Stabilize opaque type precise capturing (RFC 3617)

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -557,7 +557,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
     gate_all!(fn_delegation, "functions delegation is not yet fully implemented");
     gate_all!(postfix_match, "postfix match is experimental");
     gate_all!(mut_ref, "mutable by-reference bindings are experimental");
-    gate_all!(precise_capturing, "precise captures on `impl Trait` are experimental");
     gate_all!(global_registration, "global registration is experimental");
     gate_all!(unsafe_attributes, "`#[unsafe()]` markers for attributes are experimental");
     gate_all!(return_type_notation, "return type notation is experimental");

compiler/rustc_feature/src/accepted.rs

@@ -309,6 +309,8 @@ declare_features! (
     (accepted, param_attrs, "1.39.0", Some(60406)),
     /// Allows parentheses in patterns.
     (accepted, pattern_parentheses, "1.31.0", Some(51087)),
+    /// Allows `use<'a, 'b, A, B>` in `impl Trait + use<...>` for precise capture of generic args.
+    (accepted, precise_capturing, "CURRENT_RUSTC_VERSION", Some(123432)),
     /// Allows procedural macros in `proc-macro` crates.
     (accepted, proc_macro, "1.29.0", Some(38356)),
     /// Allows multi-segment paths in attributes and derives.

compiler/rustc_feature/src/unstable.rs

@@ -561,8 +561,6 @@ declare_features! (
     (unstable, patchable_function_entry, "1.81.0", Some(123115)),
     /// Allows postfix match `expr.match { ... }`
     (unstable, postfix_match, "1.79.0", Some(121618)),
-    /// Allows `use<'a, 'b, A, B>` in `impl Trait + use<...>` for precise capture of generic args.
-    (unstable, precise_capturing, "1.79.0", Some(123432)),
     /// Allows macro attributes on expressions, statements and non-inline modules.
     (unstable, proc_macro_hygiene, "1.30.0", Some(54727)),
     /// Allows `&raw const $place_expr` and `&raw mut $place_expr` expressions.

compiler/rustc_hir/src/hir.rs

@@ -2773,7 +2773,6 @@ impl PreciseCapturingArg<'_> {
 /// resolution to. Lifetimes don't have this problem, and for them, it's actually
 /// kind of detrimental to use a custom node type versus just using [`Lifetime`],
 /// since resolve_bound_vars operates on `Lifetime`s.
-// FIXME(precise_capturing): Investigate storing this as a path instead?
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct PreciseCapturingNonLifetimeArg {
     pub hir_id: HirId,

compiler/rustc_lint/src/impl_trait_overcaptures.rs

@@ -27,8 +27,6 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail
-    /// # #![feature(precise_capturing)]
-    /// # #![allow(incomplete_features)]
     /// # #![deny(impl_trait_overcaptures)]
     /// # use std::fmt::Display;
     /// let mut x = vec![];
@@ -56,7 +54,6 @@ declare_lint! {
     pub IMPL_TRAIT_OVERCAPTURES,
     Allow,
     "`impl Trait` will capture more lifetimes than possibly intended in edition 2024",
-    @feature_gate = precise_capturing;
     //@future_incompatible = FutureIncompatibleInfo {
     //    reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
     //    reference: "<FIXME>",
@@ -75,8 +72,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail
-    /// # #![feature(precise_capturing, lifetime_capture_rules_2024)]
-    /// # #![allow(incomplete_features)]
+    /// # #![feature(lifetime_capture_rules_2024)]
     /// # #![deny(impl_trait_redundant_captures)]
     /// fn test<'a>(x: &'a i32) -> impl Sized + use<'a> { x }
     /// ```
@@ -90,7 +86,6 @@ declare_lint! {
     pub IMPL_TRAIT_REDUNDANT_CAPTURES,
     Warn,
     "redundant precise-capturing `use<...>` syntax on an `impl Trait`",
-    @feature_gate = precise_capturing;
 }
 
 declare_lint_pass!(

compiler/rustc_parse/src/parser/ty.rs

@@ -851,7 +851,6 @@ impl<'a> Parser<'a> {
             // lifetimes and ident params (including SelfUpper). These are validated later
             // for order, duplication, and whether they actually reference params.
             let use_span = self.prev_token.span;
-            self.psess.gated_spans.gate(sym::precise_capturing, use_span);
             let (args, args_span) = self.parse_precise_capturing_args()?;
             GenericBound::Use(args, use_span.to(args_span))
         } else {

