[Xamarin.Android.Build.Tasks] Emit an Error if a custom view cannot b…

…e fixed up.

Context dotnet#1711

When using a custom view within a layout file we replace the
`namespace.classname` with an `md5hash.classname`. We do this
by using the `acwmap.txt` file to make known types onto the
`md5` hashed ones. We do this in a case sensitive manner. We
also only support Camel case and lower case type names.

	ClassLibrary1.CustomView=md5d6f7135293df7527c983d45d07471c5e.CustomTextView
	classlibrary1.CustomView=md5d6f7135293df7527c983d45d07471c5e.CustomTextView

Given that a user is able to type these manually it is highly
probable that typo's will occur. If for example a user types

	Classlibrary1.CustomView

this will NOT be fixed up. Instead the user will recieve the
following error at runtime.

	FATAL UNHANDLED EXCEPTION: Android.Views.InflateException: Binary XML file line #1: Binary XML file line #1: Error inflating class Classlibrary1.CustomTextView ---> Android.Views.InflateException: Binary XML file line #1: Error inflating class Classlibrary1.CustomTextView ---> Java.Lang.ClassNotFoundException: Didn't find class "Classlibrary1.CustomTextView"

if you are using the control in a number of places this runtime error
does nothing to help track down the problem.

Instead what we should be doing is detecting these issues and emitting
a build error. This will provide the user not only the problem but
also a link to the file causing the probem.

TODO
----

[ ] Fix up the name so it points to the file in `Resources` not `res`
[ ] Add a Unit test.
[ ] Add Error code and document.

src/Xamarin.Android.Build.Tasks/Tasks/ConvertResourcesCases.cs

@@ -1,6 +1,7 @@
 // Copyright (C) 2011 Xamarin, Inc. All rights reserved.
 
 using System;
+using System.Diagnostics;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -71,7 +72,19 @@ void FixupResources (ITaskItem item, Dictionary<string, string> acwMap)
 				MonoAndroidHelper.SetWriteable (tmpdest);
 				try {
 					AndroidResource.UpdateXmlResource (resdir, tmpdest, acwMap,
-						ResourceDirectories.Where (s => s != item).Select(s => s.ItemSpec));
+						ResourceDirectories.Where (s => s != item).Select(s => s.ItemSpec), (t, m) => {
+							switch (t) {
+								case TraceLevel.Error:
+									Log.LogCodedError ("XAXXXX", file: file, lineNumber: 0, message: m);
+									break;
+								case TraceLevel.Warning:
+									Log.LogCodedWarning ("XAXXXX", file: file, lineNumber: 0, message: m);
+									break;
+								default:
+									Log.LogDebugMessage (m);
+									break;
+							}
+						});
 
 					// We strip away an eventual UTF-8 BOM from the XML file.
 					// This is a requirement for the Android designer because the desktop Java renderer

src/Xamarin.Android.Build.Tasks/Utilities/AndroidResource.cs

@@ -1,22 +1,24 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
+using System.Text;
 using System.Text.RegularExpressions;
 using System.Xml.Linq;
 using System.Xml.XPath;
 
 namespace Monodroid {
 	static class AndroidResource {
 
-		public static void UpdateXmlResource (string res, string filename, Dictionary<string, string> acwMap, IEnumerable<string> additionalDirectories = null)
+		public static void UpdateXmlResource (string res, string filename, Dictionary<string, string> acwMap, IEnumerable<string> additionalDirectories = null, Action<TraceLevel, string> logMessage = null)
 		{
 			// use a temporary file so we only update the real file if things actually changed
 			string tmpfile = filename + ".bk";
 			try {
 				XDocument doc = XDocument.Load (filename, LoadOptions.SetLineInfo);
 
-				UpdateXmlResource (res, doc.Root, acwMap, additionalDirectories);
+				UpdateXmlResource (res, doc.Root, acwMap, additionalDirectories, logMessage);
 				using (var stream = File.OpenWrite (tmpfile))
 					using (var xw = new LinePreservedXmlWriter (new StreamWriter (stream)))
 						xw.WriteNode (doc.CreateNavigator (), false);
@@ -59,10 +61,10 @@ static IEnumerable<T> Prepend<T> (this IEnumerable<T> l, T another) where T : XN
 				yield return e;
 		}
 
-		static void UpdateXmlResource (string resourcesBasePath, XElement e, Dictionary<string, string> acwMap, IEnumerable<string> additionalDirectories = null)
+		static void UpdateXmlResource (string resourcesBasePath, XElement e, Dictionary<string, string> acwMap, IEnumerable<string> additionalDirectories = null, Action<TraceLevel, string> logMessage = null)
 		{
 			foreach (var elem in GetElements (e).Prepend (e)) {
-				TryFixCustomView (elem, acwMap);
+				TryFixCustomView (elem, acwMap, logMessage);
 			}
 
 			foreach (var path in fixResourcesAliasPaths) {
@@ -217,15 +219,22 @@ private static bool TryFixResAuto (XAttribute attr, Dictionary<string, string> a
 			return false;
 		}
 
-		private static bool TryFixCustomView (XElement elem, Dictionary<string, string> acwMap)
+		private static bool TryFixCustomView (XElement elem, Dictionary<string, string> acwMap, Action<TraceLevel, string> logMessage = null)
 		{
 			// Looks for any <My.DotNet.Class ...
 			// and tries to change it to the ACW name
 			if (acwMap.ContainsKey (elem.Name.ToString ())) {
 				elem.Name = acwMap[elem.Name.ToString ()];
 				return true;
 			}
-
+			if (logMessage == null)
+				return false;
+			var matchingKey = acwMap.FirstOrDefault(x => String.Equals(x.Key, elem.Name.ToString (), StringComparison.OrdinalIgnoreCase));
+			if (matchingKey.Key != null) {
+				// we have elements with slightly different casing.
+				// lets issue a error.
+				logMessage (TraceLevel.Error, $"We found a matching key '{matchingKey.Key}' for '{elem.Name.ToString ()}'. But the casing was incorrect. Please correct the casing");
+			}
 			return false;
 		}