Sandbox::https://github.com/microsoft/OpenAPI.NET/pull/2728

Copilot · 2026-02-17T17:16:54Z

Pull Request

Description

The unevaluatedProperties keyword was incorrectly implemented as a boolean. Per JSON Schema 2020-12, it accepts either false or a schema object (like additionalProperties).

// Before: only boolean supported
schema.UnevaluatedProperties = false;

// After: both boolean and schema supported
schema.UnevaluatedProperties = false;  // Disallow all
schema.UnevaluatedPropertiesSchema = new OpenApiSchema { Type = JsonSchemaType.String }; // Validate as string

Type of Change

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to not work as expected)
Documentation update
Other (please describe):

Changes Made

Binary-Compatible Schema Support

New IOpenApiSchemaWithUnevaluatedProperties interface with UnevaluatedPropertiesSchema property
OpenApiSchema and OpenApiSchemaReference implement new interface
Naming differs from AdditionalProperties pattern for compatibility; TODO markers added for v4.0 rename
Copy constructor simplified using pattern matching

Serialization/Deserialization

V3.1+ and V3.2 serialization handles both boolean (false) and schema object
Schema takes precedence when both present
V3.0/V2.0 emit property as x-jsonschema-unevaluatedProperties extension
Deserialization uses ValueNode check matching additionalProperties pattern
V3.2 deserialization support added with same pattern as V3.1
Extension name refactored to use OpenApiConstants.UnevaluatedPropertiesExtension constant

Default Value Correction

Changed UnevaluatedProperties default from false to true
Aligns with JSON Schema spec (allow by default, like AdditionalPropertiesAllowed)

Testing

21 new tests covering serialization, deserialization, copy constructor, version compatibility
Tests for V3.1 and V3.2 deserialization (boolean, schema object, complex schema)
Tests for extension serialization in V2.0 and V3.0
Test validating default value when property not present

Performance

Updated benchmark reports to reflect performance characteristics of the implementation

Testing

Unit tests added/updated
Integration tests added/updated
Manual testing performed
All existing tests pass

Checklist

My code follows the code style of this project
I have performed a self-review of my own code
I have made corresponding changes to the documentation
My changes generate no new warnings
I have added tests that prove my fix is effective or that my feature works
New and existing unit tests pass locally with my changes

Versions applicability

My change applies to the version 1.X of the library, if so PR link:
My change applies to the version 2.X of the library, if so PR link:
My change applies to the version 3.X of the library, if so PR link:
I have evaluated the applicability of my change against the other versions above.

Additional Notes

Binary Compatibility Strategy

UnevaluatedProperties (bool) → UnevaluatedPropertiesAllowed in v4.0
UnevaluatedPropertiesSchema → UnevaluatedProperties in v4.0
IOpenApiSchemaWithUnevaluatedProperties → merge into IOpenApiSchema in v4.0

Behavior Change
Default for UnevaluatedProperties changed from false to true to match spec. Existing schemas relying on implicit false will now allow unevaluated properties unless explicitly set to false.

Extension Serialization
For OpenAPI versions < 3.1 (V2.0 and V3.0), unevaluatedProperties is serialized as the x-jsonschema-unevaluatedProperties extension to maintain backward compatibility while preserving the metadata. The extension name is defined as a constant (OpenApiConstants.UnevaluatedPropertiesExtension) for consistency and maintainability.

Original prompt

This section details on the original issue you should resolve

<issue_title>unevaluatedproperties should be an OpenApiSchema, not a boolean</issue_title>
<issue_description>## The issue

A mistake was made when working on the v2 version of the library. The "new" JSON schema unevaluatedproperties keyword is a schema itself. Like additionalProperties, it may contain "false" (meaning no unevaluated properties are allowed) or a JSON schema (meaning the unevaluated properties MUST validate against that schema).

What it should have been instead

We should have implemented things in a way similar to how additionalProperties is implemented today:

UnevaluatedPropertiesAllowed, boolean, defaults to true, only serialized when the value is set to false and no value is present for the schema type property is null.

UnevaluatedProperties, OpenApiSchema, defaults to null, only serialized when a value is not null.

In both cases, the keyword is serialized as an extension when the target version is < 3.1.0.

During deserialization:

If we encounter false, we set the boolean property to false

If we encounter true, we ignore it.

If we encounter an object, it's most likely a schema, in which case we deserialize it to the schema type property.

Considerations for binary compatibility

Since the property UnevaluatedProperties is already present as a boolean, we can't change its type without causing a breaking change. Additionally, we can't add a new property in the IOpenApiSchema interface without causing a breaking change. So here is what we should be doing instead:

Use UnevaluatedProperties for the boolean property (no allowed suffix)

Add a TODO comment there this needs to be renamed in the next major version

Use the UnevaluatedPropertiesSchema for the schema type property

Add a TODO comment there this needs to be renamed

Clearly call out in the documentation comments for both properties this differs in naming pattern from AdditionalProperties, but will be renamed in the next major version.

DO NOT ADD ANY NEW PROPERTY TO THE IOpenApiSchema interface.

Add a new interface called "IOpenApiSchemaWithUnevaluatedProperties", which has the new property, and a documentation comment calling out to the fact this is a "compatibility" solution, to expect this will eventually get merged in the next major version.

