Allow separation of variable declaration and defintion

2 files changed, 27 insertions, 4 deletions

diff --git a/askama_derive/src/generator.rs b/askama_derive/src/generator.rs
index faf4e48..43c2a49 100644
--- a/askama_derive/src/generator.rs
+++ b/askama_derive/src/generator.rs
@@ -312,7 +312,7 @@ impl<'a> Generator<'a> {
         self.writeln("))?;");
     }
 
-    fn write_let(&mut self, ws: &WS, var: &'a Target, val: &Expr) {
+    fn write_let_decl(&mut self, ws: &WS, var: &'a Target) {
         self.handle_ws(ws);
         self.write("let ");
         match *var {
@@ -321,6 +321,20 @@ impl<'a> Generator<'a> {
                 self.write(name);
             },
         }
+        self.writeln(";");
+    }
+
+    fn write_let(&mut self, ws: &WS, var: &'a Target, val: &Expr) {
+        self.handle_ws(ws);
+        match *var {
+            Target::Name(name) => {
+                if !self.locals.contains(name) {
+                    self.write("let ");
+                    self.locals.insert(name);
+                }
+                self.write(name);
+            },
+        }
         self.write(" = ");
         self.visit_expr(val);
         self.writeln(";");
@@ -417,6 +431,7 @@ impl<'a> Generator<'a> {
                 Node::Lit(lws, val, rws) => { self.write_lit(lws, val, rws); }
                 Node::Comment() => {},
                 Node::Expr(ref ws, ref val) => { self.write_expr(ws, val); },
+                Node::LetDecl(ref ws, ref var) => { self.write_let_decl(ws, var); },
                 Node::Let(ref ws, ref var, ref val) => { self.write_let(ws, var, val); },
                 Node::Cond(ref conds, ref ws) => {
                     self.write_cond(conds, ws);
diff --git a/askama_derive/src/parser.rs b/askama_derive/src/parser.rs
index 2a6a602..c6c437c 100644
--- a/askama_derive/src/parser.rs
+++ b/askama_derive/src/parser.rs
@@ -26,6 +26,7 @@ pub enum Node<'a> {
     Lit(&'a str, &'a str, &'a str),
     Comment(),
     Expr(WS, Expr<'a>),
+    LetDecl(WS, Target<'a>),
     Let(WS, Target<'a>, Expr<'a>),
     Cond(Vec<(WS, Option<Expr<'a>>, Vec<Node<'a>>)>, WS),
     Loop(WS, Target<'a>, Expr<'a>, Vec<Node<'a>>, WS),
@@ -282,10 +283,17 @@ named!(block_let<Node>, do_parse!(
     pws: opt!(tag_s!("-")) >>
     ws!(tag_s!("let")) >>
     var: ws!(target_single) >>
-    ws!(tag_s!("=")) >>
-    val: ws!(expr_any) >>
+    val: opt!(do_parse!(
+        ws!(tag_s!("=")) >>
+        val: ws!(expr_any) >>
+        (val)
+    )) >>
     nws: opt!(tag_s!("-")) >>
-    (Node::Let(WS(pws.is_some(), nws.is_some()), var, val))
+    (if val.is_some() {
+        Node::Let(WS(pws.is_some(), nws.is_some()), var, val.unwrap())
+    } else {
+        Node::LetDecl(WS(pws.is_some(), nws.is_some()), var)
+    })
 ));
 
 named!(block_for<Node>, do_parse!(