs https://crater-reports.s3.amazonaws.com/beta-1.49-1/beta-2020-11-26/reg/traitgraph-0.1.0/log.txt

[INFO] [stdout] error[E0282]: type annotations needed
[INFO] [stdout]   --> src/algo/traversal.rs:92:35
[INFO] [stdout]    |
[INFO] [stdout] 92 |                 if *rank_entry == None.into() {
[INFO] [stdout]    |                                   ^^^^ cannot infer type for type parameter `T` declared on the enum `Option`

@rustbot modify labels: +regression-from-stable-to-beta

Activity

  1. added
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Dec 10, 2020
  2. added this to the 1.49.0 milestone on Dec 10, 2020
  3. dillona commented on Dec 11, 2020

    @dillona
    Contributor

    searched nightlies: from nightly-2020-09-24 to nightly-2020-12-11
    regressed nightly: nightly-2020-10-07
    searched commits: from a1dfd24 to 98edd1f
    regressed commit: 08e2d46

    bisected with cargo-bisect-rustc v0.6.0

    Host triple: aarch64-unknown-linux-gnu
    Reproduce with:

    cargo bisect-rustc
  4. Mark-Simulacrum commented on Dec 11, 2020

    @Mark-Simulacrum
    Member

    cc @matthewjasper @nikomatsakis -- looks like this is another bug due to #73905, but looks different from the one we're experimenting with a targeted patch for right now

  5. matthewjasper commented on Dec 11, 2020

    @matthewjasper
    Contributor

    Likely #77638

  6. Mark-Simulacrum commented on Dec 11, 2020

    @Mark-Simulacrum
    Member

    Hm ok, that seems reasonable then. Does it seem right to you to close as won't fix?

  7. matthewjasper commented on Dec 11, 2020

    @matthewjasper
    Contributor

    I think that's right

  8. camelid commented on Dec 11, 2020

    @camelid
    Member

    Closing as per simulacrum's and matthewjasper's comments.

  9. added
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    and removed
    I-prioritizeIssue needs a team member to assess the impact. Will be replaced by P-{low,medium,high,critical}
    on Dec 11, 2020
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    A-inferenceArea: Type inferenceT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.regression-from-stable-to-betaPerformance or correctness regression from stable to beta.

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