Add opt_alias_variances and use it in outlives code

compiler-errors · compiler-errors · commit 7062c4e00c4f · 2025-02-04T19:40:49.000Z
diff --git a/compiler/rustc_borrowck/src/type_check/opaque_types.rs b/compiler/rustc_borrowck/src/type_check/opaque_types.rs
@@ -284,7 +284,7 @@ where
             return;
         }
 
-        match ty.kind() {
+        match *ty.kind() {
             ty::Closure(_, args) => {
                 // Skip lifetime parameters of the enclosing item(s)
 
@@ -316,10 +316,9 @@ where
                 args.as_coroutine().resume_ty().visit_with(self);
             }
 
-            ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
-                // Skip lifetime parameters that are not captures.
-                let variances = self.tcx.variances_of(*def_id);
-
+            ty::Alias(kind, ty::AliasTy { def_id, args, .. })
+                if let Some(variances) = self.tcx.opt_alias_variances(kind, def_id) =>
+            {
                 for (v, s) in std::iter::zip(variances, args.iter()) {
                     if *v != ty::Bivariant {
                         s.visit_with(self);
diff --git a/compiler/rustc_infer/src/infer/outlives/for_liveness.rs b/compiler/rustc_infer/src/infer/outlives/for_liveness.rs
@@ -48,7 +48,7 @@ where
             return ty.super_visit_with(self);
         }
 
-        match ty.kind() {
+        match *ty.kind() {
             // We can prove that an alias is live two ways:
             // 1. All the components are live.
             //
@@ -96,10 +96,7 @@ where
                     r.visit_with(self);
                 } else {
                     // Skip lifetime parameters that are not captures.
-                    let variances = match kind {
-                        ty::Opaque => Some(self.tcx.variances_of(*def_id)),
-                        _ => None,
-                    };
+                    let variances = tcx.opt_alias_variances(kind, def_id);
 
                     for (idx, s) in args.iter().enumerate() {
                         if variances.map(|variances| variances[idx]) != Some(ty::Bivariant) {
diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -392,13 +392,16 @@ where
         // the problem is to add `T: 'r`, which isn't true. So, if there are no
         // inference variables, we use a verify constraint instead of adding
         // edges, which winds up enforcing the same condition.
-        let is_opaque = alias_ty.kind(self.tcx) == ty::Opaque;
+        //
+        // Note that this is not here for correctness; it solely affects
+        // diagnostics.
+        let kind = alias_ty.kind(self.tcx);
         if approx_env_bounds.is_empty()
             && trait_bounds.is_empty()
-            && (alias_ty.has_infer_regions() || is_opaque)
+            && (alias_ty.has_infer_regions() || kind == ty::Opaque)
         {
             debug!("no declared bounds");
-            let opt_variances = is_opaque.then(|| self.tcx.variances_of(alias_ty.def_id));
+            let opt_variances = self.tcx.opt_alias_variances(kind, alias_ty.def_id);
             self.args_must_outlive(alias_ty.args, origin, region, opt_variances);
             return;
         }
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
@@ -194,6 +194,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self.variances_of(def_id)
     }
 
+    fn opt_alias_variances(
+        self,
+        kind: impl Into<ty::AliasTermKind>,
+        def_id: DefId,
+    ) -> Option<&'tcx [ty::Variance]> {
+        self.opt_alias_variances(kind, def_id)
+    }
+
     fn type_of(self, def_id: DefId) -> ty::EarlyBinder<'tcx, Ty<'tcx>> {
         self.type_of(def_id)
     }
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
@@ -951,6 +951,29 @@ impl<'tcx> TyCtxt<'tcx> {
 
         ty
     }
+
+    // Computes the variances for an alias (opaque or RPITIT) that represent
+    // its (un)captured regions.
+    pub fn opt_alias_variances(
+        self,
+        kind: impl Into<ty::AliasTermKind>,
+        def_id: DefId,
+    ) -> Option<&'tcx [ty::Variance]> {
+        match kind.into() {
+            ty::AliasTermKind::ProjectionTy => {
+                if self.is_impl_trait_in_trait(def_id) {
+                    Some(self.variances_of(def_id))
+                } else {
+                    None
+                }
+            }
+            ty::AliasTermKind::OpaqueTy => Some(self.variances_of(def_id)),
+            ty::AliasTermKind::InherentTy
+            | ty::AliasTermKind::WeakTy
+            | ty::AliasTermKind::UnevaluatedConst
+            | ty::AliasTermKind::ProjectionConst => None,
+        }
+    }
 }
 
 struct OpaqueTypeExpander<'tcx> {
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
@@ -141,6 +141,12 @@ pub trait Interner:
     type VariancesOf: Copy + Debug + SliceLike<Item = ty::Variance>;
     fn variances_of(self, def_id: Self::DefId) -> Self::VariancesOf;
 
