New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add #[must_use] to a few standard library methods #49533

Merged
merged 1 commit into from Apr 5, 2018

Conversation

Projects
None yet
6 participants
@scottmcm
Member

scottmcm commented Mar 31, 2018

Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.

Discuss :)

warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
  --> $DIR/fn_must_use_stdlib.rs:19:5
   |
LL |     "1 2 3".split_whitespace().collect::<Vec<_>>();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:21:5
   |
LL |     "hello".to_owned();
   |     ^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:23:5
   |
LL |     String::from("world").clone();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

cc #48926

Add #[must_use] to a few standard library methods
Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.

Discuss :)
@scottmcm

This comment has been minimized.

Member

scottmcm commented Apr 1, 2018

Looks like highfive was asleep for this one, so picking, from the must_use tracking issue,

r? @nikomatsakis

@nikomatsakis

This comment has been minimized.

Contributor

nikomatsakis commented Apr 2, 2018

@bors r+

@bors

This comment has been minimized.

Contributor

bors commented Apr 2, 2018

📌 Commit fb7deda has been approved by nikomatsakis

@@ -1368,6 +1368,7 @@ pub trait Iterator {
/// [`Result`]: ../../std/result/enum.Result.html
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]

This comment has been minimized.

@cramertj

cramertj Apr 2, 2018

Member

I think this is going to be annoying for the "collect to unit" use-case. I don't know how much we want to support that, but I thought it worth pointing out.

This comment has been minimized.

@ExpHP

ExpHP Apr 2, 2018

Contributor

AFAICT Unit-returning functions never trigger the warning, even if they are the result of monomorphising a function generic in its output type. Also, there's a use case for that FromIterator implementation besides just making collect::<Result<()>> work?

kennytm added a commit to kennytm/rust that referenced this pull request Apr 3, 2018

Rollup merge of rust-lang#49533 - scottmcm:more-must-use, r=nikomatsakis
Add #[must_use] to a few standard library methods

Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.

Discuss :)

```rust
warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
  --> $DIR/fn_must_use_stdlib.rs:19:5
   |
LL |     "1 2 3".split_whitespace().collect::<Vec<_>>();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:21:5
   |
LL |     "hello".to_owned();
   |     ^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:23:5
   |
LL |     String::from("world").clone();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

cc rust-lang#48926

@kennytm kennytm referenced this pull request Apr 3, 2018

Closed

Rollup of 9 pull requests #49615

kennytm added a commit to kennytm/rust that referenced this pull request Apr 3, 2018

Rollup merge of rust-lang#49533 - scottmcm:more-must-use, r=nikomatsakis
Add #[must_use] to a few standard library methods

Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.

Discuss :)

```rust
warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
  --> $DIR/fn_must_use_stdlib.rs:19:5
   |
LL |     "1 2 3".split_whitespace().collect::<Vec<_>>();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:21:5
   |
LL |     "hello".to_owned();
   |     ^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:23:5
   |
LL |     String::from("world").clone();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

cc rust-lang#48926

bors added a commit that referenced this pull request Apr 3, 2018

Auto merge of #49620 - kennytm:rollup, r=kennytm
Rollup of 14 pull requests

Successful merges:

 - #49179 (Handle future deprecation annotations )
 - #49512 (Add support for variant and types fields for intra links)
 - #49516 (Add missing anchor for union type fields)
 - #49532 (Add test for rustdoc ignore test)
 - #49533 (Add #[must_use] to a few standard library methods)
 - #49570 (avoid IdxSets containing garbage above the universe length)
 - #49594 (Add some performance guidance to std::fs and std::io docs)
 - #49599 (Fix typo)
 - #49603 (Fix url for intra link provided method)
 - #49609 (run-pass/attr-stmt-expr: expand test cases)
 - #49612 (Fix "since" version for getpid feature.)
 - #49618 (Fix build error when compiling libcore for 16bit targets)
 - #49619 (tweak core::fmt docs)
 - #49623 (update mdbook)

Failed merges:

kennytm added a commit to kennytm/rust that referenced this pull request Apr 4, 2018

Rollup merge of rust-lang#49533 - scottmcm:more-must-use, r=nikomatsakis
Add #[must_use] to a few standard library methods

Chosen to start a precedent of using it on ones that are potentially-expensive and where using it for side effects is particularly discouraged.

