Add compiler extension to handle platforms.

Custom actions to print EULA and validate install directories are
defined in WixUIExtension compiler extension, to handle
platform-specific custom actions referred to from `DoAction` control
events. This is the least-worst solution, given the `DoAction` approach
used in the WixUI authoring and anyone customizing a WixUI set.

27 files changed, 327 insertions, 106 deletions

diff --git a/src/ext/UI/ca/uica.vcxproj b/src/ext/UI/ca/uica.vcxproj
index e06b7572..27f0faa7 100644
--- a/src/ext/UI/ca/uica.vcxproj
+++ b/src/ext/UI/ca/uica.vcxproj
@@ -11,6 +11,22 @@
       <Configuration>Release</Configuration>
       <Platform>Win32</Platform>
     </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|ARM64">
+      <Configuration>Debug</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|ARM64">
+      <Configuration>Release</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
   </ItemGroup>
 
   <PropertyGroup Label="Globals">
diff --git a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Advanced/Package.wxs b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Advanced/Package.wxs
index 5ce4b00f..c22328e6 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Advanced/Package.wxs
+++ b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Advanced/Package.wxs
@@ -1,5 +1,5 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
-    <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
+    <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a">
         <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
 
         <Feature Id="ProductFeature" Title="MsiPackage">
@@ -12,7 +12,7 @@
             </Component>
         </ComponentGroup>
 
-        <UIRef Id="WixUI_Advanced" />
+        <ui:WixUI Id="WixUI_Advanced" />
         <Property Id="ApplicationFolderName" Value="MyProgram" />
         <Property Id="WixAppFolder" Value="WixPerMachineFolder" />
     </Package>
diff --git a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_FeatureTree/Package.wxs b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_FeatureTree/Package.wxs
index aff1c077..7c4db223 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_FeatureTree/Package.wxs
+++ b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_FeatureTree/Package.wxs
@@ -1,4 +1,4 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
     <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
         <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
 
@@ -12,7 +12,7 @@
             </Component>
         </ComponentGroup>
 
-        <UIRef Id="WixUI_FeatureTree" />
+        <ui:WixUI Id="WixUI_FeatureTree" />
     </Package>
 
     <Fragment>
diff --git a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_InstallDir/Package.wxs b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_InstallDir/Package.wxs
index 7c2ceae0..b6f2344a 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_InstallDir/Package.wxs
+++ b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_InstallDir/Package.wxs
@@ -1,4 +1,4 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
     <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
         <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
 
@@ -12,7 +12,7 @@
             </Component>
         </ComponentGroup>
 
-        <UIRef Id="WixUI_InstallDir" />
+        <ui:WixUI Id="WixUI_InstallDir" />
     </Package>
 
     <Fragment>
diff --git a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Minimal/Package.wxs b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Minimal/Package.wxs
index d2ff256c..962be579 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Minimal/Package.wxs
+++ b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Minimal/Package.wxs
@@ -1,4 +1,4 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
     <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
         <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
 
@@ -12,7 +12,7 @@
             </Component>
         </ComponentGroup>
 
-        <UIRef Id="WixUI_Minimal" />
+        <ui:WixUI Id="WixUI_Minimal" />
     </Package>
 
     <Fragment>
diff --git a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Mondo/Package.wxs b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Mondo/Package.wxs
index 8d5a856a..9eca9790 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Mondo/Package.wxs
+++ b/src/ext/UI/test/WixToolsetTest.UI/TestData/WixUI_Mondo/Package.wxs
@@ -1,4 +1,4 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
     <Package Name="MsiPackage" Language="1033" Version="1.0.0.0" Manufacturer="Example Corporation" UpgradeCode="047730a5-30fe-4a62-a520-da9381b8226a" InstallerVersion="200">
         <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
 
@@ -12,7 +12,7 @@
             </Component>
         </ComponentGroup>
 
-        <UIRef Id="WixUI_Mondo" />
+        <ui:WixUI Id="WixUI_Mondo" />
     </Package>
 
     <Fragment>
diff --git a/src/ext/UI/test/WixToolsetTest.UI/UIExtensionFixture.cs b/src/ext/UI/test/WixToolsetTest.UI/UIExtensionFixture.cs
index 778bfb64..4ab7ec3f 100644
--- a/src/ext/UI/test/WixToolsetTest.UI/UIExtensionFixture.cs
+++ b/src/ext/UI/test/WixToolsetTest.UI/UIExtensionFixture.cs
@@ -7,8 +7,6 @@ namespace WixToolsetTest.UI
     using System.Linq;
     using WixBuildTools.TestSupport;
     using WixToolset.Core.TestPackage;
-    using WixToolset.Data;
-    using WixToolset.Data.Symbols;
     using WixToolset.Data.WindowsInstaller;
     using WixToolset.UI;
     using Xunit;
@@ -22,11 +20,48 @@ namespace WixToolsetTest.UI
             var bindFolder = TestData.Get(@"TestData\data");
             var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
 
