Desugar while let into loop { match { ... } }

src/libsyntax/ast.rs

@@ -581,7 +581,8 @@ pub struct QPath {
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
 pub enum MatchSource {
     MatchNormal,
-    MatchIfLetDesugar
+    MatchIfLetDesugar,
+    MatchWhileLetDesugar,
 }
 
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]

src/libsyntax/ext/build.rs

@@ -147,6 +147,8 @@ pub trait AstBuilder {
     fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr>;
     fn expr_none(&self, sp: Span) -> P<ast::Expr>;
 
+    fn expr_break(&self, sp: Span) -> P<ast::Expr>;
+
     fn expr_tuple(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr>;
 
     fn expr_fail(&self, span: Span, msg: InternedString) -> P<ast::Expr>;
@@ -688,6 +690,12 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         self.expr_path(none)
     }
 
+
+    fn expr_break(&self, sp: Span) -> P<ast::Expr> {
+        self.expr(sp, ast::ExprBreak(None))
+    }
+
+
     fn expr_tuple(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprTup(exprs))
     }