Avoid a useless clone of UserTypeProjection

Author: Zalathar

Diff for: compiler/rustc_middle/src/mir/mod.rs

@@ -1516,8 +1516,8 @@ impl<'tcx> UserTypeProjections {
         self.contents.iter().map(|&(ref user_type, _span)| user_type)
     }
 
-    pub fn push_projection(mut self, user_ty: &UserTypeProjection, span: Span) -> Self {
-        self.contents.push((user_ty.clone(), span));
+    pub fn push_user_type(mut self, base_user_ty: UserTypeAnnotationIndex, span: Span) -> Self {
+        self.contents.push((UserTypeProjection { base: base_user_ty, projs: vec![] }, span));
         self
     }
 

Diff for: compiler/rustc_mir_build/src/builder/matches/mod.rs

@@ -926,12 +926,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // Note that the variance doesn't apply here, as we are tracking the effect
                 // of `user_ty` on any bindings contained with subpattern.
 
-                let projection = UserTypeProjection {
-                    base: self.canonical_user_type_annotations.push(annotation.clone()),
-                    projs: Vec::new(),
-                };
+                let base_user_ty = self.canonical_user_type_annotations.push(annotation.clone());
                 let subpattern_user_ty =
-                    pattern_user_ty.push_projection(&projection, annotation.span);
+                    pattern_user_ty.push_user_type(base_user_ty, annotation.span);
                 self.visit_primary_bindings(subpattern, subpattern_user_ty, f)
             }