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delegation: support proper interaction of user-specified args and impl Traits#155096

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aerooneqq:delegation-user-specified-args-impl-traits
Apr 13, 2026
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delegation: support proper interaction of user-specified args and impl Traits#155096
rust-bors[bot] merged 1 commit intorust-lang:mainfrom
aerooneqq:delegation-user-specified-args-impl-traits

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@aerooneqq aerooneqq commented Apr 10, 2026 •
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This PR supports usages of user-specified args with impl Traits. When there are user-specified args in child we still need to generate synthetic generic params and use them during signature inheritance:

fn foo<T, const N: usize>(f: impl FnOnce()) {}

reuse foo::<String, 123> as bar;

//desugaring
fn bar<TSynth: impl FnOnce()>(f: _) {
    foo::<String, 123>(f)
}

When inheriting predicates we process impl Trait ones, so we need generic params to instantiate them. Other approach may involve not generating synthetic generic params and try to filter out those predicates, but fairly generating synthetic params seems more consistent?.

Fixes #154780, part of #118212.

r? @petrochenkov

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rustbot commented Apr 10, 2026

HIR ty lowering was modified

cc @fmease

@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. labels Apr 10, 2026
@petrochenkov petrochenkov added the F-fn_delegation `#![feature(fn_delegation)]` label Apr 10, 2026
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petrochenkov commented Apr 10, 2026

r=me after squashing commits.
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@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 Apr 10, 2026
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rustbot commented Apr 10, 2026

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

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petrochenkov commented Apr 10, 2026

@bors delegate+

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rust-bors Bot commented Apr 10, 2026

✌️ @aerooneqq, you can now approve this pull request!

If @petrochenkov told you to "r=me" after making some further change, then please make that change and post @bors r=petrochenkov.

@aerooneqq aerooneqq force-pushed the delegation-user-specified-args-impl-traits branch from 21818db to 51888a1 Compare April 13, 2026 07:55
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aerooneqq commented Apr 13, 2026

@bors r=petrochenkov

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rust-bors Bot commented Apr 13, 2026

📌 Commit 51888a1 has been approved by petrochenkov

It is now in the queue for this repository.

@rust-bors rust-bors Bot 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 13, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Apr 13, 2026
@JonathanBrouwer
Rollup merge of rust-lang#155096 - aerooneqq:delegation-user-specifie…
5e3d872 
…d-args-impl-traits, r=petrochenkov

delegation: support proper interaction of user-specified args and impl Traits

This PR supports usages of user-specified args with impl Traits. When there are user-specified args in child we still need to generate synthetic generic params and use them during signature inheritance:
```rust
fn foo<T, const N: usize>(f: impl FnOnce()) {}

reuse foo::<String, 123> as bar;

//desugaring
fn bar<TSynth: impl FnOnce()>(f: _) {
    foo::<String, 123>(f)
}
```
When inheriting predicates we process impl Trait ones, so we need generic params to instantiate them. Other approach may involve not generating synthetic generic params and try to filter out those predicates, but fairly generating synthetic params seems more consistent?.

Fixes rust-lang#154780, part of rust-lang#118212.

r? @petrochenkov
This was referenced Apr 13, 2026
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rust-bors Bot pushed a commit that referenced this pull request Apr 13, 2026
@bors
Auto merge of #155239 - JonathanBrouwer:rollup-XUNKT4X, r=JonathanBro…
a72e2a7 
…uwer

Rollup of 10 pull requests

Successful merges:

 - #155227 (`rust-analyzer` subtree update)
 - #153335 (Add #![unstable_removed(..)] attribute to track removed features)
 - #154932 (Handle RTN projections in assoc type restriction diagnostics)
 - #155096 (delegation: support proper interaction of user-specified args and impl Traits)
 - #155106 (cg_llvm: scalable vectors with `simd_cast` and `simd_select`)
 - #155140 (add regression test for OpenOptionsExt downstream compat)
 - #155182 (Make the expansion of guard metavars begin guard non-terminals)
 - #155226 (delegation: revert execution of hir_crate_items before delayed lowering)
 - #153997 (Use closures more consistently in `dep_graph.rs`.)
 - #155003 (update thin-vec)
@rust-bors rust-bors Bot merged commit ab551b1 into rust-lang:main Apr 13, 2026
11 checks passed
@rustbot rustbot added this to the 1.97.0 milestone Apr 13, 2026
rust-timer added a commit that referenced this pull request Apr 13, 2026
@rust-timer
Unrolled build for #155096
15cd94e 
Rollup merge of #155096 - aerooneqq:delegation-user-specified-args-impl-traits, r=petrochenkov

delegation: support proper interaction of user-specified args and impl Traits

This PR supports usages of user-specified args with impl Traits. When there are user-specified args in child we still need to generate synthetic generic params and use them during signature inheritance:
```rust
fn foo<T, const N: usize>(f: impl FnOnce()) {}

reuse foo::<String, 123> as bar;

//desugaring
fn bar<TSynth: impl FnOnce()>(f: _) {
    foo::<String, 123>(f)
}
```
When inheriting predicates we process impl Trait ones, so we need generic params to instantiate them. Other approach may involve not generating synthetic generic params and try to filter out those predicates, but fairly generating synthetic params seems more consistent?.

Fixes #154780, part of #118212.

r? @petrochenkov
github-actions Bot pushed a commit to rust-lang/rustc-dev-guide that referenced this pull request Apr 13, 2026
@bors
Auto merge of #155239 - JonathanBrouwer:rollup-XUNKT4X, r=JonathanBro…
bc20942 
…uwer

Rollup of 10 pull requests

Successful merges:

 - rust-lang/rust#155227 (`rust-analyzer` subtree update)
 - rust-lang/rust#153335 (Add #![unstable_removed(..)] attribute to track removed features)
 - rust-lang/rust#154932 (Handle RTN projections in assoc type restriction diagnostics)
 - rust-lang/rust#155096 (delegation: support proper interaction of user-specified args and impl Traits)
 - rust-lang/rust#155106 (cg_llvm: scalable vectors with `simd_cast` and `simd_select`)
 - rust-lang/rust#155140 (add regression test for OpenOptionsExt downstream compat)
 - rust-lang/rust#155182 (Make the expansion of guard metavars begin guard non-terminals)
 - rust-lang/rust#155226 (delegation: revert execution of hir_crate_items before delayed lowering)
 - rust-lang/rust#153997 (Use closures more consistently in `dep_graph.rs`.)
 - rust-lang/rust#155003 (update thin-vec)
github-actions Bot pushed a commit to rust-lang/rust-analyzer that referenced this pull request Apr 16, 2026
@bors
Auto merge of #155239 - JonathanBrouwer:rollup-XUNKT4X, r=JonathanBro…
d697b08 
…uwer

Rollup of 10 pull requests

Successful merges:

 - rust-lang/rust#155227 (`rust-analyzer` subtree update)
 - rust-lang/rust#153335 (Add #![unstable_removed(..)] attribute to track removed features)
 - rust-lang/rust#154932 (Handle RTN projections in assoc type restriction diagnostics)
 - rust-lang/rust#155096 (delegation: support proper interaction of user-specified args and impl Traits)
 - rust-lang/rust#155106 (cg_llvm: scalable vectors with `simd_cast` and `simd_select`)
 - rust-lang/rust#155140 (add regression test for OpenOptionsExt downstream compat)
 - rust-lang/rust#155182 (Make the expansion of guard metavars begin guard non-terminals)
 - rust-lang/rust#155226 (delegation: revert execution of hir_crate_items before delayed lowering)
 - rust-lang/rust#153997 (Use closures more consistently in `dep_graph.rs`.)
 - rust-lang/rust#155003 (update thin-vec)
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F-fn_delegation `#![feature(fn_delegation)]` S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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[ICE]: delegation: TyKind::Error constructed but no error reported

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