compiler/rustc_trait_selection/src/error_reporting/infer/region.rs

@@ -17,8 +17,8 @@ use rustc_span::{BytePos, ErrorGuaranteed, Span, Symbol};
 use rustc_type_ir::Upcast as _;
 
 use super::nice_region_error::find_anon_type;
-use super::{nice_region_error, ObligationCauseAsDiagArg};
-use crate::error_reporting::infer::ObligationCauseExt as _;
+use super::ObligationCauseAsDiagArg;
+use crate::error_reporting::infer::ObligationCauseExt;
 use crate::error_reporting::TypeErrCtxt;
 use crate::errors::{
     self, note_and_explain, FulfillReqLifetime, LfBoundNotSatisfied, OutlivesBound,
@@ -1212,22 +1212,8 @@ pub fn unexpected_hidden_region_diagnostic<'a, 'tcx>(
                 hidden_region,
                 "",
             );
-            if let Some(reg_info) = tcx.is_suitable_region(generic_param_scope, hidden_region) {
-                if infcx.tcx.features().precise_capturing {
-                    suggest_precise_capturing(tcx, opaque_ty_key.def_id, hidden_region, &mut err);
-                } else {
-                    let fn_returns = tcx.return_type_impl_or_dyn_traits(reg_info.def_id);
-                    nice_region_error::suggest_new_region_bound(
-                        tcx,
-                        &mut err,
-                        fn_returns,
-                        hidden_region.to_string(),
-                        None,
-                        format!("captures `{hidden_region}`"),
-                        None,
-                        Some(reg_info.def_id),
-                    )
-                }
+            if let Some(_) = tcx.is_suitable_region(generic_param_scope, hidden_region) {
+                suggest_precise_capturing(tcx, opaque_ty_key.def_id, hidden_region, &mut err);
             }
         }
         ty::RePlaceholder(_) => {

tests/rustdoc-json/impl-trait-precise-capturing.rs

@@ -1,5 +1,3 @@
-#![feature(precise_capturing)]
-
 //@ is "$.index[*][?(@.name=='hello')].inner.function.decl.output.impl_trait[1].use[0]" \"\'a\"
 //@ is "$.index[*][?(@.name=='hello')].inner.function.decl.output.impl_trait[1].use[1]" \"T\"
 //@ is "$.index[*][?(@.name=='hello')].inner.function.decl.output.impl_trait[1].use[2]" \"N\"

tests/rustdoc/impl-trait-precise-capturing.rs

@@ -1,7 +1,6 @@
 //@ aux-build:precise-capturing.rs
 
 #![crate_name = "foo"]
-#![feature(precise_capturing)]
 
 extern crate precise_capturing;
 

tests/ui/async-await/multiple-lifetimes/ret-impl-trait-one.stderr

@@ -26,10 +26,10 @@ LL | |     (a, b)
 LL | | }
    | |_^
    |
-help: to declare that `impl Trait<'a>` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> + 'b {
-   |                                                                                ++++
+LL | async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<'a> + use<'a, 'b> {
+   |                                                                                +++++++++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/borrowck/alias-liveness/opaque-type-param.stderr

@@ -7,6 +7,11 @@ LL | fn foo<'a>(s: &'a str) -> impl Trait + 'static {
    |        hidden type `impl Trait + 'static` captures the lifetime `'a` as defined here
 LL |     bar(s)
    |     ^^^^^^
+   |
+help: add a `use<...>` bound to explicitly capture `'a`
+   |
+LL | fn foo<'a>(s: &'a str) -> impl Trait + 'static + use<'a> {
+   |                                                +++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/const-generics/generic_const_exprs/issue-109141.stderr

@@ -30,10 +30,10 @@ LL |     fn a(&self) -> impl Iterator {
 LL |         self.0.iter_mut()
    |         ^^^^^^^^^^^^^^^^^
    |
-help: to declare that `impl Iterator` captures `'_`, you can add an explicit `'_` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'_`
    |
-LL |     fn a(&self) -> impl Iterator + '_ {
-   |                                  ++++
+LL |     fn a(&self) -> impl Iterator + use<'_> {
+   |                                  +++++++++
 
 error: aborting due to 3 previous errors
 

tests/ui/feature-gates/feature-gate-lifetime-capture-rules-2024.stderr

@@ -8,10 +8,10 @@ LL | fn foo(x: &Vec<i32>) -> impl Sized {
 LL |     x
    |     ^
    |
-help: to declare that `impl Sized` captures `'_`, you can add an explicit `'_` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'_`
    |
-LL | fn foo(x: &Vec<i32>) -> impl Sized + '_ {
-   |                                    ++++
+LL | fn foo(x: &Vec<i32>) -> impl Sized + use<'_> {
+   |                                    +++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/alias-liveness/rpit-hidden-erased-unsoundness.stderr

