Add helper for Default

Co-authored-by: dpetrick <[email protected]>

src/ast/ast_conversion.rs

@@ -62,6 +62,15 @@ pub trait DefaultIn<'a> {
     fn default_in(arena: &'a bumpalo::Bump) -> Self;
 }
 
+impl<'a, T> DefaultIn<'a> for T
+where
+    T: Default,
+{
+    fn default_in(_ctx: &'a bumpalo::Bump) -> Self {
+        Self::default()
+    }
+}
+
 impl<'a> DefaultIn<'a> for Document<'a> {
     fn default_in(arena: &'a bumpalo::Bump) -> Self {
         Document {

src/validate/mod.rs

@@ -24,7 +24,7 @@
 //! As such, the [`DefaultRules`](rules::DefaultRules) rule is a [`ValidationRule`] itself that's
 //! composed using the [`ComposedVisitor`](crate::visit::ComposedVisitor) utility.
 //!
-//! All rules must implement the [`DefaultIn`](crate::ast::DefaultIn) trait, which makes it easier to quickly run a validation
+//! All rules must implement the [`DefaultIn`](crate::ast::DefaultIn) or `Default` trait, which makes it easier to quickly run a validation
 //! rule and isolates them from external state, since no validation requires any external state.
 //!
 //! For example, this is one way to run a validation rule, in this case `DefaultRules`:

src/validate/rules/lone_anonymous_operation.rs

@@ -6,20 +6,12 @@ use crate::{ast::*, visit::*};
 ///
 /// See [`ValidationRule`]
 /// [Reference](https://spec.graphql.org/October2021/#sec-Lone-Anonymous-Operation)
+#[derive(Default)]
 pub struct LoneAnonymousOperation {
     operations: usize,
     has_anonymous: bool,
 }
 
-impl<'a> DefaultIn<'a> for LoneAnonymousOperation {
-    fn default_in(_arena: &'a bumpalo::Bump) -> Self {
-        Self {
-            operations: 0,
-            has_anonymous: false
-        }
-    }
-}
-
 impl<'a> ValidationRule<'a> for LoneAnonymousOperation {}
 
 impl<'a> Visitor<'a, ValidationContext<'a>> for LoneAnonymousOperation {