Implement a `explicit_generic_args_with_impl_trait` feature gate #86176

nbdd0121 · 2021-06-09T20:01:09Z

Implements #83701

When this gate is enabled, explicit generic arguments can be specified even if impl Trait is used in argument position. Generic arguments can only be specified for explicit generic parameters but not for the synthetic type parameters from impl Trait

So code like this will be accepted:

#![feature(explicit_generic_args_with_impl_trait)]

fn foo<T: ?Sized>(_f: impl AsRef<T>) {}
fn main() {
    foo::<str>("".to_string());
}

rust-highfive · 2021-06-09T20:01:12Z

r? @steveklabnik

(rust-highfive has picked a reviewer for you, use r? to override)

bors · 2021-06-10T23:35:07Z

☔ The latest upstream changes (presumably #80080) made this pull request unmergeable. Please resolve the merge conflicts.

crlf0710 · 2021-06-26T15:47:32Z

r? @matthewjasper

bors · 2021-07-27T19:38:50Z

☔ The latest upstream changes (presumably #83484) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2021-07-28T09:07:08Z

☔ The latest upstream changes (presumably #86735) made this pull request unmergeable. Please resolve the merge conflicts.

JohnTitor · 2021-07-28T20:29:33Z

r? @bjorn3 as per GitHub suggestions

bjorn3 · 2021-07-28T20:56:00Z

I have no experience with the typechecker, maybe

r? @lcnr

(another github suggestion)

jackh726 · 2021-07-28T22:04:33Z

I will take this review if @lcnr can't.

That being said, I think it's prudent to get a sign off from the lang team here. I imagine this probably falls under the "make more reversible decisions" part of the initiative process. So probably just need someone to give the okay. So cc @rust-lang/lang

joshtriplett · 2021-07-28T22:23:23Z

I agree---since this is nightly-only, I think it's fine to go ahead with it.

I'll nominate this for consideration at a future meeting, but in the interim, go ahead.

bors · 2021-07-30T14:44:48Z

☔ The latest upstream changes (presumably #87237) made this pull request unmergeable. Please resolve the merge conflicts.

jackh726

A couple nits, but r=me for this after those are addressed.

#83701 needs modified to "become" a tracking issue before/when this lands (or a new issue could be opened)

jackh726 · 2021-08-02T01:21:50Z

compiler/rustc_feature/src/active.rs

@@ -687,6  687,9 @@ declare_features! (
    /// Trait upcasting is casting, e.g., `dyn Foo -> dyn Bar` where `Foo: Bar`.
    (incomplete, trait_upcasting, "1.56.0", Some(65991), None),

+    /// Allows explicit generic arguments specification with `impl Trait` present.
+    (active, explicit_generic_args_with_impl_trait, "1.56.0", Some(83701), None),


I suppose we can just co-opt that issue to be a tracking issue, yeah.

jackh726 · 2021-08-02T01:23:58Z

compiler/rustc_typeck/src/astconv/generics.rs

@@ -459,7  459,28 @@ impl<'o, 'tcx> dyn AstConv<'tcx>   'o {

        let default_counts = gen_params.own_defaults();
        let param_counts = gen_params.own_counts();
-        let named_type_param_count = param_counts.types - has_self as usize;
+        let synth_type_param_count = if tcx.features().explicit_generic_args_with_impl_trait {


I'd like a small comment here just explaining what we're doing.

src/test/ui/impl-trait/explicit-generic-args-for-impl.rs

src/test/ui/impl-trait/explicit-generic-args-for-impl.stderr

jackh726 · 2021-08-02T01:31:31Z

src/test/ui/impl-trait/feature-gate-explicit_generic_args_with_impl_trait.stderr

@@ -0,0  1,9 @@
+error[E0632]: cannot provide explicit generic arguments when `impl Trait` is used in argument position


