support for additionalItems (#89)

support for additionalItems with pre draft2020-12 semantics

parser/src/json/schema.rs

@@ -15,7 +15,7 @@ const DEFAULT_DRAFT: Draft = Draft::Draft202012;
 const TYPES: [&str; 6] = ["null", "boolean", "number", "string", "array", "object"];
 
 // Keywords that are implemented in this module
-const IMPLEMENTED: [&str; 22] = [
+const IMPLEMENTED: [&str; 23] = [
     // Core
     "anyOf",
     "oneOf",
@@ -26,6 +26,7 @@ const IMPLEMENTED: [&str; 22] = [
     "type",
     // Array
     "items",
+    "additionalItems",
     "prefixItems",
     "minItems",
     "maxItems",
@@ -611,6 +612,7 @@ fn compile_type(ctx: &Context, tp: &str, schema: &HashMap<&str, &Value>) -> Resu
             get("maxItems"),
             get("prefixItems"),
             get("items"),
+            get("additionalItems"),
         ),
         "object" => compile_object(
             ctx,
@@ -726,7 +728,22 @@ fn compile_array(
     max_items: Option<&Value>,
     prefix_items: Option<&Value>,
     items: Option<&Value>,
+    additional_items: Option<&Value>,
 ) -> Result<Schema> {
+    let (prefix_items, items) = {
+        // Note that draft detection falls back to Draft202012 if the draft is unknown, so let's relax the draft constraint a bit
+        // and assume we're in an old draft if additionalItems is present or items is an array
+        if ctx.draft <= Draft::Draft201909 || additional_items.is_some() || matches!(items, Some(Value::Array(..))) {
+            match (items, additional_items) {
+                // Treat array items as prefixItems and additionalItems as items in draft 2019-09 and earlier
+                (Some(Value::Array(..)), _) => (items, additional_items),
+                // items is treated as items, and additionalItems is ignored if items is not an array (or is missing)
+                _ => (None, items),
+            }
+        } else {
+            (prefix_items, items)
+        }
+    };
     let min_items = match min_items {
         None => 0,
         Some(val) => val