Teach libsyntax about `while let`

2 files changed, 18 insertions, 1 deletions

diff --git a/src/libsyntax/parse/classify.rs b/src/libsyntax/parse/classify.rs
index cb57318445e..d46d078c776 100644
--- a/src/libsyntax/parse/classify.rs
+++ b/src/libsyntax/parse/classify.rs
@@ -28,6 +28,7 @@ pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
         | ast::ExprMatch(..)
         | ast::ExprBlock(_)
         | ast::ExprWhile(..)
+        | ast::ExprWhileLet(..)
         | ast::ExprLoop(..)
         | ast::ExprForLoop(..) => false,
         _ => true
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index e7f40cf0722..5f304fb0aeb 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -26,7 +26,7 @@ use ast::{ExprField, ExprTupField, ExprFnBlock, ExprIf, ExprIfLet, ExprIndex, Ex
 use ast::{ExprLit, ExprLoop, ExprMac};
 use ast::{ExprMethodCall, ExprParen, ExprPath, ExprProc};
 use ast::{ExprRepeat, ExprRet, ExprStruct, ExprTup, ExprUnary, ExprUnboxedFn};
-use ast::{ExprVec, ExprWhile, ExprForLoop, Field, FnDecl};
+use ast::{ExprVec, ExprWhile, ExprWhileLet, ExprForLoop, Field, FnDecl};
 use ast::{Once, Many};
 use ast::{FnUnboxedClosureKind, FnMutUnboxedClosureKind};
 use ast::{FnOnceUnboxedClosureKind};
@@ -2935,7 +2935,11 @@ impl<'a> Parser<'a> {
         self.mk_expr(lo, hi, ExprForLoop(pat, expr, loop_block, opt_ident))
     }
 
+    /// Parse a 'while' or 'while let' expression ('while' token already eaten)
     pub fn parse_while_expr(&mut self, opt_ident: Option<ast::Ident>) -> P<Expr> {
+        if self.is_keyword(keywords::Let) {
+            return self.parse_while_let_expr(opt_ident);
+        }
         let lo = self.last_span.lo;
         let cond = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL);
         let body = self.parse_block();
@@ -2943,6 +2947,18 @@ impl<'a> Parser<'a> {
         return self.mk_expr(lo, hi, ExprWhile(cond, body, opt_ident));
     }
 
+    /// Parse a 'while let' expression ('while' token already eaten)
+    pub fn parse_while_let_expr(&mut self, opt_ident: Option<ast::Ident>) -> P<Expr> {
+        let lo = self.last_span.lo;
+        self.expect_keyword(keywords::Let);
+        let pat = self.parse_pat();
+        self.expect(&token::EQ);
+        let expr = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL);
+        let body = self.parse_block();
+        let hi = body.span.hi;
+        return self.mk_expr(lo, hi, ExprWhileLet(pat, expr, body, opt_ident));
+    }
+
     pub fn parse_loop_expr(&mut self, opt_ident: Option<ast::Ident>) -> P<Expr> {
         let lo = self.last_span.lo;
         let body = self.parse_block();