Percent-encode JSON pointer reference tokens in JsonSchemaExporter $ref values

src/libraries/System.Text.Json/src/System/Text/Json/Schema/JsonSchemaExporter.cs

@@ -553,34 +553,14 @@ private static string FormatJsonPointer(ReadOnlySpan<string> path)
 
                 foreach (string segment in path)
                 {
-                    ReadOnlySpan<char> span = segment.AsSpan();
                     sb.Append('/');
 
-                    do
-                    {
-                        // Per RFC 6901 the characters '~' and '/' must be escaped.
-                        int pos = span.IndexOfAny('~', '/');
-                        if (pos < 0)
-                        {
-                            sb.Append(span);
-                            break;
-                        }
-
-                        sb.Append(span.Slice(0, pos));
+                    // Per RFC 6901 the characters '~' and '/' are escaped as '~0' and '~1'.
+                    string escapedToken = segment.Replace("~", "~0").Replace("/", "~1");
 
-                        if (span[pos] == '~')
-                        {
-                            sb.Append("~0");
-                        }
-                        else
-                        {
-                            Debug.Assert(span[pos] == '/');
-                            sb.Append("~1");
-                        }
-
-                        span = span.Slice(pos + 1);
-                    }
-                    while (!span.IsEmpty);
+                    // Per RFC 6901 section 6 the JSON Pointer is embedded in a URI fragment,
+                    // so percent-encode any characters that are not valid in a URI fragment.
+                    sb.Append(Uri.EscapeDataString(escapedToken));
                 }
 
                 return sb.ToString();

src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.TestTypes.cs

@@ -1169,6 +1169,29 @@ of the type which points to the first occurrence. */
                     }
                 """);
 
+            yield return new TestData<ClassWithPropertyNameRequiringFragmentEncoding>(
+                Value: new ClassWithPropertyNameRequiringFragmentEncoding { Value = new() },
+                ExpectedJsonSchema: """
+                    {
+                        "type": ["object","null"],
+                        "properties": {
+                            "hello%20world": {
+                                "type": "object",
+                                "properties": {
+                                    "Value" : {"type":"integer"},
+                                    "Next": {
+                                        "type": ["object","null"],
+                                        "properties": {
+                                            "Value" : {"type":"integer"},
+                                            "Next": {"$ref":"#/properties/hello%2520world/properties/Next"}
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                """);
+
             yield return new TestData<ClassWithOptionalObjectParameter>(
                 Value: new(value: null),
                 AdditionalValues: [new(true), new(42), new(""), new(new object()), new(Array.Empty<int>())],
@@ -1614,6 +1637,12 @@ public class ClassWithJsonPointerEscapablePropertyNames
             public PocoWithRecursiveMembers Value { get; set; }
         }
 
+        public class ClassWithPropertyNameRequiringFragmentEncoding
+        {
+            [JsonPropertyName("hello%20world")]
+            public PocoWithRecursiveMembers Value { get; set; }
+        }
+
         public class ClassWithOptionalObjectParameter(object? value = null)
         {
             public object? Value { get; } = value;

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/Serialization/JsonSchemaExporterTests.cs

@@ -115,6 +115,7 @@ public sealed partial class JsonSchemaExporterTests_SourceGen()
         [JsonSerializable(typeof(PocoCombiningPolymorphicTypeAndDerivedTypes))]
         [JsonSerializable(typeof(ClassWithComponentModelAttributes))]
         [JsonSerializable(typeof(ClassWithJsonPointerEscapablePropertyNames))]
+        [JsonSerializable(typeof(ClassWithPropertyNameRequiringFragmentEncoding))]
         [JsonSerializable(typeof(ClassWithOptionalObjectParameter))]
         [JsonSerializable(typeof(ClassWithPropertiesUsingCustomConverters))]
         // Collection types