Implement the unsafe-fields RFC.

[veluca93]

RFC: rust-lang/rfcs#3458

Tracking:

• Tracking issue for RFC 3458: Unsafe fields #132922

r? jswrenn

[rustbot]

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

[rustbot]

Changes to the size of AST and/or HIR nodes.

cc @nnethercote

[jswrenn]

Thanks for implementing this! Here's a first round of comments. :-)

[jswrenn]

@bors try @rust-timer queue

[bors]

⌛ Trying commit db32d80 with merge ce25ffa...

[bors]

☀️ Try build successful - checks-actions
Build commit: ce25ffa (ce25ffa95be3a8577d9d1ff09eafe449df2dcfc3)

[rust-timer]

Finished benchmarking commit (ce25ffa): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.7%)

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)	1.8%	[1.8%, 1.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-3.1%, 1.8%]	2

Cycles

Results (secondary 1.7%)

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)	-	-	0
Regressions ❌ (secondary)	1.7%	[1.7%, 1.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.2%, secondary 0.3%)

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)	0.2%	[0.0%, 0.5%]	128
Regressions ❌ (secondary)	0.3%	[0.0%, 0.5%]	29
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.0%, 0.5%]	128

Bootstrap: 787.726s -> 783.8s (-0.50%)
Artifact size: 335.35 MiB -> 335.31 MiB (-0.01%)

[jswrenn]

The UI testing checklist I'd like to see completed before we merge this:

• if feature(unsafe_fields):
  • the 'incomplete features' warning is emitted
  • unsafe can be applied to the fields of struct-like variant fields of structs, enums and unions
    • the unsafe field's type must be Copy or ManuallyDrop
  • unsafe cannot be applied to tuple-like struct fields
  • unsafe cannot be applied to tuple-like enum fields
• if not feature(unsafe_fields), even in cfg'd-out code:
  • unsafe cannot be applied to the fields of struct-like struct fields
  • unsafe cannot be applied to the fields of struct-like enum fields
  • unsafe cannot be applied to the fields of struct-like (i.e., all) unions
• even if not feature(unsafe_fields):
  • initializing, destructuring, referencing, reading, and writing the unsafe fields of a struct/enum/union can only occur in an unsafe context (see these tests as a rough point of reference)
  • initializing, destructuring, referencing, reading, and writing the safe fields of a struct/enum/union (even one that that has other unsafe fields) does not require unsafe

[bors]

☔ The latest upstream changes (presumably #133280) made this pull request unmergeable. Please resolve the merge conflicts.

[jswrenn]

This is looking pretty good. Be sure to update the commit message, too! It's no longer a draft implementation — it's just an implementation. :-)

[compiler-errors]

Generally looks okay. I've got some minor comments about style and code deduplication.

[jswrenn]

@bors r+

[bors]

📌 Commit 9022bb2 has been approved by jswrenn

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9022bb2 with merge 6e1c11591fc7e98015f8e793a15c8faf0bda67f1...

[bors]

☀️ Test successful - checks-actions
Approved by: jswrenn
Pushing 6e1c115 to master...

[rust-timer]

Finished benchmarking commit (6e1c115): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.8%, secondary -2.4%)

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)	2.3%	[1.4%, 3.1%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-2.4%	[-4.6%, -1.2%]	3
All ❌✅ (primary)	0.8%	[-2.1%, 3.1%]	3

Cycles

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

Binary size

Results (primary 0.2%, secondary 0.3%)

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)	0.2%	[0.0%, 0.5%]	129
Regressions ❌ (secondary)	0.3%	[0.0%, 0.5%]	31
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.0%, 0.5%]	129

Bootstrap: 797.021s -> 795.784s (-0.16%)
Artifact size: 336.26 MiB -> 336.31 MiB (0.02%)