Introduce a new phase in the build pipeline.

A useful point in the build pipeline is after all the files in the
project have been compiled but before they've been linked.
The WiX core and extensions can operate on symbols across
the project but without operating at the source-code level.

This phase is currently named "optimize," after a moderately-similar
phase in other compiler architectures. The name is, for now, a stake in
the ground and a better alternate is welcome.

14 files changed, 253 insertions, 7 deletions

diff --git a/src/api/wix/WixToolset.Extensibility/BaseOptimizerExtension.cs b/src/api/wix/WixToolset.Extensibility/BaseOptimizerExtension.cs
new file mode 100644
index 00000000..5bb89272
--- /dev/null
+++ b/src/api/wix/WixToolset.Extensibility/BaseOptimizerExtension.cs
@@ -0,0 +1,26 @@
+// 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.Extensibility
+{
+    using WixToolset.Extensibility.Data;
+
+    /// <summary>
+    /// Base class for creating an optimizer extension.
+    /// </summary>
+    public abstract class BaseOptimizerExtension : IOptimizerExtension
+    {
+        /// <summary>
+        /// Called after all files have been compiled, before built-in optimizations, and before all sections are linked into a single section.
+        /// </summary>
+        public virtual void PreOptimize(IOptimizeContext context)
+        {
+        }
+
+        /// <summary>
+        /// Called after all files have been compiled, after built-in optimizations, and before all sections are linked into a single section.
+        /// </summary>
+        public virtual void PostOptimize(IOptimizeContext context)
+        {
+        }
+    }
+}
diff --git a/src/api/wix/WixToolset.Extensibility/Data/ICompileContext.cs b/src/api/wix/WixToolset.Extensibility/Data/ICompileContext.cs
index 7006fde8..cfccd0a9 100644
--- a/src/api/wix/WixToolset.Extensibility/Data/ICompileContext.cs
+++ b/src/api/wix/WixToolset.Extensibility/Data/ICompileContext.cs
@@ -55,7 +55,7 @@ namespace WixToolset.Extensibility.Data
         XDocument Source { get; set; }
 
         /// <summary>
-        /// Cancellation token to abort cancellation.
+        /// Cancellation token.
         /// </summary>
         CancellationToken CancellationToken { get; set; }
     }
diff --git a/src/api/wix/WixToolset.Extensibility/Data/IOptimizeContext.cs b/src/api/wix/WixToolset.Extensibility/Data/IOptimizeContext.cs
new file mode 100644
index 00000000..5684ebcd
--- /dev/null
+++ b/src/api/wix/WixToolset.Extensibility/Data/IOptimizeContext.cs
@@ -0,0 +1,61 @@
+// 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.Extensibility.Data
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Threading;
+    using WixToolset.Data;
+
+    /// <summary>
+    /// Context provided to the optimizer.
+    /// </summary>
+    public interface IOptimizeContext
+    {
+        /// <summary>
+        /// Service provider made available to the optimizer and its extensions.
+        /// </summary>
+        IServiceProvider ServiceProvider { get; }
+
+        /// <summary>
+        /// Set of extensions provided to the optimizer.
+        /// </summary>
+        IReadOnlyCollection<IOptimizerExtension> Extensions { get; set; }
+
+        /// <summary>
+        /// Intermediate folder.
+        /// </summary>
+        string IntermediateFolder { get; set; }
+
+        /// <summary>
+        /// Collection of bindpaths used to bind files.
+        /// </summary>
+        IReadOnlyCollection<IBindPath> BindPaths { get; set; }
+
+        /// <summary>
+        /// Bind variables used during optimization.
+        /// </summary>
+        IDictionary<string, string> BindVariables { get; set; }
+
+        /// <summary>
+        /// Gets or sets the platform which the optimizer will use when defaulting 64-bit symbol properties.
+        /// </summary>
+        /// <value>The platform which the optimizer will use when defaulting 64-bit symbol properties.</value>
+        Platform Platform { get; set; }
+
+        /// <summary>
+        /// Collection of intermediates to optimize.
+        /// </summary>
+        IReadOnlyCollection<Intermediate> Intermediates { get; set; }
+
+        /// <summary>
+        /// Collection of localization files to use in the optimizer.
+        /// </summary>
+        IReadOnlyCollection<Localization> Localizations { get; set; }
+
+        /// <summary>
+        /// Cancellation token.
+        /// </summary>
+        CancellationToken CancellationToken { get; set; }
+    }
+}
diff --git a/src/api/wix/WixToolset.Extensibility/IOptimizerExtension.cs b/src/api/wix/WixToolset.Extensibility/IOptimizerExtension.cs
new file mode 100644
index 00000000..589e7ecc
--- /dev/null
+++ b/src/api/wix/WixToolset.Extensibility/IOptimizerExtension.cs
@@ -0,0 +1,22 @@
+// 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.Extensibility
+{
+    using WixToolset.Extensibility.Data;
+
+    /// <summary>
+    /// Interface that all optimizer extensions implement.
+    /// </summary>
+    public interface IOptimizerExtension
+    {
+        /// <summary>
+        /// Called after all files have been compiled, before built-in optimizations, and before all sections are linked into a single section.
+        /// </summary>
+        void PreOptimize(IOptimizeContext context);
+
+        /// <summary>
+        /// Called after all files have been compiled, after built-in optimizations, and before all sections are linked into a single section.
+        /// </summary>
+        void PostOptimize(IOptimizeContext context);
+    }
+}
diff --git a/src/wix/WixToolset.Core/CommandLine/BuildCommand.cs b/src/wix/WixToolset.Core/CommandLine/BuildCommand.cs
index 68dbd768..2ad18073 100644
--- a/src/wix/WixToolset.Core/CommandLine/BuildCommand.cs
+++ b/src/wix/WixToolset.Core/CommandLine/BuildCommand.cs
@@ -10,7 +10,6 @@ namespace WixToolset.Core.CommandLine
     using System.Threading.Tasks;
     using System.Xml.Linq;
     using WixToolset.Data;
-    using WixToolset.Data.Bind;
     using WixToolset.Extensibility;
     using WixToolset.Extensibility.Data;
     using WixToolset.Extensibility.Services;
@@ -112,6 +111,8 @@ namespace WixToolset.Core.CommandLine
                 return Task.FromResult(this.Messaging.LastErrorNumber);
             }
 
