Set "required" schema attribute

schemars/src/schema.rs

@@ -3,6 +3,7 @@ use crate::{MakeSchema, MakeSchemaError, Result};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 use std::collections::BTreeMap as Map;
+use std::collections::BTreeSet as Set;
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, MakeSchema)]
 #[serde(untagged)]
@@ -30,13 +31,13 @@ impl From<SchemaRef> for Schema {
     }
 }
 
-fn extend<A, E: Extend<A>>(mut a: E, b: impl IntoIterator<Item = A>) -> E {
-    a.extend(b);
-    a
-}
-
 impl Schema {
     pub fn flatten(self, other: Self) -> Result {
+        fn extend<A, E: Extend<A>>(mut a: E, b: impl IntoIterator<Item = A>) -> E {
+            a.extend(b);
+            a
+        }
+
         let s1 = self.ensure_flattenable()?;
         let s2 = other.ensure_flattenable()?;
         Ok(Schema::Object(SchemaObject {
@@ -112,8 +113,8 @@ pub struct SchemaObject {
     pub items: Option<SingleOrVec<Schema>>,
     #[serde(skip_serializing_if = "Map::is_empty")]
     pub properties: Map<String, Schema>,
-    #[serde(skip_serializing_if = "Vec::is_empty")]
-    pub required: Vec<String>,
+    #[serde(skip_serializing_if = "Set::is_empty")]
+    pub required: Set<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub all_of: Option<Vec<Schema>>,
     #[serde(skip_serializing_if = "Option::is_none")]

schemars/tests/expected/property-name-struct.json

@@ -12,5 +12,10 @@
     "new_name_2": {
       "type": "integer"
     }
-  }
+  },
+  "required": [
+    "camelCase",
+    "new_name_1",
+    "new_name_2"
+  ]
 }

schemars/tests/expected/schema-name-custom.json

@@ -22,6 +22,13 @@
       }
     }
   },
+  "required": [
+    "inner",
+    "t",
+    "u",
+    "v",
+    "w"
+  ],
   "definitions": {
     "another-new-name": {
       "type": "object"

schemars/tests/expected/schema-name-default.json

@@ -22,6 +22,13 @@
       }
     }
   },
+  "required": [
+    "inner",
+    "t",
+    "u",
+    "v",
+    "w"
+  ],
   "definitions": {
     "MySimpleStruct": {
       "type": "object"

schemars/tests/expected/schema-openapi3.json

@@ -151,7 +151,10 @@
         "$ref": {
           "type": "string"
         }
-      }
+      },
+      "required": [
+        "$ref"
+      ]
     },
     "SingleOrVec_For_InstanceType": {
       "anyOf": [

schemars/tests/expected/schema.json

@@ -187,7 +187,10 @@
         "$ref": {
           "type": "string"
         }
-      }
+      },
+      "required": [
+        "$ref"
+      ]
     },
     "SingleOrVec_For_InstanceType": {
       "anyOf": [