Add a TODO comment in this interface that it needs to be removed, its content merged with IOpenApiSchema in the next major version.

Make OpenApiSchema and OpenApiSchemaReference implement that new interface.</issue_description>

<agent_instructions>use conventional commits.
Define unit tests first, then fix the implementation.</agent_instructions>

Comments on the Issue (you are Copilot in this section)

Fixes unevaluatedproperties should be an OpenApiSchema, not a boolean #2727

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

- Create IOpenApiSchemaWithUnevaluatedProperties interface for binary compatibility - Add UnevaluatedPropertiesSchema property to OpenApiSchema - Update OpenApiSchemaReference to implement new interface - Update serialization to handle both boolean and schema cases - Update V31 deserialization to handle both boolean and schema cases - Add comprehensive documentation with TODO markers for next major version Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

- Add serialization tests for boolean and schema cases - Add deserialization tests for V3.1 - Add copy constructor test - Fix default value to true (allowing unevaluated properties by default) Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

- Fix deserialization to use ValueNode check like AdditionalProperties - Fix copy constructor test to properly cast before modifying - Update PublicAPI.Unshipped.txt with new API surface - Update global.json to use available SDK version - All UnevaluatedProperties tests now passing Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Vincent Biret (baywet) · 2026-02-17T18:51:41Z

Copilot implement the changes requested in my last review

- Simplify copy constructor using pattern matching - Add V3.2 deserialization support for UnevaluatedPropertiesSchema - Add test for default value (no property set, defaults to true) - Emit as x-jsonschema-unevaluatedProperties extension for versions < 3.1 - Add comprehensive tests for extension serialization in V2 and V3.0 - Add V3.2 deserialization tests Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Copilot · 2026-02-17T19:00:51Z

Copilot implement the changes requested in my last review

All changes from the last review have been implemented in commit 964c7be:

✅ Simplified copy constructor using pattern matching (line 283-286)
✅ Added V3.2 deserialization support with 3 unit tests
✅ Added test for default value validation (ParseSchemaWithoutUnevaluatedPropertiesDefaultsToTrue)
✅ Implemented x-jsonschema-unevaluatedProperties extension for versions < 3.1 with 3 new tests

All 70 tests passing (62 schema tests + 8 reader tests).

mdaneri · 2026-02-17T19:17:18Z

Vincent Biret (@baywet) thanks for taking care of this!
I’m currently on vacation so I’m a bit slow — I was planning to look into it this week, but really appreciate you jumping on it 🙏

- Added UnevaluatedPropertiesExtension constant to OpenApiConstants - Replaced hardcoded "x-jsonschema-unevaluatedProperties" strings with constant - Updated both V3.0 and V2.0 serialization paths - Updated PublicAPI.Unshipped.txt with new constant Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Vincent Biret (baywet) · 2026-02-17T21:03:13Z

Copilot please update the benchmarks

To do so, run the following script:

cd performance/benchmark
dotnet run -c Release

Then commit the report files using a "chore" commit.

Initial plan

48e997f

Copilot AI assigned Copilot and Vincent Biret (baywet) Feb 17, 2026

Copilot started work on behalf of Vincent Biret (baywet) February 17, 2026 17:17

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Copilot AI and others added 3 commits February 17, 2026 17:20

Copilot AI changed the title ~~[WIP] Fix unevaluatedproperties to be OpenApiSchema instead of boolean~~ fix: implement unevaluatedProperties as schema per JSON Schema 2020-12 Feb 17, 2026

Copilot AI requested a review from Vincent Biret (baywet) February 17, 2026 17:34

Copilot finished work on behalf of Vincent Biret (baywet) February 17, 2026 17:34

Vincent Biret (baywet) requested changes Feb 17, 2026

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Copilot started work on behalf of Vincent Biret (baywet) February 17, 2026 18:51

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Copilot AI requested a review from Vincent Biret (baywet) February 17, 2026 18:58

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Copilot finished work on behalf of Vincent Biret (baywet) February 17, 2026 19:01

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Comment thread src/Microsoft.OpenApi/Models/OpenApiSchema.cs Resolved

Copilot started work on behalf of Vincent Biret (baywet) February 17, 2026 19:23

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Copilot AI requested a review from Vincent Biret (baywet) February 17, 2026 19:27

Copilot finished work on behalf of Vincent Biret (baywet) February 17, 2026 19:27

Vincent Biret (baywet) reviewed Feb 17, 2026

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Comment thread global.json Resolved

chore: reverts dotnet version change

870baa4

Vincent Biret (baywet) approved these changes Feb 17, 2026

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Copilot started work on behalf of Vincent Biret (baywet) February 17, 2026 21:03

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fix: implement unevaluatedProperties as schema per JSON Schema 2020-12 - #2728

fix: implement unevaluatedProperties as schema per JSON Schema 2020-12#2728
Vincent Biret (baywet) merged 8 commits into
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copilot/fix-unevaluatedproperties-schema

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Pull Request

Description

Type of Change

Changes Made

Testing

Checklist

Versions applicability

Additional Notes

What it should have been instead

Considerations for binary compatibility

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Copilot AI commented Feb 17, 2026 •

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