Add variances to RPITITs

compiler/rustc_hir_analysis/src/variance/mod.rs

@@ -5,6 +5,7 @@
 
 use itertools::Itertools;
 use rustc_arena::DroplessArena;
+use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
@@ -63,8 +64,29 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
             let crate_map = tcx.crate_variances(());
             return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
         }
+        DefKind::AssocTy => match tcx.opt_rpitit_info(item_def_id.to_def_id()) {
+            Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
+                return variance_of_opaque(
+                    tcx,
+                    opaque_def_id.expect_local(),
+                    ForceCaptureTraitArgs::Yes,
+                );
+            }
+            None | Some(ty::ImplTraitInTraitData::Impl { .. }) => {}
+        },
         DefKind::OpaqueTy => {
-            return variance_of_opaque(tcx, item_def_id);
+            let force_capture_trait_args = if let hir::OpaqueTyOrigin::FnReturn {
+                parent: _,
+                in_trait_or_impl: Some(hir::RpitContext::Trait),
+            } =
+                tcx.hir_node_by_def_id(item_def_id).expect_opaque_ty().origin
+            {
+                ForceCaptureTraitArgs::Yes
+            } else {
+                ForceCaptureTraitArgs::No
+            };
+
+            return variance_of_opaque(tcx, item_def_id, force_capture_trait_args);
         }
         _ => {}
     }
@@ -73,8 +95,18 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
     span_bug!(tcx.def_span(item_def_id), "asked to compute variance for wrong kind of item");
 }
 
+#[derive(Debug, Copy, Clone)]
+enum ForceCaptureTraitArgs {
+    Yes,
+    No,
+}
+
 #[instrument(level = "trace", skip(tcx), ret)]
-fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
+fn variance_of_opaque(
+    tcx: TyCtxt<'_>,
+    item_def_id: LocalDefId,
+    force_capture_trait_args: ForceCaptureTraitArgs,
+) -> &[ty::Variance] {
     let generics = tcx.generics_of(item_def_id);
 
     // Opaque types may only use regions that are bound. So for
@@ -115,9 +147,7 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
         #[instrument(level = "trace", skip(self), ret)]
         fn visit_ty(&mut self, t: Ty<'tcx>) {
             match t.kind() {
-                ty::Alias(_, ty::AliasTy { def_id, args, .. })
-                    if matches!(self.tcx.def_kind(*def_id), DefKind::OpaqueTy) =>
-                {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
                     self.visit_opaque(*def_id, args);
                 }
                 _ => t.super_visit_with(self),
@@ -135,6 +165,15 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
         let mut generics = generics;
         while let Some(def_id) = generics.parent {
             generics = tcx.generics_of(def_id);
+
+            // Don't mark trait params generic if we're in an RPITIT.
+            if matches!(force_capture_trait_args, ForceCaptureTraitArgs::Yes)
+                && generics.parent.is_none()
+            {
+                debug_assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
+                break;
+            }
+
             for param in &generics.own_params {
                 match param.kind {
                     ty::GenericParamDefKind::Lifetime => {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1100,9 +1100,12 @@ fn should_encode_variances<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, def_kind: Def
         | DefKind::Fn
         | DefKind::Ctor(..)
         | DefKind::AssocFn => true,
+        DefKind::AssocTy => {
+            // Only encode variances for RPITITs (for traits)
+            matches!(tcx.opt_rpitit_info(def_id), Some(ty::ImplTraitInTraitData::Trait { .. }))
+        }
         DefKind::Mod
         | DefKind::Field
-        | DefKind::AssocTy
         | DefKind::AssocConst
         | DefKind::TyParam
         | DefKind::ConstParam

compiler/rustc_middle/src/ty/context.rs

@@ -539,6 +539,10 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self.trait_def(trait_def_id).implement_via_object
     }
 
+    fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {
+        self.is_impl_trait_in_trait(def_id)
+    }
+
     fn delay_bug(self, msg: impl ToString) -> ErrorGuaranteed {
         self.dcx().span_delayed_bug(DUMMY_SP, msg.to_string())
     }

compiler/rustc_type_ir/src/interner.rs

@@ -261,6 +261,8 @@ pub trait Interner:
 
     fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;
 
