Use AssemblyName.Clone when possible.

src/Shared/AssemblyNameExtension.cs

@@ -57,7 +57,7 @@ internal enum PartialComparisonFlags : int
     /// between the two is done lazily on demand.
     /// </summary>
     [Serializable]
-    sealed internal class AssemblyNameExtension
+    internal sealed class AssemblyNameExtension
     {
         private AssemblyName asAssemblyName = null;
         private string asString = null;
@@ -592,11 +592,7 @@ internal AssemblyNameExtension Clone()
 
             if (asAssemblyName != null)
             {
-#if FEATURE_ASSEMBLYNAME_CLONE
-                newExtension.asAssemblyName = (AssemblyName)asAssemblyName.Clone();
-#else
-                newExtension.asAssemblyName = new AssemblyName(asAssemblyName.FullName);
-#endif
+                newExtension.asAssemblyName = asAssemblyName.CloneIfPossible();
             }
 
             newExtension.asString = asString;

src/Shared/AssemblyUtilities.cs

@@ -11,22 +11,28 @@ namespace Microsoft.Build.Shared
     /// </summary>
     internal static class AssemblyUtilities
     {
+        // True when the cached method info objects have been set.
+        private static bool s_initialized;
+
+        // Cached method info
+        private static MethodInfo s_assemblyNameCloneMethod;
+        private static PropertyInfo s_assemblylocationProperty;
+
         public static string GetAssemblyLocation(Assembly assembly)
         {
 #if FEATURE_ASSEMBLY_LOCATION
             return assembly.Location;
 #else
             // Assembly.Location is only available in .netstandard1.5, but MSBuild needs to target 1.3.
             // use reflection to access the property
+            Initialize();
 
-            var locationProperty = assembly.GetType().GetProperty("Location", typeof(string));
-
-            if (locationProperty == null)
+            if (s_assemblylocationProperty == null)
             {
                 throw new NotSupportedException("Type Assembly does not have the Location property");
             }
 
-            return (string)locationProperty.GetValue(assembly);
+            return (string)s_assemblylocationProperty.GetValue(assembly);
 #endif
         }
 
@@ -39,5 +45,37 @@ public static Type GetTypeInfo(this Type t)
             return t;
         }
 #endif
+
+        public static AssemblyName CloneIfPossible(this AssemblyName assemblyNameToClone)
+        {
+#if FEATURE_ASSEMBLYNAME_CLONE
+            return (AssemblyName) assemblyNameToClone.Clone();
+#else
+
+            Initialize();
+
+            if (s_assemblyNameCloneMethod == null)
+            {
+                return new AssemblyName(assemblyNameToClone.FullName);
+            }
+
+            // Try to Invoke the Clone method via reflection. If the method exists (it will on .NET
+            // Core 2.0 or later) use that result, otherwise use new AssemblyName(FullName).
+            return (AssemblyName) s_assemblyNameCloneMethod.Invoke(assemblyNameToClone, null) ??
+                   new AssemblyName(assemblyNameToClone.FullName);
+#endif
+        }
+
+        /// <summary>
+        /// Initialize static fields. Doesn't need to be thread safe.
+        /// </summary>
+        private static void Initialize()
+        {
+            if (s_initialized) return;
+
+            s_assemblyNameCloneMethod = typeof(AssemblyName).GetMethod("Clone");
+            s_assemblylocationProperty = typeof(Assembly).GetProperty("Location", typeof(string));
+            s_initialized = true;
+        }
     }
 }

src/Tasks/AppConfig/DependentAssembly.cs

@@ -22,35 +22,23 @@ internal sealed class DependentAssembly
         private BindingRedirect[] _bindingRedirects = null;
 
         /// <summary>
-        /// The partial assemblyname, there should be no version.
+        /// The partial <see cref="AssemblyName"/>, there should be no version.
         /// </summary>
-        private AssemblyName _partialAssemblyName = null;
+        private AssemblyName _partialAssemblyName;
 
         /// <summary>
-        /// The partial assemblyname, there should be no version.
+        /// The partial <see cref="AssemblyName"/>, there should be no version.
         /// </summary>
         internal AssemblyName PartialAssemblyName
         {
             set
             {
-#if FEATURE_ASSEMBLYNAME_CLONE
-                _partialAssemblyName = (AssemblyName)value.Clone();
-#else
-                _partialAssemblyName = new AssemblyName(value.FullName);
-#endif
+                _partialAssemblyName = value.CloneIfPossible();
                 _partialAssemblyName.Version = null;
             }
             get
             {
-                if (_partialAssemblyName == null)
-                {
-                    return null;
-                }
-#if FEATURE_ASSEMBLYNAME_CLONE
-                return (AssemblyName)_partialAssemblyName.Clone();
-#else
-                return new AssemblyName(_partialAssemblyName.FullName);
-#endif
+                return _partialAssemblyName?.CloneIfPossible();
             }
         }
 

src/Tasks/AssemblyDependency/ReferenceTable.cs

@@ -1070,14 +1070,9 @@ IEnumerable<AssemblyNameExtension> preUnificationAssemblyNames
         {
             foreach (AssemblyNameExtension preUnificationAssemblyName in preUnificationAssemblyNames)
             {
-                string name = preUnificationAssemblyName.Name;
                 // First, unify the assembly name so that we're dealing with the right version.
                 // Not AssemblyNameExtension because we're going to write to it.
-#if FEATURE_ASSEMBLYNAME_CLONE
-                AssemblyNameExtension dependentAssembly = new AssemblyNameExtension((AssemblyName)preUnificationAssemblyName.AssemblyName.Clone());
-#else
-                AssemblyNameExtension dependentAssembly = new AssemblyNameExtension(new AssemblyName(preUnificationAssemblyName.AssemblyName.FullName));
-#endif
+                AssemblyNameExtension dependentAssembly = new AssemblyNameExtension(preUnificationAssemblyName.AssemblyName.CloneIfPossible());
 
                 Version unifiedVersion;
                 bool isPrerequisite;
@@ -1883,11 +1878,7 @@ out AssemblyNameReference[] conflictingReferences
                 byte[] pkt = assemblyName.GetPublicKeyToken();
                 if (pkt != null && pkt.Length > 0)
                 {
-#if FEATURE_ASSEMBLYNAME_CLONE
-                    AssemblyName baseKey = (AssemblyName)assemblyName.AssemblyName.Clone();
-#else
-                    AssemblyName baseKey = new AssemblyName(assemblyName.AssemblyName.FullName);
-#endif
+                    AssemblyName baseKey = assemblyName.AssemblyName.CloneIfPossible();
                     Version version = baseKey.Version;
                     baseKey.Version = null;
                     string key = baseKey.ToString();
@@ -2377,11 +2368,7 @@ out string redistName
                 foreach (DependentAssembly remappedAssembly in _remappedAssemblies)
                 {
                     // First, exclude anything without the simple name match
-#if FEATURE_ASSEMBLYNAME_CLONE
-                    AssemblyNameExtension comparisonAssembly = new AssemblyNameExtension((AssemblyName)remappedAssembly.PartialAssemblyName.Clone());
-#else
-                    AssemblyNameExtension comparisonAssembly = new AssemblyNameExtension(new AssemblyName(remappedAssembly.PartialAssemblyName.FullName));
-#endif
+                    AssemblyNameExtension comparisonAssembly = new AssemblyNameExtension(remappedAssembly.PartialAssemblyName.CloneIfPossible());
                     if (assemblyName.CompareBaseNameTo(comparisonAssembly) == 0)
                     {
                         // Comparison assembly is a partial name. Give it our version.