retrieves name of the template from the file.

added unit test to unpack and pack an app with modern controls.

src/PAModel/CanvasDocument.cs

@@ -405,7 +405,7 @@ internal void ApplyBeforeMsAppWriteTransforms(ErrorContainer errors)
         var templateDefaults = new Dictionary<string, ControlTemplate>();
         foreach (var template in _templates.UsedTemplates)
         {
-            if (!ControlTemplateParser.TryParseTemplate(_templateStore, template.Template, _properties.DocumentAppType, templateDefaults, out _, out _))
+            if (!ControlTemplateParser.TryParseTemplate(_templateStore, template.Template, _properties.DocumentAppType, templateDefaults, out _, out _, template.Name))
             {
                 errors.GenericError($"Unable to parse template file {template.Name}");
                 throw new DocumentException();

src/PAModel/Serializers/SourceSerializer.cs

@@ -310,7 +310,8 @@ private static void LoadTemplateFiles(ErrorContainer errors, CanvasDocument app,
         foreach (var file in new DirectoryReader(packagesPath).EnumerateFiles(string.Empty, "*.xml", searchSubdirectories: false))
         {
             var xmlContents = file.GetContents();
-            if (!ControlTemplateParser.TryParseTemplate(new TemplateStore(), xmlContents, app._properties.DocumentAppType, loadedTemplates, out var parsedTemplate, out var templateName))
+            var templateNameFromFile = file._relativeName.Substring(0, file._relativeName.LastIndexOf('_'));
+            if (!ControlTemplateParser.TryParseTemplate(new TemplateStore(), xmlContents, app._properties.DocumentAppType, loadedTemplates, out var parsedTemplate, out var templateName, templateNameFromFile))
             {
                 errors.GenericError($"Unable to parse template file {file._relativeName}");
                 throw new DocumentException();

src/PAModelTests/TemplateStoreTests.cs

@@ -44,4 +44,31 @@ public void TestHostControlInstancesWithHostType(string appName)
             Assert.IsTrue(MsAppTest.Compare(root, tempFile.FullPath, Console.Out));
         }
     }
+
+    // Validate a modern control that has a dynamic template.
+    // The template has a valid template name, but makes reference to another template.
+    // This example app has two modern controls (combobox and dropdown) that make reference to the same template.
+    [DataTestMethod]
+    [DataRow("ComboboxDropdown.msapp")]
+    public void TestModernControlWithDynamicTemplate(string appName)
+    {
+        //arrange
+        var root = Path.Combine(Environment.CurrentDirectory, "Apps", appName);
+        Assert.IsTrue(File.Exists(root), "MSAPP not found");
+
+        //act
+        (var msapp, var errors) = CanvasDocument.LoadFromMsapp(root);
+        errors.ThrowOnErrors();
+
+        //assert
+        Assert.IsTrue(msapp._templateStore.Contents.ContainsKey("PowerApps_CoreControls_DropdownCanvasTemplate_dataField"));
+        Assert.IsTrue(msapp._templateStore.Contents.ContainsKey("PowerApps_CoreControls_ComboboxCanvasTemplate_dataField"));
+
+        // Repack the app and validate it matches the initial msapp
+        using (var tempFile = new TempFile())
+        {
+            MsAppSerializer.SaveAsMsApp(msapp, tempFile.FullPath, new ErrorContainer());
+            Assert.IsTrue(MsAppTest.Compare(root, tempFile.FullPath, Console.Out));
+        }
+    }
 }