Allow variables to be inherited in blocks

rinja_derive/src/generator.rs

@@ -1157,11 +1157,19 @@ impl<'a> Generator<'a> {
             self.input,
             self.contexts,
             Some(heritage),
+            // 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>`. Except... compiler is triggered because then
-            // the `'b` lifetime is marked as unused.
-            MapChain::with_parent(unsafe { mem::transmute(&self.locals) }),
+            // 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,
         );

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");
+}