@@ -8,10 +8,10 @@ LL | fn step2<'a, 'b: 'a>() -> impl Sized + 'a {
 LL |     step1::<'a, 'b>()
    |     ^^^^^^^^^^^^^^^^^
    |
-help: to declare that `impl Sized + 'a` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | fn step2<'a, 'b: 'a>() -> impl Sized + 'a + 'b {
-   |                                           ++++
+LL | fn step2<'a, 'b: 'a>() -> impl Sized + 'a + use<'a, 'b> {
+   |                                           +++++++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/alias-liveness/rpit-hide-lifetime-for-swap.stderr

@@ -8,10 +8,10 @@ LL | fn hide<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a {
 LL |     x
    |     ^
    |
-help: to declare that `impl Swap + 'a` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | fn hide<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a + 'b {
-   |                                                                          ++++
+LL | fn hide<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a + use<'a, 'b, T> {
+   |                                                                          ++++++++++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/call_method_ambiguous.next.stderr

@@ -1,5 +1,5 @@
 error[E0282]: type annotations needed
-  --> $DIR/call_method_ambiguous.rs:28:13
+  --> $DIR/call_method_ambiguous.rs:26:13
    |
 LL |         let mut iter = foo(n - 1, m);
    |             ^^^^^^^^

tests/ui/impl-trait/call_method_ambiguous.rs

@@ -2,8 +2,6 @@
 //@[next] compile-flags: -Znext-solver
 //@[current] run-pass
 
-#![feature(precise_capturing)]
-
 trait Get {
     fn get(&mut self) -> u32;
 }

tests/ui/impl-trait/hidden-lifetimes.stderr

@@ -8,10 +8,10 @@ LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a {
 LL |     x
    |     ^
    |
-help: to declare that `impl Swap + 'a` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a + 'b {
-   |                                                                     ++++
+LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a + use<'a, 'b, T> {
+   |                                                                     ++++++++++++++++
 
 error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
   --> $DIR/hidden-lifetimes.rs:46:5
@@ -23,10 +23,10 @@ LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl S
 LL |     x
    |     ^
    |
-help: to declare that `impl Swap + 'a` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a + 'b {
-   |                                                                                     ++++
+LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a + use<'a, 'b, T> {
+   |                                                                                     ++++++++++++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/impl-trait/in-trait/cannot-capture-intersection.rs

@@ -1,5 +1,3 @@
-#![feature(precise_capturing)]
-
 use std::future::Future;
 use std::pin::Pin;
 

tests/ui/impl-trait/in-trait/cannot-capture-intersection.stderr

@@ -1,5 +1,5 @@
 error[E0700]: hidden type for `impl Future<Output = i32>` captures lifetime that does not appear in bounds
-  --> $DIR/cannot-capture-intersection.rs:24:9
+  --> $DIR/cannot-capture-intersection.rs:22:9
    |
 LL |     fn foo<'a, 'b>(&'a self, x: &'b i32) -> impl Future<Output = i32> {
    |                                             ------------------------- opaque type defined here

tests/ui/impl-trait/must_outlive_least_region_or_bound.stderr

@@ -7,10 +7,10 @@ LL | fn elided(x: &i32) -> impl Copy { x }
    |              |        opaque type defined here
    |              hidden type `&i32` captures the anonymous lifetime defined here
    |
-help: to declare that `impl Copy` captures `'_`, you can add an explicit `'_` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'_`
    |
-LL | fn elided(x: &i32) -> impl Copy + '_ { x }
-   |                                 ++++
+LL | fn elided(x: &i32) -> impl Copy + use<'_> { x }
+   |                                 +++++++++
 
