Remove DiagnosticSource.Write trim warnings in SqlDiagnosticListener

[charlesroddie]

Description

Removes the 15 IL2026 warnings in SqlDiagnosticListener, one per DiagnosticSource.Write<T> call.

The [RequiresUnreferencedCode] attribute on Write<T> is in fact untrue! Write<T> does no reflection intrinsically: it passes the payload to subscribers as object. The reason it's there is that subscribers could reflect over the payload. However that is their responsibility, and they will receive their own trim warnings when they do.

So this attribute was always misguided, and so suppressing it is common, e.g. in DiagnosticsHandler in dotnet/runtime and HostingApplicationDiagnostics in ASP.NET Core. Following those examples, all events now go through one private WriteEvent<T> helper with an UnconditionalSuppressMessage on IL2026.

This helper's T has the same PublicProperties annotation as Write<T>. This is pragmatic. This keeps existing consumers working, so this PR doesn't change behaviour under trimming and only corrects trim warnings. Some of these consumers, including the current OpenTelemetry SqlClient implementation, not only require these properties but suppress their own warnings, so removing this annotation would not only stop code from working under NativeAOT, but do so silently.

The claims above were checked in a NativeAOT test app: see details below.

Trim/AOT warnings with -p:IsAotCompatible=true (unique by location and code):

TFM	Before	After
net8.0	50	35
net9.0	52	37

No public API changes. Independent of #4683 and #4684.

Issues

Part of #1947.

Testing

• Built net462, net8.0 and net9.0 with -p:IsAotCompatible=true; no warnings remain in SqlDiagnosticListener.cs.
• DiagnosticTest (21 tests covering connection open and command execution events, sync, async and error paths) passes on net8.0.
• Transaction commit/rollback events have no automated tests; they use the same helper.

NativeAOT verification of Description claims

A console app (net10.0, PublishAot, win-x64) subscribed to SqlClientDiagnosticListener with a reflecting observer (GetType().GetProperty, once unsuppressed and once with UnconditionalSuppressMessage) and with OpenTelemetry.Instrumentation.SqlClient 1.18.0 plus an in-memory exporter, then ran SELECT 1 and SELECT 1/0 against LocalDB. It was published against main, this PR, and this PR with the PublicProperties annotation removed.

	main	This PR	Annotation removed
SqlDiagnosticListener trim warnings	9	0	0
Payload Command/Connection readable by reflection	Yes	Yes	No
OpenTelemetry spans	2	2	0
OpenTelemetry trim warnings	0	0	0

• The app's unsuppressed reflection produced IL2075 in all three builds; its suppressed reflection produced none.
• main shows 9 warnings rather than 15 because the app doesn't use transactions.
• In all NativeAOT builds the error span lacks db.response.status_code (present under JIT), because SqlException.Number isn't reflectable. This PR doesn't change that.

🤖 Generated with Claude Code

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[Copilot]

🟡 Changes recommended

The trimming guarantees need a publish-trimmed test covering the preserved nested members.

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Pull request overview

Centralizes diagnostic event writes to suppress redundant trim warnings while preserving reflected payload members.

Changes:

• Routes all 15 diagnostic writes through WriteEvent<T>.
• Adds trimming annotations and nested-member dependencies.

File summaries

File	Description
SqlDiagnosticListener.cs	Adds the annotated diagnostic-write helper.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

🔵 Needs a closer look

A trimmed runtime test is needed to validate that the reflection-dependent members survive linking.

Review details

Suppressed comments (1)

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Diagnostics/SqlDiagnosticListener.cs:490

• The PR's core runtime guarantee is not exercised: an AOT-compatible build only shows that IL2026 is suppressed, while the existing diagnostic tests run untrimmed and cannot prove that these two reflected members survive linking. Please add a trimmed-publish smoke test that subscribes to an error event, reflects SqlException.Number, and resolves/invokes SqlConnection.RetrieveStatistics; otherwise a misplaced or ineffective dependency annotation would pass all current validation but break OpenTelemetry in trimmed applications.

        [DynamicDependency(nameof(SqlException.Number), typeof(SqlException))]
        [DynamicDependency(nameof(SqlConnection.RetrieveStatistics), typeof(SqlConnection))]

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟢 Approval recommended

The focused refactoring preserves existing event behavior while correctly centralizing trim annotations and suppression.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Balanced

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