-            var results = build.BuildAndQuery(Build, "Property");
-            WixAssert.CompareLineByLine(new[]
-            {
-                "Property:WixUI_Mode\tAdvanced",
-            }, results.Where(s => s.StartsWith("Property:WixUI_Mode")).ToArray());
+            var results = build.BuildAndQuery(Build, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:AdvancedWelcomeEulaDlg\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIPrintEula\t65\tWixUiCa_X86\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIValidatePath\t65\tWixUiCa_X86\t"));
+        }
+
+        [Fact]
+        public void CanBuildUsingWixUIAdvancedX64()
+        {
+            var folder = TestData.Get(@"TestData\WixUI_Advanced");
+            var bindFolder = TestData.Get(@"TestData\data");
+            var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
+
+            var results = build.BuildAndQuery(BuildX64, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:AdvancedWelcomeEulaDlg\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIPrintEula\t65\tWixUiCa_X64\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIValidatePath\t65\tWixUiCa_X64\t"));
+        }
+
+        [Fact]
+        public void CanBuildUsingWixUIAdvancedARM64()
+        {
+            var folder = TestData.Get(@"TestData\WixUI_Advanced");
+            var bindFolder = TestData.Get(@"TestData\data");
+            var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
+
+            var results = build.BuildAndQuery(BuildARM64, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:AdvancedWelcomeEulaDlg\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetDefaultPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerMachineFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixSetPerUserFolder\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIPrintEula\t65\tWixUiCa_A64\t"));
+            Assert.Single(results, result => result.StartsWith("CustomAction:WixUIValidatePath\t65\tWixUiCa_A64\t"));
         }
 
         [Fact]
@@ -36,11 +71,10 @@ namespace WixToolsetTest.UI
             var bindFolder = TestData.Get(@"TestData\data");
             var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
 
-            var results = build.BuildAndQuery(Build, "Property");
-            WixAssert.CompareLineByLine(new[]
-            {
-                "Property:WixUI_Mode\tFeatureTree",
-            }, results.Where(s => s.StartsWith("Property:WixUI_Mode")).ToArray());
+            var results = build.BuildAndQuery(Build, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:WelcomeDlg\t"));
+            Assert.Single(results, result => result.StartsWith("Dialog:CustomizeDlg\t"));
+            Assert.Empty(results.Where(result => result.StartsWith("Dialog:SetupTypeDlg\t")));
         }
 
         [Fact]
@@ -50,11 +84,8 @@ namespace WixToolsetTest.UI
             var bindFolder = TestData.Get(@"TestData\data");
             var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
 
-            var results = build.BuildAndQuery(Build, "Property");
-            WixAssert.CompareLineByLine(new[]
-            {
-                "Property:WixUI_Mode\tInstallDir",
-            }, results.Where(s => s.StartsWith("Property:WixUI_Mode")).ToArray());
+            var results = build.BuildAndQuery(Build, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:InstallDirDlg\t"));
         }
 
         [Fact]
@@ -64,11 +95,8 @@ namespace WixToolsetTest.UI
             var bindFolder = TestData.Get(@"TestData\data");
             var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
 
-            var results = build.BuildAndQuery(Build, "Property");
-            WixAssert.CompareLineByLine(new[]
-            {
-                "Property:WixUI_Mode\tMinimal",
-            }, results.Where(s => s.StartsWith("Property:WixUI_Mode")).ToArray());
+            var results = build.BuildAndQuery(Build, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:WelcomeEulaDlg\t"));
         }
 
         [Fact]
@@ -92,10 +120,8 @@ namespace WixToolsetTest.UI
                 });
 
                 var wid = WindowsInstallerData.Load(Path.Combine(intermediateFolder, @"bin\test.wixpdb"));
-                var propertyTable = wid.Tables["Property"];
-
-                var propertyRow = propertyTable.Rows.Single(r => r.GetPrimaryKey() == "WixUI_Mode");
-                WixAssert.StringEqual("Minimal", propertyRow.FieldAsString(1));
+                var dialogTable = wid.Tables["Dialog"];
+                var dialogRow = dialogTable.Rows.Single(r => r.GetPrimaryKey() == "WelcomeEulaDlg");
             }
         }
 
