Fix splat ICEs and ban it in closures by teor2345 · Pull Request #158645 · rust-lang/rust

teor2345 · 2026-07-01T08:12:36Z

This PR is part of the splat lang experiment #153629.

It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs:
Close #158482

Improves the message and error handling in another ICE (but doesn't fix it):
cc #158603

And bans splat on closures and rust-call, because they already de-tuple arguments:
Close #158605

In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet):
cc #158644

rustbot · 2026-07-01T08:12:41Z

r? @folkertdev

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folkertdev

A first pass. Overall this PR seems kind of large, it would be easier to review if split up into smaller chunks.

View changes since this review

folkertdev · 2026-07-01T08:32:24Z

+                Extern::Explicit(abi_str, span)
+                    if abi_str.symbol_unescaped.as_str() == "rust-call" =>
+                {
+                    SplatSemantic::NoRustCall(span)
+                }
+                Extern::Explicit(_abi_str, _span) => SplatSemantic::Yes,


Suggested change

Extern::Explicit(abi_str, span)

if abi_str.symbol_unescaped.as_str() == "rust-call" =>

{

SplatSemantic::NoRustCall(span)

}

Extern::Explicit(_abi_str, _span) => SplatSemantic::Yes,

Extern::Explicit(abi_str, span) => match abi_str.symbol_unescaped {

sym::rust_dash_call => SplatSemantic::NoRustCall(span),

_ => SplatSemantic::Yes,

},

and add a comment on why here too perhaps?

I think the rust_dash_call symbol only exists in rust-analyzer, not in the compiler, but I did add the comment.

rustbot · 2026-07-01T08:36:48Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

teor2345

A first pass. Overall this PR seems kind of large, it would be easier to review if split up into smaller chunks.

Yeah I wondered about that, I'll split it up today, now I know which parts actually fail in CI.

@rustbot label +F-splat +I-ICE +T-compiler +C-bug

View changes since this review

teor2345 · 2026-07-02T02:14:03Z

I split the extra tests into PR #158677, most of them didn't need any compiler changes to work, so they are fine to merge separately.

teor2345 · 2026-07-02T04:32:58Z

I dropped the large refactor because it broke some unrelated UI tests. Later I'll see if I can get it to work, and submit it as a separate PR. Otherwise this should be ready to review, and independent of #158677 merging.

Let me know if you'd like the PR split further?

@rustbot ready

rustbot · 2026-07-02T04:33:02Z

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teor2345 · 2026-07-02T05:48:09Z

@rustbot ready

@rustbot

…eywiser Add extra splat tests This PR is part of the splat lang experiment rust-lang#153629. It adds a bunch of tests for existing splat functionality, but doesn't make any compiler code changes. Edit: split off from PR rust-lang#158645 @rustbot label +F-splat +T-compiler

teor2345 · 2026-07-03T02:47:20Z

            TyKind::FnPtr(bfty) => {
                self.check_fn_ptr_safety(bfty.decl_span, bfty.safety);
-                self.check_fn_decl(&bfty.decl, SelfSemantic::No);
+                self.check_fn_decl(&bfty.decl, SelfSemantic::No, SplatSemantic::Yes);


This is wrong because FnPtrs can be rust-call, I'll add a test
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=511e43db9905a3a38acb86b175535fe2

@rustbot author

View changes since the review

…uwer Rollup of 18 pull requests Successful merges: - #158871 (add relnotes for 1.97.0) - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158655 (Fix coroutine MIR saved local remapping) - #158666 (Carry the `b_offset` inside `BackendRepr::ScalarPair`) - #158920 (Update wasm-component-ld to 0.5.26) - #158926 (wrapping_sh* methods: clarify underspecified reference) - #158927 (add core test run with `-Zforce-intrinsic-fallback`) - #151379 (Stabilize `VecDeque::retain_back` from `truncate_front`) - #158807 (Add regression test for CString::clone_into unwind safety) - #158862 (Fix the span for parameter suggestion ) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158894 (Make the ordering of non-terminal binds in ambiguity error messages deterministic) - #158902 (add codegen test for range length bound propagation) - #158913 (Update `browser-ui-test` version to `0.24.1`) - #158935 (std: support real fd methods on Emscripten) - #158951 (Merge three `MaxUniverse`s into one)

