alloc: implement FromIterator for Box<str>

[calebsander]

Box<[T]> implements FromIterator<T> using Vec<T> + into_boxed_slice().
Add analogous FromIterator implementations for Box<str>
matching the current implementations for String.
Remove the Global allocator requirement for FromIterator<Box<str>> too.

ACP: rust-lang/libs-team#196

[rust-highfive]

r? @kennytm

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[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.

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

[calebsander]

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

[pitaj]

I believe this does require an ACP (insta-stable new implementation of stable trait on stable type). Please create one if you haven't already. Link it here and then label this PR as S-waiting-on-ACP.

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

[calebsander]

ACP: rust-lang/libs-team#196

[calebsander]

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

[dtolnay]

@rust-lang/libs-api:
@rfcbot fcp merge

+ impl FromIterator<char> for Box<str>
+ impl FromIterator<&char> for Box<str>
+ impl FromIterator<&str> for Box<str>
+ impl FromIterator<String> for Box<str>
+ impl<A: Allocator> FromIterator<Box<str, A>> for Box<str>
+ impl FromIterator<Cow<'_, str>> for Box<str>

- impl FromIterator<Box<str>> for String
+ impl<A: Allocator> FromIterator<Box<str, A>> for String

- impl Extend<Box<str>> for String
+ impl<A: Allocator> Extend<Box<str, A>> for String

[rfcbot]

Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[bors]

⌛ Testing commit c92c228 with merge ce8c2dc...

[rust-log-analyzer]

The job aarch64-gnu failed! Check out the build log: (web) (plain)

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

   Compiling rustc_lint v0.0.0 (/checkout/compiler/rustc_lint)
[RUSTC-TIMING] rustc_metadata test:false 43.201
   Compiling rustc_ty_utils v0.0.0 (/checkout/compiler/rustc_ty_utils)

Session terminated, killing shell...::group::Clock drift check
##[error]The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.
  network time: Sun, 19 May 2024 00:01:52 GMT
##[endgroup]
 ...killed.
##[error]The operation was canceled.

[bors]

💔 Test failed - checks-actions

[dtolnay]

Can't tell what failed.

@bors retry

[bors]

⌛ Testing commit c92c228 with merge bfa3635...

[bors]

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing bfa3635 to master...

[rust-timer]

Finished benchmarking commit (bfa3635): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary 4.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	4.1%	[4.0%, 4.2%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.1%	[4.0%, 4.2%]	2

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 667.801s -> 671.223s (0.51%)
Artifact size: 316.10 MiB -> 316.05 MiB (-0.01%)

[apiraino]

Adding relnotes label because someone reported this in #126685 (up to t-release to decide)

@rustbot label +relnotes