@@ -106,11 +132,10 @@ namespace WixToolsetTest.UI
             var bindFolder = TestData.Get(@"TestData\data");
             var build = new Builder(folder, typeof(UIExtensionFactory), new[] { bindFolder });
 
-            var results = build.BuildAndQuery(Build, "Property");
-            WixAssert.CompareLineByLine(new[]
-            {
-                "Property:WixUI_Mode\tMondo",
-            }, results.Where(s => s.StartsWith("Property:WixUI_Mode")).ToArray());
+            var results = build.BuildAndQuery(Build, "Dialog", "CustomAction");
+            Assert.Single(results, result => result.StartsWith("Dialog:WelcomeDlg\t"));
+            Assert.Single(results, result => result.StartsWith("Dialog:CustomizeDlg\t"));
+            Assert.Single(results, result => result.StartsWith("Dialog:SetupTypeDlg\t"));
         }
 
         [Fact]
@@ -133,6 +158,18 @@ namespace WixToolsetTest.UI
                                   .AssertSuccess();
         }
 
+        private static void BuildX64(string[] args)
+        {
+            var result = WixRunner.Execute(args.Concat(new[] { "-arch", "x64" }).ToArray())
+                                  .AssertSuccess();
+        }
+
+        private static void BuildARM64(string[] args)
+        {
+            var result = WixRunner.Execute(args.Concat(new[] { "-arch", "arm64" }).ToArray())
+                                  .AssertSuccess();
+        }
+
         private static void BuildInGerman(string[] args)
         {
             var localizedArgs = args.Append("-culture").Append("de-DE").ToArray();
diff --git a/src/ext/UI/wixext/UICompiler.cs b/src/ext/UI/wixext/UICompiler.cs
new file mode 100644
index 00000000..46b856c0
--- /dev/null
+++ b/src/ext/UI/wixext/UICompiler.cs
@@ -0,0 +1,118 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolset.UI
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Xml.Linq;
+    using WixToolset.Data;
+    using WixToolset.Data.Symbols;
+    using WixToolset.Extensibility;
+
+    /// <summary>
+    /// The decompiler for the WiX Toolset UI Extension.
+    /// </summary>
+    public sealed class UICompiler : BaseCompilerExtension
+    {
+        public override XNamespace Namespace => "http://wixtoolset.org/schemas/v4/wxs/ui";
+
+        /// <summary>
+        /// Processes an element for the Compiler.
+        /// </summary>
+        /// <param name="sourceLineNumbers">Source line number for the parent element.</param>
+        /// <param name="parentElement">Parent element of element to process.</param>
+        /// <param name="element">Element to process.</param>
+        /// <param name="contextValues">Extra information about the context in which this element is being parsed.</param>
+        public override void ParseElement(Intermediate intermediate, IntermediateSection section, XElement parentElement, XElement element, IDictionary<string, string> context)
+        {
+            switch (parentElement.Name.LocalName)
+            {
+                case "Fragment":
+                case "Module":
+                case "PatchFamily":
+                case "Package":
+                case "UI":
+                    switch (element.Name.LocalName)
+                    {
+                        case "WixUI":
+                            this.ParseWixUIElement(intermediate, section, element);
+                            break;
+                        default:
+                            this.ParseHelper.UnexpectedElement(parentElement, element);
+                            break;
+                    }
+                    break;
+                default:
+                    this.ParseHelper.UnexpectedElement(parentElement, element);
+                    break;
+            }
+        }
+
+        /// <summary>
+        /// Parses a WixUI element.
+        /// </summary>
+        private void ParseWixUIElement(Intermediate intermediate, IntermediateSection section, XElement element)
+        {
+            var sourceLineNumbers = this.ParseHelper.GetSourceLineNumbers(element);
+            string id = null;
+
+            foreach (var attrib in element.Attributes())
+            {
+                if (String.IsNullOrEmpty(attrib.Name.NamespaceName) || this.Namespace == attrib.Name.Namespace)
+                {
+                    switch (attrib.Name.LocalName)
+                    {
+                        case "Id":
+                            id = this.ParseHelper.GetAttributeIdentifierValue(sourceLineNumbers, attrib);
+                            break;
+                        default:
+                            this.ParseHelper.UnexpectedAttribute(element, attrib);
+                            break;
+                    }
+                }
+                else
+                {
+                    this.ParseHelper.ParseExtensionAttribute(this.Context.Extensions, intermediate, section, element, attrib);
+                }
+            }
+
+            if (null == id)
+            {
+                this.Messaging.Write(ErrorMessages.ExpectedAttribute(sourceLineNumbers, element.Name.LocalName, "Id"));
+            }
+            else
+            {
+                this.ParseHelper.CreateSimpleReference(section, sourceLineNumbers, SymbolDefinitions.WixUI, id);
+
+                // Because these custom actions are "scheduled" via `DoAction` control events, we have to create the
+                // custom action definitions here, so the `DoAction` references are static and the targets are
+                // dynamically created to properly reflect the platform-specific DLL and avoid having duplicate ids
+                // in the UI .wixlib.
+                var platform = this.Context.Platform == Platform.ARM64 ? "A64" : this.Context.Platform.ToString();
+                var source = $"WixUiCa_{platform}";
+
+                section.AddSymbol(new CustomActionSymbol(sourceLineNumbers, new Identifier(AccessModifier.Global, "WixUIPrintEula"))
+                {
+                    TargetType = CustomActionTargetType.Dll,
+                    Target = "PrintEula",
+                    SourceType = CustomActionSourceType.Binary,
+                    Source = source,
+                    IgnoreResult = true,
+                    ExecutionType = CustomActionExecutionType.Immediate,
+                });
+
+                section.AddSymbol(new CustomActionSymbol(sourceLineNumbers, new Identifier(AccessModifier.Global, "WixUIValidatePath"))
+                {
+                    TargetType = CustomActionTargetType.Dll,
+                    Target = "ValidatePath",
+                    SourceType = CustomActionSourceType.Binary,
+                    Source = source,
+                    IgnoreResult = true,
+                    ExecutionType = CustomActionExecutionType.Immediate,
+                });
+            }
+
+            this.ParseHelper.ParseForExtensionElements(this.Context.Extensions, intermediate, section, element);
+        }
+    }
+}
diff --git a/src/ext/UI/wixext/UIExtensionFactory.cs b/src/ext/UI/wixext/UIExtensionFactory.cs
index 141aa39f..a16a9899 100644
--- a/src/ext/UI/wixext/UIExtensionFactory.cs
+++ b/src/ext/UI/wixext/UIExtensionFactory.cs
@@ -11,6 +11,7 @@ namespace WixToolset.UI
         protected override IReadOnlyCollection<Type> ExtensionTypes => new[]
         {
             typeof(UIExtensionData),
+            typeof(UICompiler),
         };
     }
 }
diff --git a/src/ext/UI/wixlib/Common_Platform.wxi b/src/ext/UI/wixlib/Common_Platform.wxi
index ffaa7114..0c03629c 100644
--- a/src/ext/UI/wixlib/Common_Platform.wxi
+++ b/src/ext/UI/wixlib/Common_Platform.wxi
@@ -2,18 +2,15 @@
 
