Override default `Write` methods for cursor-like types #137107

thaliaarchi · 2025-02-16T04:04:07Z

Override the default io::Write methods for cursor-like types to provide more efficient versions.

Writes to resizable containers already write everything, so implement write_all and write_all_vectored in terms of those. For fixed-sized containers, cut out unnecessary error checking and looping for those same methods.

`impl Write for T`	`vectored`	`all`	`all_vectored`	`fmt`
`&mut [u8]`	Y	Y	new
`Vec<u8>`	Y	Y	new	#137762
`VecDeque<u8>`	Y	Y	new	#137762
`std::io::Cursor<&mut [u8]>`	Y	new	new
`std::io::Cursor<&mut Vec<u8>>`	Y	new	new	#137762
`std::io::Cursor<Vec<u8>>`	Y	new	new	#137762
`std::io::Cursor<Box<[u8]>>`	Y	new	new
`std::io::Cursor<[u8; N]>`	Y	new	new
`core::io::BorrowedCursor<'_>`	new	new	new

Tracked in #136756.

Open questions

Is it guaranteed by Write::write_all that the maximal write is performed when not everything can be written? Its documentation describes the behavior of the default implementation, which writes until a 0-length write is encountered, thus implying that a maximal write is expected. In contrast, Read::read_exact declares that the contents of the buffer are unspecified for short reads. If it were allowed, these cursor-like types could bail on the write altogether if it has insufficient capacity.

rustbot · 2025-02-16T04:04:15Z

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thaliaarchi · 2025-02-16T04:05:35Z

r? libs, since you're probably busy on the release

All other methods in this file have #[inline] and these methods are very similar to those of &[u8] which are already inlined here.

thaliaarchi · 2025-02-28T01:11:44Z

I've extracted the write_fmt changes as #137762.

thaliaarchi · 2025-03-03T20:05:35Z

@joboet Friendly 2-week ping. Would you mind taking a look at this?

joboet · 2025-03-05T17:45:10Z

I've extracted the write_fmt changes as #137762.

Thank you, that helps!

@joboet Friendly 2-week ping. Would you mind taking a look at this?

Sure! Sorry for the delay, I've been a bit busy recently.

Anyway, this looks fine to me!
@bors r+

bors · 2025-03-05T17:45:12Z

📌 Commit 41bdd2b has been approved by joboet

It is now in the queue for this repository.

…rsors, r=joboet Override default `Write` methods for cursor-like types Override the default `io::Write` methods for cursor-like types to provide more efficient versions. Writes to resizable containers already write everything, so implement `write_all` and `write_all_vectored` in terms of those. For fixed-sized containers, cut out unnecessary error checking and looping for those same methods. | `impl Write for T` | `vectored` | `all` | `all_vectored` | `fmt` | | ------------------------------- | ---------- | ----- | -------------- | ------- | | `&mut [u8]` | Y | Y | new | | | `Vec<u8>` | Y | Y | new | rust-lang#137762 | | `VecDeque<u8>` | Y | Y | new | rust-lang#137762 | | `std::io::Cursor<&mut [u8]>` | Y | new | new | | | `std::io::Cursor<&mut Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Box<[u8]>>` | Y | new | new | | | `std::io::Cursor<[u8; N]>` | Y | new | new | | | `core::io::BorrowedCursor<'_>` | new | new | new | | Tracked in rust-lang#136756. # Open questions Is it guaranteed by `Write::write_all` that the maximal write is performed when not everything can be written? Its documentation describes the behavior of the default implementation, which writes until a 0-length write is encountered, thus implying that a maximal write is expected. In contrast, `Read::read_exact` declares that the contents of the buffer are unspecified for short reads. If it were allowed, these cursor-like types could bail on the write altogether if it has insufficient capacity.