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

…uwer Rollup of 25 pull requests Successful merges: - #158871 (add relnotes for 1.97.0) - #158968 (stdarch subtree update) - #154445 (rustdoc: Represent `--output-format=json` coverage and ir differently) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158495 (Rename HAS_CT_PROJECTION to HAS_CONST_ALIAS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158655 (Fix coroutine MIR saved local remapping) - #158666 (Carry the `b_offset` inside `BackendRepr::ScalarPair`) - #158912 (Introduce new bootstrap config section for PGO configuration) - #158920 (Update wasm-component-ld to 0.5.26) - #158926 (wrapping_sh* methods: clarify underspecified reference) - #158927 (add core test run with `-Zforce-intrinsic-fallback`) - #158932 (Do not build the compiler when invoking `x perf compare`) - #158937 (Emit the emscripten entry point as `__main_argc_argv`) - #151379 (Stabilize `VecDeque::retain_back` from `truncate_front`) - #156548 ( Library support for aarch64-unknown-linux-pauthtest target) - #158307 (CI job for parallel frontend ui tests) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158741 (Simplify `Option::into_flat_iter` signature) - #158807 (Add regression test for CString::clone_into unwind safety) - #158862 (Fix the span for parameter suggestion ) - #158883 (tests: fix enum-match.rs to handle LLVM 23)

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

Rollup of 25 pull requests Successful merges: - #158871 (add relnotes for 1.97.0) - #158968 (stdarch subtree update) - #157690 (codegen_ssa: pack small const aggregates into immediate stores) - #158541 (Move `std::io::Write` to `core::io`) - #154445 (rustdoc: Represent `--output-format=json` coverage and ir differently) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158495 (Rename HAS_CT_PROJECTION to HAS_CONST_ALIAS) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158655 (Fix coroutine MIR saved local remapping) - #158666 (Carry the `b_offset` inside `BackendRepr::ScalarPair`) - #158870 (std: merge the unix-like io::error modules into one file) - #158920 (Update wasm-component-ld to 0.5.26) - #158926 (wrapping_sh* methods: clarify underspecified reference) - #158927 (add core test run with `-Zforce-intrinsic-fallback`) - #158932 (Do not build the compiler when invoking `x perf compare`) - #158937 (Emit the emscripten entry point as `__main_argc_argv`) - #151379 (Stabilize `VecDeque::retain_back` from `truncate_front`) - #156144 (Better docs for PartialEq (includes macro rename)) - #156548 ( Library support for aarch64-unknown-linux-pauthtest target) - #158307 (CI job for parallel frontend ui tests) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158741 (Simplify `Option::into_flat_iter` signature)

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

…uwer Rollup of 17 pull requests Successful merges: - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158535 (Support `#[track_caller]` on EII declarations) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places")

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment #153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close #158482 Improves the message and error handling in another ICE (but doesn't fix it): cc #158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close #158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc #158644~~

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

…uwer Rollup of 21 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159005 (Use `as_lang_item` instead of repeatedly matching)

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

…uwer Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes)

Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment rust-lang#153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close rust-lang#158482 Improves the message and error handling in another ICE (but doesn't fix it): cc rust-lang#158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close rust-lang#158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc rust-lang#158644~~

Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158541 (Move `std::io::Write` to `core::io`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158960 (Fix bootstrap submodule path prefix matching) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159036 (bootstrap: expand '@argfile' arguments to rustc shim)

Rollup merge of #158645 - teor2345:splat-fn-fixes, r=folkertdev Fix splat ICEs and ban it in closures This PR is part of the splat lang experiment #153629. It fixes one ICE, and cleans up the surrounding error handling to avoid future ICEs: Close #158482 Improves the message and error handling in another ICE (but doesn't fix it): cc #158603 And bans splat on closures and rust-call, because they already de-tuple arguments: Close #158605 ~~In the process I discovered another symbol mangling bug with splatting, which I added a test for (but didn't fix yet): cc #158644~~

rustbot assigned folkertdev Jul 1, 2026

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 Jul 1, 2026

This was referenced Jul 1, 2026

Fix ICE in label_fn_like for splatted args and add UI tests #157434

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[ICE] due to #[splat] in a function pointer type #158603

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teor2345 commented Jul 1, 2026

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rustbot added C-bug Category: This is a bug. F-splat `#![feature(splat)]` I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ labels Jul 1, 2026

teor2345 mentioned this pull request Jul 2, 2026

Add extra splat tests #158677

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teor2345 force-pushed the splat-fn-fixes branch from 81fcc4e to babf77b Compare July 2, 2026 02:59

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Tracking Issue for argument splatting lang experiment #153629

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JonathanBrouwer mentioned this pull request Jul 8, 2026

Rollup of 25 pull requests #158973

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Rollup of 25 pull requests #158977

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Rollup of 25 pull requests #158986

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Rollup of 17 pull requests #159007

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Rollup of 18 pull requests #159013

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Rollup of 21 pull requests #159020

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Rollup of 21 pull requests #159024

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Rollup of 24 pull requests #159037

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Rollup of 25 pull requests #159045

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Rollup of 24 pull requests #159046

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rust-bors Bot merged commit 16a60ff into rust-lang:main Jul 10, 2026
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