Drop FnMut trait bounds from ExtractIf data structures #616

dtolnay · 2025-04-13T19:46:31Z

This is going to be required for resolving rust-lang/rust#137654.

Of the 4 distinct signatures shown in that issue, the one we'd like to standardize on is the one currently being used by alloc::collections::linked_list::ExtractIf, which is no F: Debug bound, no F: FnMut bound, only T: Debug bound.

Without this change in hashbrown, the desired Debug impls in std for std::collections::hash_map::ExtractIf and std::collections::hash_set::ExtractIf fail to compile.

error[E0277]: expected a `FnMut(&K, &mut V)` closure, found `F`
    --> library/std/src/collections/hash/map.rs:1683:11
     |
1683 |     base: base::ExtractIf<'a, K, V, F>,
     |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnMut(&K, &mut V)` closure, found `F`
     |
note: required by a bound in `hashbrown::hash_map::ExtractIf`
    --> hashbrown/src/map.rs:2601:8
     |
2599 | pub struct ExtractIf<'a, K, V, F, A: Allocator = Global>
     |            --------- required by a bound in this struct
2600 | where
2601 |     F: FnMut(&K, &mut V) -> bool,
     |        ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `ExtractIf`
help: consider restricting type parameter `F` with trait `FnMut`
     |
1682 | pub struct ExtractIf<'a, K, V, F: for<'a, 'b> FnMut(&'a K, &'b mut V)> {
     |                                 +++++++++++++++++++++++++++++++++++++

Update hashbrown dependency to unblock ExtractIf improvements Release notes: https://github.com/rust-lang/hashbrown/releases/tag/v0.15.3 Relevant to me, this release includes rust-lang/hashbrown#616 which unblocks rust-lang#139764.

Update hashbrown dependency to unblock ExtractIf improvements Release notes: https://github.com/rust-lang/hashbrown/releases/tag/v0.15.3 Relevant to me, this release includes rust-lang/hashbrown#616 which unblocks rust-lang/rust#139764.

Consistent trait bounds for ExtractIf Debug impls Closes rust-lang#137654. Refer to that issue for a table of the **4** different impl signatures we previously had in the standard library for Debug impls of various ExtractIf iterator types. The one we are standardizing on is the one so far only used by `alloc::collections::linked_list::ExtractIf`, which is _no_ `F: Debug` bound, _no_ `F: FnMut` bound, only `T: Debug` bound. This PR applies the following signature changes: ```diff /* alloc::collections::btree_map */ pub struct ExtractIf<'a, K, V, F, A = Global> where - F: 'a + FnMut(&K, &mut V) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, K, V, F, + A, > where K: Debug, V: Debug, - F: FnMut(&K, &mut V) -> bool, + A: Allocator + Clone, ``` ```diff /* alloc::collections::btree_set */ pub struct ExtractIf<'a, T, F, A = Global> where - T: 'a, - F: 'a + FnMut(&T) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: FnMut(&T) -> bool, A: Allocator + Clone, ``` ```diff /* alloc::collections::linked_list */ impl Debug for ExtractIf<'a, T, F, + A, > where T: Debug, + A: Allocator, ``` ```diff /* alloc::vec */ impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: Debug, A: Allocator, - A: Debug, ``` ```diff /* std::collections::hash_map */ pub struct ExtractIf<'a, K, V, F> where - F: FnMut(&K, &mut V) -> bool, impl Debug for ExtractIf<'a, K, V, F> where + K: Debug, + V: Debug, - F: FnMut(&K, &mut V) -> bool, ``` ```diff /* std::collections::hash_set */ pub struct ExtractIf<'a, T, F> where - F: FnMut(&T) -> bool, impl Debug for ExtractIf<'a, T, F> where + T: Debug, - F: FnMut(&T) -> bool, ``` I have made the following changes to bring these types into better alignment with one another. - Delete `F: Debug` bounds. These are especially problematic because Rust closures do not come with a Debug impl, rendering the impl useless. - Delete `A: Debug` bounds. Allocator parameters are unstable for now, but in the future this would become an API commitment that we do not debug-print a representation of the allocator when printing an iterator. - Delete `F: FnMut` bounds. Requires `hashbrown` PR: rust-lang/hashbrown#616. **API commitment:** we commit to not doing RefCell voodoo inside ExtractIf to have some way for its Debug impl (which takes &self) to call a FnMut closure, if this is even possible. - Add `T: Debug` bounds (or `K`/`V`), even on Debug impls that do not currently make use of them, but might in the future. **Breaking change.** Must backport into Rust 1.87 (current beta) or do a de-stabilization PR in beta to delay those types by one release. - Render using `debug_struct` + `finish_non_exhaustive`, instead of `debug_tuple`. - Do not render the _entire_ underlying collection. - Show a "peek" field indicating the current position of the iterator.

