Rollup merge of #134797 - spastorino:ergonomic-ref-counting-1, r=nikomatsakis

Ergonomic ref counting

This is an experimental first version of ergonomic ref counting.

This first version implements most of the RFC but doesn't implement any of the optimizations. This was left for following iterations.

RFC: https://github.com/rust-lang/rfcs/pull/3680
Tracking issue: https://github.com/rust-lang/rust/issues/132290
Project goal: https://github.com/rust-lang/rust-project-goals/issues/107

r? ```@nikomatsakis```

compiler/rustc_lint/src/context.rs

@@ -683,6 +683,10 @@ impl<'tcx> LateContext<'tcx> {
         self.tcx.type_is_copy_modulo_regions(self.typing_env(), ty)
     }
 
+    pub fn type_is_use_cloned_modulo_regions(&self, ty: Ty<'tcx>) -> bool {
+        self.tcx.type_is_use_cloned_modulo_regions(self.typing_env(), ty)
+    }
+
     /// Gets the type-checking results for the current body,
     /// or `None` if outside a body.
     pub fn maybe_typeck_results(&self) -> Option<&'tcx ty::TypeckResults<'tcx>> {

compiler/rustc_lint/src/dangling.rs

@@ -159,7 +159,10 @@ fn is_temporary_rvalue(expr: &Expr<'_>) -> bool {
         ExprKind::Path(..) => false,
 
         // Calls return rvalues.
-        ExprKind::Call(..) | ExprKind::MethodCall(..) | ExprKind::Binary(..) => true,
+        ExprKind::Call(..)
+        | ExprKind::MethodCall(..)
+        | ExprKind::Use(..)
+        | ExprKind::Binary(..) => true,
 
         // Inner blocks are rvalues.
         ExprKind::If(..) | ExprKind::Loop(..) | ExprKind::Match(..) | ExprKind::Block(..) => true,