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Add MAX_UTF{8, 16}_LEN constants #98198

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Add MAX_UTF{8, 16}_LEN constants #98198

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Dylan-DPC
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Closes #45795

Adds two constants for better readability.

@rustbot rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Jun 17, 2022
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Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

  • Stabilizing library features
  • Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
  • Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
  • Changing public documentation in ways that create new stability guarantees
  • Changing observable runtime behavior of library APIs

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r? @joshtriplett

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 17, 2022
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yvt
yvt reviewed Jun 18, 2022
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Changes the wording (somewhat based on that of char::len_{utf8,utf16}), adds intra-doc links to char::encode_{utf8,utf16}, and adds the "Use char::* instead" sentences from #95566.

library/core/src/char/methods.rs Outdated Show resolved Hide resolved
library/core/src/char/methods.rs Outdated Show resolved Hide resolved
library/core/src/char/mod.rs Outdated Show resolved Hide resolved
library/core/src/char/mod.rs Outdated Show resolved Hide resolved
Dylan-DPC and others added 4 commits June 18, 2022 16:46
@Dylan-DPC @yvt
Update library/core/src/char/methods.rs
31c555d 
Co-authored-by: yvt <i@yvt.jp>
@Dylan-DPC @yvt
Update library/core/src/char/mod.rs
5b417e2 
Co-authored-by: yvt <i@yvt.jp>
@Dylan-DPC @yvt
Update library/core/src/char/methods.rs
c3c6d9e 
Co-authored-by: yvt <i@yvt.jp>
@Dylan-DPC @yvt
Update library/core/src/char/mod.rs
5155ca8 
Co-authored-by: yvt <i@yvt.jp>
scottmcm
scottmcm reviewed Jun 24, 2022
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library/core/src/char/methods.rs
@@ -45,6 +45,16 @@ impl char {
#[stable(feature = "assoc_char_consts", since = "1.52.0")]
pub const UNICODE_VERSION: (u8, u8, u8) = crate::unicode::UNICODE_VERSION;

/// The maximum number of bytes required to [encode](char::encode_utf8) a
/// `char` in UTF-8.
#[stable(feature = "max_len", since = "1.63.0")]
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I think these should go in unstable with a tracking issue, no?

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I could but i thought since these were constants that replaced literal values we could directly stabilise them. I'm fine with adding unstable feature if that's the way to go

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There's basically three possible ways forward:

  1. This is an internal code readability change, so the consts are pub(crate) and it goes in with a T-libs review.
  2. This is a new API going in unstable, so it can go in with just a review on a "seems reasonable" basis.
  3. This goes in insta-stable, at which point is needs a full T-libs-api FCP.

Basically we only do 3 if forced (because some things can't go in unstable). So please make it unstable with a tracking issue, and then it can just be approved. (Consider also doing some commit squashing.)

scottmcm
scottmcm reviewed Jun 24, 2022
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library/core/src/char/mod.rs
/// The maximum number of bytes required to [encode](char::encode_utf8) a
/// `char` in UTF-8. Use [`char::MAX_UTF8_LEN`] instead.
#[stable(feature = "max_len", since = "1.63.0")]
pub const MAX_UTF8_LEN: usize = char::MAX_UTF8_LEN;
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pondering: are the module-level constants still desirable, now that we can have type-associated ones? It's unclear to me how to apply precedent from #68490 here -- the char module certainly can't go away. But if the doc comment on this constant says not to use it, why add it?

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yeh i didn't think of type-associated ones, will change it to that

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bors commented Jun 26, 2022

☔ The latest upstream changes (presumably #98190) made this pull request unmergeable. Please resolve the merge conflicts.

@JohnCSimon JohnCSimon added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 24, 2022
@Dylan-DPC Dylan-DPC added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 24, 2022
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@Dylan-DPC
ping from triage - can you post your status on this PR? This has sat untouched for a while. Thanks!

FYI: when a PR is ready for review, send a message containing
@rustbot ready to switch to S-waiting-on-review so the PR is in the reviewer's backlog.

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closing this for the time being. will create a new PR with the changes when I get to it

@Dylan-DPC Dylan-DPC closed this Feb 4, 2023
@Dylan-DPC Dylan-DPC deleted the 45795/max_utf_len branch February 4, 2023 06:07
@Enselic Enselic mentioned this pull request Sep 26, 2023
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[std::char] Add MAX_UTF8_LEN and MAX_UTF16_LEN
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