error on non-rustic ABIs using unsized parameters #148302

folkertdev · 2025-10-30T15:59:36Z

tracking issue: #48055

The idea is that the layout of an unsized type is unstable (following the rust layout rules), and hence stable ABIs should not use unsized types. On stable, unsized types (or generics with a ?Sized bound) are not accepted as parameters, so the errors introduced by this PR can only be observed when the unstable unsized_fn_params feature is enabled.

r? @bjorn3
cc @RalfJung

compiler/rustc_monomorphize/src/mono_checks/abi_check.rs

folkertdev · 2025-10-30T16:01:06Z

tests/ui/abi/non-rustic-unsized.rs

+extern "C" fn c_polymorphic<T: ?Sized>(_: T) {}
+//~^ ERROR this function definition uses unsized type `[u8]` which is not supported with the chosen ABI


The mention of [u8] here is a bit unfortunate, but I think it's the best we can do.

bjorn3 · 2025-10-30T17:51:51Z

Would have been nice if we could also get rid of the checks for unsized params in the call conv calculation code, but alas this checks runs after the call conv calculation code, so removing those checks would probably cause issues.

bjorn3 · 2025-11-04T14:40:53Z

@bors try @rust-timer queue

r=me if perf is neutral

error on non-rustic ABIs using unsized parameters

rust-bors · 2025-11-04T16:53:10Z

☀️ Try build successful (CI)
Build commit: 6c023aa (6c023aae4513f7488ee0dd128e4cd69beca8309a, parent: 90b65889799733f21ebdf59d96411aa531c5900a)

rust-timer · 2025-11-05T00:05:52Z

Finished benchmarking commit (6c023aa): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (secondary -3.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.6%	[-3.6%, -3.6%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 476.459s -> 473.98s (-0.52%)
Artifact size: 390.66 MiB -> 390.71 MiB (0.01%)

bjorn3 · 2025-11-05T08:36:58Z

@bors r+

bors · 2025-11-05T08:37:01Z

📌 Commit 52bfde2 has been approved by bjorn3

It is now in the queue for this repository.

error on non-rustic ABIs using unsized parameters tracking issue: #48055 This came up in #144529 (comment). The idea is that the layout of an unsized type is unstable (following the rust layout rules), and hence stable ABIs should not use unsized types. On stable, unsized types (or generics with a `?Sized` bound) are not accepted as parameters, so the errors introduced by this PR can only be observed when the unstable `unsized_fn_params` feature is enabled. r? `@bjorn3` cc `@RalfJung`

bors · 2025-11-05T10:30:39Z

⌛ Testing commit 52bfde2 with merge 345a2e1...

bors · 2025-11-05T10:54:40Z

💔 Test failed - checks-actions

rustbot · 2025-11-05T11:12:28Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

bjorn3 · 2025-11-05T11:13:48Z

@bors r+

bors · 2025-11-05T11:13:50Z

📌 Commit 8e44e3f has been approved by bjorn3

It is now in the queue for this repository.

bors · 2025-11-05T14:07:09Z

⌛ Testing commit 8e44e3f with merge 1ef7943...

bors · 2025-11-05T17:14:42Z

☀️ Test successful - checks-actions
Approved by: bjorn3
Pushing 1ef7943 to master...

github-actions · 2025-11-05T17:17:37Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 53efb3d (parent) -> 1ef7943 (this PR)

Test differences

Show 14 test diffs

Stage 0

errors::verify_monomorphize_abi_error_unsupported_unsized_parameter_9: [missing] -> pass (J1)
errors::verify_monomorphize_abi_error_unsupported_vector_type_10: [missing] -> pass (J1)
errors::verify_monomorphize_abi_error_unsupported_vector_type_9: pass -> [missing] (J1)
errors::verify_monomorphize_abi_required_target_feature_10: pass -> [missing] (J1)
errors::verify_monomorphize_abi_required_target_feature_11: [missing] -> pass (J1)

