(#102929) Implement `String:leak`

[finnbear]

Implementation of String::leak (#102929)

ACP: https://github.com/rust-lang/libs-team/issues/109

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @m-ou-se (or someone else) soon.

Please see the contribution instructions for more information.

[rustbot]

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.

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[finnbear]

@rustbot label +T-libs-api -T-libs

[finnbear]

@rustbot label +S-waiting-on-review -S-waiting-on-author

[rust-log-analyzer]

The job x86_64-gnu-llvm-13 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Finished release [optimized] target(s) in 10.26s
Check compiletest suite=run-make-fulldeps mode=run-make (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)

running 233 tests
............i.....ii..F................................................................. 88/233
Some tests failed in compiletest suite=run-make-fulldeps mode=run-make host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu
...................................i...ii................
failures:


---- [run-make] src/test/run-make-fulldeps/alloc-no-oom-handling stdout ----

error: make failed
status: exit status: 2
command: "make"
--- stdout -------------------------------
LD_LIBRARY_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling:/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu/release/deps:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib" '/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc' --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling -L /checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling  --edition=2021 -Dwarnings --crate-type=rlib ../../../../library/alloc/src/lib.rs --cfg no_global_oom_handling
--- stderr -------------------------------
error[E0425]: cannot find function `from_utf8_unchecked_mut` in this scope
    --> ../../../../library/alloc/src/string.rs:1879:18
     |
     |
1879 |         unsafe { from_utf8_unchecked_mut(slice) }
     |
help: consider importing one of these items
     |
47   | use core::str::from_utf8_unchecked_mut;

[klensy]

https://rustc-dev-guide.rust-lang.org/git.html#no-merge-policy you can squash commits.

[finnbear]

In an attempt to undo the merge commit, I messed up git beyond my ability to repair it, so this PR is superseded by #103280

[rust-log-analyzer]

The job x86_64-gnu-llvm-13 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

error: make failed
status: exit status: 2
command: "make"
--- stdout -------------------------------
LD_LIBRARY_PATH="/checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling:/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-bootstrap-tools/x86_64-unknown-linux-gnu/release/deps:/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/lib" '/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc' --out-dir /checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling -L /checkout/obj/build/x86_64-unknown-linux-gnu/test/run-make-fulldeps/alloc-no-oom-handling/alloc-no-oom-handling  --edition=2021 -Dwarnings --crate-type=rlib ../../../../library/alloc/src/lib.rs --cfg no_global_oom_handling
--- stderr -------------------------------
error[E0425]: cannot find function `from_utf8_unchecked_mut` in this scope
    --> ../../../../library/alloc/src/string.rs:1879:18
     |
     |
1879 |         unsafe { from_utf8_unchecked_mut(slice) }
     |
help: consider importing one of these items
     |
47   | use core::str::from_utf8_unchecked_mut;