Rollup of 29 pull requests Successful merges: - rust-lang#135733 (Implement `&pin const self` and `&pin mut self` sugars) - rust-lang#137107 (Override default `Write` methods for cursor-like types) - rust-lang#137303 (Remove `MaybeForgetReturn` suggestion) - rust-lang#137327 (Undeprecate env::home_dir) - rust-lang#137358 (Match Ergonomics 2024: add context and examples to the unstable book) - rust-lang#137534 ([rustdoc] hide item that is not marked as doc(inline) and whose src is doc(hidden)) - rust-lang#137565 (Try to point of macro expansion from resolver and method errors if it involves macro var) - rust-lang#137612 (Update bootstrap to edition 2024) - rust-lang#137637 (Check dyn flavor before registering upcast goal on wide pointer cast in MIR typeck) - rust-lang#137643 (Add DWARF test case for non-C-like `repr128` enums) - rust-lang#137685 (self-contained linker: conservatively default to `-znostart-stop-gc` on x64 linux) - rust-lang#137744 (Re-add `Clone`-derive on `Thir`) - rust-lang#137758 (fix usage of ty decl macro fragments in attributes) - rust-lang#137764 (Ensure that negative auto impls are always applicable) - rust-lang#137772 (Fix char count in `Display` for `ByteStr`) - rust-lang#137798 (ci: use ubuntu 24 on arm large runner) - rust-lang#137802 (miri native-call support: all previously exposed provenance is accessible to the callee) - rust-lang#137805 (adjust Layout debug printing to match the internal field name) - rust-lang#137808 (Do not require that unsafe fields lack drop glue) - rust-lang#137820 (Clarify why InhabitedPredicate::instantiate_opt exists) - rust-lang#137825 (Provide more context on resolve error caused from incorrect RTN) - rust-lang#137827 (Add timestamp to unstable feature usage metrics) - rust-lang#137832 (Fix crash in BufReader::peek()) - rust-lang#137910 (Improve error message for `AsyncFn` trait failure for RPIT) - rust-lang#137920 (interpret/provenance_map: consistently use range_is_empty) - rust-lang#138038 (Update `compiler-builtins` to 0.1.151) - rust-lang#138046 (trim channel value in `get_closest_merge_commit`) - rust-lang#138052 (strip `-Wlinker-messages` wrappers from `rust-lld` rmake test) - rust-lang#138053 (Increase the max. custom try jobs requested to `20`) r? `@ghost` `@rustbot` modify labels: rollup

…rsors, r=joboet Override default `Write` methods for cursor-like types Override the default `io::Write` methods for cursor-like types to provide more efficient versions. Writes to resizable containers already write everything, so implement `write_all` and `write_all_vectored` in terms of those. For fixed-sized containers, cut out unnecessary error checking and looping for those same methods. | `impl Write for T` | `vectored` | `all` | `all_vectored` | `fmt` | | ------------------------------- | ---------- | ----- | -------------- | ------- | | `&mut [u8]` | Y | Y | new | | | `Vec<u8>` | Y | Y | new | rust-lang#137762 | | `VecDeque<u8>` | Y | Y | new | rust-lang#137762 | | `std::io::Cursor<&mut [u8]>` | Y | new | new | | | `std::io::Cursor<&mut Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Box<[u8]>>` | Y | new | new | | | `std::io::Cursor<[u8; N]>` | Y | new | new | | | `core::io::BorrowedCursor<'_>` | new | new | new | | Tracked in rust-lang#136756. # Open questions Is it guaranteed by `Write::write_all` that the maximal write is performed when not everything can be written? Its documentation describes the behavior of the default implementation, which writes until a 0-length write is encountered, thus implying that a maximal write is expected. In contrast, `Read::read_exact` declares that the contents of the buffer are unspecified for short reads. If it were allowed, these cursor-like types could bail on the write altogether if it has insufficient capacity.

thaliaarchi · 2025-03-06T00:46:59Z

@bors rollup

bors · 2025-03-06T00:47:01Z

@thaliaarchi: 🔑 Insufficient privileges: not in try users

…rsors, r=joboet Override default `Write` methods for cursor-like types Override the default `io::Write` methods for cursor-like types to provide more efficient versions. Writes to resizable containers already write everything, so implement `write_all` and `write_all_vectored` in terms of those. For fixed-sized containers, cut out unnecessary error checking and looping for those same methods. | `impl Write for T` | `vectored` | `all` | `all_vectored` | `fmt` | | ------------------------------- | ---------- | ----- | -------------- | ------- | | `&mut [u8]` | Y | Y | new | | | `Vec<u8>` | Y | Y | new | rust-lang#137762 | | `VecDeque<u8>` | Y | Y | new | rust-lang#137762 | | `std::io::Cursor<&mut [u8]>` | Y | new | new | | | `std::io::Cursor<&mut Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Box<[u8]>>` | Y | new | new | | | `std::io::Cursor<[u8; N]>` | Y | new | new | | | `core::io::BorrowedCursor<'_>` | new | new | new | | Tracked in rust-lang#136756. # Open questions Is it guaranteed by `Write::write_all` that the maximal write is performed when not everything can be written? Its documentation describes the behavior of the default implementation, which writes until a 0-length write is encountered, thus implying that a maximal write is expected. In contrast, `Read::read_exact` declares that the contents of the buffer are unspecified for short reads. If it were allowed, these cursor-like types could bail on the write altogether if it has insufficient capacity.

