[SVLS-9784] Forward loaded dotnet runtime version to Compat metadata

Datadog.Serverless.Compat.Tests/CompatibilityLayerTests.cs

@@ -79,6 +79,46 @@ public void GetPackageVersion_ShouldReturnVersion_WhenAssemblyAttributeExists()
         Assert.NotEqual("unknown", result);
     }
 
+    [Theory]
+    [InlineData("dotnet", "dotnet")]
+    [InlineData("dotnet-isolated", "dotnet-isolated")]
+    [InlineData(null, null)]
+    [InlineData("unexpected", null)]
+    public void GetRuntimeName_UsesExplicitWorkerOrReturnsNull(string? workerRuntime, string? expected)
+    {
+        var envVars = new MockEnvironmentVariableProvider();
+        envVars.Set("FUNCTIONS_WORKER_RUNTIME", workerRuntime);
+
+        Assert.Equal(expected, CompatibilityLayer.GetRuntimeName(envVars));
+    }
+
+    [Theory]
+    [InlineData("dotnet-isolated", "8.0.12", "dotnet-isolated8.0.12")]
+    [InlineData("dotnet", "8.0.12", "dotnet8.0.12")]
+    [InlineData(null, "8.0.12", null)]
+    [InlineData("dotnet", null, null)]
+    public void ConfigureVersionMetadata_ReportsExplicitVersionsOrRemovesStaleHint(
+        string? runtimeName, string? runtimeVersion, string? expected)
+    {
+        var startInfo = new System.Diagnostics.ProcessStartInfo("/custom/compat");
+        startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_VERSION"] = "stale";
+        startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_RUNTIME"] = "stale";
+        startInfo.EnvironmentVariables["FUNCTIONS_WORKER_RUNTIME_VERSION"] = "stale";
+        startInfo.EnvironmentVariables["FUNCTIONS_WORKER_RUNTIME"] = "platform-owned";
+        CompatibilityLayer.ConfigureVersionMetadata(startInfo, "1.12.0", runtimeName, runtimeVersion);
+        Assert.Equal("1.12.0", startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_VERSION"]);
+        if (expected is null)
+        {
+            Assert.False(startInfo.EnvironmentVariables.ContainsKey("DD_SERVERLESS_COMPAT_RUNTIME"));
+        }
+        else
+        {
+            Assert.Equal(expected, startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_RUNTIME"]);
+        }
+        Assert.Equal("stale", startInfo.EnvironmentVariables["FUNCTIONS_WORKER_RUNTIME_VERSION"]);
+        Assert.Equal("platform-owned", startInfo.EnvironmentVariables["FUNCTIONS_WORKER_RUNTIME"]);
+    }
+
     [Theory]
     [InlineData("FlexConsumption", null, true)]
     [InlineData("FlexConsumption", "test-rg", false)]

Datadog.Serverless/CompatibilityLayer.cs

@@ -71,7 +71,7 @@
         if (!string.IsNullOrEmpty(executablePath))
         {
             Logger.LogDebug($"Detected user-configured executable path DD_SERVERLESS_COMPAT_PATH={executablePath}");
             return executablePath;
         }
 
         return environment switch
@@ -361,7 +361,7 @@
                 CreateNoWindow = true,
             };
 
-            startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_VERSION"] = packageVersion;
+            ConfigureVersionMetadata(startInfo, packageVersion, GetRuntimeName(envVars), GetRuntimeProductVersion());
 
             // Configure named pipes with unique names to avoid conflicts in multi-function scenarios
             ConfigureNamedPipes(startInfo, os);
@@ -374,4 +374,31 @@
             Logger.LogError(ex, $"Exception when starting {executablePath}");
         }
     }
+
+    internal static string? GetRuntimeName(IEnvironmentVariableProvider envVars) =>
+        envVars.GetEnvironmentVariable("FUNCTIONS_WORKER_RUNTIME") switch
+        {
+            "dotnet" => "dotnet",
+            "dotnet-isolated" => "dotnet-isolated",
+            _ => null
+        };
+
+    internal static string? GetRuntimeProductVersion() =>
+        Environment.Version.Major >= 5 ? Environment.Version.ToString() : null;
+
+    internal static void ConfigureVersionMetadata(
+        ProcessStartInfo startInfo,
+        string packageVersion,
+        string? runtimeName,
+        string? runtimeVersion)
+    {
+        startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_VERSION"] = packageVersion;
+        if (string.IsNullOrWhiteSpace(runtimeName) || string.IsNullOrWhiteSpace(runtimeVersion))
+        {
+            startInfo.EnvironmentVariables.Remove("DD_SERVERLESS_COMPAT_RUNTIME");
+            return;
+        }
+
+        startInfo.EnvironmentVariables["DD_SERVERLESS_COMPAT_RUNTIME"] = runtimeName + runtimeVersion;
+    }
 }