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odd new_ret_no_self warning: return type that wraps Self #3313

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matthiaskrgr opened this issue Oct 13, 2018 · 7 comments
Closed

odd new_ret_no_self warning: return type that wraps Self #3313

matthiaskrgr opened this issue Oct 13, 2018 · 7 comments
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@matthiaskrgr
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@matthiaskrgr matthiaskrgr commented Oct 13, 2018

clippy @ 601cc9d

This code comes from rls

impl ConcurrentJob {
    pub fn new() -> (ConcurrentJob, JobToken) {
        let (tx, rx) = bounded(0);
        let job = ConcurrentJob { chan: rx };
        let token = JobToken { _chan: tx };
        (job, token)
    }

    fn is_completed(&self) -> bool {
        is_closed(&self.chan)
    }
}

It causes the following clippy warning:

warning: methods called `new` usually return `Self`
  --> src/concurrency.rs:62:5
   |
62 | /     pub fn new() -> (ConcurrentJob, JobToken) {
63 | |         let (tx, rx) = bounded(0);
64 | |         let job = ConcurrentJob { chan: rx };
65 | |         let token = JobToken { _chan: tx };
66 | |         (job, token)
67 | |     }
   | |_____^
   |
note: lint level defined here
  --> src/main.rs:21:9
   |
21 | #![warn(clippy::all, rust_2018_idioms)]
   |         ^^^^^^^^^^^
   = note: #[warn(clippy::new_ret_no_self)] implied by #[warn(clippy::all)]
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#new_ret_no_self

I tried fixing this by making both ConcurrentJobs be Self however, ciippy kept warning, probably because it does not understand that the constructor actually returns a tuple of Self and something else?

impl ConcurrentJob {
    pub fn new() -> (Self, JobToken) {
        let (tx, rx) = bounded(0);
        let job = Self { chan: rx };
        let token = JobToken { _chan: tx };
        (job, token)
    }

    fn is_completed(&self) -> bool {
        is_closed(&self.chan)
    }
}

=>

warning: methods called `new` usually return `Self`
  --> src/concurrency.rs:62:5
   |
62 | /     pub fn new() -> (Self, JobToken) {
63 | |         let (tx, rx) = bounded(0);
64 | |         let job = Self { chan: rx };
65 | |         let token = JobToken { _chan: tx };
66 | |         (job, token)
67 | |     }
   | |_____^
   |
note: lint level defined here
  --> src/main.rs:21:9
   |
21 | #![warn(clippy::all, rust_2018_idioms)]
   |         ^^^^^^^^^^^
   = note: #[warn(clippy::new_ret_no_self)] implied by #[warn(clippy::all)]
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#new_ret_no_self
@matthiaskrgr
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@matthiaskrgr matthiaskrgr commented Oct 15, 2018

Found another one in my own code

error: methods called `new` usually return `Self`
  --> src/library.rs:48:5
   |
48 | /     pub(crate) fn new() -> Result<Self, (ErrorKind, String)> {
49 | |         let cargo_cfg = match cargo::util::config::Config::default() {
50 | |             Ok(cargo_cfg) => cargo_cfg,
51 | |             _ => {
...  |
87 | |         })
88 | |     }
   | |_____^
   |
   = note: `-D clippy::new-ret-no-self` implied by `-D warnings`
   = help: for further information visit https://rust-lang-nursery.github.io/rust-clippy/v0.0.212/index.html#new_ret_no_self

I consider this a FP.

@flip1995 flip1995 added the C-bug label Oct 15, 2018
@flip1995
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@flip1995 flip1995 commented Oct 15, 2018

@JoshMcguigan
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@JoshMcguigan JoshMcguigan commented Oct 16, 2018

Where does clippy look to determine what is considered standard behavior? Does the Rust standard library have any examples of a new method returning (self, other), Result<Self, Err>, or Option<Self>?

I'm not trying to express an opinion one way or another here, I'd just like to understand how it is determined whether something like this should be considered a false positive or not?

@programmerjake
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@programmerjake programmerjake commented Oct 16, 2018

NonNull::new returns Option<Self>

@oli-obk
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@oli-obk oli-obk commented Oct 16, 2018

Where does clippy look to determine what is considered standard behavior?

Mostly the libstd. There's no established process except for judgement calls though.

We could walk the return type and if it contains Self anywhere accept that.