+    fn opt_alias_variances(
+        self,
+        kind: impl Into<ty::AliasTermKind>,
+        def_id: Self::DefId,
+    ) -> Option<Self::VariancesOf>;
+
     fn type_of(self, def_id: Self::DefId) -> ty::EarlyBinder<Self, Self::Ty>;
 
     type AdtDef: AdtDef<Self>;
diff --git a/compiler/rustc_type_ir/src/outlives.rs b/compiler/rustc_type_ir/src/outlives.rs
@@ -230,8 +230,7 @@ pub fn compute_alias_components_recursive<I: Interner>(
         unreachable!("can only call `compute_alias_components_recursive` on an alias type")
     };
 
-    let opt_variances =
-        if kind == ty::Opaque { Some(cx.variances_of(alias_ty.def_id)) } else { None };
+    let opt_variances = cx.opt_alias_variances(kind, alias_ty.def_id);
 
     let mut visitor = OutlivesCollector { cx, out, visited: Default::default() };
 
diff --git a/compiler/rustc_type_ir/src/predicate.rs b/compiler/rustc_type_ir/src/predicate.rs
@@ -469,6 +469,17 @@ impl AliasTermKind {
     }
 }
 
+impl From<ty::AliasTyKind> for AliasTermKind {
+    fn from(value: ty::AliasTyKind) -> Self {
+        match value {
+            ty::Projection => AliasTermKind::ProjectionTy,
+            ty::Opaque => AliasTermKind::OpaqueTy,
+            ty::Weak => AliasTermKind::WeakTy,
+            ty::Inherent => AliasTermKind::InherentTy,
+        }
+    }
+}
+
 /// Represents the unprojected term of a projection goal.
 ///
 /// * For a projection, this would be `<Ty as Trait<...>>::N<...>`.
diff --git a/compiler/rustc_type_ir/src/relate.rs b/compiler/rustc_type_ir/src/relate.rs
@@ -236,28 +236,14 @@ impl<I: Interner> Relate<I> for ty::AliasTy<I> {
                 ExpectedFound::new(a, b)
             }))
         } else {
-            let args = match a.kind(relation.cx()) {
-                ty::Opaque => relate_args_with_variances(
-                    relation,
-                    a.def_id,
-                    relation.cx().variances_of(a.def_id),
-                    a.args,
-                    b.args,
+            let cx = relation.cx();
+            let args = if let Some(variances) = cx.opt_alias_variances(a.kind(cx), a.def_id) {
+                relate_args_with_variances(
+                    relation, a.def_id, variances, a.args, 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)?
-                }
+                )?
+            } else {
+                relate_args_invariantly(relation, a.args, b.args)?
             };
             Ok(ty::AliasTy::new_from_args(relation.cx(), a.def_id, args))
         }
diff --git a/tests/ui/impl-trait/precise-capturing/rpitit-outlives-2.rs b/tests/ui/impl-trait/precise-capturing/rpitit-outlives-2.rs
@@ -0,0 +1,17 @@
+//@ check-pass
+
+#![feature(precise_capturing_in_traits)]
+
+struct Invariant<T>(*mut T);
+
+trait Foo {
+    fn hello<'s: 's>(&'s self) -> Invariant<impl Sized + use<Self>>;
+}
+
+fn outlives_static(_: impl Sized + 'static) {}
+
+fn hello<'s, T: Foo + 'static>(x: &'s T) {
+    outlives_static(x.hello());
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/precise-capturing/rpitit-outlives.rs b/tests/ui/impl-trait/precise-capturing/rpitit-outlives.rs
@@ -0,0 +1,15 @@
+//@ check-pass
+
+#![feature(precise_capturing_in_traits)]
+
+struct Invariant<T>(*mut T);
+
+trait Foo {
+    fn hello<'s: 's>(&'s self) -> Invariant<impl Sized + use<Self>>;
+}
+
+fn hello<'s, T: Foo + 'static>(x: &'s T) -> Invariant<impl Sized + 'static> {
+    x.hello()
+}
+
+fn main() {}

Original file line number	Diff line number	Diff line change
`@@ -194,6 +194,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {`
`194`	`194`	`self.variances_of(def_id)`
`195`	`195`	`}`
`196`	`196`
	`197`	`+ fn opt_alias_variances(`
	`198`	`+ self,`
	`199`	`+ kind: impl Into<ty::AliasTermKind>,`
	`200`	`+ def_id: DefId,`
	`201`	`+ ) -> Option<&'tcx [ty::Variance]> {`
	`202`	`+ self.opt_alias_variances(kind, def_id)`
	`203`	`+ }`
	`204`	`+`
`197`	`205`	`fn type_of(self, def_id: DefId) -> ty::EarlyBinder<'tcx, Ty<'tcx>> {`
`198`	`206`	`self.type_of(def_id)`
`199`	`207`	`}`