 
 <Include xmlns="http://wixtoolset.org/schemas/v4/wxs">
-  <?include caSuffix.wxi ?>
-    <Fragment>
-    <!-- print EULA functionality -->
-        <CustomAction Id="WixUIPrintEula$(var.Suffix)" DllEntry="PrintEula" Return="ignore" Execute="immediate" BinaryRef="WixUIWixca$(var.Suffix)" />
-    </Fragment>
+    <?include ..\..\caDecor.wxi ?>
 
-    <Fragment>
-    <!-- Validate install directory -->
-        <CustomAction Id="WixUIValidatePath$(var.Suffix)" DllEntry="ValidatePath" Return="ignore" Execute="immediate" BinaryRef="WixUIWixca$(var.Suffix)" />
-    </Fragment>
+    <!-- 
+      Custom actions to print EULA amd validate install directories are defined
+      in WixUIExtension compiler extension, to handle platform-specific custom
+      actions referred to from `DoAction` control events.
+    -->
 
     <Fragment>
-        <Binary Id="WixUIWixca$(var.Suffix)" SourceFile="!(bindpath.$(var.platform))uica.dll" />
+        <Binary Id="WixUiCa$(var.Suffix)" SourceFile="!(bindpath.$(var.platform))uica.dll" />
     </Fragment>
 </Include>
diff --git a/src/ext/UI/wixlib/Common_arm64.wxs b/src/ext/UI/wixlib/Common_arm64.wxs
new file mode 100644
index 00000000..61dd5ddd
--- /dev/null
+++ b/src/ext/UI/wixlib/Common_arm64.wxs
@@ -0,0 +1,7 @@
+<!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information. -->
+
+
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+    <?define platform=arm64 ?>
+    <?include Common_Platform.wxi ?>
+</Wix>
diff --git a/src/ext/UI/wixlib/Common_x64.wxs b/src/ext/UI/wixlib/Common_x64.wxs
new file mode 100644
index 00000000..89204605
--- /dev/null
+++ b/src/ext/UI/wixlib/Common_x64.wxs
@@ -0,0 +1,7 @@
+<!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information. -->
+
+
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+    <?define platform=x64 ?>
+    <?include Common_Platform.wxi ?>
+</Wix>
diff --git a/src/ext/UI/wixlib/WixUI_Advanced.wxs b/src/ext/UI/wixlib/WixUI_Advanced.wxs
index 7d1f4df0..2ea7a97d 100644
--- a/src/ext/UI/wixlib/WixUI_Advanced.wxs
+++ b/src/ext/UI/wixlib/WixUI_Advanced.wxs
@@ -53,7 +53,6 @@ Todo:
             <TextStyle Id="WixUI_Font_Emphasized" FaceName="!(loc.Advanced_Font_FaceName)" Size="!(loc.Advanced_Font_Emphasized_Size)" Bold="yes" />
 
