Auto merge of #51052 - nikomatsakis:obsolete-arrow, r=petrochenkov

restore emplacement syntax (obsolete)

Fix https://github.com/rust-lang/rust/issues/50832

r? @petrochenkov

src/libsyntax/ast.rs

@@ -1010,6 +1010,7 @@ impl Expr {
     pub fn precedence(&self) -> ExprPrecedence {
         match self.node {
             ExprKind::Box(_) => ExprPrecedence::Box,
+            ExprKind::ObsoleteInPlace(..) => ExprPrecedence::ObsoleteInPlace,
             ExprKind::Array(_) => ExprPrecedence::Array,
             ExprKind::Call(..) => ExprPrecedence::Call,
             ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
@@ -1068,6 +1069,8 @@ pub enum RangeLimits {
 pub enum ExprKind {
     /// A `box x` expression.
     Box(P<Expr>),
+    /// First expr is the place; second expr is the value.
+    ObsoleteInPlace(P<Expr>, P<Expr>),
     /// An array (`[a, b, c, d]`)
     Array(Vec<P<Expr>>),
     /// A function call