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Add arg splat experiment initial tuple impl#153697

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teor2345 wants to merge 11 commits into
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teor2345:fn-arg-splat-experiment
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Add arg splat experiment initial tuple impl#153697
teor2345 wants to merge 11 commits into
rust-lang:mainfrom
teor2345:fn-arg-splat-experiment

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@teor2345 teor2345 commented Mar 11, 2026 •
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This PR is part of the argument splatting lang experiment, and FFI overloading / C++ interop project goals:

Example code using existing unstable features:

Discussion of implementation strategy:

The PR is the initial implementation of the feature:

  • splat incomplete feature gate
  • #[splat] attribute on function arguments
  • Splatted function argument TypeInfo
  • #[splat] function parameter check at THIR level
  • splatted MIR lowering (as tupled arguments)
  • feature gate and UI tests for item type filtering, non-splattable arguments, splattable tuples, generics, and the "overloading at home" example
    • about half the diff (1100 lines) is tests and test output

Once this PR merges, we can add further functionality, then test it out in interop tools.

Further Work

Out of Scope for this PR

  • Change codegen to de-tuple caller and callee
  • Better diagnostics
  • Full support for splatted function pointer arguments

@rustbot 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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 11, 2026
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rustbot commented Mar 11, 2026

r? @JohnTitor

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@teor2345 teor2345 mentioned this pull request Mar 11, 2026
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oli-obk
oli-obk reviewed Mar 11, 2026
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Comment thread compiler/rustc_builtin_macros/src/splat.rs Outdated
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JohnTitor commented Mar 11, 2026

It should be better for someone on https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/On.20overloading/with/573924937 to review this, @oli-obk could you take over?

@oli-obk oli-obk assigned oli-obk and unassigned JohnTitor Mar 11, 2026
@oli-obk oli-obk added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Mar 12, 2026
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oli-obk commented Mar 12, 2026

Let's wait for the ongoing discussion on Zulip to figure out whether we need to have a proc macro, an AST manipulating attribute (like define_opaque), or just a normal attribute

@teor2345 teor2345 marked this pull request as draft March 13, 2026 06:49
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 13, 2026
@teor2345 teor2345 force-pushed the fn-arg-splat-experiment branch from 89102bf to c784a57 Compare March 16, 2026 07:35
@rustbot rustbot added the A-attributes Area: Attributes (`#[…]`, `#![…]`) label Mar 16, 2026
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Comment thread compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs Outdated
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Comment thread compiler/rustc_hir/src/target.rs
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Comment thread tests/ui/splat/splat-non-function.rs Outdated
@teor2345 teor2345 force-pushed the fn-arg-splat-experiment branch from c784a57 to 2d9e563 Compare March 20, 2026 01:37
@rustbot rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-query-system Area: The rustc query system (https://rustc-dev-guide.rust-lang.org/query.html) labels Mar 20, 2026
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@teor2345 teor2345 mentioned this pull request Mar 20, 2026
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@rustbot rustbot added the T-clippy Relevant to the Clippy team. label Mar 20, 2026
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teor2345 commented May 7, 2026

@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels May 7, 2026
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@rustbot rustbot added has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 11, 2026
@teor2345 teor2345 force-pushed the fn-arg-splat-experiment branch from 6b05355 to 881fb4b Compare May 11, 2026 22:00
@rustbot rustbot removed has-merge-commits PR has merge commits, merge with caution. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 11, 2026
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teor2345 commented May 11, 2026

Just some rust-analyzer refactors, so I needed to move splat FIXME comments into the new refactored code.

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@teor2345 teor2345 force-pushed the fn-arg-splat-experiment branch from 881fb4b to 0e4aed3 Compare May 13, 2026 01:44
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rustbot commented May 13, 2026

This PR was rebased onto a different main 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.

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rust-bors Bot commented May 26, 2026

☔ The latest upstream changes (presumably #156967) made this pull request unmergeable. Please resolve the merge conflicts.

This was referenced Jun 3, 2026
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A-attributes Area: Attributes (`#[…]`, `#![…]`) A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-query-system Area: The rustc query system (https://rustc-dev-guide.rust-lang.org/query.html) perf-regression Performance regression. S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-clippy Relevant to the Clippy team. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. T-rust-analyzer Relevant to the rust-analyzer team, which will review and decide on the PR/issue.

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