Rollup merge of rust-lang#139764 - dtolnay:extractif, r=Amanieu Consistent trait bounds for ExtractIf Debug impls Closes rust-lang#137654. Refer to that issue for a table of the **4** different impl signatures we previously had in the standard library for Debug impls of various ExtractIf iterator types. The one we are standardizing on is the one so far only used by `alloc::collections::linked_list::ExtractIf`, which is _no_ `F: Debug` bound, _no_ `F: FnMut` bound, only `T: Debug` bound. This PR applies the following signature changes: ```diff /* alloc::collections::btree_map */ pub struct ExtractIf<'a, K, V, F, A = Global> where - F: 'a + FnMut(&K, &mut V) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, K, V, F, + A, > where K: Debug, V: Debug, - F: FnMut(&K, &mut V) -> bool, + A: Allocator + Clone, ``` ```diff /* alloc::collections::btree_set */ pub struct ExtractIf<'a, T, F, A = Global> where - T: 'a, - F: 'a + FnMut(&T) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: FnMut(&T) -> bool, A: Allocator + Clone, ``` ```diff /* alloc::collections::linked_list */ impl Debug for ExtractIf<'a, T, F, + A, > where T: Debug, + A: Allocator, ``` ```diff /* alloc::vec */ impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: Debug, A: Allocator, - A: Debug, ``` ```diff /* std::collections::hash_map */ pub struct ExtractIf<'a, K, V, F> where - F: FnMut(&K, &mut V) -> bool, impl Debug for ExtractIf<'a, K, V, F> where + K: Debug, + V: Debug, - F: FnMut(&K, &mut V) -> bool, ``` ```diff /* std::collections::hash_set */ pub struct ExtractIf<'a, T, F> where - F: FnMut(&T) -> bool, impl Debug for ExtractIf<'a, T, F> where + T: Debug, - F: FnMut(&T) -> bool, ``` I have made the following changes to bring these types into better alignment with one another. - Delete `F: Debug` bounds. These are especially problematic because Rust closures do not come with a Debug impl, rendering the impl useless. - Delete `A: Debug` bounds. Allocator parameters are unstable for now, but in the future this would become an API commitment that we do not debug-print a representation of the allocator when printing an iterator. - Delete `F: FnMut` bounds. Requires `hashbrown` PR: rust-lang/hashbrown#616. **API commitment:** we commit to not doing RefCell voodoo inside ExtractIf to have some way for its Debug impl (which takes &self) to call a FnMut closure, if this is even possible. - Add `T: Debug` bounds (or `K`/`V`), even on Debug impls that do not currently make use of them, but might in the future. **Breaking change.** Must backport into Rust 1.87 (current beta) or do a de-stabilization PR in beta to delay those types by one release. - Render using `debug_struct` + `finish_non_exhaustive`, instead of `debug_tuple`. - Do not render the _entire_ underlying collection. - Show a "peek" field indicating the current position of the iterator.

Consistent trait bounds for ExtractIf Debug impls Closes rust-lang#137654. Refer to that issue for a table of the **4** different impl signatures we previously had in the standard library for Debug impls of various ExtractIf iterator types. The one we are standardizing on is the one so far only used by `alloc::collections::linked_list::ExtractIf`, which is _no_ `F: Debug` bound, _no_ `F: FnMut` bound, only `T: Debug` bound. This PR applies the following signature changes: ```diff /* alloc::collections::btree_map */ pub struct ExtractIf<'a, K, V, F, A = Global> where - F: 'a + FnMut(&K, &mut V) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, K, V, F, + A, > where K: Debug, V: Debug, - F: FnMut(&K, &mut V) -> bool, + A: Allocator + Clone, ``` ```diff /* alloc::collections::btree_set */ pub struct ExtractIf<'a, T, F, A = Global> where - T: 'a, - F: 'a + FnMut(&T) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: FnMut(&T) -> bool, A: Allocator + Clone, ``` ```diff /* alloc::collections::linked_list */ impl Debug for ExtractIf<'a, T, F, + A, > where T: Debug, + A: Allocator, ``` ```diff /* alloc::vec */ impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: Debug, A: Allocator, - A: Debug, ``` ```diff /* std::collections::hash_map */ pub struct ExtractIf<'a, K, V, F> where - F: FnMut(&K, &mut V) -> bool, impl Debug for ExtractIf<'a, K, V, F> where + K: Debug, + V: Debug, - F: FnMut(&K, &mut V) -> bool, ``` ```diff /* std::collections::hash_set */ pub struct ExtractIf<'a, T, F> where - F: FnMut(&T) -> bool, impl Debug for ExtractIf<'a, T, F> where + T: Debug, - F: FnMut(&T) -> bool, ``` I have made the following changes to bring these types into better alignment with one another. - Delete `F: Debug` bounds. These are especially problematic because Rust closures do not come with a Debug impl, rendering the impl useless. - Delete `A: Debug` bounds. Allocator parameters are unstable for now, but in the future this would become an API commitment that we do not debug-print a representation of the allocator when printing an iterator. - Delete `F: FnMut` bounds. Requires `hashbrown` PR: rust-lang/hashbrown#616. **API commitment:** we commit to not doing RefCell voodoo inside ExtractIf to have some way for its Debug impl (which takes &self) to call a FnMut closure, if this is even possible. - Add `T: Debug` bounds (or `K`/`V`), even on Debug impls that do not currently make use of them, but might in the future. **Breaking change.** Must backport into Rust 1.87 (current beta) or do a de-stabilization PR in beta to delay those types by one release. - Render using `debug_struct` + `finish_non_exhaustive`, instead of `debug_tuple`. - Do not render the _entire_ underlying collection. - Show a "peek" field indicating the current position of the iterator.

