Trim `BorrowedCursor` API #143829

a1phyr · 2025-07-12T11:08:00Z

This PR removes some method from the unstable BorrowedCursor type. A rational for each change can be found in the message of each commit.

I don't think that an ACP is required for this, please tell me if it is not the case.

Cc #78485 #117693

This method was not really useful: at no point one would only need to read the initialized part of the cursor without mutating it.

I assume that this method was there for completeness, but there is hardly any useful use of it: the buffer it gave was not always connected to the start of the cursor and its use required `unsafe` anyway to mark the bytes as initialized.

This enable removing the `start` field, so `BorrowedCursor` fits in a single register. Because `written` is almost always used in difference with another call, this changes nothing else in practice.

rustbot · 2025-07-12T11:08:04Z

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joshtriplett · 2025-07-13T09:49:20Z

I'm surprised by the removal of init_ref(); I'd expect that to be a common need.

a1phyr · 2025-07-13T15:37:48Z

Why for? It gives read-only bytes that you're not supposed to read, just like the buffer of Read::read method. You were maybe thinking of filled bytes, which the API purposefully does not give access to (and the reason of #142885)?

scottmcm · 2025-07-13T22:25:47Z

I don't think me as a reviewer is the right people to make choices here. Feels like more an unresolved question on a tracking issue -- after all, one can always stabilize a subset and decide whether to remove methods later.

r? libs-api

joshtriplett · 2025-07-15T16:02:03Z

Why for? It gives read-only bytes that you're not supposed to read, just like the buffer of Read::read method. You were maybe thinking of filled bytes

Yes, I was, thank you.

the8472 · 2025-07-15T16:06:06Z

We discussed this during today's libs-api meeting. The changes look ok and we agree with the motivations.

But there have been some recent requests to make further changes to the API that you might be interested in:
#t-libs > Future of read_buf
#t-libs > BorrowedBuf/BorrowedCursor optimized for past, not future

ChrisDenton · 2025-07-15T16:53:50Z

The implementation and test changes look good to me

@bors r+

bors · 2025-07-15T16:53:53Z

📌 Commit 65df668 has been approved by ChrisDenton

It is now in the queue for this repository.

a1phyr · 2025-07-15T22:51:39Z

But there have been some recent requests to make further changes to the API that you might be interested in:

Thanks, I didn't know about the first one!

I have not sent a PR/ACP/Zulip thread yet (I don't know which you be right), but I have a draft of changing the init field a boolean, which further simplify the API: https://github.com/a1phyr/rust/tree/improve_buf_api

About accessing the filled bytes, forbidding it was does on purpose, but I think that reevaluating this idea might be interesting.

…enton Trim `BorrowedCursor` API This PR removes some method from the unstable `BorrowedCursor` type. A rational for each change can be found in the message of each commit. I don't think that an ACP is required for this, please tell me if it is not the case. Cc rust-lang#78485 rust-lang#117693

Rollup of 11 pull requests Successful merges: - #143595 (add `const_make_global`; err for `const_allocate` ptrs if didn't call) - #143678 (Added error for invalid char cast) - #143793 (Opaque type collection: Guard against endlessly recursing free alias types) - #143820 (Fixed a core crate compilation failure when enabling the `optimize_for_size` feature on some targets) - #143829 (Trim `BorrowedCursor` API) - #143856 (Linting public reexport of private dependencies) - #143891 (Port `#[coverage]` to the new attribute system) - #143914 (Reword mismatched-lifetime-syntaxes text based on feedback) - #143922 (Improve path segment joining) - #143926 (Remove deprecated fields in bootstrap) - #143975 (type_id_eq: check that the hash fully matches the type) r? `@ghost` `@rustbot` modify labels: rollup

…enton Trim `BorrowedCursor` API This PR removes some method from the unstable `BorrowedCursor` type. A rational for each change can be found in the message of each commit. I don't think that an ACP is required for this, please tell me if it is not the case. Cc rust-lang#78485 rust-lang#117693