             <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
-            <Property Id="WixUI_Mode" Value="Advanced" />
 
             <DialogRef Id="BrowseDlg" />
             <DialogRef Id="DiskCostDlg" />
diff --git a/src/ext/UI/wixlib/WixUI_FeatureTree.wxs b/src/ext/UI/wixlib/WixUI_FeatureTree.wxs
index e999f2fe..6f36bdb8 100644
--- a/src/ext/UI/wixlib/WixUI_FeatureTree.wxs
+++ b/src/ext/UI/wixlib/WixUI_FeatureTree.wxs
@@ -29,7 +29,6 @@ Patch dialog sequence:
             <TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
 
             <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
-            <Property Id="WixUI_Mode" Value="FeatureTree" />
 
             <DialogRef Id="ErrorDlg" />
             <DialogRef Id="FatalError" />
diff --git a/src/ext/UI/wixlib/WixUI_InstallDir.wxs b/src/ext/UI/wixlib/WixUI_InstallDir.wxs
index afe7820f..f8eb3b11 100644
--- a/src/ext/UI/wixlib/WixUI_InstallDir.wxs
+++ b/src/ext/UI/wixlib/WixUI_InstallDir.wxs
@@ -30,7 +30,6 @@ Patch dialog sequence:
             <TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
 
             <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
-            <Property Id="WixUI_Mode" Value="InstallDir" />
 
             <DialogRef Id="BrowseDlg" />
             <DialogRef Id="DiskCostDlg" />
diff --git a/src/ext/UI/wixlib/WixUI_Minimal.wxs b/src/ext/UI/wixlib/WixUI_Minimal.wxs
index 08dba96d..8ac9751f 100644
--- a/src/ext/UI/wixlib/WixUI_Minimal.wxs
+++ b/src/ext/UI/wixlib/WixUI_Minimal.wxs
@@ -24,7 +24,6 @@ Patch dialog sequence:
             <TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
 
             <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
-            <Property Id="WixUI_Mode" Value="Minimal" />
 
             <DialogRef Id="ErrorDlg" />
             <DialogRef Id="FatalError" />
diff --git a/src/ext/UI/wixlib/WixUI_Mondo.wxs b/src/ext/UI/wixlib/WixUI_Mondo.wxs
index 2d53b9dd..6a4b15b1 100644
--- a/src/ext/UI/wixlib/WixUI_Mondo.wxs
+++ b/src/ext/UI/wixlib/WixUI_Mondo.wxs
@@ -31,7 +31,6 @@ Patch dialog sequence:
             <TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
 
             <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
-            <Property Id="WixUI_Mode" Value="Mondo" />
 
