Respect IgnoreReadOnlyProperties/IgnoreReadOnlyFields in JsonSchemaExporter

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JsonSchemaExporter emitted read-only members that the serializer never writes when IgnoreReadOnlyProperties/IgnoreReadOnlyFields are enabled, so the schema disagreed with the actual serialized payload.

var options = new JsonSerializerOptions(JsonSerializerOptions.Default) { IgnoreReadOnlyProperties = true };

JsonSerializer.Serialize(new C(), options);       // {}
options.GetJsonSchemaAsNode(typeof(C));           // before: { "type": [...], "properties": { "S": ... } }
                                                  // after:  { "type": [...] }
class C { public string S => "Hello"; }

Changes

• JsonSchemaExporter: the property filter previously skipped only members with both Get and Set null. It now uses the flags the serializer itself computes:

  if (property is { CanSerialize: false, CanDeserializeOrPopulate: false } or { IsExtensionData: true })

  CanSerialize/CanDeserializeOrPopulate already account for the ignore-read-only policy, [JsonIgnore], and ShouldSerialize overrides, so no new option plumbing is needed. Read-only collection properties are unaffected — they remain serializable and stay in the schema.

• Tests: shared TestData entries for a POCO with read-only properties, with and without IgnoreReadOnlyProperties (exercised under both reflection and source gen), plus a reflection-only theory for IgnoreReadOnlyFields. Fields are kept out of the shared data because source gen drops non-[JsonInclude] fields at generation time and gives [JsonInclude] readonly fields an UnsafeAccessor setter, making them non-read-only at runtime.

• Fixes JsonSchemaExporter doesn't respect IgnoreReadOnlyProperties/IgnoreReadOnlyFields #131632

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Review details

Suppressed comments (1)

src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.TestTypes.cs:851

• The comment says read-only members are omitted when IgnoreReadOnlyProperties/IgnoreReadOnlyFields are enabled, but this test still expects the read-only collection property to be present. Please clarify that only members actually ignored by those settings (e.g., non-collection read-only properties/fields) are omitted, while collection properties can still be serialized/populated.

            // Read-only members are omitted when IgnoreReadOnlyProperties/IgnoreReadOnlyFields are enabled.

• Files reviewed: 3/3 changed files
• Comments generated: 0 new
• Review effort level: Lite

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Review details

Suppressed comments (2)

src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.TestTypes.cs:859

• ReadOnlyCollectionProperty is declared as a non-nullable List<int>, so the schema for the property should not include "null" in its type union. This expected JSON currently marks it as nullable.

                    "properties": {
                        "Name": { "type": ["string", "null"] },
                        "ReadOnlyCollectionProperty": { "type": ["array", "null"], "items": { "type": "integer" } }
                    }

src/libraries/System.Text.Json/tests/Common/JsonSchemaExporterTests.TestTypes.cs:844

• ReadOnlyCollectionProperty is declared as a non-nullable List<int>, so the schema for the property should not include "null" in its type union. In this file, non-nullable collection properties (e.g. PocoWithRecursiveCollectionElement.Children) are expected to emit "type": "array" without null.

This issue also appears on line 856 of the same file.

                        "Name": { "type": ["string", "null"] },
                        "ReadOnlyProperty": { "type": "integer" },
                        "ReadOnlyCollectionProperty": { "type": ["array", "null"], "items": { "type": "integer" } }
                    }

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Lite