 error[E0700]: hidden type for `impl Copy` captures lifetime that does not appear in bounds
   --> $DIR/must_outlive_least_region_or_bound.rs:6:44
@@ -21,10 +21,10 @@ LL | fn explicit<'a>(x: &'a i32) -> impl Copy { x }
    |             |                  opaque type defined here
    |             hidden type `&'a i32` captures the lifetime `'a` as defined here
    |
-help: to declare that `impl Copy` captures `'a`, you can add an explicit `'a` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'a`
    |
-LL | fn explicit<'a>(x: &'a i32) -> impl Copy + 'a { x }
-   |                                          ++++
+LL | fn explicit<'a>(x: &'a i32) -> impl Copy + use<'a> { x }
+   |                                          +++++++++
 
 error: lifetime may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:9:46
@@ -108,10 +108,10 @@ LL | fn move_lifetime_into_fn<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Fn(&'a u32
 LL |     move |_| println!("{}", y)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: to declare that `impl Fn(&'a u32)` captures `'b`, you can add an explicit `'b` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'b`
    |
-LL | fn move_lifetime_into_fn<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Fn(&'a u32) + 'b {
-   |                                                                              ++++
+LL | fn move_lifetime_into_fn<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Fn(&'a u32) + use<'a, 'b> {
+   |                                                                              +++++++++++++
 
 error[E0310]: the parameter type `T` may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:47:5

tests/ui/impl-trait/nested-return-type4.stderr

@@ -8,14 +8,10 @@ LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized
 LL |     async move { let _s = s; }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: to declare that `impl Future<Output = impl Sized>` captures `'s`, you can add an explicit `'s` lifetime bound
+help: add a `use<...>` bound to explicitly capture `'s`
    |
-LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> + 's {
-   |                                                                              ++++
-help: to declare that `impl Sized` captures `'s`, you can add an explicit `'s` lifetime bound
-   |
-LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized + 's> {
-   |                                                                             ++++
+LL | fn test<'s: 's>(s: &'s str) -> impl std::future::Future<Output = impl Sized> + use<'s> {
+   |                                                                              +++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/precise-capturing/apit.rs

@@ -1,5 +1,3 @@
-#![feature(precise_capturing)]
-
 fn hello(_: impl Sized + use<>) {}
 //~^ ERROR `use<...>` precise capturing syntax not allowed in argument-position `impl Trait`
 

tests/ui/impl-trait/precise-capturing/apit.stderr

@@ -1,5 +1,5 @@
 error: `use<...>` precise capturing syntax not allowed in argument-position `impl Trait`
-  --> $DIR/apit.rs:3:26
+  --> $DIR/apit.rs:1:26
    |
 LL | fn hello(_: impl Sized + use<>) {}
    |                          ^^^^^

tests/ui/impl-trait/precise-capturing/bad-lifetimes.rs

@@ -1,5 +1,3 @@
-#![feature(precise_capturing)]
-
 fn no_elided_lt() -> impl Sized + use<'_> {}
 //~^ ERROR missing lifetime specifier
 //~| ERROR expected lifetime parameter in `use<...>` precise captures list, found `'_`

tests/ui/impl-trait/precise-capturing/bad-lifetimes.stderr

@@ -1,5 +1,5 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/bad-lifetimes.rs:3:39
+  --> $DIR/bad-lifetimes.rs:1:39
    |
 LL | fn no_elided_lt() -> impl Sized + use<'_> {}
    |                                       ^^ expected named lifetime parameter
@@ -11,21 +11,21 @@ LL | fn no_elided_lt() -> impl Sized + use<'static> {}
    |                                       ~~~~~~~
 
 error[E0261]: use of undeclared lifetime name `'missing`
-  --> $DIR/bad-lifetimes.rs:10:37
+  --> $DIR/bad-lifetimes.rs:8:37
    |
 LL | fn missing_lt() -> impl Sized + use<'missing> {}
    |              -                      ^^^^^^^^ undeclared lifetime
    |              |
    |              help: consider introducing lifetime `'missing` here: `<'missing>`
 
 error: expected lifetime parameter in `use<...>` precise captures list, found `'_`
-  --> $DIR/bad-lifetimes.rs:3:39
+  --> $DIR/bad-lifetimes.rs:1:39
    |
 LL | fn no_elided_lt() -> impl Sized + use<'_> {}
    |                                       ^^
 
 error: expected lifetime parameter in `use<...>` precise captures list, found `'static`
-  --> $DIR/bad-lifetimes.rs:7:36
+  --> $DIR/bad-lifetimes.rs:5:36
    |
 LL | fn static_lt() -> impl Sized + use<'static> {}
    |                                    ^^^^^^^