             <DialogRef Id="ErrorDlg" />
             <DialogRef Id="FatalError" />
diff --git a/src/ext/UI/wixlib/caSuffix.wxi b/src/ext/UI/wixlib/caSuffix.wxi
deleted file mode 100644
index 18436269..00000000
--- a/src/ext/UI/wixlib/caSuffix.wxi
+++ /dev/null
@@ -1,27 +0,0 @@
-<!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information. -->
-
-<Include xmlns="http://wixtoolset.org/schemas/v4/wxs">
-    <?ifndef platform ?>
-        <?error Required value "platform" not defined in include caSuffix.wxi ?>
-    <?endif?>
-
-    <?ifdef Suffix ?>
-        <?undef Suffix ?>
-        <?undef DeferredSuffix ?>
-    <?endif?>
-
-    <?if $(var.platform)="x86" ?>
-        <?define Suffix="" ?>
-        <?define DeferredSuffix="" ?>
-    <?endif?>
-
-    <?if $(var.platform)="x64" ?>
-        <?define Suffix="_x64" ?>
-        <?define DeferredSuffix="_64" ?>
-    <?endif?>
-
-    <?if $(var.platform)="arm" ?>
-        <?define Suffix="_ARM" ?>
-        <?define DeferredSuffix="_ARM" ?>
-    <?endif?>
-</Include>
diff --git a/src/ext/UI/wixlib/ui.wixproj b/src/ext/UI/wixlib/ui.wixproj
index 2b335f01..ead77af4 100644
--- a/src/ext/UI/wixlib/ui.wixproj
+++ b/src/ext/UI/wixlib/ui.wixproj
@@ -27,7 +27,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\ca\uica.vcxproj" Properties="Platform=x86" ReferenceOutputAssembly="false" />
+    <ProjectReference Include="..\ca\uica.vcxproj" Properties="Platform=x86" />
+    <ProjectReference Include="..\ca\uica.vcxproj" Properties="Platform=x64" />
+    <ProjectReference Include="..\ca\uica.vcxproj" Properties="Platform=ARM64" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/test/burn/TestData/FilesInUseTests/PackageA/PackageA.wxs b/src/test/burn/TestData/FilesInUseTests/PackageA/PackageA.wxs
index a96c2a11..0902ff1a 100644
--- a/src/test/burn/TestData/FilesInUseTests/PackageA/PackageA.wxs
+++ b/src/test/burn/TestData/FilesInUseTests/PackageA/PackageA.wxs
@@ -1,10 +1,10 @@
 <!-- Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information. -->
 
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
   <Fragment>
     <ComponentGroup Id="ProductComponents" />
 
-    <UIRef Id="WixUI_Minimal" />
+    <ui:WixUI Id="WixUI_Minimal" />
     <WixVariable Id="WixUILicenseRtf" Value="license.txt" />
   </Fragment>
 </Wix>
diff --git a/src/test/wix/TestData/WixprojLibraryVcxprojDll/Library.wxs b/src/test/wix/TestData/WixprojLibraryVcxprojDll/Library.wxs
index eed46112..f61c0ebe 100644
--- a/src/test/wix/TestData/WixprojLibraryVcxprojDll/Library.wxs
+++ b/src/test/wix/TestData/WixprojLibraryVcxprojDll/Library.wxs
@@ -1,11 +1,9 @@
-<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs" xmlns:ui="http://wixtoolset.org/schemas/v4/wxs/ui">
   <Fragment>
     <ComponentGroup Id='VcxprojDllComponentGroup' Directory='ApplicationFolder'>
       <Component>
         <File Source='VcxprojDll.dll' />
       </Component>
     </ComponentGroup>
-
-    <UIRef Id="WixUI_Minimal" />
   </Fragment>
 </Wix>
diff --git a/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/Package.wxs b/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/Package.wxs
index 17a5b29b..c228bb33 100644
--- a/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/Package.wxs
+++ b/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/Package.wxs
@@ -12,7 +12,5 @@
         <File Source='web.config' />
       </Component>
     </Feature>
-
-    <UIRef Id="WixUI_Minimal" />
   </Package>
 </Wix>
diff --git a/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/WixprojPackageCsprojWebApplicationNetCore.wixproj b/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/WixprojPackageCsprojWebApplicationNetCore.wixproj
index f9852465..c9f56d1d 100644
--- a/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/WixprojPackageCsprojWebApplicationNetCore.wixproj
+++ b/src/test/wix/TestData/WixprojPackageCsprojWebApplicationNetCore/WixprojPackageCsprojWebApplicationNetCore.wixproj
@@ -11,7 +11,6 @@
   <ItemGroup>
     <!-- SkipPublish="true" BindPath="$(MSBuildProjectDirectory)\does\not\exist" BindName="Xxx" Publish="true" -->
     <ProjectReference Include="..\CsprojWebApplicationNetCore\CsprojWebApplicationNetCore.csproj" Publish="true" />
-    <PackageReference Include="WixToolset.UI.wixext" Version="4.0.0-preview.0" />
   </ItemGroup>
 
   <!-- <Import Sdk="WixToolset.Sdk" Project='D:\src\wix4\build\wix\Debug\netcoreapp3.1\Sdk\Sdk.targets' /> -->
diff --git a/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/Package.wxs b/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/Package.wxs
index 00ef4d05..c0370683 100644
--- a/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/Package.wxs
+++ b/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/Package.wxs
@@ -16,7 +16,5 @@
 
