Fix bug #661400 - fix complicated namespace resolution issue.

Namespaces in nested external schemas have to be validated against
immediately-containing schema. If there is a schema A with urn:x
targetNamespace imports a schema B with urn:y targetNamespace which
in turn includes another schema C, then C must be validated its namespace
against B, not A.

mcs/class/System.XML/System.Xml.Schema/XmlSchema.cs

@@ -92,6 +92,7 @@ namespace System.Xml.Schema
 			groups = new XmlSchemaObjectTable();
 			notations = new XmlSchemaObjectTable();
 			schemaTypes = new XmlSchemaObjectTable();
+			compilationItems = new XmlSchemaObjectCollection ();
 		}
 
 		#region Properties
@@ -360,7 +361,6 @@ namespace System.Xml.Schema
 
 			// Compile the content of this schema
 
-			compilationItems = new XmlSchemaObjectCollection ();
 			for (int i = 0; i < Items.Count; i++) {
 				compilationItems.Add (Items [i]);
 			}
@@ -574,7 +574,7 @@ namespace System.Xml.Schema
 			} else if (includedSchema != null) {
 				if (TargetNamespace == null && 
 					includedSchema.TargetNamespace != null) {
-					error (handler, "Target namespace is required to include a schema which has its own target namespace");
+					includedSchema.error (handler, String.Format ("On {0} element, targetNamespace is required to include a schema which has its own target namespace", ext.GetType ().Name));
 					return;
 				}
 				else if (TargetNamespace != null && 
@@ -591,11 +591,13 @@ namespace System.Xml.Schema
 		void AddExternalComponentsTo (XmlSchema s, XmlSchemaObjectCollection items, ValidationEventHandler handler, Hashtable handledUris, XmlResolver resolver, XmlSchemaSet col)
 		{
 			foreach (XmlSchemaExternal ext in s.Includes)
-				ProcessExternal (handler, handledUris, resolver, ext, col);
-//				if (ext.Schema != null)
-//					AddExternalComponentsTo (ext.Schema, items);
-			foreach (XmlSchemaObject obj in s.Items)
+				s.ProcessExternal (handler, handledUris, resolver, ext, col);
+			foreach (XmlSchemaObject obj in s.compilationItems)
 				items.Add (obj);
+			// Items might be already resolved (recursive schema imports), or might not be (other cases), so we add items only when appropriate here. (duplicate check is anyways done elsewhere)
+			foreach (XmlSchemaObject obj in s.Items)
+				if (!items.Contains (obj))
+					items.Add (obj);
 		}
 
 		internal bool IsNamespaceAbsent (string ns)

mcs/class/System.XML/Test/System.Xml.Schema/XmlSchemaTests.cs

@@ -627,5 +627,12 @@ namespace MonoTests.System.Xml
 			while (reader.Read()) {}
 		}
 #endif
+
+		[Test]
+		public void TestImportSchemaThatIncludesAnother ()
+		{
+			XmlSchema xs = GetSchema ("Test/XmlFiles/xsd/importNamespaceTest2.xsd");
+			xs.Compile (null);
+		}
 	}
 }

mcs/class/System.XML/Test/XmlFiles/xsd/imcludedNamespace2.xsd

+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:y"
+  xmlns="urn:y">
+  <xs:element name="foo" />
+</xs:schema>
+

mcs/class/System.XML/Test/XmlFiles/xsd/importNamespaceTest2.xsd

+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:x"
+  xmlns="urn:x" xmlns:y="urn:y">
+  <xs:import namespace="urn:y" schemaLocation="importedNamespace2.xsd" />
+  <xs:element name="foo" type="y:foo" />
+</xs:schema>

mcs/class/System.XML/Test/XmlFiles/xsd/importedNamespace2.xsd

+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="urn:y"
+  xmlns="urn:y" xmlns:x="urn:x" />
+  <xs:include schemaLocation="includedNamespace2.xsd" />
+</xs:schema>