[ci-fix] Needs review: Fix PolymorphicTests order-dependent assertion on tvOS Mono (refs #128765)

[github-actions]

Workflow artifact: ci-fix
Artifact kind: help
Linked KBE: #128765

Note

This is an AI/Copilot-generated draft PR that attempts to fix the CI failure described in KBE #128765. It has NOT been build-validated (environment lacks .NET 11 SDK). Human review is needed.

Root cause

The test MetadataServices_NullPolymorphismOptions_DoesNotActivateAttributeClassifier uses Assert.Collection (order-sensitive) to verify JsonPolymorphismOptions.DerivedTypes. It expects [Dog, Cat] matching the attribute declaration order on AttrClassifiedAnimal:

[JsonDerivedType(typeof(AttrClassifiedDog), "dog")]
[JsonDerivedType(typeof(AttrClassifiedCat), "cat")]
public class AttrClassifiedAnimal { ... }

On tvOS Mono, Type.GetCustomAttributes() returns these attributes in reverse order ([Cat, Dog]), causing the test to fail. The ECMA specification does not guarantee attribute ordering from reflection APIs.

Fix

Replace the order-sensitive Assert.Collection with:

• Assert.Equal(2, options.DerivedTypes.Count) — verifies the expected number of types
• Assert.Contains(...) for each type — verifies presence and discriminator without order dependency

Remove the [ActiveIssue] annotation since this fix addresses the root cause rather than disabling the test.

What is unverified / help needed

• Build not validated: Environment has .NET 8/9 SDKs; the project targets .NET 11 preview.
• Semantic question: Is the ordering of DerivedTypes semantically significant for JSON serialization behavior? If so, the real fix may be in the product code (ensuring deterministic ordering). If not, this test fix is correct.
• Other tests: There may be similar order-dependent assertions elsewhere in the polymorphic test suite that could have the same issue on Mono.

Suggested reviewers / area contacts

• @eiriktsarpalis (area-System.Text.Json owner)
• @SteveSandersonMS

Validation

• Command: dotnet build src/libraries/System.Text.Json/tests/System.Text.Json.Tests/System.Text.Json.Tests.csproj
• Result: not run because environment lacks .NET 11 SDK

Evidence

• Failing build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1438268
• First build it occurred: 2026-05-25T09:02:27Z (persistent across entire scanned window; true origin may predate 2026-05-24)
• Suspected regressing change: none identified; likely a Mono attribute-ordering difference exposed when this test started running on tvOS

---

Filed by ci-failure-fix, which attempts validated fixes for [ci-scan] Known Build Errors and otherwise loops in owners. Comment here or on the workflow file to suggest changes; ci-failure-scan-feedback reads in-scope feedback daily and opens (or updates) a PR with prompt edits.

Note

🔒 Integrity filter blocked 2 items

The following items were blocked because they don't meet the GitHub integrity level.

• [ci-scan] Test failure: CustomAttributeDecoderTests.TestCustomAttributeDecoderGenericUsingReflection on maccatalyst #128450 issue_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• [ci-scan] Test failure: CryptoStreamTests.ReadWrite_Success MemberData not found on maccatalyst #128451 issue_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

Generated by CI Outer-Loop Failure Fixer · ● 60.4M · ◷

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-text-json
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

Updates a System.Text.Json polymorphism test to avoid relying on reflection attribute ordering, improving cross-runtime stability (notably for Mono on Apple mobile targets).

Changes:

• Remove the [ActiveIssue] skip from MetadataServices_NullPolymorphismOptions_DoesNotActivateAttributeClassifier.
• Replace order-sensitive Assert.Collection validation of JsonPolymorphismOptions.DerivedTypes with order-insensitive count + membership assertions.

Show a summary per file

File	Description
src/libraries/System.Text.Json/tests/Common/PolymorphicTests.TypeClassifier.cs	Makes derived-type assertions order-insensitive and removes the tvOS Mono skip for the affected test.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1

[github-actions]

Workflow state for the Holistic Review Orchestrator.

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[github-actions]

Holistic Review

Motivation: Justified. The test MetadataServices_NullPolymorphismOptions_DoesNotActivateAttributeClassifier asserted DerivedTypes in the exact order the [JsonDerivedType] attributes are declared, but reflection attribute enumeration order is not guaranteed by ECMA and differs on tvOS Mono, producing a spurious failure (issue #128765). Making the assertion order-independent addresses the real root cause rather than only suppressing the failure via [ActiveIssue].

Approach: Sound and minimal. Replacing the order-sensitive Assert.Collection with a count check plus two Assert.Contains predicates preserves the test's intent (both derived types with correct discriminators are present) while removing the incorrect ordering dependency. Removing the [ActiveIssue] annotation is appropriate since the fix is a genuine correction, and the change is confined to a single test file. DerivedTypes ordering is not semantically significant for serialization correctness — discriminator resolution is keyed by type and discriminator name, not list position — so relaxing the ordering assertion does not weaken meaningful coverage.

Summary: ✅ LGTM. Test-only change that correctly removes an unwarranted reflection-ordering assumption; low risk with no product-code impact. Two non-blocking notes for the human merger: (1) issue #128765 can be closed once this merges, since the [ActiveIssue] suppression is being removed; (2) as the PR description itself notes, it is worth a quick check for other order-sensitive Assert.Collection/Assert.Equal assertions over reflection-derived collections in the polymorphic test suite that could exhibit the same Mono ordering fragility. The author flagged that the change was not build-validated (environment lacked the required SDK); the edit is straightforward and syntactically correct, but CI should confirm the build and the tvOS Mono run.

Note

This review was generated by this repository's Holistic Review agentic workflow to complement the built-in Copilot review.

Generated by Holistic Review · 49.3 AIC · ⌖ 10.3 AIC · ⊞ 10K

[kotlarmilos]

Mono mobile doesn't run on CI anymore