       <MergeRef Id='WinFormsModule' />
     </Feature>
-
-    <UIRef Id="WixUI_Minimal" />
   </Package>
 </Wix>
diff --git a/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/WixprojPackageVcxprojWindowsApp.wixproj b/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/WixprojPackageVcxprojWindowsApp.wixproj
index 84deecb6..7dc26a2d 100644
--- a/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/WixprojPackageVcxprojWindowsApp.wixproj
+++ b/src/test/wix/TestData/WixprojPackageVcxprojWindowsApp/WixprojPackageVcxprojWindowsApp.wixproj
@@ -5,7 +5,5 @@
     <ProjectReference Include="..\VcxprojWindowsApp\VcxprojWindowsApp.vcxproj" />
     <ProjectReference Include="..\WixprojLibraryVcxprojDll\WixprojLibraryVcxprojDll.wixproj" />
     <ProjectReference Include="..\WixprojModuleCsprojWinFormsNetFx\WixprojModuleCsprojWinFormsNetFx.wixproj" />
-
-    <PackageReference Include="WixToolset.UI.wixext" Version="4.0.0-preview.0" />
   </ItemGroup>
 </Project>
diff --git a/src/wix/WixToolset.Converters/WixConverter.cs b/src/wix/WixToolset.Converters/WixConverter.cs
index 7bd2f81a..b8a83326 100644
--- a/src/wix/WixToolset.Converters/WixConverter.cs
+++ b/src/wix/WixToolset.Converters/WixConverter.cs
@@ -57,6 +57,7 @@ namespace WixToolset.Converters
         private static readonly XNamespace WixBalNamespace = "http://wixtoolset.org/schemas/v4/wxs/bal";
         private static readonly XNamespace WixDependencyNamespace = "http://wixtoolset.org/schemas/v4/wxs/dependency";
         private static readonly XNamespace WixFirewallNamespace = "http://wixtoolset.org/schemas/v4/wxs/firewall";
+        private static readonly XNamespace WixUiNamespace = "http://wixtoolset.org/schemas/v4/wxs/ui";
         private static readonly XNamespace WixUtilNamespace = "http://wixtoolset.org/schemas/v4/wxs/util";
         private static readonly XNamespace WixVSNamespace = "http://wixtoolset.org/schemas/v4/wxs/vs";
 
@@ -142,6 +143,7 @@ namespace WixToolset.Converters
         private static readonly XName UtilXmlConfigElementName = WixUtilNamespace + "XmlConfig";
         private static readonly XName CustomActionElementName = WixNamespace + "CustomAction";
         private static readonly XName CustomActionRefElementName = WixNamespace + "CustomActionRef";
+        private static readonly XName UIRefElementName = WixNamespace + "UIRef";
         private static readonly XName PropertyElementName = WixNamespace + "Property";
         private static readonly XName Wix4ElementName = WixNamespace + "Wix";
         private static readonly XName Wix3ElementName = Wix3Namespace + "Wix";
@@ -259,6 +261,7 @@ namespace WixToolset.Converters
                 { WixConverter.WixElementWithoutNamespaceName, this.ConvertElementWithoutNamespace },
                 { WixConverter.IncludeElementWithoutNamespaceName, this.ConvertElementWithoutNamespace },
                 { WixConverter.VerbElementName, this.ConvertVerbElement },
+                { WixConverter.UIRefElementName, this.ConvertUIRefElement },
             };
 
             this.Messaging = messaging;
@@ -1275,14 +1278,14 @@ namespace WixToolset.Converters
                             xPackage.SetAttributeValue("Scope", "perUser");
                             break;
                         case "elevated":
+                        {
+                            var xAllUsers = xPackage.Elements(PropertyElementName).SingleOrDefault(p => p.Attribute("Id")?.Value == "ALLUSERS");
+                            if (xAllUsers?.Attribute("Value")?.Value == "1")
                             {
-                                var xAllUsers = xPackage.Elements(PropertyElementName).SingleOrDefault(p => p.Attribute("Id")?.Value == "ALLUSERS");
-                                if (xAllUsers?.Attribute("Value")?.Value == "1")
-                                {
-                                    xAllUsers?.Remove();
-                                }
+                                xAllUsers?.Remove();
                             }
-                            break;
+                        }
+                        break;
                     }
 
                     xInstallPrivileges?.Remove();
@@ -1439,7 +1442,7 @@ namespace WixToolset.Converters
             }
 
             if (!String.IsNullOrEmpty(newElementName)
-                && this.OnError(ConverterTestType.ReferencesReplaced, element, "Custom action and property reference {0} have been replaced with strongly-typed elements.", id))
+                && this.OnError(ConverterTestType.ReferencesReplaced, element, "UI, custom action, and property reference {0} has been replaced with strongly-typed element.", id))
             {
                 this.XRoot.SetAttributeValue(XNamespace.Xmlns + newNamespaceName, newNamespace.NamespaceName);
 