Or if we want to be more strict, we only accept Result<Self, T>, Option<T> and tuples containing one element of type T

@cramertj
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@cramertj cramertj commented Oct 16, 2018

This also resulted in many errors in futures on new functions that return *mut Self, Result<Self, E>, (Self, Someother), etc. +1 for "walk return type and see if it contains Self anywhere". (cc rust-lang/futures-rs#1291)

matthiaskrgr added a commit to matthiaskrgr/rust-clippy that referenced this issue Oct 18, 2018
matthiaskrgr added a commit to matthiaskrgr/rust-clippy that referenced this issue Oct 18, 2018
…tion.

fix trivial typo on the way
flip1995 added a commit that referenced this issue Oct 18, 2018
new_ret_no_self: add sample from #3313 to Known Problems section.
@matthiaskrgr matthiaskrgr changed the title odd new_ret_no_self warning odd new_ret_no_self warning: return type that wraps Self Oct 19, 2018
@JoshMcguigan
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@JoshMcguigan JoshMcguigan commented Oct 19, 2018

I've started working on this.

bors bot added a commit that referenced this issue Oct 24, 2018
Merge #3338
3338: new_ret_no_self false positives r=flip1995 a=JoshMcguigan

~~WORK IN PROGRESS~~

I plan to fix all of the false positives in #3313 in this PR, but I wanted to open it now to start gathering feedback.

In this first commit, I've updated the lint to allow tuple return types as long as `Self` shows up at least once, in any position of the tuple. I believe this is the broadest possible interpretation of what should be allowed for tuple return types, but I would certainly be okay making the lint more strict. 

fixes #3313 

Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
bors bot added a commit that referenced this issue Oct 24, 2018
Merge #3338
3338: new_ret_no_self false positives r=flip1995 a=JoshMcguigan

~~WORK IN PROGRESS~~

I plan to fix all of the false positives in #3313 in this PR, but I wanted to open it now to start gathering feedback.

In this first commit, I've updated the lint to allow tuple return types as long as `Self` shows up at least once, in any position of the tuple. I believe this is the broadest possible interpretation of what should be allowed for tuple return types, but I would certainly be okay making the lint more strict. 

fixes #3313 

Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
@bors bors bot closed this in #3338 Oct 24, 2018
matthiaskrgr added a commit to matthiaskrgr/rust-clippy that referenced this issue Oct 25, 2018
…lems section."

This reverts commit fd2f6dd.

Issue rust-lang#3313 has been fixed.
bors bot added a commit that referenced this issue Oct 25, 2018
Merge #3358
3358: Revert "new_ret_no_self: add sample from #3313 to Known Problems section." r=oli-obk a=matthiaskrgr

This reverts commit fd2f6dd.

Issue #3313 has been fixed.

Co-authored-by: Matthias Krüger <matthias.krueger@famsik.de>
Emerentius pushed a commit to Emerentius/rust-clippy that referenced this issue Apr 10, 2020
The lint was changed to be more lenient than the documentation implies in PR rust-lang#3338.
Related issue rust-lang#3313
bors added a commit that referenced this issue Apr 13, 2020
Update documentation for new_ret_no_self

changelog: Update documentation for lint new_ret_no_self to reflect that the return type must only contain `Self`, not be `Self`

The lint was changed to be more lenient than the documentation implies in PR #3338 (Related issue #3313)
bors added a commit that referenced this issue Apr 13, 2020
Update documentation for new_ret_no_self

changelog: Update documentation for lint new_ret_no_self to reflect that the return type must only contain `Self`, not be `Self`

The lint was changed to be more lenient than the documentation implies in PR #3338 (Related issue #3313)
flip1995 pushed a commit to flip1995/rust-clippy that referenced this issue May 5, 2020
Changes:
````
new_ret_no_self: add sample from rust-lang#3313 to Known Problems section.
Support multiline comments and hopefully fix panic
Check for comments in collapsible ifs
Resolve ICE in needless range loop lint
RIIR update_lints: Update changelog links
Rename if_let_redundant_pattern_matching to redundant_pattern_matching
Add lint for redundant pattern matching for explicit return boolean
Fix issue rust-lang#3322: reword help message for len_zero
Simplify manual_memcpy suggestion in some cases
Fix dogfood
Update known problems for unnecessary_fold
RIIR update_lints: Replace lint count in README.md
Rename `active_lints` to `usable_lints`
Add comment on WalkDir vs. fs::read_dir
sort_by -> sort_by_key
Some more documentation for clippy_dev
Use `WalkDir` to also gather from subdirectories
Avoid linting `boxed_local` on trait implementations.
Website: Make lint categories linkable
Restore clippy_dummy's placeholder name
Swap order of methods in `needless_range_loop` suggestion in some cases
Revert "Exclude pattern guards from unnecessary_fold lint"
Exclude pattern guards from unnecessary_fold lint
````
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