Allow idents to start with _

rinja_parser/src/lib.rs

@@ -633,7 +633,12 @@ fn path_or_identifier(i: &str) -> ParseResult<'_, PathOrIdentifier<'_>> {
             path.extend(rest);
             Ok((i, PathOrIdentifier::Path(path)))
         }
-        (None, name, []) if name.chars().next().map_or(true, char::is_lowercase) => {
+        (None, name, [])
+            if name
+                .chars()
+                .next()
+                .map_or(true, |c| c == '_' || c.is_lowercase()) =>
+        {
             Ok((i, PathOrIdentifier::Identifier(name)))
         }
         (None, start, tail) => {

testing/tests/let.rs

@@ -21,3 +21,13 @@ fn let_macro() {
     let template = A { y: false };
     assert_eq!(template.render().unwrap(), "blob")
 }
+
+// Ensures that variables name can start with `_`.
+#[test]
+fn underscore() {
+    #[derive(Template)]
+    #[template(source = r#"{% let _x = 7 %}{{ _x }}"#, ext = "html")]
+    struct X;
+
+    assert_eq!(X.render().unwrap(), "7")
+}