get_ambient_variance to inherent method

compiler/rustc_middle/src/mir/visit.rs

@@ -1369,12 +1369,12 @@ pub enum PlaceContext {
 impl PlaceContext {
     /// Returns `true` if this place context represents a drop.
     #[inline]
-    pub fn is_drop(&self) -> bool {
+    pub fn is_drop(self) -> bool {
         matches!(self, PlaceContext::MutatingUse(MutatingUseContext::Drop))
     }
 
     /// Returns `true` if this place context represents a borrow.
-    pub fn is_borrow(&self) -> bool {
+    pub fn is_borrow(self) -> bool {
         matches!(
             self,
             PlaceContext::NonMutatingUse(
@@ -1384,7 +1384,7 @@ impl PlaceContext {
     }
 
     /// Returns `true` if this place context represents an address-of.
-    pub fn is_address_of(&self) -> bool {
+    pub fn is_address_of(self) -> bool {
         matches!(
             self,
             PlaceContext::NonMutatingUse(NonMutatingUseContext::RawBorrow)
@@ -1394,7 +1394,7 @@ impl PlaceContext {
 
     /// Returns `true` if this place context represents a storage live or storage dead marker.
     #[inline]
-    pub fn is_storage_marker(&self) -> bool {
+    pub fn is_storage_marker(self) -> bool {
         matches!(
             self,
             PlaceContext::NonUse(NonUseContext::StorageLive | NonUseContext::StorageDead)
@@ -1403,18 +1403,18 @@ impl PlaceContext {
 
     /// Returns `true` if this place context represents a use that potentially changes the value.
     #[inline]
-    pub fn is_mutating_use(&self) -> bool {
+    pub fn is_mutating_use(self) -> bool {
         matches!(self, PlaceContext::MutatingUse(..))
     }
 
     /// Returns `true` if this place context represents a use.
     #[inline]
-    pub fn is_use(&self) -> bool {
+    pub fn is_use(self) -> bool {
         !matches!(self, PlaceContext::NonUse(..))
     }
 
     /// Returns `true` if this place context represents an assignment statement.
-    pub fn is_place_assignment(&self) -> bool {
+    pub fn is_place_assignment(self) -> bool {
         matches!(
             self,
             PlaceContext::MutatingUse(
@@ -1424,4 +1424,19 @@ impl PlaceContext {
             )
         )
     }
+
+    /// The variance of a place in the given context.
+    pub fn ambient_variance(self) -> ty::Variance {
+        use NonMutatingUseContext::*;
+        use NonUseContext::*;
+        match self {
+            PlaceContext::MutatingUse(_) => ty::Invariant,
+            PlaceContext::NonUse(StorageDead | StorageLive | VarDebugInfo) => ty::Invariant,
+            PlaceContext::NonMutatingUse(
+                Inspect | Copy | Move | PlaceMention | SharedBorrow | FakeBorrow | RawBorrow
+                | Projection,
+            ) => ty::Covariant,
+            PlaceContext::NonUse(AscribeUserTy(variance)) => variance,
+        }
+    }
 }