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Trim BorrowedCursor API #143829

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Trim BorrowedCursor API #143829

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@a1phyr a1phyr commented Jul 12, 2025 •
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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
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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.
@a1phyr
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.
@a1phyr
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.
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rustbot commented Jul 12, 2025

r? @scottmcm

rustbot has assigned @scottmcm.
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@rustbot 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 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
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joshtriplett commented Jul 13, 2025 •
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I'm surprised by the removal of init_ref(); I'd expect that to be a common need.

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a1phyr commented Jul 13, 2025

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)?

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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

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