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: rust-lang/rfcs#3680
Tracking issue: rust-lang/rust#132290
Project goal: rust-lang/rust-project-goals#107

r? ```@nikomatsakis```

Author: matthiaskrgr

src/expr.rs

@@ -137,6 +137,10 @@ pub(crate) fn format_expr(
         ast::ExprKind::Tup(ref items) => {
             rewrite_tuple(context, items.iter(), expr.span, shape, items.len() == 1)
         }
+        ast::ExprKind::Use(_, _) => {
+            // FIXME: properly implement this
+            Ok(context.snippet(expr.span()).to_owned())
+        }
         ast::ExprKind::Let(ref pat, ref expr, _span, _) => rewrite_let(context, shape, pat, expr),
         ast::ExprKind::If(..)
         | ast::ExprKind::ForLoop { .. }

src/utils.rs

@@ -513,6 +513,7 @@ pub(crate) fn is_block_expr(context: &RewriteContext<'_>, expr: &ast::Expr, repr
         | ast::ExprKind::Become(..)
         | ast::ExprKind::Yeet(..)
         | ast::ExprKind::Tup(..)
+        | ast::ExprKind::Use(..)
         | ast::ExprKind::Type(..)
         | ast::ExprKind::Yield(None)
         | ast::ExprKind::Underscore => false,