...in fact, I imagine the longer for that part of the diagnostic will probably co-opt some of this logic

jackh726 · 2021-08-02T01:33:40Z

r? @jackh726

When this gate is enabled, explicit generic arguments can be specified even if `impl Trait` is used in argument position. Generic arguments can only be specified for explicit generic parameters but not for the synthetic type parameters from `impl Trait`

jackh726 · 2021-08-02T14:03:59Z

@bors r

bors · 2021-08-02T14:04:00Z

📌 Commit 9b90e7e has been approved by jackh726

Rollup of 6 pull requests Successful merges: - rust-lang#86176 (Implement a `explicit_generic_args_with_impl_trait` feature gate) - rust-lang#87654 (Add documentation for the order of Option and Result) - rust-lang#87659 (Fix invalid suggestions for non-ASCII characters in byte constants) - rust-lang#87673 (Tweak opaque type mismatch error) - rust-lang#87687 (Inline some macros) - rust-lang#87690 (Add missing "allocated object" doc link to `<*mut T>::add`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

…ackh726 Provide extra note if synthetic type args are specified Implement the unresolved question in rust-lang#83701 as suggested in rust-lang#86176 (comment). r? `@jackh726`

…ackh726 Provide extra note if synthetic type args are specified Implement the unresolved question in rust-lang#83701 as suggested in rust-lang#86176 (comment). r? ``@jackh726``

…1,nagisa Stabilize explicit_generic_args_with_impl_trait This is a stabilisation PR for `explicit_generic_args_with_impl_trait`. * [tracking issue](rust-lang#83701) - [Stabilisation report](rust-lang#83701 (comment)) - [FCP entered](rust-lang#83701 (comment)) * [implementation PR](rust-lang#86176) * [Reference PR](rust-lang/reference#1212) * There is no mention of using the turbofish operator in the book (other than an entry in the operator list in the appendix), so there is no documentation to change/add there, unless we felt like we should add a section on using turbofish, but that seems orthogonal to `explicit_generic_args_with_impl_trait`

rust-highfive assigned steveklabnik Jun 9, 2021

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nbdd0121 force-pushed the explicit-generic-args branch from 43a3064 to ebefa0c Compare June 10, 2021 23:52

rust-highfive assigned matthewjasper and unassigned steveklabnik Jun 26, 2021

JohnCSimon added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 12, 2021

nbdd0121 force-pushed the explicit-generic-args branch 2 times, most recently from 15a1422 to 35b80d9 Compare July 28, 2021 01:07

nbdd0121 force-pushed the explicit-generic-args branch from 35b80d9 to ffb2892 Compare July 28, 2021 20:19

rust-highfive assigned bjorn3 and unassigned matthewjasper Jul 28, 2021

rust-highfive assigned lcnr and unassigned bjorn3 Jul 28, 2021

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nbdd0121 force-pushed the explicit-generic-args branch from ffb2892 to 5527810 Compare July 31, 2021 19:37

jackh726 approved these changes Aug 2, 2021

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rust-highfive assigned jackh726 and unassigned lcnr Aug 2, 2021

jackh726 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 Aug 2, 2021

nbdd0121 force-pushed the explicit-generic-args branch from 5527810 to 9b90e7e Compare August 2, 2021 03:17

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 2, 2021

jackh726 mentioned this pull request Aug 2, 2021

Tracking issue for explicit_generic_args_with_impl_trait #83701

Closed

3 tasks

camsteffen mentioned this pull request Aug 2, 2021

Rollup of 6 pull requests #87698

Merged

bors merged commit 14f3418 into rust-lang:master Aug 2, 2021

rustbot added this to the 1.56.0 milestone Aug 2, 2021

nbdd0121 deleted the explicit-generic-args branch August 2, 2021 22:14

jonas-schievink mentioned this pull request Aug 10, 2021

No way to use fn with both const generics and impl Trait #85475

Closed

nbdd0121 mentioned this pull request Feb 14, 2022

Provide extra note if synthetic type args are specified #93982

Merged

nrc mentioned this pull request May 9, 2022

Stabilize explicit_generic_args_with_impl_trait #96868

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Implement a `explicit_generic_args_with_impl_trait` feature gate #86176

Implement a `explicit_generic_args_with_impl_trait` feature gate #86176

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bors commented Aug 2, 2021

		@@ -0,0 1,9 @@
		error[E0632]: cannot provide explicit generic arguments when `impl Trait` is used in argument position

Implement a explicit_generic_args_with_impl_trait feature gate #86176

Implement a explicit_generic_args_with_impl_trait feature gate #86176

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Implement a `explicit_generic_args_with_impl_trait` feature gate #86176

Implement a `explicit_generic_args_with_impl_trait` feature gate #86176