From bfba4b1a707dd82e44d74cd70b589b3e8e69fcfb Mon Sep 17 00:00:00 2001
From: Viktor Hofer <viktor.hofer@microsoft.com>
Date: Mon, 2 Feb 2026 14:21:11 +0100
Subject: [PATCH] Respect NetCoreSdkRoot property in TaskHostParameters

The property got added with https://github.com/dotnet/sdk/commit/e0c4dda2e07d99203f83254b7ff5d117fb8e2220

The RuntimeIdentifierGraphPath property is incorrect to use as customers set that to a custom .json file in certain scenarios (i.e. new RID).
---
 .../TaskFactories/AssemblyTaskFactory.cs      | 20 ++++++++++++++-----
 src/Build/Resources/Constants.cs              |  5 +++++
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs b/src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs
index 5c4478317d0..fd5f910b0b8 100644
--- a/src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs
+++ b/src/Build/Instance/TaskFactories/AssemblyTaskFactory.cs
@@ -656,20 +656,30 @@ private static TaskHostParameters AddNetHostParamsIfNeeded(
             }
 
             string dotnetHostPath = getProperty(Constants.DotnetHostPathEnvVarName)?.EvaluatedValue;
-            string ridGraphPath = getProperty(Constants.RuntimeIdentifierGraphPath)?.EvaluatedValue;
+            string netCoreSdkRoot = getProperty(Constants.NetCoreSdkRoot)?.EvaluatedValue?.TrimEnd('/', '\\');
 
-            if (string.IsNullOrEmpty(dotnetHostPath) || string.IsNullOrEmpty(ridGraphPath))
+            // The NetCoreSdkRoot property got added with .NET 11, so for earlier SDKs we fall back to the RID graph path
+            if (string.IsNullOrEmpty(netCoreSdkRoot))
             {
-                return currentParams;
+                string ridGraphPath = getProperty(Constants.RuntimeIdentifierGraphPath)?.EvaluatedValue;
+                if (!string.IsNullOrEmpty(ridGraphPath))
+                {
+                    netCoreSdkRoot = Path.GetDirectoryName(ridGraphPath);
+                }
             }
 
-            string msBuildAssemblyPath = Path.GetDirectoryName(ridGraphPath) ?? string.Empty;
+            // Both DOTNET_HOST_PATH and NetCoreSdkRoot are required to launch .NET task host.
+            // If both are not present, return the original parameters.
+            if (string.IsNullOrEmpty(dotnetHostPath) || string.IsNullOrEmpty(netCoreSdkRoot))
+            {
+                return currentParams;
+            }
 
             return new TaskHostParameters(
                 runtime: currentParams.Runtime,
                 architecture: currentParams.Architecture,
                 dotnetHostPath: dotnetHostPath,
-                msBuildAssemblyPath: msBuildAssemblyPath);
+                msBuildAssemblyPath: netCoreSdkRoot);
         }
 
         /// <summary>
diff --git a/src/Build/Resources/Constants.cs b/src/Build/Resources/Constants.cs
index 7d439a637c1..c1ac7f1fd1f 100644
--- a/src/Build/Resources/Constants.cs
+++ b/src/Build/Resources/Constants.cs
@@ -120,6 +120,11 @@ internal static class Constants
         /// </summary>
         internal const string RuntimeIdentifierGraphPath = nameof(RuntimeIdentifierGraphPath);
 
+        /// <summary>
+        /// The project property name used to get the root of the .NET Core SDK.
+        /// </summary>
+        internal const string NetCoreSdkRoot = nameof(NetCoreSdkRoot);
+
         /// <summary>
         /// Defines the name of dotnet process based on the operating system.
         /// </summary>