[AzureMonitor] fix AOT warnings (part 6) (Azure#49756)

* add additional test coverage for Options before refactoring for AOT support

* suppress warnings for IL2026 and IL3050

* cleanup

* readme

* pr feedback

Author: Timothy Mothra

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/README.md

@@ -259,3 +259,27 @@ For more information on Azure SDK, please refer to [this website](https://azure.
 ## Contributing
 
 See [CONTRIBUTING.md](https://github.com/Azure/azure-sdk-for-net/blob/main/CONTRIBUTING.md) for details on contribution process.
+
+## AOT (Ahead-of-Time) Support
+
+This library supports usage in .NET applications compiled with [AOT (Ahead-of-Time) compilation](https://learn.microsoft.com/dotnet/core/deploying/native-aot/).
+All core features of the Azure Monitor Exporter are compatible with AOT, including telemetry export for traces, metrics, and logs.
+
+**Important:**  
+While AOT is supported, automatic configuration binding from `appsettings.json` or other `IConfiguration` sources is **not** supported in AOT-compiled applications.
+This is due to .NET limitations on reflection-based binding APIs (such as `ConfigurationBinder.Bind` and `Get<T>()`) in AOT scenarios.  
+  
+**Workaround:**  
+In AOT scenarios, you can configure the Azure Monitor Exporter using one of the following approaches:
+
+- **Environment Variable:** Set the `APPLICATIONINSIGHTS_CONNECTION_STRING` environment variable to configure the connection string.
+
+- **Programmatic Configuration:** Set the `AzureMonitorExporterOptions` directly in your application code:
+    ```csharp
+    builder.Services.AddOpenTelemetry()
+        .UseAzureMonitorExporter(options =>
+        {
+            options.ConnectionString = "<your-connection-string>";
+            // Set other options as needed
+        });
+    ```

sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/DefaultAzureMonitorExporterOptions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Azure.Monitor.OpenTelemetry.Exporter.Internals.Diagnostics;
 using Azure.Monitor.OpenTelemetry.Exporter.Internals.Platform;
 using Microsoft.Extensions.Configuration;
@@ -29,7 +30,7 @@ public void Configure(AzureMonitorExporterOptions options)
             {
                 if (_configuration != null)
                 {
-                    _configuration.GetSection(AzureMonitorExporterSectionFromConfig).Bind(options);
+                    BindIConfigurationOptions(_configuration, options);
 
                     // IConfiguration can read from EnvironmentVariables or InMemoryCollection if configured to do so.
                     var connectionStringFromIConfig = _configuration[EnvironmentVariableConstants.APPLICATIONINSIGHTS_CONNECTION_STRING];
@@ -51,5 +52,12 @@ public void Configure(AzureMonitorExporterOptions options)
                 AzureMonitorExporterEventSource.Log.ConfigureFailed(ex);
             }
         }
+
+        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Binding options is a known source of trim warnings; this is a deliberate usage.")]
+        [UnconditionalSuppressMessage("AOT", "IL3050", Justification = "Binding options is a known source of AOT warnings; this is a deliberate usage.")]
+        private static void BindIConfigurationOptions(IConfiguration configuration, AzureMonitorExporterOptions options)
+        {
+            configuration.GetSection(AzureMonitorExporterSectionFromConfig).Bind(options);
+        }
     }
 }