Rollup of 15 pull requests Successful merges: - #142304 (tests: Add `RUST_BACKTRACE` and `-Cpanic` revisions to `panic-main.rs` test) - #143388 (Various refactors to the LTO handling code) - #143409 (Enable xgot feature for mips64 musl targets) - #143592 (UWP: link ntdll functions using raw-dylib) - #143595 (add `const_make_global`; err for `const_allocate` ptrs if didn't call) - #143678 (Added error for invalid char cast) - #143820 (Fixed a core crate compilation failure when enabling the `optimize_for_size` feature on some targets) - #143829 (Trim `BorrowedCursor` API) - #143846 (pass --gc-sections if -Zexport-executable-symbols is enabled and improve tests) - #143851 (ci cleanup: rustdoc-gui-test now installs browser-ui-test) - #143856 (Linting public reexport of private dependencies) - #143895 (Dont collect assoc ty item bounds from trait where clause for host effect predicates) - #143922 (Improve path segment joining) - #143964 (Fix handling of SCRIPT_ARG in docker images) - #144016 (trait_sel: `MetaSized` always holds temporarily) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 15 pull requests Successful merges: - #142304 (tests: Add `RUST_BACKTRACE` and `-Cpanic` revisions to `panic-main.rs` test) - #143388 (Various refactors to the LTO handling code) - #143409 (Enable xgot feature for mips64 musl targets) - #143592 (UWP: link ntdll functions using raw-dylib) - #143595 (add `const_make_global`; err for `const_allocate` ptrs if didn't call) - #143678 (Added error for invalid char cast) - #143820 (Fixed a core crate compilation failure when enabling the `optimize_for_size` feature on some targets) - #143829 (Trim `BorrowedCursor` API) - #143851 (ci cleanup: rustdoc-gui-test now installs browser-ui-test) - #143856 (Linting public reexport of private dependencies) - #143895 (Dont collect assoc ty item bounds from trait where clause for host effect predicates) - #143922 (Improve path segment joining) - #143964 (Fix handling of SCRIPT_ARG in docker images) - #144002 (Update poison.rs) - #144016 (trait_sel: `MetaSized` always holds temporarily) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143829 - a1phyr:trim_borrowed_buf, r=ChrisDenton Trim `BorrowedCursor` API This PR removes some method from the unstable `BorrowedCursor` type. A rational for each change can be found in the message of each commit. I don't think that an ACP is required for this, please tell me if it is not the case. Cc #78485 #117693

a1phyr added 3 commits July 9, 2025 18:11

core: Remove BorrowedCursor::init_ref method

803b4d2

This method was not really useful: at no point one would only need to read the initialized part of the cursor without mutating it.

core: Remove BorrowedCursor::uninit_mut

34555f1

I assume that this method was there for completeness, but there is hardly any useful use of it: the buffer it gave was not always connected to the start of the cursor and its use required `unsafe` anyway to mark the bytes as initialized.

core: Change BorrowedCursor::written's origin

65df668

This enable removing the `start` field, so `BorrowedCursor` fits in a single register. Because `written` is almost always used in difference with another call, this changes nothing else in practice.

rustbot assigned scottmcm Jul 12, 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 Jul 12, 2025

joshtriplett added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. I-libs-api-nominated Nominated for discussion during a libs-api team meeting. labels Jul 13, 2025

rustbot assigned m-ou-se and unassigned scottmcm Jul 13, 2025

the8472 removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Jul 15, 2025

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 Jul 15, 2025

matthiaskrgr mentioned this pull request Jul 16, 2025

Rollup of 12 pull requests #144035

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matthiaskrgr mentioned this pull request Jul 16, 2025

Rollup of 12 pull requests #144036

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Rollup of 11 pull requests #144038

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Rollup of 15 pull requests #144041

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fmease mentioned this pull request Jul 17, 2025

Rollup of 15 pull requests #144044

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bors merged commit b9fd2bc into rust-lang:master Jul 17, 2025
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rustbot added this to the 1.90.0 milestone Jul 17, 2025

samlii mentioned this pull request Jul 18, 2025

Build error: no method named uninit_mut found for struct BorrowedCursor SUPERCILEX/clipboard-history#67

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