Rollup merge of #112790 - WaffleLapkin:syntactically, r=Nilstrieb

Syntactically accept `become` expressions (explicit tail calls experiment)

This adds `ast::ExprKind::Become`, implements parsing and properly gates the feature.

cc `@scottmcm`

2 files changed, 2 insertions, 0 deletions

diff --git a/src/tools/rustfmt/src/expr.rs b/src/tools/rustfmt/src/expr.rs
index e179b4646ef..5600f7778f2 100644
--- a/src/tools/rustfmt/src/expr.rs
+++ b/src/tools/rustfmt/src/expr.rs
@@ -232,6 +232,7 @@ pub(crate) fn format_expr(
         ast::ExprKind::Ret(Some(ref expr)) => {
             rewrite_unary_prefix(context, "return ", &**expr, shape)
         }
+        ast::ExprKind::Become(ref expr) => rewrite_unary_prefix(context, "become ", &**expr, shape),
         ast::ExprKind::Yeet(None) => Some("do yeet".to_owned()),
         ast::ExprKind::Yeet(Some(ref expr)) => {
             rewrite_unary_prefix(context, "do yeet ", &**expr, shape)
diff --git a/src/tools/rustfmt/src/utils.rs b/src/tools/rustfmt/src/utils.rs
index ca171657407..890a05b8c82 100644
--- a/src/tools/rustfmt/src/utils.rs
+++ b/src/tools/rustfmt/src/utils.rs
@@ -505,6 +505,7 @@ pub(crate) fn is_block_expr(context: &RewriteContext<'_>, expr: &ast::Expr, repr
         | ast::ExprKind::Range(..)
         | ast::ExprKind::Repeat(..)
         | ast::ExprKind::Ret(..)
+        | ast::ExprKind::Become(..)
         | ast::ExprKind::Yeet(..)
         | ast::ExprKind::Tup(..)
         | ast::ExprKind::Type(..)