[Xamarin.Android.Build.Tasks] The "ConvertResourcesCases" task failed unexpectedly. (#1371)

Fixes? https://devdiv.visualstudio.com/DevDiv/_workitems/edit/571365

We have a report that `ConvertResourcesCases` is failing with the
following error:

	error MSB4018: The "ConvertResourcesCases" task failed unexpectedly.
	Android/Xamarin.Android.Common.targets(1334,2): error MSB4018: System.IO.FileNotFoundException: <some path>/design_layout_snackbar.xml.tmp does not exist

This is completely weird, especially as the Task is not being called
concurrently (or so we hope & assume). What I suspect is happening is
Visual Studio for Mac is running the `UpdateAndroidResources` target
at the same time the user started a build.

Because the name of the temp files was just `foo.xml.tmp` it is
highly possible that one instance of the task is deleting the file
while another instance is still running. This is difficult to
replicate.

Attempt to "fix" things by using `System.IO.Path.GetTempFileName()`
instead of appending `.tmp` to the filename. This should avoid
filename collisions.

However, if our suspicion is correct that the `UpdateAndroidResources`
target is concurrently executing alongside a Build, this patch will
*not* fix the concurrent target execution scenario.

Author: dellis1972

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

@@ -54,11 +54,11 @@ void FixupResources (ITaskItem item, Dictionary<string, string> acwMap)
 			foreach (string file in xmls) {
 				Log.LogDebugMessage ("  Processing: {0}", file);
 				var srcmodifiedDate = File.GetLastWriteTimeUtc (file);
-				var tmpdest = file + ".tmp";
+				var tmpdest = Path.GetTempFileName ();
 				MonoAndroidHelper.CopyIfChanged (file, tmpdest);
 				MonoAndroidHelper.SetWriteable (tmpdest);
 				try {
-					AndroidResource.UpdateXmlResource (tmpdest, acwMap,
+					AndroidResource.UpdateXmlResource (resdir, tmpdest, acwMap,
 						ResourceDirectories.Where (s => s != item).Select(s => s.ItemSpec));
 
 					// We strip away an eventual UTF-8 BOM from the XML file.

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

@@ -86,11 +86,12 @@ public override bool Execute ()
 				var destfilename = p.Value;
 				var srcmodifiedDate = File.GetLastWriteTimeUtc (filename);
 				var dstmodifiedDate = File.Exists (destfilename) ? File.GetLastAccessTimeUtc (destfilename) : DateTime.MinValue;
-				var tmpdest = p.Value + ".tmp";
+				var tmpdest = Path.GetTempFileName ();
+				var res = Path.Combine (Path.GetDirectoryName (filename), "..");
 				MonoAndroidHelper.CopyIfChanged (filename, tmpdest);
 				MonoAndroidHelper.SetWriteable (tmpdest);
 				try {
-					AndroidResource.UpdateXmlResource (tmpdest, acw_map);
+					AndroidResource.UpdateXmlResource (res, tmpdest, acw_map);
 					if (MonoAndroidHelper.CopyIfChanged (tmpdest, destfilename)) {
 						MonoAndroidHelper.SetWriteable (destfilename);
 						MonoAndroidHelper.SetLastAccessAndWriteTimeUtc (destfilename, srcmodifiedDate, Log);

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

@@ -9,17 +9,14 @@
 namespace Monodroid {
 	static class AndroidResource {
 
-		public static void UpdateXmlResource (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)
 		{
 			// 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);
 
-				// The assumption here is that the file we're fixing up is in a directory below the
-				// obj/${Configuration}/res/ directory and so appending ../gives us the actual path to
-				// 'res/'
-				UpdateXmlResource (Path.Combine (Path.GetDirectoryName (filename), ".."), doc.Root, acwMap, additionalDirectories);
+				UpdateXmlResource (res, doc.Root, acwMap, additionalDirectories);
 				using (var stream = File.OpenWrite (tmpfile))
 					using (var xw = new LinePreservedXmlWriter (new StreamWriter (stream)))
 						xw.WriteNode (doc.CreateNavigator (), false);