@@ -1452,6 +1455,21 @@ namespace WixToolset.Converters
             }
         }
 
+        private void ConvertUIRefElement(XElement element)
+        {
+            var id = element.Attribute("Id")?.Value;
+
+            if (id?.StartsWith("WixUI_") == true
+                && this.OnError(ConverterTestType.ReferencesReplaced, element, "UI, custom action, and property reference {0} has been replaced with strongly-typed element.", id))
+            {
+                this.XRoot.SetAttributeValue(XNamespace.Xmlns + "ui", WixUiNamespace.NamespaceName);
+
+                element.AddBeforeSelf(new XElement(WixUiNamespace + "WixUI", new XAttribute("Id", id)));
+
+                element.Remove();
+            }
+        }
+
         private void ConvertCustomActionRefElement(XElement element)
         {
             var newElementName = String.Empty;
@@ -1471,7 +1489,7 @@ namespace WixToolset.Converters
             }
 
             if (!String.IsNullOrEmpty(newElementName)
-                && this.OnError(ConverterTestType.ReferencesReplaced, element, "Custom action and property reference {0} have been replaced with strongly-typed elements.", id))
+                && this.OnError(ConverterTestType.ReferencesReplaced, element, "UI, custom action, and property reference {0} has been replaced with strongly-typed element.", id))
             {
                 element.AddAfterSelf(new XElement(WixUtilNamespace + newElementName));
                 element.Remove();
@@ -2532,7 +2550,7 @@ namespace WixToolset.Converters
             DefiningStandardDirectoryDeprecated,
 
             /// <summary>
-            /// Naked custom action and property references replaced with elements.
+            /// Naked UI, custom action, and property references replaced with elements.
             /// </summary>
             ReferencesReplaced,
 
diff --git a/src/wix/test/WixToolsetTest.Converters/UIExtensionFixture.cs b/src/wix/test/WixToolsetTest.Converters/UIExtensionFixture.cs
new file mode 100644
index 00000000..5f3809d4
--- /dev/null
+++ b/src/wix/test/WixToolsetTest.Converters/UIExtensionFixture.cs
@@ -0,0 +1,59 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolsetTest.Converters
+{
+    using System;
+    using System.Xml.Linq;
+    using WixBuildTools.TestSupport;
+    using WixToolset.Converters;
+    using WixToolsetTest.Converters.Mocks;
+    using Xunit;
+
+    public class UIExtensionFixture : BaseConverterFixture
+    {
+        [Fact]
+        public void FixUIRefs()
+        {
+            var parse = String.Join(Environment.NewLine,
+                "<Wix xmlns='http://schemas.microsoft.com/wix/2006/wi'>",
+                "  <Fragment>",
+                "    <UIRef Id=\"WixUI_Advanced\" />",
+                "    <UIRef Id=\"WixUI_FeatureTree\" />",
+                "    <UIRef Id=\"WixUI_BobsSpecialUI\" />",
+                "    <UI>",
+                "      <UIRef Id=\"WixUI_Advanced\" />",
+                "      <UIRef Id=\"WixUI_FeatureTree\" />",
+                "      <UIRef Id=\"WixUI_BobsSpecialUI\" />",
+                "    </UI>",
+                "  </Fragment>",
+                "</Wix>");
+
+            var expected = new[]
+            {
+                "<Wix xmlns=\"http://wixtoolset.org/schemas/v4/wxs\" xmlns:ui=\"http://wixtoolset.org/schemas/v4/wxs/ui\">",
+                "  <Fragment>",
+                "    <ui:WixUI Id=\"WixUI_Advanced\" />",
+                "    <ui:WixUI Id=\"WixUI_FeatureTree\" />",
+                "    <ui:WixUI Id=\"WixUI_BobsSpecialUI\" />",
+                "    <UI>",
+                "      <ui:WixUI Id=\"WixUI_Advanced\" />",
+                "      <ui:WixUI Id=\"WixUI_FeatureTree\" />",
+                "      <ui:WixUI Id=\"WixUI_BobsSpecialUI\" />",
+                "    </UI>",
+                "  </Fragment>",
+                "</Wix>"
+            };
+
+            var document = XDocument.Parse(parse, LoadOptions.PreserveWhitespace | LoadOptions.SetLineInfo);
+
+            var messaging = new MockMessaging();
+            var converter = new WixConverter(messaging, 2, null, null);
+
+            var errors = converter.ConvertDocument(document);
+            Assert.Equal(7, errors);
+
+            var actualLines = UnformattedDocumentLines(document);
+            WixAssert.CompareLineByLine(expected, actualLines);
+        }
+    }
+}