…kingjubilee Rollup of 12 pull requests Successful merges: - rust-lang#136667 (Revert vita's c_char back to i8) - rust-lang#136780 (std: move stdio to `sys`) - rust-lang#137107 (Override default `Write` methods for cursor-like types) - rust-lang#137363 (compiler: factor Windows x86-32 ABI impl into its own file) - rust-lang#137528 (Windows: Fix error in `fs::rename` on Windows 1607) - rust-lang#137537 (Prevent `rmake.rs` from using unstable features, and fix 3 run-make tests that currently do) - rust-lang#137777 (Specialize `OsString::push` and `OsString as From` for UTF-8) - rust-lang#137832 (Fix crash in BufReader::peek()) - rust-lang#137904 (Improve the generic MIR in the default `PartialOrd::le` and friends) - rust-lang#138115 (Suggest typo fix for static lifetime) - rust-lang#138125 (Simplify `printf` and shell format suggestions) - rust-lang#138129 (Stabilize const_char_classify, const_sockaddr_setters) r? `@ghost` `@rustbot` modify labels: rollup

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#136667 (Revert vita's c_char back to i8) - rust-lang#137107 (Override default `Write` methods for cursor-like types) - rust-lang#137777 (Specialize `OsString::push` and `OsString as From` for UTF-8) - rust-lang#137832 (Fix crash in BufReader::peek()) - rust-lang#137904 (Improve the generic MIR in the default `PartialOrd::le` and friends) - rust-lang#138115 (Suggest typo fix for static lifetime) - rust-lang#138125 (Simplify `printf` and shell format suggestions) - rust-lang#138129 (Stabilize const_char_classify, const_sockaddr_setters) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#137107 - thaliaarchi:io-optional-methods/cursors, r=joboet Override default `Write` methods for cursor-like types Override the default `io::Write` methods for cursor-like types to provide more efficient versions. Writes to resizable containers already write everything, so implement `write_all` and `write_all_vectored` in terms of those. For fixed-sized containers, cut out unnecessary error checking and looping for those same methods. | `impl Write for T` | `vectored` | `all` | `all_vectored` | `fmt` | | ------------------------------- | ---------- | ----- | -------------- | ------- | | `&mut [u8]` | Y | Y | new | | | `Vec<u8>` | Y | Y | new | rust-lang#137762 | | `VecDeque<u8>` | Y | Y | new | rust-lang#137762 | | `std::io::Cursor<&mut [u8]>` | Y | new | new | | | `std::io::Cursor<&mut Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Vec<u8>>` | Y | new | new | rust-lang#137762 | | `std::io::Cursor<Box<[u8]>>` | Y | new | new | | | `std::io::Cursor<[u8; N]>` | Y | new | new | | | `core::io::BorrowedCursor<'_>` | new | new | new | | Tracked in rust-lang#136756. # Open questions Is it guaranteed by `Write::write_all` that the maximal write is performed when not everything can be written? Its documentation describes the behavior of the default implementation, which writes until a 0-length write is encountered, thus implying that a maximal write is expected. In contrast, `Read::read_exact` declares that the contents of the buffer are unspecified for short reads. If it were allowed, these cursor-like types could bail on the write altogether if it has insufficient capacity.

rustbot assigned cuviper Feb 16, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 16, 2025

rustbot assigned joboet and unassigned cuviper Feb 16, 2025

thaliaarchi mentioned this pull request Feb 16, 2025

Tracking issue for optional io::Read/io::Write methods #136756

Open

thaliaarchi added 2 commits February 27, 2025 17:07

Inline VecDeque<u8> and BorrowedCursor methods

67cc82a

All other methods in this file have #[inline] and these methods are very similar to those of &[u8] which are already inlined here.

Override default Write methods for cursor-like types

41bdd2b

thaliaarchi force-pushed the io-optional-methods/cursors branch from a76c82c to 41bdd2b Compare February 28, 2025 01:10

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 Mar 5, 2025

jieyouxu mentioned this pull request Mar 5, 2025

Rollup of 29 pull requests #138071

Closed

jieyouxu mentioned this pull request Mar 5, 2025

Rollup of 15 pull requests #138072

Closed

workingjubilee mentioned this pull request Mar 7, 2025

Rollup of 12 pull requests #138146

Closed

matthiaskrgr mentioned this pull request Mar 7, 2025

Rollup of 8 pull requests #138151

Merged

bors merged commit 458095a into rust-lang:master Mar 7, 2025
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rustbot added this to the 1.87.0 milestone Mar 7, 2025

thaliaarchi deleted the io-optional-methods/cursors branch March 7, 2025 18:35

thaliaarchi mentioned this pull request Mar 7, 2025

Implement write_all_vectored for VecDeque #136819

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Override default `Write` methods for cursor-like types #137107

Override default `Write` methods for cursor-like types #137107

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Override default Write methods for cursor-like types #137107

Override default Write methods for cursor-like types #137107

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Override default `Write` methods for cursor-like types #137107

Override default `Write` methods for cursor-like types #137107

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