From d17a4a7f9ac94ea0901cd6f200ea73833eac6c05 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 5 Feb 2025 18:03:26 +0000
Subject: Add opt_alias_variances and use it in outlives code

---
 compiler/rustc_middle/src/ty/context.rs |  8 ++++++++
 compiler/rustc_middle/src/ty/util.rs    | 23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+)

(limited to 'compiler/rustc_middle/src')

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index c6fc5f98f56..82b4fe193f0 100644
--- 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
index 318bd0c7ec0..632a16d6b4b 100644
--- 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> {
-- 
cgit 1.4.1-3-g733a5