fix: only override struct description if tag is set

fixtures/schema_extend_description.json

@@ -0,0 +1,40 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://github.com/invopop/jsonschema/extend-description-object",
+  "$ref": "#/$defs/ExtendDescriptionObject",
+  "$defs": {
+    "ExtendDescriptionObject": {
+      "properties": {
+        "extend": {
+          "type": "string",
+	  "description": "extend description"
+        },
+        "tag": {
+          "type": "string",
+	  "description": "tag description"
+        },
+        "tag_extend": {
+          "type": "string",
+	  "description": "tag description"
+        },
+        "generic_tag": {
+          "type": "string",
+	  "description": "generic description"
+        },
+        "generic_tag_extend": {
+          "type": "string",
+	  "description": "generic description"
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "required": [
+        "extend",
+        "tag",
+        "tag_extend",
+        "generic_tag",
+        "generic_tag_extend"
+      ]
+    }
+  }
+}

reflect.go

@@ -609,7 +609,11 @@ func (r *Reflector) lookupID(t reflect.Type) ID {
 }
 
 func (t *Schema) structKeywordsFromTags(f reflect.StructField, parent *Schema, propertyName string) {
-	t.Description = f.Tag.Get("jsonschema_description")
+	description, ok := f.Tag.Lookup("jsonschema_description")
+	if ok {
+		t.Description = description
+	}
+
 
 	tags := splitOnUnescapedCommas(f.Tag.Get("jsonschema"))
 	tags = t.genericKeywords(tags, parent, propertyName)

reflect_test.go

@@ -675,3 +675,24 @@ func TestJSONSchemaAlias(t *testing.T) {
 	compareSchemaOutput(t, "fixtures/schema_alias.json", r, &AliasObjectB{})
 	compareSchemaOutput(t, "fixtures/schema_alias_2.json", r, &AliasObjectC{})
 }
+
+type WithExtendDescription string
+
+func (WithExtendDescription) JSONSchemaExtend(base *Schema) {
+	base.Description = "extend description"
+}
+
+type ExtendDescriptionObject struct {
+	Extend WithExtendDescription `json:"extend"`
+
+	Tag       WithExtendDescription `json:"tag" jsonschema_description:"tag description"`
+	TagExtend WithExtendDescription `json:"tag_extend" jsonschema_description:"tag description"`
+
+	GenericTag       WithExtendDescription `json:"generic_tag" jsonschema:"description=generic description"`
+	GenericTagExtend WithExtendDescription `json:"generic_tag_extend" jsonschema:"description=generic description"`
+}
+
+func TestJsonSchemaExtendDescription(t *testing.T) {
+	r := &Reflector{}
+	compareSchemaOutput(t, "fixtures/schema_extend_description.json", r, &ExtendDescriptionObject{})
+}