feat: Add support for changes to "required" properties (#19)

src/diff_walker.rs

@@ -260,6 +260,36 @@ impl DiffWalker {
         Ok(())
     }
 
+    fn diff_required(
+        &mut self,
+        json_path: &str,
+        lhs: &mut SchemaObject,
+        rhs: &mut SchemaObject,
+    ) -> Result<(), Error> {
+        let lhs_required = &lhs.object().required;
+        let rhs_required = &rhs.object().required;
+
+        for removed in lhs_required.difference(rhs_required) {
+            self.changes.push(Change {
+                path: json_path.to_owned(),
+                change: ChangeKind::RequiredRemove {
+                    property: removed.clone(),
+                },
+            });
+        }
+
+        for added in rhs_required.difference(lhs_required) {
+            self.changes.push(Change {
+                path: json_path.to_owned(),
+                change: ChangeKind::RequiredAdd {
+                    property: added.clone(),
+                },
+            });
+        }
+
+        Ok(())
+    }
+
     fn resolve_ref<'a>(root_schema: &'a RootSchema, reference: &str) -> Option<&'a Schema> {
         if let Some(definition_name) = reference.strip_prefix("#/definitions/") {
             let schema_object = root_schema.definitions.get(definition_name)?;
@@ -302,6 +332,7 @@ impl DiffWalker {
         self.diff_range(json_path, lhs, rhs)?;
         self.diff_additional_properties(json_path, lhs, rhs)?;
         self.diff_array_items(json_path, lhs, rhs)?;
+        self.diff_required(json_path, lhs, rhs)?;
         Ok(())
     }
 }

src/lib.rs

@@ -877,4 +877,55 @@ mod tests {
             @"[]"
         );
     }
+
+    #[test]
+    fn drop_required() {
+        let lhs = json! {{
+            "required": ["value"]
+        }};
+        let rhs = json! {{
+            "required": [],
+        }};
+
+        let diff = diff(lhs, rhs).unwrap();
+
+        assert_debug_snapshot!(
+            diff,
+            @r###"
+        [
+            Change {
+                path: "",
+                change: RequiredRemove {
+                    property: "value",
+                },
+            },
+        ]
+        "###
+        );
+    }
+
+    #[test]
+    fn add_required() {
+        let lhs = json! {{
+            "required": []
+        }};
+        let rhs = json! {{
+            "required": ["value"],
+        }};
+
+        let diff = diff(lhs, rhs).unwrap();
+        assert_debug_snapshot!(
+            diff,
+            @r###"
+        [
+            Change {
+                path: "",
+                change: RequiredAdd {
+                    property: "value",
+                },
+            },
+        ]
+        "###
+        );
+    }
 }

src/types.rs

@@ -92,6 +92,16 @@ pub enum ChangeKind {
         /// The new length of the tuple
         new_length: usize,
     },
+    /// A previously required property has been removed
+    RequiredRemove {
+        /// The property that is no longer required
+        property: String,
+    },
+    /// A previously optional property has been made required
+    RequiredAdd {
+        /// The property that is now required
+        property: String,
+    },
 }
 
 impl ChangeKind {
@@ -128,6 +138,8 @@ impl ChangeKind {
             Self::TupleToArray { .. } => false,
             Self::ArrayToTuple { .. } => true,
             Self::TupleChange { .. } => true,
+            Self::RequiredRemove { .. } => false,
+            Self::RequiredAdd { .. } => true,
         }
     }
 }