parser: ensure correct drop order for `Parsed`

According to [RFC 1857] the fields of a struct are dropped in the same
order as they are declared. For `struct S { a: A, b: B }` field `a` is
dropped before field `b`.

Our struct `Parsed` is self referencial. Its field `ast` depends on
`source`, so `source` must outlife `ast`. This PR changes the order of
the fields to reflect this requirement. In practice it should not
matter, because we know that the variant of `Node` won't access the
string data during their `Drop`, but better safe than sorry - maybe
`Node` changes in the future.

[RFC 1857]: https://rust-lang.github.io/rfcs/1857-stabilize-drop-order.html

1 files changed, 3 insertions, 2 deletions

diff --git a/askama_parser/src/lib.rs b/askama_parser/src/lib.rs
index cf105cb..bc29a22 100644
--- a/askama_parser/src/lib.rs
+++ b/askama_parser/src/lib.rs
@@ -28,9 +28,10 @@ mod _parsed {
     use super::{Ast, Node, ParseError, Syntax};
 
     pub struct Parsed {
+        // `source` must outlive `ast`, so `ast` must be declared before `source`
+        ast: Ast<'static>,
         #[allow(dead_code)]
         source: String,
-        ast: Ast<'static>,
     }
 
     impl Parsed {
@@ -44,7 +45,7 @@ mod _parsed {
                 Err(e) => return Err(e),
             };
 
-            Ok(Self { source, ast })
+            Ok(Self { ast, source })
         }
 
         // The return value's lifetime must be limited to `self` to uphold the unsafe invariant.