add ptr::from_{ref,mut}

[RalfJung]

We have methods to avoid almost all as casts around raw pointer handling, except for the initial cast from reference to raw pointer. These new methods close that gap.

(I also moved null_mut next to null to keep the file consistently organized.)

r? libs-api

Tracking issue: #106116

[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

[RalfJung]

@rust-lang/libs-api how do we make progress on this PR? It's just been sitting here for 3 weeks now.

[dtolnay]

Seems good to me. Please file a tracking issue.

[RalfJung]

@bors r=dtolnay

[bors]

📌 Commit 15f72dd has been approved by dtolnay

It is now in the queue for this repository.

[bors]

⌛ Testing commit 15f72dd with merge ccbb3295ef7b6c51c1f5a1e9d5019f33b05ab64d...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

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

[dtolnay]

curl: (6) Could not resolve host: ci-mirrors.rust-lang.org

@bors retry

[bors]

⌛ Testing commit 15f72dd with merge 7e4f466...

[bors]

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing 7e4f466 to master...

[rust-timer]

Finished benchmarking commit (7e4f466): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.0%	[-4.0%, -4.0%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

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