[fix] Document IVT matrix sync requirement and external consumers in Friends.cs #16527

🤖 This is an automated fix generated in response to issue #16524 (Repository Quality Improvement: InternalsVisibleTo Duplication & Maintenance Fragility), addressing Tasks 1, 3, and 4 from the report.

Root cause

InternalsVisibleTo (IVT) grants for the ~18 testhost.* TFM/architecture variants are hand-duplicated verbatim between src/Microsoft.TestPlatform.CoreUtilities/Friends.cs and src/Microsoft.TestPlatform.CrossPlatEngine/Friends.cs, with no comment cross-referencing the two files or the TestHostAllTargetFrameworks property in Directory.Build.props that drives the TFM list. A future TFM change (as happened when net481 was added) requires synchronized manual edits with no build-time check, and a missed entry fails silently with an unhelpful CS0122 far from the root cause.

Separately, src/Microsoft.TestPlatform.ObjectModel/Friends.cs and src/vstest.console/Friends.cs grant IVT access to assemblies that live outside this repository (in-the-box Visual Studio components: Microsoft.VisualStudio.TestPlatform.Extensions.VSTestIntegration, MSAppContainerAdapter, MSPhoneAdapter, Microsoft.VisualStudio.TestWindow.Host). Nothing marks them as external/intentional, so a future dead-code cleanup pass could mistakenly flag and remove them.

Fix

Comment-only changes, no behavior change:

• Task 1 — Added a header comment above the testhost.* TFM/arch matrix in both CoreUtilities/Friends.cs and CrossPlatEngine/Friends.cs, cross-referencing the sibling file and noting it must stay in sync with TestHostAllTargetFrameworks in Directory.Build.props (currently net462;net8.0;net47;net471;net472;net48;net481, times x86/arm64/neutral).
• Task 4 — Added an inline comment explaining the intentionally asymmetric testhost.UnitTests grant in CoreUtilities/Friends.cs (not present in CrossPlatEngine/Friends.cs): only CoreUtilities' internals are unit-tested directly from testhost.UnitTests; CrossPlatEngine internals are exercised via CrossPlatEngine.UnitTests instead.
• Task 3 — Annotated the out-of-repo Visual Studio IVT consumers in ObjectModel/Friends.cs and vstest.console/Friends.cs with a one-line comment so they aren't mistaken for dead code by a future cleanup effort (automated or manual).

Task 2 (a unit test asserting IVT/TFM matrix consistency) and Task 5 (exploring a generator/MSBuild-item-based consolidation) are larger, riskier changes left as follow-up per the report's own priority/effort guidance (both rated Medium/Large effort vs. the Small-effort documentation tasks done here).

Test

This is a documentation/comment-only change with no compilable-behavior difference, so no new automated test is applicable — the same reasoning the report itself uses when scoping Task 1/3/4 as documentation-only. Verified via dotnet build -c Release (no warnings/errors introduced) for all four modified projects:

• Microsoft.TestPlatform.CoreUtilities
• Microsoft.TestPlatform.CrossPlatEngine
• Microsoft.TestPlatform.ObjectModel
• vstest.console

The changes have been pushed to branch fix/issue-16524-f4c357a2cbe01440 and are ready to review.

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From bf3a8cbb92e4c16d57ed4fbe58171894b84f1119 Mon Sep 17 00:00:00 2001
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From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Mon, 28 Sep 2026 12:57:10 +0000
Subject: [PATCH] Document IVT matrix sync requirement and external consumers
 in Friends.cs
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Addresses Tasks 1, 3, and 4 from issue #16524 (InternalsVisibleTo
duplication & maintenance fragility quality-improvement report).

- CoreUtilities/Friends.cs and CrossPlatEngine/Friends.cs now carry a
  header comment above the testhost.* TFM/arch matrix cross-referencing
  the sibling file and TestHostAllTargetFrameworks in
  Directory.Build.props, so a future TFM change is a documented,
  discoverable two-file edit.
- The asymmetric testhost.UnitTests grant in CoreUtilities/Friends.cs
  (absent from CrossPlatEngine/Friends.cs) is now explained inline.
- ObjectModel/Friends.cs and vstest.console/Friends.cs annotate the
  IVT entries that reference out-of-repo Visual Studio consumers
  (VSTestIntegration, MSAppContainerAdapter, MSPhoneAdapter,
  TestWindow.Host) so future cleanup passes don't mistake them for
  dead code.

No behavior change; comment-only edits verified with Release builds of
CoreUtilities, CrossPlatEngine, ObjectModel, and vstest.console.

🤖 Automated fix for #16524.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/Microsoft.TestPlatform.CoreUtilities/Friends.cs   | 8 ++++++++
 src/Microsoft.TestPlatform.CrossPlatEngine/Friends.cs | 5 +++++
 src/Microsoft.TestPlatform.ObjectModel/Friends.cs     | 6 ++++++
 src/vstest.console/Friends.cs                         | 2 ++
 4 files changed, 21 insertions(+)

diff --git a/src/Microsoft.TestPlatform.CoreUtilities/Friends.cs b/src/Microsoft.TestPlatform.CoreUtilities/Friends.cs
index 542dbfe..f4bb431 100644
--- a/src/Microsoft.TestPlatform.CoreUtilities/Fr
... (truncated)

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🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