From 30a9a384e2997d12c2fa04bc5721661b3fd01ddf Mon Sep 17 00:00:00 2001
From: Graham Esau <gesau@hotmail.co.uk>
Date: Mon, 19 Aug 2024 12:08:47 +0100
Subject: [PATCH] Improve `flatten` behavioure with `additionalProperties`

---
 schemars/src/_private.rs                      | 23 ++++++--
 ..._flattened_struct_deny_unknown_fields.json | 52 +++++++++++++++++
 schemars/tests/flatten.rs                     | 57 +++++++++++++++++++
 3 files changed, 127 insertions(+), 5 deletions(-)
 create mode 100644 schemars/tests/expected/test_flattened_struct_deny_unknown_fields.json

diff --git a/schemars/src/_private.rs b/schemars/src/_private.rs
index 43a46db..a40cc2b 100644
--- a/schemars/src/_private.rs
+++ b/schemars/src/_private.rs
@@ -185,17 +185,23 @@ pub fn flatten(schema: &mut Schema, other: Schema) {
         Err(true) => {
             schema
                 .ensure_object()
-                .entry("additionalProperties")
-                .or_insert(true.into());
+                .insert("additionalProperties".to_owned(), true.into());
         }
         Ok(obj2) => {
             let obj1 = schema.ensure_object();
 
             for (key, value2) in obj2 {
                 match obj1.entry(key) {
-                    Entry::Vacant(vacant) => {
-                        vacant.insert(value2);
-                    }
+                    Entry::Vacant(vacant) => match vacant.key().as_str() {
+                        "additionalProperties" | "unevaluatedProperties" => {
+                            if value2 != Value::Bool(false) {
+                                vacant.insert(value2);
+                            }
+                        }
+                        _ => {
+                            vacant.insert(value2);
+                        }
+                    },
                     Entry::Occupied(occupied) => {
                         match occupied.key().as_str() {
                             "required" => {
@@ -212,6 +218,13 @@ pub fn flatten(schema: &mut Schema, other: Schema) {
                                     }
                                 }
                             }
+                            "additionalProperties" | "unevaluatedProperties" => {
+                                // Even if an outer type has `deny_unknown_fields`, unknown fields
+                                // may be accepted by the flattened type
+                                if occupied.get() == &Value::Bool(false) {
+                                    *occupied.into_mut() = value2;
+                                }
+                            }
                             _ => {
                                 // leave the original value as it is (don't modify `schema`)
                             }
diff --git a/schemars/tests/expected/test_flattened_struct_deny_unknown_fields.json b/schemars/tests/expected/test_flattened_struct_deny_unknown_fields.json
new file mode 100644
index 0000000..1ac94b5
--- /dev/null
+++ b/schemars/tests/expected/test_flattened_struct_deny_unknown_fields.json
@@ -0,0 +1,52 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "title": "Tuple_of_OuterAllowUnknownFields_and_MiddleDenyUnknownFields",
+  "type": "array",
+  "prefixItems": [
+    {
+      "$ref": "#/$defs/OuterAllowUnknownFields"
+    },
+    {
+      "$ref": "#/$defs/MiddleDenyUnknownFields"
+    }
+  ],
+  "minItems": 2,
+  "maxItems": 2,
+  "$defs": {
+    "OuterAllowUnknownFields": {
+      "type": "object",
+      "properties": {
+        "outer_field": {
+          "type": "boolean"
+        },
+        "middle_field": {
+          "type": "boolean"
+        },
+        "inner_field": {
+          "type": "boolean"
+        }
+      },
+      "required": [
+        "outer_field",
+        "middle_field",
+        "inner_field"
+      ]
+    },
+    "MiddleDenyUnknownFields": {
+      "type": "object",
+      "properties": {
+        "middle_field": {
+          "type": "boolean"
+        },
+        "inner_field": {
+          "type": "boolean"
+        }
+      },
+      "additionalProperties": false,
+      "required": [
+        "middle_field",
+        "inner_field"
+      ]
+    }
+  }
+}
\ No newline at end of file
diff --git a/schemars/tests/flatten.rs b/schemars/tests/flatten.rs
index 321c419..ffd8d1f 100644
--- a/schemars/tests/flatten.rs
+++ b/schemars/tests/flatten.rs
@@ -76,6 +76,24 @@ struct FlattenMap {
     value: BTreeMap<String, Value>,
 }
 
+#[allow(dead_code)]
+#[derive(JsonSchema)]
+#[schemars(rename = "FlattenValue", deny_unknown_fields)]
+struct FlattenValueDenyUnknownFields {
+    flag: bool,
+    #[serde(flatten)]
+    value: Value,
+}
+
+#[allow(dead_code)]
+#[derive(JsonSchema)]
+#[schemars(rename = "FlattenValue", deny_unknown_fields)]
+struct FlattenMapDenyUnknownFields {
+    flag: bool,
+    #[serde(flatten)]
+    value: BTreeMap<String, Value>,
+}
+
 #[test]
 fn test_flattened_value() -> TestResult {
     test_default_generated_schema::<FlattenValue>("flattened_value")
@@ -86,3 +104,42 @@ fn test_flattened_map() -> TestResult {
     // intentionally using the same file as test_flattened_value, as the schema should be identical
     test_default_generated_schema::<FlattenMap>("flattened_value")
 }
+
+#[test]
+fn test_flattened_value_deny_unknown_fields() -> TestResult {
+    // intentionally using the same file as test_flattened_value, as the schema should be identical
+    test_default_generated_schema::<FlattenValueDenyUnknownFields>("flattened_value")
+}
+
+#[test]
+fn test_flattened_map_deny_unknown_fields() -> TestResult {
+    // intentionally using the same file as test_flattened_value, as the schema should be identical
+    test_default_generated_schema::<FlattenMapDenyUnknownFields>("flattened_value")
+}
+
+#[derive(JsonSchema)]
+pub struct OuterAllowUnknownFields {
+    pub outer_field: bool,
+    #[serde(flatten)]
+    pub middle: MiddleDenyUnknownFields,
+}
+
+#[derive(JsonSchema)]
+#[serde(deny_unknown_fields)]
+pub struct MiddleDenyUnknownFields {
+    pub middle_field: bool,
+    #[serde(flatten)]
+    pub inner: InnerAllowUnknownFields,
+}
+
+#[derive(JsonSchema)]
+pub struct InnerAllowUnknownFields {
+    pub inner_field: bool,
+}
+
+#[test]
+fn test_flattened_struct_deny_unknown_fields() -> TestResult {
+    test_default_generated_schema::<(OuterAllowUnknownFields, MiddleDenyUnknownFields)>(
+        "test_flattened_struct_deny_unknown_fields",
+    )
+}