Add inherent constructors on str

[robertbastian]

#131114

Unresolved questions

Do we mark the core::str functions as future-deprecation? This will causes warnings when core::str is imported and str::from_utf8 is used, because the compiler decides to interpret that as the module, not the type.

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[bors]

☔ The latest upstream changes (presumably #131269) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-log-analyzer]

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#16 2.795 Building wheels for collected packages: reuse
#16 2.796   Building wheel for reuse (pyproject.toml): started
#16 3.043   Building wheel for reuse (pyproject.toml): finished with status 'done'
#16 3.044   Created wheel for reuse: filename=reuse-4.0.3-cp310-cp310-manylinux_2_35_x86_64.whl size=132715 sha256=dfa09868353292d98f811d3efdb0d54d07389e808efc71d68e3b93c514bf8bec
#16 3.044   Stored in directory: /tmp/pip-ephem-wheel-cache-8zpmccr7/wheels/3d/8d/0a/e0fc6aba4494b28a967ab5eaf951c121d9c677958714e34532
#16 3.047 Installing collected packages: boolean-py, binaryornot, tomlkit, reuse, python-debian, markupsafe, license-expression, jinja2, chardet, attrs
#16 3.435 Successfully installed attrs-23.2.0 binaryornot-0.4.4 boolean-py-4.0 chardet-5.2.0 jinja2-3.1.4 license-expression-30.3.0 markupsafe-2.1.5 python-debian-0.1.49 reuse-4.0.3 tomlkit-0.13.0
#16 3.436 WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
#16 DONE 3.5s
---
    Checking core v0.0.0 (/checkout/library/core)
   Compiling libc v0.2.159
   Compiling memchr v2.5.0
   Compiling std v0.0.0 (/checkout/library/std)
error: use of function `str::converts::from_utf8` that will be deprecated in a future Rust version: replaced by the `from_utf8` method on the `str` type
   |
30 | pub use converts::{from_utf8, from_utf8_unchecked};
   |                    ^^^^^^^^^
   |
---

error[E0711]: feature `const_str_from_utf8_unchecked_mut` is declared unstable, but was previously declared stable
   --> core/src/str/mod.rs:350:5
    |
350 |     #[rustc_const_unstable(feature = "const_str_from_utf8_unchecked_mut", issue = "91005")]

error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
   --> core/src/char/methods.rs:680:18
    |
    |
680 |         unsafe { str::from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
    |
    = help: add `#![feature(const_str_from_utf8_unchecked_mut)]` to the crate attributes to enable

error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
   --> core/src/str/converts.rs:130:25
    |
130 |             Ok(unsafe { str::from_utf8_unchecked_mut(v) })
    |
    = help: add `#![feature(const_str_from_utf8_unchecked_mut)]` to the crate attributes to enable

error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
   --> core/src/str/converts.rs:207:14
    |
207 |     unsafe { str::from_utf8_unchecked_mut(v) }
    |
    = help: const-stable functions can only call other const-stable functions

error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
error: `str::<impl str>::from_utf8_unchecked_mut` is not yet stable as a const fn
   --> core/src/str/mod.rs:288:29
    |
288 |                 Ok(unsafe { Self::from_utf8_unchecked_mut(v) })
    |
    = help: add `#![feature(const_str_from_utf8_unchecked_mut)]` to the crate attributes to enable

For more information about this error, try `rustc --explain E0711`.

[bors]

☔ The latest upstream changes (presumably #131767) made this pull request unmergeable. Please resolve the merge conflicts.

[scottmcm]

Do we mark the core::str functions as future-deprecation?

I think it'll make your life much easier to do it in different PRs. Add the new ones first, then you can do separate PRs to update different parts of things to use the new ones, then once you're through that you can PR the future-deprecation.

(Keeping it locally will help you make those other PRs, but no need to check it in for a while.)