feat: inner option support

garde/src/error.rs

@@ -92,10 +92,21 @@ pub struct Path {
 #[doc(hidden)]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum Kind {
+    None,
     Key,
     Index,
 }
 
+#[doc(hidden)]
+#[derive(Default)]
+pub struct NoKey(());
+
+impl std::fmt::Display for NoKey {
+    fn fmt(&self, _: &mut std::fmt::Formatter) -> std::fmt::Result {
+        Ok(())
+    }
+}
+
 pub trait PathComponentKind: std::fmt::Display + ToCompactString + private::Sealed {
     fn component_kind() -> Kind;
 }
@@ -116,6 +127,7 @@ impl_path_component_kind!(@'a; &'a str => Key);
 impl_path_component_kind!(@'a; Cow<'a, str> => Key);
 impl_path_component_kind!(String => Key);
 impl_path_component_kind!(CompactString => Key);
+impl_path_component_kind!(NoKey => None);
 
 impl<'a, T: PathComponentKind> private::Sealed for &'a T {}
 impl<'a, T: PathComponentKind> PathComponentKind for &'a T {
@@ -204,6 +216,7 @@ impl std::fmt::Display for Path {
             }
             if let Some((kind, _)) = components.peek() {
                 match kind {
+                    Kind::None => {}
                     Kind::Key => f.write_str(".")?,
                     Kind::Index => f.write_str("[")?,
                 }

garde/src/rules/inner.rs

@@ -10,6 +10,8 @@
 //!
 //! The entrypoint is the [`Inner`] trait. Implementing this trait for a type allows that type to be used with the `#[garde(inner(..))]` rule.
 
+use crate::error::{NoKey, PathComponentKind};
+
 pub fn apply<T, U, K, F>(field: &T, f: F)
 where
     T: Inner<U, Key = K>,
@@ -19,7 +21,7 @@ where
 }
 
 pub trait Inner<T> {
-    type Key;
+    type Key: PathComponentKind;
 
     fn validate_inner<F>(&self, f: F)
     where
@@ -60,3 +62,16 @@ impl<'a, T> Inner<T> for &'a [T] {
         }
     }
 }
+
+impl<T> Inner<T> for Option<T> {
+    type Key = NoKey;
+
+    fn validate_inner<F>(&self, mut f: F)
+    where
+        F: FnMut(&T, &Self::Key),
+    {
+        if let Some(item) = self {
+            f(item, &NoKey::default())
+        }
+    }
+}