Switch from AssemblyLoadContext.InitializeDefaultContext to AssemblyLoadContext.Resolving event

AssemblyLoadContext.InitializeDefaultContext was removed for .NET Core 1.0 RTM. Replaced its use
with AssemblyLoadContext.Resolving event.

src/Microsoft.PowerShell.CoreCLR.AssemblyLoadContext/CoreCLR/CorePsAssemblyLoadContext.cs

@@ -15,9 +15,9 @@ using System.Runtime.Loader;
 namespace System.Management.Automation
 {
     /// <summary>
-    /// The powershell custom AssemblyLoadContext implementation
+    /// The powershell custom assembly loader implementation
     /// </summary>
-    internal partial class PowerShellAssemblyLoadContext : AssemblyLoadContext
+    internal partial class PowerShellAssemblyLoadContext
     {
         #region Resource_Strings
 
@@ -37,13 +37,6 @@ namespace System.Management.Automation
 
         #region Constructor
 
-        /// <summary>
-        /// This constructor is for testability purpose only
-        /// </summary>
-        protected PowerShellAssemblyLoadContext()
-        {
-        }
-
         /// <summary>
         /// Constructor
         /// </summary>
@@ -77,12 +70,18 @@ namespace System.Management.Automation
             //  - Key: namespace qualified type name (FullName)
             //  - Value: strong name of the TPA that contains the type represented by Key.
             coreClrTypeCatalog = InitializeTypeCatalog();
+
+            this.loadContext = AssemblyLoadContext.Default;
+            loadContext.Resolving += Resolve;
         }
 
         #endregion Constructor
 
         #region Fields
 
+        // AssemblyLoadContext used by this loader
+        private readonly AssemblyLoadContext loadContext;
+
         // Serialized type catalog file
         private readonly object syncObj = new object();
         private readonly string[] basePaths;
@@ -118,10 +117,15 @@ namespace System.Management.Automation
         #region Protected_Internal_Methods
 
         /// <summary>
-        /// Implement the AssemblyLoadContext.Load(AssemblyName). Search the requested assembly in probing paths.
+        /// The global instance of PowerShellAssemblyLoadContext
+        /// </summary>
+        internal static PowerShellAssemblyLoadContext Instance { get; set; }
+
+        /// <summary>
+        /// Implement the AssemblyLoadContext.Resolving event handler. Search the requested assembly in probing paths.
         /// Search the file "[assemblyName.Name][.ni].dll" in probing paths. If the file is found and it matches the requested AssemblyName, load it with LoadFromAssemblyPath.
         /// </summary>
-        protected override Assembly Load(AssemblyName assemblyName)
+        internal Assembly Resolve(AssemblyLoadContext sender, AssemblyName assemblyName)
         {
             // Probe the assembly cache
             Assembly asmLoaded;
@@ -153,7 +157,7 @@ namespace System.Management.Automation
                         if (File.Exists(asmFilePath))
                         {
                             isAssemblyFileFound = true;
-                            AssemblyName asmNameFound = GetAssemblyName(asmFilePath);
+                            AssemblyName asmNameFound = AssemblyLoadContext.GetAssemblyName(asmFilePath);
                             if (IsAssemblyMatching(assemblyName, asmNameFound))
                             {
                                 isAssemblyFileMatching = true;
@@ -187,8 +191,8 @@ namespace System.Management.Automation
                 try
                 {
                     asmLoaded = asmFilePath.EndsWith(".ni.dll", StringComparison.OrdinalIgnoreCase)
-                        ? LoadFromNativeImagePath(asmFilePath, null)
+                        ? loadContext.LoadFromNativeImagePath(asmFilePath, null)
-                        : LoadFromAssemblyPath(asmFilePath);
+                        : loadContext.LoadFromAssemblyPath(asmFilePath);
                 }
                 // Since .NET CLI built versions of PowerShell have all the
                 // built-in assemblies in the TPA list, the above will throw,
@@ -211,6 +215,14 @@ namespace System.Management.Automation
             return asmLoaded;
         }
 
+        /// <summary>
+        /// Load an assembly from its name.
+        /// </summary>
+        internal Assembly LoadFromAssemblyName(AssemblyName assemblyName)
+        {
+            return loadContext.LoadFromAssemblyName(assemblyName);
+        }
+
         /// <summary>
         /// Load an assembly from its file path.
         /// </summary>
@@ -239,7 +251,7 @@ namespace System.Management.Automation
             #endregion Validation
 
             Assembly asmLoaded;
-            AssemblyName assemblyName = GetAssemblyName(assemblyPath);
+            AssemblyName assemblyName = AssemblyLoadContext.GetAssemblyName(assemblyPath);
 
             // Probe the assembly cache
             if (TryGetAssemblyFromCache(assemblyName, out asmLoaded))
@@ -256,8 +268,8 @@ namespace System.Management.Automation
                 {
                     // Load the assembly through 'LoadFromNativeImagePath' or 'LoadFromAssemblyPath'
                     asmLoaded = assemblyPath.EndsWith(".ni.dll", StringComparison.OrdinalIgnoreCase)
-                        ? LoadFromNativeImagePath(assemblyPath, null)
+                        ? loadContext.LoadFromNativeImagePath(assemblyPath, null)
-                        : LoadFromAssemblyPath(assemblyPath);
+                        : loadContext.LoadFromAssemblyPath(assemblyPath);
                 }
                 // Since .NET CLI built versions of PowerShell have all the
                 // built-in assemblies in the TPA list, the above will throw,
@@ -290,7 +302,7 @@ namespace System.Management.Automation
         /// </summary>
         internal Assembly LoadFrom(Stream assembly)
         {
-            var asm = LoadFromStream(assembly);
+            var asm = loadContext.LoadFromStream(assembly);
             TryAddAssemblyToCache(asm);
             return asm;
         }
@@ -503,8 +515,6 @@ namespace System.Management.Automation
     /// </summary>
     public class PowerShellAssemblyLoadContextInitializer
     {
-        private static bool IsInitialized = false;
-
         // Porting note: it's much easier to send an LPStr on Linux
         private const UnmanagedType stringType = 
             #if LINUX
@@ -519,19 +529,9 @@ namespace System.Management.Automation
         /// </summary>
         public static void SetPowerShellAssemblyLoadContext([MarshalAs(stringType)]string basePaths)
         {
-            if (!IsInitialized)
+            if (PowerShellAssemblyLoadContext.Instance == null)
             {
-                var psAsmLoadContext = new PowerShellAssemblyLoadContext(basePaths);
+                PowerShellAssemblyLoadContext.Instance = new PowerShellAssemblyLoadContext(basePaths);
-                try
-                {
-                    AssemblyLoadContext.InitializeDefaultContext(psAsmLoadContext);
-                }
-                catch (System.InvalidOperationException)
-                {
-                    // We may not be able to set the default context. If we're under the
-                    // xUnit test harness, it has already been set.
-                }
-                IsInitialized = true;
             }
         }
     }

src/System.Management.Automation/utils/ClrFacade.cs

@@ -391,13 +391,7 @@ namespace System.Management.Automation
         {
             if (_psLoadContext == null)
             {
-                _psLoadContext = AssemblyLoadContext.Default as PowerShellAssemblyLoadContext;
+                _psLoadContext = PowerShellAssemblyLoadContext.Instance;
-                if (_psLoadContext == null)
-                {
-                    // The default load context may not be ours. This can happen during,
-                    // for instance, xUnit testing.
-                    _psLoadContext = new PowerShellAssemblyLoadContext(String.Empty);
-                }
             }
             return _psLoadContext;
         }