+    fn is_impl_trait_in_trait(self, def_id: Self::DefId) -> bool;
+
     fn delay_bug(self, msg: impl ToString) -> Self::ErrorGuaranteed;
 
     fn is_general_coroutine(self, coroutine_def_id: Self::DefId) -> bool;

compiler/rustc_type_ir/src/relate.rs

@@ -254,6 +254,16 @@ impl<I: Interner> Relate<I> for ty::AliasTy<I> {
                     b.args,
                     false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
                 )?,
+                ty::Projection if relation.cx().is_impl_trait_in_trait(a.def_id) => {
+                    relate_args_with_variances(
+                        relation,
+                        a.def_id,
+                        relation.cx().variances_of(a.def_id),
+                        a.args,
+                        b.args,
+                        false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
+                    )?
+                }
                 ty::Projection | ty::Weak | ty::Inherent => {
                     relate_args_invariantly(relation, a.args, b.args)?
                 }

tests/ui/impl-trait/in-trait/variance.rs

@@ -1,22 +1,25 @@
-#![feature(rustc_attrs)]
+#![feature(rustc_attrs, precise_capturing_in_traits)]
 #![allow(internal_features)]
 #![rustc_variance_of_opaques]
 
-trait Captures<'a> {}
-impl<T> Captures<'_> for T {}
-
 trait Foo<'i> {
     fn implicit_capture_early<'a: 'a>() -> impl Sized {}
-    //~^ [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
+    //~^ [Self: o, 'i: o, 'a: *, 'a: o, 'i: o]
+
+    fn explicit_capture_early<'a: 'a>() -> impl Sized + use<'i, 'a, Self> {}
+    //~^ [Self: o, 'i: o, 'a: *, 'i: o, 'a: o]
 
-    fn explicit_capture_early<'a: 'a>() -> impl Sized + Captures<'a> {}
-    //~^ [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
+    fn not_captured_early<'a: 'a>() -> impl Sized + use<'i, Self> {}
+    //~^ [Self: o, 'i: o, 'a: *, 'i: o]
 
     fn implicit_capture_late<'a>(_: &'a ()) -> impl Sized {}
-    //~^ [Self: o, 'i: *, 'a: o, 'i: o]
+    //~^ [Self: o, 'i: o, 'a: o, 'i: o]
+
+    fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + use<'i, 'a, Self> {}
+    //~^ [Self: o, 'i: o, 'i: o, 'a: o]
 
-    fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}
-    //~^ [Self: o, 'i: *, 'a: o, 'i: o]
+    fn not_cpatured_late<'a>(_: &'a ()) -> impl Sized + use<'i, Self> {}
+    //~^ [Self: o, 'i: o, 'i: o]
 }
 
 fn main() {}

tests/ui/impl-trait/in-trait/variance.stderr

@@ -1,26 +1,38 @@
-error: [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
-  --> $DIR/variance.rs:9:44
+error: [Self: o, 'i: o, 'a: *, 'a: o, 'i: o]
+  --> $DIR/variance.rs:6:44
    |
 LL |     fn implicit_capture_early<'a: 'a>() -> impl Sized {}
    |                                            ^^^^^^^^^^
 
-error: [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
-  --> $DIR/variance.rs:12:44
+error: [Self: o, 'i: o, 'a: *, 'i: o, 'a: o]
+  --> $DIR/variance.rs:9:44
+   |
+LL |     fn explicit_capture_early<'a: 'a>() -> impl Sized + use<'i, 'a, Self> {}
+   |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: [Self: o, 'i: o, 'a: *, 'i: o]
+  --> $DIR/variance.rs:12:40
    |
-LL |     fn explicit_capture_early<'a: 'a>() -> impl Sized + Captures<'a> {}
-   |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn not_captured_early<'a: 'a>() -> impl Sized + use<'i, Self> {}
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: [Self: o, 'i: *, 'a: o, 'i: o]
+error: [Self: o, 'i: o, 'a: o, 'i: o]
   --> $DIR/variance.rs:15:48
    |
 LL |     fn implicit_capture_late<'a>(_: &'a ()) -> impl Sized {}
    |                                                ^^^^^^^^^^
 
-error: [Self: o, 'i: *, 'a: o, 'i: o]
+error: [Self: o, 'i: o, 'i: o, 'a: o]
   --> $DIR/variance.rs:18:48
    |
-LL |     fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}
-   |                                                ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + use<'i, 'a, Self> {}
+   |                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: [Self: o, 'i: o, 'i: o]
+  --> $DIR/variance.rs:21:44
+   |
+LL |     fn not_cpatured_late<'a>(_: &'a ()) -> impl Sized + use<'i, Self> {}
+   |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 6 previous errors
 

tests/ui/impl-trait/precise-capturing/forgot-to-capture-type.rs

@@ -1,10 +1,11 @@
+#![feature(precise_capturing_in_traits)]
+
 fn type_param<T>() -> impl Sized + use<> {}
 //~^ ERROR `impl Trait` must mention all type parameters in scope
 