Stage 1

errors::verify_monomorphize_abi_error_unsupported_unsized_parameter_9: [missing] -> pass (J0)
errors::verify_monomorphize_abi_error_unsupported_vector_type_10: [missing] -> pass (J0)
errors::verify_monomorphize_abi_error_unsupported_vector_type_9: pass -> [missing] (J0)
errors::verify_monomorphize_abi_required_target_feature_10: pass -> [missing] (J0)
errors::verify_monomorphize_abi_required_target_feature_11: [missing] -> pass (J0)
[ui] tests/ui/abi/non-rustic-unsized.rs: [missing] -> pass (J1)

Stage 2

[ui] tests/ui/abi/non-rustic-unsized.rs: [missing] -> pass (J2)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 1ef7943ee607160a564655b6596f83670ef95df5 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-x86_64-illumos: 8519.4s -> 6130.9s (-28.0%)
dist-x86_64-apple: 7866.2s -> 6502.1s (-17.3%)
dist-i686-linux: 7648.3s -> 6355.7s (-16.9%)
x86_64-gnu-llvm-20-1: 3262.9s -> 3726.1s (+14.2%)
aarch64-apple: 8858.0s -> 9900.7s (+11.8%)
dist-x86_64-freebsd: 5663.0s -> 5026.6s (-11.2%)
dist-aarch64-apple: 6319.8s -> 7020.2s (+11.1%)
x86_64-gnu-llvm-20-3: 6109.8s -> 6773.6s (+10.9%)
arm-android: 6432.9s -> 5766.0s (-10.4%)
x86_64-rust-for-linux: 3070.8s -> 2759.8s (-10.1%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-11-05T19:54:12Z

Finished benchmarking commit (1ef7943): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.5%, secondary -2.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	2.1%	[0.9%, 3.3%]	3
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-3.6%	[-5.3%, -1.7%]	11
All ❌✅ (primary)	0.5%	[-1.3%, 2.2%]	2

Cycles

Results (primary -3.5%, secondary -1.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.3%	[3.0%, 6.0%]	5
Improvements ✅ (primary)	-3.5%	[-3.5%, -3.5%]	1
Improvements ✅ (secondary)	-5.3%	[-9.5%, -1.8%]	7
All ❌✅ (primary)	-3.5%	[-3.5%, -3.5%]	1

Binary size

Results (secondary -0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

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

Bootstrap: 473.384s -> 474.243s (0.18%)
Artifact size: 390.72 MiB -> 390.98 MiB (0.07%)

folkertdev added the F-unsized_fn_params `#![feature(unsized_fn_params)]` label Oct 30, 2025

rustbot assigned bjorn3 Oct 30, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 30, 2025

folkertdev commented Oct 30, 2025

View reviewed changes

folkertdev force-pushed the non-rustic-unsized branch from b594a4e to 52bfde2 Compare October 30, 2025 16:28

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rust-bors bot added a commit that referenced this pull request Nov 4, 2025

Auto merge of #148302 - folkertdev:non-rustic-unsized, r=<try>

6c023aa

error on non-rustic ABIs using unsized parameters

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 4, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 5, 2025

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 5, 2025

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bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Nov 5, 2025

error on non-rustic ABIs using unsized parameters

8e44e3f

folkertdev force-pushed the non-rustic-unsized branch from 52bfde2 to 8e44e3f Compare November 5, 2025 11:12

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 5, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 5, 2025

bors merged commit 1ef7943 into rust-lang:master Nov 5, 2025
12 checks passed

rustbot added this to the 1.93.0 milestone Nov 5, 2025

		extern "C" fn c_polymorphic<T: ?Sized>(_: T) {}
		//~^ ERROR this function definition uses unsized type `[u8]` which is not supported with the chosen ABI

error on non-rustic ABIs using unsized parameters #148302

error on non-rustic ABIs using unsized parameters #148302

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Overall result: ❌ regressions - no action needed

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Test differences

Stage 0

Stage 1

Stage 2

Job duration changes

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rust-timer commented Nov 5, 2025

Overall result: ❌ regressions - no action needed

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