feat(reflect): Add method to modify the schema after processing

fixtures/custom_type_extend.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://github.com/invopop/jsonschema/schema-extend-test",
+  "$ref": "#/$defs/SchemaExtendTest",
+  "$defs": {
+    "SchemaExtendTest": {
+      "properties": {
+        "LastName": {
+          "type": "string",
+          "description": "some extra words"
+        },
+        "middle_name": {
+          "type": "string"
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "required": [
+        "LastName"
+      ]
+    }
+  }
+}

reflect.go

@@ -108,7 +108,14 @@ type customSchemaImpl interface {
 	JSONSchema() *Schema
 }
 
+// Function to be run after the schema has been generated.
+// this will let you modify a schema afterwards
+type extendSchemaImpl interface {
+	JSONSchemaExtend(*Schema)
+}
+
 var customType = reflect.TypeOf((*customSchemaImpl)(nil)).Elem()
+var extendType = reflect.TypeOf((*extendSchemaImpl)(nil)).Elem()
 
 // customSchemaGetFieldDocString
 type customSchemaGetFieldDocString interface {
@@ -395,6 +402,8 @@ func (r *Reflector) reflectTypeToSchema(definitions Definitions, t reflect.Type)
 		panic("unsupported type " + t.String())
 	}
 
+	r.reflectSchemaExtend(definitions, t, st)
+
 	// Always try to reference the definition which may have just been created
 	if def := r.refDefinition(definitions, t); def != nil {
 		return def
@@ -422,6 +431,19 @@ func (r *Reflector) reflectCustomSchema(definitions Definitions, t reflect.Type)
 	return nil
 }
 
+func (r *Reflector) reflectSchemaExtend(definitions Definitions, t reflect.Type, s *Schema) *Schema {
+	if t.Implements(extendType) {
+		v := reflect.New(t)
+		o := v.Interface().(extendSchemaImpl)
+		o.JSONSchemaExtend(s)
+		if ref := r.refDefinition(definitions, t); ref != nil {
+			return ref
+		}
+	}
+
+	return s
+}
+
 func (r *Reflector) reflectSliceOrArray(definitions Definitions, t reflect.Type, st *Schema) {
 	if t == rawMessageType {
 		return

reflect_test.go

@@ -310,6 +310,25 @@ type KeyNamed struct {
 	RenamedByComputation int `jsonschema_description:"Description was preserved"`
 }
 
+type SchemaExtendTestBase struct {
+	FirstName  string `json:"FirstName"`
+	LastName   string `json:"LastName"`
+	Age        uint   `json:"age"`
+	MiddleName string `json:"middle_name,omitempty"`
+}
+
+type SchemaExtendTest struct {
+	SchemaExtendTestBase `json:",inline"`
+}
+
+func (SchemaExtendTest) JSONSchemaExtend(base *Schema) {
+	base.Properties.Delete("FirstName")
+	base.Properties.Delete("age")
+	val, _ := base.Properties.Get("LastName")
+	(val).(*Schema).Description = "some extra words"
+	base.Required = []string{"LastName"}
+}
+
 type Expression struct {
 	Value int `json:"value" jsonschema_extras:"foo=bar=='baz'"`
 }
@@ -444,6 +463,7 @@ func TestSchemaGeneration(t *testing.T) {
 		}, "fixtures/keynamed.json"},
 		{MapType{}, &Reflector{}, "fixtures/map_type.json"},
 		{ArrayType{}, &Reflector{}, "fixtures/array_type.json"},
+		{SchemaExtendTest{}, &Reflector{}, "fixtures/custom_type_extend.json"},
 		{Expression{}, &Reflector{}, "fixtures/schema_with_expression.json"},
 	}