Discuss :)

```rust
warning: unused return value of `std::iter::Iterator::collect` which must be used: if you really need to exhaust the iterator, consider `.for_each(drop)` instead
  --> $DIR/fn_must_use_stdlib.rs:19:5
   |
LL |     "1 2 3".split_whitespace().collect::<Vec<_>>();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::borrow::ToOwned::to_owned` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:21:5
   |
LL |     "hello".to_owned();
   |     ^^^^^^^^^^^^^^^^^^^

warning: unused return value of `std::clone::Clone::clone` which must be used: cloning is often expensive and is not expected to have side effects
  --> $DIR/fn_must_use_stdlib.rs:23:5
   |
LL |     String::from("world").clone();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

cc rust-lang#48926

bors added a commit that referenced this pull request Apr 4, 2018

Auto merge of #49642 - kennytm:rollup, r=kennytm
Rollup of 20 pull requests

Successful merges:

 - #49179 (Handle future deprecation annotations )
 - #49512 (Add support for variant and types fields for intra links)
 - #49515 (fix targetted value background)
 - #49516 (Add missing anchor for union type fields)
 - #49532 (Add test for rustdoc ignore test)
 - #49533 (Add #[must_use] to a few standard library methods)
 - #49540 (Fix miri Discriminant() for non-ADT)
 - #49559 (Introduce Vec::resize_with method (see #41758))
 - #49570 (avoid IdxSets containing garbage above the universe length)
 - #49577 (Stabilize String::replace_range)
 - #49599 (Fix typo)
 - #49603 (Fix url for intra link provided method)
 - #49607 (Stabilize iterator methods in 1.27)
 - #49609 (run-pass/attr-stmt-expr: expand test cases)
 - #49612 (Fix "since" version for getpid feature.)
 - #49618 (Fix build error when compiling libcore for 16bit targets)
 - #49619 (tweak core::fmt docs)
 - #49623 (update mdbook)
 - #49637 (Stabilize parent_id())
 - #49639 (Update Cargo)

Failed merges:

bors added a commit that referenced this pull request Apr 4, 2018

Auto merge of #49642 - kennytm:rollup, r=kennytm
Rollup of 25 pull requests

Successful merges:

 - #49179 (Handle future deprecation annotations )
 - #49512 (Add support for variant and types fields for intra links)
 - #49515 (fix targetted value background)
 - #49516 (Add missing anchor for union type fields)
 - #49532 (Add test for rustdoc ignore test)
 - #49533 (Add #[must_use] to a few standard library methods)
 - #49540 (Fix miri Discriminant() for non-ADT)
 - #49559 (Introduce Vec::resize_with method (see #41758))
 - #49570 (avoid IdxSets containing garbage above the universe length)
 - #49577 (Stabilize String::replace_range)
 - #49599 (Fix typo)
 - #49603 (Fix url for intra link provided method)
 - #49607 (Stabilize iterator methods in 1.27)
 - #49609 (run-pass/attr-stmt-expr: expand test cases)
 - #49612 (Fix "since" version for getpid feature.)
 - #49618 (Fix build error when compiling libcore for 16bit targets)
 - #49619 (tweak core::fmt docs)
 - #49637 (Stabilize parent_id())
 - #49639 (Update Cargo)
 - #49628 (Re-write the documentation index)
 - #49594 (Add some performance guidance to std::fs and std::io docs)
 - #49625 (miri: add public alloc_kind accessor)
 - #49634 (Add a test for the fix to issue #43058)
 - #49641 (Regression test for #46314)
 - #49547 (Unignore borrowck test)

Failed merges:

@alexcrichton alexcrichton merged commit fb7deda into rust-lang:master Apr 5, 2018

1 check passed

continuous-integration/travis-ci/pr The Travis CI build passed
Details

@scottmcm scottmcm deleted the scottmcm:more-must-use branch Apr 5, 2018

@zackmdavis zackmdavis referenced this pull request Sep 24, 2018

Open

Tracking issue for RFC 2383, "Lint Reasons RFC" #54503

1 of 6 tasks complete
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment