Fix forward-compat crash loading old 2.x extensions on .NET Framework (#9710) by @Evangelink in #9739 (backport to rel/4.3)#9740
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…microsoft#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>
Evangelink
approved these changes
Jul 8, 2026
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Backport of #9739 to rel/4.3
/cc @Evangelink