 trait Foo {
     fn bar() -> impl Sized + use<>;
     //~^ ERROR `impl Trait` must mention the `Self` type of the trait
-    //~| ERROR `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
 }
 
 fn main() {}

tests/ui/impl-trait/precise-capturing/forgot-to-capture-type.stderr

@@ -1,16 +1,5 @@
-error: `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
-  --> $DIR/forgot-to-capture-type.rs:5:30
-   |
-LL |     fn bar() -> impl Sized + use<>;
-   |                              ^^^^^
-   |
-   = note: currently, return-position `impl Trait` in traits and trait implementations capture all lifetimes in scope
-   = note: see issue #130044 <https://github.com/rust-lang/rust/issues/130044> for more information
-   = help: add `#![feature(precise_capturing_in_traits)]` to the crate attributes to enable
-   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
-
 error: `impl Trait` must mention all type parameters in scope in `use<...>`
-  --> $DIR/forgot-to-capture-type.rs:1:23
+  --> $DIR/forgot-to-capture-type.rs:3:23
    |
 LL | fn type_param<T>() -> impl Sized + use<> {}
    |               -       ^^^^^^^^^^^^^^^^^^
@@ -20,7 +9,7 @@ LL | fn type_param<T>() -> impl Sized + use<> {}
    = note: currently, all type parameters are required to be mentioned in the precise captures list
 
 error: `impl Trait` must mention the `Self` type of the trait in `use<...>`
-  --> $DIR/forgot-to-capture-type.rs:5:17
+  --> $DIR/forgot-to-capture-type.rs:7:17
    |
 LL | trait Foo {
    | --------- `Self` type parameter is implicitly captured by this `impl Trait`
@@ -29,5 +18,5 @@ LL |     fn bar() -> impl Sized + use<>;
    |
    = note: currently, all type parameters are required to be mentioned in the precise captures list
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

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

@@ -1,25 +1,24 @@
 //@ compile-flags: -Zunstable-options --edition=2024
-//@ revisions: normal rpitit
-//@[normal] check-pass
+//@ check-pass
+
+#![feature(precise_capturing_in_traits)]
 
 fn hello<'a>() -> impl Sized + use<'a> {}
-//[normal]~^ WARN all possible in-scope parameters are already captured
+//~^ WARN all possible in-scope parameters are already captured
 
 struct Inherent;
 impl Inherent {
     fn inherent(&self) -> impl Sized + use<'_> {}
-    //[normal]~^ WARN all possible in-scope parameters are already captured
+    //~^ WARN all possible in-scope parameters are already captured
 }
 
-#[cfg(rpitit)]
 trait Test<'a> {
     fn in_trait() -> impl Sized + use<'a, Self>;
-    //[rpitit]~^ ERROR `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
+    //~^ WARN all possible in-scope parameters are already captured
 }
-#[cfg(rpitit)]
 impl<'a> Test<'a> for () {
     fn in_trait() -> impl Sized + use<'a> {}
-    //[rpitit]~^ ERROR `use<...>` precise capturing syntax is currently not allowed in return-position `impl Trait` in traits
+    //~^ WARN all possible in-scope parameters are already captured
 }
 
 fn main() {}

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

@@ -0,0 +1,36 @@
+warning: all possible in-scope parameters are already captured, so `use<...>` syntax is redundant
+  --> $DIR/redundant.rs:6:19
+   |
+LL | fn hello<'a>() -> impl Sized + use<'a> {}
+   |                   ^^^^^^^^^^^^^-------
+   |                                |
+   |                                help: remove the `use<...>` syntax
+   |
+   = note: `#[warn(impl_trait_redundant_captures)]` on by default
+
+warning: all possible in-scope parameters are already captured, so `use<...>` syntax is redundant
+  --> $DIR/redundant.rs:11:27
+   |
+LL |     fn inherent(&self) -> impl Sized + use<'_> {}
+   |                           ^^^^^^^^^^^^^-------
+   |                                        |
+   |                                        help: remove the `use<...>` syntax
+
+warning: all possible in-scope parameters are already captured, so `use<...>` syntax is redundant
+  --> $DIR/redundant.rs:16:22
+   |
+LL |     fn in_trait() -> impl Sized + use<'a, Self>;
+   |                      ^^^^^^^^^^^^^-------------
+   |                                   |
+   |                                   help: remove the `use<...>` syntax
+
+warning: all possible in-scope parameters are already captured, so `use<...>` syntax is redundant
+  --> $DIR/redundant.rs:20:22
+   |
+LL |     fn in_trait() -> impl Sized + use<'a> {}
+   |                      ^^^^^^^^^^^^^-------
+   |                                   |
+   |                                   help: remove the `use<...>` syntax
+
+warning: 4 warnings emitted
+