Consistent trait bounds for ExtractIf Debug impls Closes #137654. Refer to that issue for a table of the **4** different impl signatures we previously had in the standard library for Debug impls of various ExtractIf iterator types. The one we are standardizing on is the one so far only used by `alloc::collections::linked_list::ExtractIf`, which is _no_ `F: Debug` bound, _no_ `F: FnMut` bound, only `T: Debug` bound. This PR applies the following signature changes: ```diff /* alloc::collections::btree_map */ pub struct ExtractIf<'a, K, V, F, A = Global> where - F: 'a + FnMut(&K, &mut V) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, K, V, F, + A, > where K: Debug, V: Debug, - F: FnMut(&K, &mut V) -> bool, + A: Allocator + Clone, ``` ```diff /* alloc::collections::btree_set */ pub struct ExtractIf<'a, T, F, A = Global> where - T: 'a, - F: 'a + FnMut(&T) -> bool, Allocator + Clone, impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: FnMut(&T) -> bool, A: Allocator + Clone, ``` ```diff /* alloc::collections::linked_list */ impl Debug for ExtractIf<'a, T, F, + A, > where T: Debug, + A: Allocator, ``` ```diff /* alloc::vec */ impl Debug for ExtractIf<'a, T, F, A> where T: Debug, - F: Debug, A: Allocator, - A: Debug, ``` ```diff /* std::collections::hash_map */ pub struct ExtractIf<'a, K, V, F> where - F: FnMut(&K, &mut V) -> bool, impl Debug for ExtractIf<'a, K, V, F> where + K: Debug, + V: Debug, - F: FnMut(&K, &mut V) -> bool, ``` ```diff /* std::collections::hash_set */ pub struct ExtractIf<'a, T, F> where - F: FnMut(&T) -> bool, impl Debug for ExtractIf<'a, T, F> where + T: Debug, - F: FnMut(&T) -> bool, ``` I have made the following changes to bring these types into better alignment with one another. - Delete `F: Debug` bounds. These are especially problematic because Rust closures do not come with a Debug impl, rendering the impl useless. - Delete `A: Debug` bounds. Allocator parameters are unstable for now, but in the future this would become an API commitment that we do not debug-print a representation of the allocator when printing an iterator. - Delete `F: FnMut` bounds. Requires `hashbrown` PR: rust-lang/hashbrown#616. **API commitment:** we commit to not doing RefCell voodoo inside ExtractIf to have some way for its Debug impl (which takes &self) to call a FnMut closure, if this is even possible. - Add `T: Debug` bounds (or `K`/`V`), even on Debug impls that do not currently make use of them, but might in the future. **Breaking change.** Must backport into Rust 1.87 (current beta) or do a de-stabilization PR in beta to delay those types by one release. - Render using `debug_struct` + `finish_non_exhaustive`, instead of `debug_tuple`. - Do not render the _entire_ underlying collection. - Show a "peek" field indicating the current position of the iterator.

Drop FnMut trait bounds from ExtractIf data structures

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cuviper approved these changes Apr 13, 2025

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This was referenced Apr 13, 2025

Consistent trait bounds for ExtractIf Debug impls rust-lang/rust#139764

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Debug impls of ExtractIf have inconsistent trait bounds rust-lang/rust#137654

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Amanieu added this pull request to the merge queue Apr 15, 2025

Merged via the queue into rust-lang:master with commit 24d0480 Apr 15, 2025
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dtolnay deleted the extractif branch April 15, 2025 23:07

This was referenced Apr 28, 2025

[beta] Delay hash_extract_if stabilization from 1.87 to 1.88 rust-lang/rust#139765

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Update hashbrown dependency to unblock ExtractIf improvements rust-lang/rust#140535

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Drop FnMut trait bounds from ExtractIf data structures #616

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dtolnay commented Apr 13, 2025

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Drop FnMut trait bounds from ExtractIf data structures #616

Drop FnMut trait bounds from ExtractIf data structures #616

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dtolnay commented Apr 13, 2025

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