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

[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

[dillona]

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

[Mark-Simulacrum]

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

[matthewjasper]

Likely #77638

[Mark-Simulacrum]

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

[matthewjasper]

I think that's right

[camelid]

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