Skip to content

Debug impls of ExtractIf have inconsistent trait bounds #137654

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.

Sign up for GitHub

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

Jump to bottom
Open
dtolnay opened this issue Feb 26, 2025 · 5 comments · May be fixed by #139764
Open

Debug impls of ExtractIf have inconsistent trait bounds #137654

dtolnay opened this issue Feb 26, 2025 · 5 comments · May be fixed by #139764
Labels
C-bug Category: This is a bug. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

Comments

@dtolnay
Copy link
Member

dtolnay commented Feb 26, 2025

std::vec::ExtractIf has:

impl<T, F> Debug for ExtractIf<'_, T, F>
where
    T: Debug,
    F: Debug;

std::collections::linked_list::ExtractIf has:

impl<T, F> Debug for ExtractIf<'_, T, F>
where
    T: Debug;

std::collections::hash_set::ExtractIf has:

impl<T, F> Debug for ExtractIf<'_, T, F>
where
    F: FnMut(&T) -> bool;

std::collections::btree_set::ExtractIf has:

impl<T, F> Debug for ExtractIf<'_, T, F>
where
    T: Debug,
    F: FnMut(&T) -> bool;
Vec LinkedList HashSet BTreeSet
T: Debug ☑️ ☑️ ☑️
F: Debug ☑️
F: FnMut ☑️ ☑️

There should not need to be 4 different permutations for these 4 effectively-identical interfaces. We should be able to decide:

  • Should collection elements be printed or not.
  • Should the predicate be printed or not. Almost certainly not, given that closures do not implement Debug.
  • Should the Debug impl ever need to invoke the predicate. Almost certainly not.
@dtolnay dtolnay added C-bug Category: This is a bug. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Feb 26, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Feb 26, 2025
@dtolnay
Copy link
Member Author

dtolnay commented Feb 26, 2025

This is time-sensitive for Rust 1.87 if we want to change any of the impls that were just stabilized in nightly.

@jieyouxu jieyouxu removed the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Feb 26, 2025
@Noratrieb Noratrieb added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Feb 26, 2025
@m-ou-se
Copy link
Member

m-ou-se commented Mar 18, 2025

The ExtractIf types for Vec, LinkedList and HashSet have been stabilized in 1.87, which is still in nightly.

The one for BTreeSet is still unstable.

@m-ou-se
Copy link
Member

m-ou-se commented Mar 18, 2025

There should not need to be 4 different permutations for these 4 effectively-identical interfaces. We should be able to decide:

* Should collection elements be printed or not.

* Should the predicate be printed or not. Almost certainly not, given that closures do not implement Debug.

* Should the Debug impl ever need to invoke the predicate. Almost certainly not.

It sounds to me like it should in all cases be T: Debug only, like the one of LinkedList.

@BurntSushi
Copy link
Member

I agree. Just T: Debug only seems like the right call here. Nice catch @dtolnay!

This was referenced Apr 13, 2025
Merged
Draft
@dtolnay
Copy link
Member Author

dtolnay commented Apr 13, 2025

@Amanieu Amanieu removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Apr 15, 2025
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
C-bug Category: This is a bug. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
Projects
None yet
Milestone
No milestone
Development

Successfully merging a pull request may close this issue.

Consistent trait bounds for ExtractIf Debug impls dtolnay/rust
7 participants
@Amanieu @BurntSushi @m-ou-se @dtolnay @jieyouxu @rustbot @Noratrieb