Lint must_use on mem::replace by cuviper · Pull Request #71256 · rust-lang/rust

cuviper · 2020-04-17T18:42:52Z

This adds a hint on mem::replace, "if you don't need the old value,
you can just assign the new value directly". This is in similar spirit
to the must_use on ManuallyDrop::take.

This adds a hint on `mem::replace`, "if you don't need the old value, you can just assign the new value directly". This is in similar spirit to the `must_use` on `ManuallyDrop::take`.

rust-highfive · 2020-04-17T18:42:55Z

r? @kennytm

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cuviper · 2020-04-17T19:09:15Z

Huh, I didn't expect that this would already affect code in the compiler itself. I'll look into it.

cuviper · 2020-04-17T21:46:06Z

OK, github-actions CI/PR passed now.

estebank · 2020-04-19T19:21:04Z

I'm ok with the code changes. Couldn't find whether the lint is only warn-by-default. If it is, then r=me, after the nitpick about the test.

cuviper · 2020-04-20T01:22:50Z

I'm ok with the code changes. Couldn't find whether the lint is only warn-by-default. If it is, then r=me, after the nitpick about the test.

Yes, it is a warning by default -- the way that I check is with -Whelp:

$ rustc -Whelp | grep must_use
unused-must-use warn unused result of a type flagged as `#[must_use]`

I addressed the test nitpick too, so...

@bors r=estebank

bors · 2020-04-20T01:22:52Z

📌 Commit 7fca9f8 has been approved by estebank

Lint must_use on mem::replace This adds a hint on `mem::replace`, "if you don't need the old value, you can just assign the new value directly". This is in similar spirit to the `must_use` on `ManuallyDrop::take`.

Dylan-DPC-zz · 2020-04-20T12:38:41Z

fails since cargo doesn't use the result somewhere, (fixing it)

Dylan-DPC-zz · 2020-04-20T12:38:45Z

@bors r-

fix mem replace unused `mem::replace` will be linted as must_use, so modifying this. This is currently blocking rust-lang/rust#71256

cuviper · 2020-04-20T14:30:56Z

I see, cargo already had a warning in the normal build, but #![cfg_attr(test, deny(warnings))] stopped it in full CI. Thanks for going ahead with that fix!

Dylan-DPC-zz · 2020-04-20T14:32:10Z

the blocking pr is now merged

@bors r=estebank

bors · 2020-04-20T14:32:12Z

📌 Commit 7fca9f8 has been approved by estebank

cuviper · 2020-04-20T15:07:34Z

Do I need to update the cargo submodule too? Or are you handling that elsewhere?

Dylan-DPC-zz · 2020-04-20T15:11:29Z

Uh right we probably have to update cargo first

Dylan-DPC-zz · 2020-04-20T15:52:40Z

@bors r-

ehuss · 2020-04-20T16:42:36Z

I'll post a cargo update tomorrowish after the beta branch. There are several big changes that I don't feel comfortable sliding into beta at the last moment.

cuviper · 2020-04-22T16:46:58Z

Cargo was updated in #71402, so let's give this another shot.

@bors r=estebank

bors · 2020-04-22T16:47:00Z

📌 Commit 7fca9f8 has been approved by estebank

@ghost

Rollup of 5 pull requests Successful merges: - rust-lang#71256 (Lint must_use on mem::replace) - rust-lang#71350 (Error code explanation extra check) - rust-lang#71369 (allow wasm32 compilation of librustc_data_structures/profiling.rs) - rust-lang#71400 (proc_macro::is_available()) - rust-lang#71440 (Implement `Copy` for `AllocErr`) Failed merges: r? @ghost

Lint must_use on mem::replace
7c4ca59
This adds a hint on `mem::replace`, "if you don't need the old value, you can just assign the new value directly". This is in similar spirit to the `must_use` on `ManuallyDrop::take`.

rust-highfive assigned kennytm Apr 17, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 17, 2020

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Fix unused results from mem::replace
ccecae5

cuviper commented Apr 17, 2020
View reviewed changes

Comment threadsrc/test/ui/issues/issue-23611-enum-swap-in-drop.rs Outdated

kennytm requested a review from estebank April 19, 2020 15:52

allow(unused_must_use) in issue-23611-enum-swap-in-drop.rs
7fca9f8

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 20, 2020

Dylan-DPC-zz mentioned this pull request Apr 20, 2020
Rollup of 4 pull requests #71345
Closed

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Apr 20, 2020

Dylan-DPC-zz mentioned this pull request Apr 20, 2020
fix mem replace unused rust-lang/cargo#8138
Merged

kennytm added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 20, 2020

bors added a commit to rust-lang/cargo that referenced this pull request Apr 20, 2020
Auto merge of#8138- Dylan-DPC:fix/transmute_unused, r=alexcrichton
6a41339
fix mem replace unused `mem::replace` will be linted as must_use, so modifying this. This is currently blocking rust-lang/rust#71256

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Apr 20, 2020

bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Apr 20, 2020

Dylan-DPC-zz added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 20, 2020

ehuss mentioned this pull request Apr 21, 2020
Update cargo, rls #71402
Merged

cuviper mentioned this pull request Apr 22, 2020
discussion/tracking issue for #[must_use] functions in the standard library #48926
Closed

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Apr 22, 2020

Dylan-DPC-zz mentioned this pull request Apr 22, 2020
Rollup of 5 pull requests #71445
Merged

bors merged commit 10e47f5 into rust-lang:masterApr 23, 2020

nicokoch referenced this pull request in gridbugs/rodio Apr 23, 2020
Add comments explaining Drop impl for FrameData
99c0c36

nicokoch mentioned this pull request Apr 23, 2020
Fix stack overflow on audio change RustAudio/rodio#285
Merged

taiki-e mentioned this pull request May 12, 2020
mem::replace -> mem::take lint is too aggressive rust-lang/rust-clippy#5586
Closed

cuviper deleted the must_use_replace branch May 30, 2020 21:55

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