Add Import() extension method for INamespace

ICSharpCode.NRefactory/TypeSystem/ICompilation.cs

@@ -50,13 +50,18 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		
 		/// <summary>
 		/// Gets the root namespace of this compilation.
-		/// This is a merged .
+		/// This is a merged version of the root namespaces of all assemblies.
 		/// </summary>
 		INamespace RootNamespace { get; }
 		
 		/// <summary>
 		/// Gets the root namespace for a given extern alias.
 		/// </summary>
+		/// <remarks>
+		/// If <paramref name="alias"/> is <c>null</c> or an empty string, this method
+		/// returns the global root namespace.
+		/// If alias with the specified name exists, this method returns null.
+		/// </remarks>
 		INamespace GetNamespaceForExternAlias(string alias);
 		
 		IType FindType(KnownTypeCode typeCode);

ICSharpCode.NRefactory/TypeSystem/Implementation/SimpleCompilation.cs

@@ -120,6 +120,8 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 		
 		protected virtual INamespace CreateRootNamespace()
 		{
+			// SimpleCompilation does not support extern aliases; but derived classes might.
+			// CreateRootNamespace() is virtual so that derived classes can change the global namespace.
 			INamespace[] namespaces = new INamespace[referencedAssemblies.Count + 1];
 			namespaces[0] = mainAssembly.RootNamespace;
 			for (int i = 0; i < referencedAssemblies.Count; i++) {
@@ -134,6 +136,9 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 		
 		public virtual INamespace GetNamespaceForExternAlias(string alias)
 		{
+			if (string.IsNullOrEmpty(alias))
+				return this.RootNamespace;
+			// SimpleCompilation does not support extern aliases; but derived classes might.
 			return null;
 		}
 		

ICSharpCode.NRefactory/TypeSystem/TypeSystemExtensions.cs

@@ -286,6 +286,30 @@ namespace ICSharpCode.NRefactory.TypeSystem
 		{
 			return (IProperty)compilation.Import((IMember)property);
 		}
+		
+		/// <summary>
+		/// Imports a namespace from another compilation.
+		/// </summary>
+		/// <remarks>
+		/// This method may return null if the namespace does not exist in the target compilation.
+		/// </remarks>
+		public static INamespace Import(this ICompilation compilation, INamespace ns)
+		{
+			if (compilation == null)
+				throw new ArgumentNullException("compilation");
+			if (ns == null)
+				return null;
+			if (ns.ParentNamespace == null) {
+				// root namespace
+				return compilation.GetNamespaceForExternAlias(ns.ExternAlias);
+			} else {
+				INamespace parent = Import(compilation, ns.ParentNamespace);
+				if (parent != null)
+					return parent.GetChildNamespace(ns.Name);
+				else
+					return null;
+			}
+		}
 		#endregion
 		
 		#region GetDelegateInvokeMethod