[beta][clippy] backport multiple FP fixes for a warn-by-default lint

[flip1995]

This backports the PR rust-lang/rust-clippy#6016 fixing multiple FPs:

rust-lang/rust-clippy#5902
rust-lang/rust-clippy#5979
rust-lang/rust-clippy#5985

We didn't have any complaints about this lint, since me merged this PR.

cc @ebroto (sorry I forgot about this, since we talked about the backport 3 weeks ago 😐)

r? @pietroalbini

[rust-highfive]

⚠️ Warning ⚠️

• Pull requests are usually filed against the master branch for this repo, but this one is against beta. Please double check that you specified the right target!

[emilyalbini]

@bors r+ p=10 rollup=never

[bors]

📌 Commit 4a91098 has been approved by pietroalbini

[bors]

⌛ Testing commit 4a91098 with merge 06bcf4d722aaf93e0d95b05e54fa4e0ff2466b23...

[rust-log-analyzer]

The job i686-msvc-2 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @rust-lang/infra. (Feature Requests)

[emilyalbini]

Spurious failure.

@bors retry

[bors]

⌛ Testing commit 4a91098 with merge 03de2742e0f7e4d5628e1367f7551f487ab07ce7...

[bors]

💔 Test failed - checks-actions

[flip1995]

Again the same error? 🤔

Caused by:
  failed to fetch `https://github.com/rust-lang/crates.io-index`

Caused by:
  error inflating zlib stream; class=Zlib (5)

[emilyalbini]

@bors retry

[bors]

⌛ Testing commit 4a91098 with merge e28d2bd...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: pietroalbini
Pushing e28d2bd to beta...