Fix forward-compat crash loading old 2.x extensions on .NET Framework (#9710) by Evangelink · Pull Request #9739 · microsoft/testfx

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

_{This advisory comment was generated automatically. Grades are heuristic

and informational — they do not block merging. Re-run with
/grade-tests.}

🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 46.3 AIC · ⌖ 6.97 AIC · ⊞ 9.5K · [◷]( · ◷)

Copilot

Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Amaury Levé (Evangelink) · 2026-07-08T14:36:25Z

Summary

Fixes#9710. A newer Microsoft.Testing.Platform combined with an older (2.x) extension crashes with MissingMethodException on .NET Framework:

Method not found: 'Void Polyfills.Polyfill.Deconstruct(...)'.
at Microsoft.Testing.Extensions.Telemetry.AppInsightsProvider.<IngestLoopAsync>d__18.MoveNext()

Root cause

Old 2.x extension assemblies (Telemetry, TrxReport, TrxReport.Abstractions, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helper, which they access from the platform assembly via [InternalsVisibleTo] (they don't embed their own copy). Their baked-in member references are resolved by the runtime against the platform assembly. Newer platform code stopped using those helpers, so they were dropped — and loading an old extension's netstandard2.0 / .NET Framework asset now throws. The .NET assets bind these to the BCL and are unaffected, which is why the original report crashed on net472 while net8.0 passed.

Fix

src/Polyfills/PolyfillBackwardCompatibility.cs — restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync), guarded #if !NETCOREAPP so they land only in the netstandard2.0 platform asset (the one loaded on .NET Framework). The type is already internal with IVT to these extensions; [Embedded] only hides it from new compile-time references — the CLR still resolves old baked MemberRefs at runtime. A prominent comment warns against re-deleting them as "unused polyfills."

Test

TelemetryForwardCompatibilityTests — reproduces the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled (which is what forces AppInsightsProvider.IngestLoopAsync — the crashing method — to actually run). The existing ForwardCompatibilityTests missed this because it pinned 2.2.1 (no longer references the platform Polyfill) and ran telemetry opted out.

Verification (`build.cmd -pack` + acceptance run)

Without the shim: test fails — exit code -532462766 (0xE0434352, CLR unhandled exception) crashing in AppInsightsProvider. Faithfully reproduces System.MissingMethodException after upgrade to 2.3.0 #9710.
With the shim: test passes.

Notes for reviewers

The exact old-extension Polyfill surface was confirmed by decompiling the shipped 2.0.0netstandard2.0 nupkgs, so the shim covers every extension that referenced it (not just Telemetry). Happy to trim it to telemetry-only (Deconstruct) if preferred, but restoring the full set makes any old 2.x extension load correctly on .NET Framework.

…#9710) A newer Microsoft.Testing.Platform combined with an older (2.x) extension whose netstandard2.0 asset was compiled against the platform's internal Polyfills.Polyfill helper (shared via InternalsVisibleTo) threw MissingMethodException in AppInsightsProvider.IngestLoopAsync on .NET Framework, crashing the process. - Restore the exact Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains x2, AppendJoin x2, CopyToAsync, SaveAsync), guarded to the non-.NET-Core TFMs so they land only in the netstandard2.0 platform asset that is loaded on .NET Framework. The type is already internal with IVT to the extensions; [Embedded] only hides it from new compile-time references, so the CLR still resolves old baked MemberRefs at runtime. - Add TelemetryForwardCompatibilityTests reproducing the crash: current platform + oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled. Verified red without the shim (exit code -532462766) and green with it. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-07-08T14:42:16Z

🧪 Test quality grade — PR #9739

Grade	Test	Notes
A (90–100)	new `TelemetryForwardCompatibilityTests. NewerPlatform_ WithOldestSupportedTelemetryExtension_ TelemetryEnabled_ OnNetFramework_ ShouldNotCrash`	Clear AAA structure; three complementary assertions cover exit code, summary, and regression-specific failure mode.

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Pull request overview

Fixes #9710, where a newer Microsoft.Testing.Platform crashes with MissingMethodException on .NET Framework when loading an older (2.x) extension. Old 2.x extension assemblies (Telemetry, TrxReport, VSTestBridge) were compiled against the platform's internal Polyfills.Polyfill helpers and resolve those MemberRefs from the platform assembly at runtime via [InternalsVisibleTo]. Newer platform code stopped using those helpers, so they were dropped — breaking the netstandard2.0 load path. The fix restores the exact member set, guarded to the non-netcore asset, and adds a regression test.

Changes:

Restore the Polyfills.Polyfill members old 2.x extensions reference (Deconstruct, Contains×2, AppendJoin×2, CopyToAsync, SaveAsync) in a new #if !NETCOREAPP file, with a prominent comment warning against re-deleting them as "unused."
Add TelemetryForwardCompatibilityTests reproducing the crash with the oldest supported 2.x telemetry extension (2.0.0) on net462 with telemetry enabled.

Show a summary per file

File	Description
`src/Polyfills/PolyfillBackwardCompatibility.cs`	New netstandard2.0/.NET Framework-only file restoring the internal `Polyfill` members old 2.x extensions bind to at runtime, preventing `MissingMethodException`.
`test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/TelemetryForwardCompatibilityTests.cs`	New acceptance test reproducing #9710 (newest platform + oldest 2.x telemetry extension on `net462`, telemetry enabled) and guarding against regression.

Review details

Files reviewed: 2/2 changed files
Comments generated: 0
Review effort level: Medium

github-actions

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✅ 15/15 dimensions clean — no findings.

Dimension	Severity	Verdict
Algorithmic Correctness	MAJOR	LGTM
Threading & Concurrency	BLOCKING	LGTM
Public API & Binary Compatibility	BLOCKING	LGTM
Cross-TFM Compatibility	MAJOR	LGTM
Defensive Coding	MAJOR	LGTM
Flakiness Patterns	BLOCKING	LGTM
Test Isolation	MAJOR	LGTM
Assertion Quality	MAJOR	LGTM
Test Completeness & Coverage	MAJOR	LGTM
Code Structure & Simplification	MODERATE	LGTM
Naming & Conventions	NIT	LGTM
Documentation Accuracy	NIT	LGTM
Performance & Allocations	MAJOR	LGTM
Resource & IDisposable Management	MAJOR	LGTM
Scope & PR Discipline	MODERATE	LGTM

Summary: Clean, well-scoped fix. The polyfill implementations are correct and binary-compatible with old 2.x extension MemberRef tokens. The #if !NETCOREAPP guard correctly targets the netstandard2.0 build (which is what .NET Framework loads). The acceptance test faithfully reproduces the crash conditions (net462 + telemetry enabled + oldest 2.x extension) and the IMPORTANT comment provides strong protection against future accidental removal.

Amaury Levé (Evangelink) · 2026-07-08T14:51:52Z

/backport to rel/4.3

github-actions · 2026-07-08T14:52:10Z

Started backporting to rel/4.3: https://github.com/microsoft/testfx/actions/runs/28952108089

New 2.3.1 UNRELEASED servicing section for the .NET Framework MissingMethodException regression (#9710) fixed by #9739, being backported to rel/4.3 via #9740. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

@Evangelink

…#9710) by @Evangelink in #9739 (backport to rel/4.3) (#9740) Co-authored-by: Amaury Levé <amauryleve@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

CopilotAI review requested due to automatic review settings July 8, 2026 14:36

Copilotstarted reviewing on behalf of Amaury Levé (Evangelink)July 8, 2026 14:36 View session

CopilotAI reviewed Jul 8, 2026
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nohwnd-bot mentioned this pull request Jul 8, 2026
Fix forward-compat crash loading old 2.x extensions on .NET Framework (#9710) by @Evangelink in #9739 (backport to rel/4.3) #9740
Merged

CopilotAI mentioned this pull request Jul 8, 2026
Update changelogs for MTP 2.3 / MSTest 4.3 release #9742
Merged

Amaury Levé (Evangelink) enabled auto-merge (squash) July 8, 2026 15:27

Amaury Levé (Evangelink) added the state/needs-review Awaiting review from the team. label Jul 8, 2026

Petr Pokorny (0101) approved these changes Jul 8, 2026
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Amaury Levé (Evangelink) mentioned this pull request Jul 8, 2026
Restore Polyfills.Polyfill.Deconstruct for binary compatibility (#9710) #9738
Closed

Amaury Levé (Evangelink) disabled auto-merge July 8, 2026 16:45

Amaury Levé (Evangelink) merged commit dff367b into mainJul 8, 2026
37 of 41 checks passed

Amaury Levé (Evangelink) deleted the dev/amauryleve/improve-backcompat-acceptance-test branch July 8, 2026 16:45