From b003f104490599c49d27842c9a25b158e7cccdcb Mon Sep 17 00:00:00 2001
From: John Gallagher <jgallagher@bignerdranch.com>
Date: Thu, 2 Oct 2014 23:28:15 -0400
Subject: [PATCH] Desugar `while let` into `loop { match { ... } }`

---
 src/libsyntax/ast.rs       | 3 ++-
 src/libsyntax/ext/build.rs | 8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 675249b2591..4ed3ee01598 100644
--- a/src/libsyntax/ast.rs
+++ b/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)]
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 87983e1aea3..98ac6fe6a6c 100644
--- a/src/libsyntax/ext/build.rs
+++ b/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))
     }