[0.12.3] Fix crash in logging when property named "$ref" (#410)

Co-authored-by: Mike Harder <mharder@microsoft.com>

Author: yungshinlintw

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+# 0.12.3 2025-10-13
+
+- Fix crash in logging when property named "$ref"
+
 ## 0.12.2 2025-09-22
 
 - bump dependency `js-yaml` from `^3.13.0` to `^4.1.0`

openapi-diff/src/core/OpenApiDiff.Core/Logging/ObjectPath.cs

@@ -76,9 +76,23 @@ private static JToken FromObject(JObject o, string name)
             {
                 return null;
             }
+            
             var @ref = o["$ref"];
-            var unrefed = @ref != null ? ParseRef(@ref.Value<string>()).CompletePath(o.Root).Last().token : o;
-            return unrefed[name];
+            
+            // Handle $ref resolution based on its type
+            if (@ref != null && @ref.Type == JTokenType.String)
+            {
+                // Case 1: $ref is a string reference (e.g., "#/definitions/FieldType")
+                // Resolve the reference by parsing the path and following it to the target
+                var unrefed = ParseRef(@ref.Value<string>()).CompletePath(o.Root).Last().token;
+                return unrefed[name];
+            }
+            else
+            {
+                // Case 2: $ref is not a string (e.g., a JSON object defining a schema)
+                // or $ref doesn't exist - use the current object directly
+                return o[name];
+            }
         }
 
         private static IEnumerable<(JToken token, string name)> CompletePath(IEnumerable<Func<JToken, string>> path, JToken token)

openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger/new/type_changed_02.json

@@ -0,0 +1,48 @@
+{
+  "swagger": 2.0,
+  "info": {
+    "title": "type_changed",
+    "version": "1.0"
+  },
+  "host": "localhost:8000",
+  "schemes": [ "http", "https" ],
+  "consumes": [ "text/plain", "text/json" ],
+  "produces": [ "text/plain" ],
+  "paths": {
+    "/api/Parameters": {
+      "put": {
+        "tag": [ "Parameters" ],
+        "operationId": "Parameters_Put",
+        "produces": [
+          "text/plain"
+        ],
+        "parameters": [
+          {
+            "name": "database",
+            "in": "body",
+            "required": true,
+            "type": "object",
+            "schema": { "$ref": "#/definitions/Database" }
+          }
+        ]
+      }
+    }
+  },
+  "definitions": {
+    "Database": {
+      "properties": {
+        "$ref": {
+          "type": "integer",
+          "readOnly": true,
+          "description": "Property named '$ref'. Unusual but valid."
+        },
+        "b": {
+          "type": "integer",
+          "readOnly": true,
+          "default": 0,
+          "description": "This property shows the number of databases returned."
+        }
+      }
+    }
+  }
+}

openapi-diff/src/modeler/AutoRest.Swagger.Tests/Resource/Swagger/old/type_changed_02.json

@@ -0,0 +1,48 @@
+{
+  "swagger": 2.0,
+  "info": {
+    "title": "type_changed",
+    "version": "1.0"
+  },
+  "host": "localhost:8000",
+  "schemes": [ "http", "https" ],
+  "consumes": [ "text/plain", "text/json" ],
+  "produces": [ "text/plain" ],
+  "paths": {
+    "/api/Parameters": {
+      "put": {
+        "tag": [ "Parameters" ],
+        "operationId": "Parameters_Put",
+        "produces": [
+          "text/plain"
+        ],
+        "parameters": [
+          {
+            "name": "database",
+            "in": "body",
+            "required": true,
+            "type": "object",
+            "schema": { "$ref": "#/definitions/Database" }
+          }
+        ]
+      }
+    }
+  },
+  "definitions": {
+    "Database": {
+      "properties": {
+        "$ref": {
+          "type": "string",
+          "readOnly": true,
+          "description": "Property named '$ref'. Unusual but valid."
+        },
+        "b": {
+          "type": "integer",
+          "readOnly": true,
+          "default": 0,
+          "description": "This property shows the number of databases returned."
+        }
+      }
+    }
+  }
+}

openapi-diff/src/modeler/AutoRest.Swagger.Tests/SwaggerModelerCompareTests.cs

@@ -165,6 +165,21 @@ public void TypeObjectChanged()
             Assert.Equal("new/type_changed_01.json#/definitions/Database/properties/a", error.NewJsonRef);
         }
 
+        /// <summary>
+        /// Verifies that if you change the type of a schema property named "$ref" (unusual but valid), it's caught.
+        /// </summary>
+        [Fact]
+        public void PropertyNamedRefTypeChanged()
+        {
+            var messages = CompareSwagger("type_changed_02.json").ToArray();
+            var missing = messages.Where(m => m.Id == ComparisonMessages.TypeChanged.Id);
+            Assert.NotEmpty(missing);
+            var error = missing.Where(err => err.NewJsonRef.StartsWith("new/type_changed_02.json#/definitions/")).FirstOrDefault();
+            Assert.NotNull(error);
+            Assert.Equal(Category.Error, error.Severity);
+            Assert.Equal("new/type_changed_02.json#/definitions/Database/properties/$ref", error.NewJsonRef);
+        }
+
         /// <summary>
         /// Verifies that if you change the default value of a schema, it's caught.
         /// </summary>

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@azure/oad",
-  "version": "0.12.2",
+  "version": "0.12.3",
   "author": {
     "name": "Microsoft Corporation",
     "email": "azsdkteam@microsoft.com",