Allow variables inheritance in block

rinja_derive/src/generator.rs

@@ -1152,16 +1152,28 @@
                 .or_insert_with(|| import.clone());
         }
 
+        let buf_writable = mem::take(&mut self.buf_writable);
         let mut child = Self::new(
             self.input,
             self.contexts,
             Some(heritage),
-            // Variables are NOT inherited from the parent scope.
-            MapChain::default(),
+            // FIXME: Fix the broken lifetimes.
+            //
+            // `transmute` is here to fix the lifetime nightmare around `&self.locals` not
+            // living long enough. The correct solution would be to make `MapChain` take two
+            // lifetimes `&'a MapChain<'a, 'b, K, V>`, making the `parent` field take
+            // `<'b, 'b, ...>`. Except... it doesn't work because `self` still doesn't live long
+            // enough here for some reason...
+            MapChain::with_parent(unsafe {
+                mem::transmute::<
+                    &MapChain<'_, Cow<'_, str>, LocalMeta>,
+                    &MapChain<'_, Cow<'_, str>, LocalMeta>,
+                >(&self.locals)
+            }),
             self.buf_writable.discard,
             self.is_in_filter_block,
         );
-        child.buf_writable = mem::take(&mut self.buf_writable);
+        child.buf_writable = buf_writable;
 
         // Handle inner whitespace suppression spec and process block nodes
         child.prepare_ws(def.ws1);

testing/templates/base-decl.txt

@@ -0,0 +1,2 @@
+{%- let variable = 42 -%}
+{%- block extended %}{% endblock -%}

testing/templates/use-var.txt

@@ -0,0 +1 @@
+{{ variable }}

testing/tests/block_fragments.rs

@@ -145,3 +145,21 @@ fn test_fragment_include() {
     let fragment_include = FragmentInclude { s: "world" };
     assert_eq!(fragment_include.render().unwrap(), "\nINCLUDED: world\n");
 }
+
+// This test ensures that parent variables are inherited in the block.
+// This is a regression test for <https://github.com/rinja-rs/rinja/issues/246>.
+#[test]
+fn test_variable_inheritance_in_block() {
+    #[derive(Template)]
+    #[template(
+        source = r#"{% extends "base-decl.txt" %}
+{%- block extended -%}
+--> {{ variable }}
+{% include "use-var.txt" -%}
+{% endblock %}"#,
+        ext = "txt"
+    )]
+    struct Y;
+
+    assert_eq!(Y.render().unwrap(), "--> 42\n42");
+}