+            this.OptimizePhase(wixobjs, wxls, this.commandLine.BindPaths, this.commandLine.BindVariables, cancellationToken);
+
             if (inputsOutputs.OutputType == OutputType.Library)
             {
                 using (new IntermediateFieldContext("wix.lib"))
@@ -207,6 +208,22 @@ namespace WixToolset.Core.CommandLine
             return intermediates;
         }
 
+        private void OptimizePhase(IReadOnlyCollection<Intermediate> intermediates, IReadOnlyCollection<Localization> localizations, IReadOnlyCollection<IBindPath> bindPaths, Dictionary<string, string> bindVariables, CancellationToken cancellationToken)
+        {
+            var context = this.ServiceProvider.GetService<IOptimizeContext>();
+            context.Extensions = this.ExtensionManager.GetServices<IOptimizerExtension>();
+            context.IntermediateFolder = this.IntermediateFolder;
+            context.BindPaths = bindPaths;
+            context.BindVariables = bindVariables;
+            context.Platform = this.Platform;
+            context.Intermediates = intermediates;
+            context.Localizations = localizations;
+            context.CancellationToken = cancellationToken;
+
+            var optimizer = this.ServiceProvider.GetService<IOptimizer>();
+            optimizer.Optimize(context);
+        }
+
         private void LibraryPhase(IReadOnlyCollection<Intermediate> intermediates, IReadOnlyCollection<Localization> localizations, IEnumerable<string> libraryFiles, ISymbolDefinitionCreator creator, bool bindFiles, IReadOnlyCollection<IBindPath> bindPaths, Dictionary<string, string> bindVariables, string outputPath, CancellationToken cancellationToken)
         {
             var libraries = this.LoadLibraries(libraryFiles, creator);
diff --git a/src/wix/WixToolset.Core/IOptimizer.cs b/src/wix/WixToolset.Core/IOptimizer.cs
new file mode 100644
index 00000000..85c90b80
--- /dev/null
+++ b/src/wix/WixToolset.Core/IOptimizer.cs
@@ -0,0 +1,17 @@
+// 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.Core
+{
+    using WixToolset.Extensibility.Data;
+
+    /// <summary>
+    /// Interface for built-in optimizer.
+    /// </summary>
+    public interface IOptimizer
+    {
+        /// <summary>
+        /// Called after all files have been compiled and before all sections are linked into a single section.
+        /// </summary>
+        void Optimize(IOptimizeContext context);
+    }
+}
diff --git a/src/wix/WixToolset.Core/OptimizeContext.cs b/src/wix/WixToolset.Core/OptimizeContext.cs
new file mode 100644
index 00000000..93b6c354
--- /dev/null
+++ b/src/wix/WixToolset.Core/OptimizeContext.cs
@@ -0,0 +1,39 @@
+// 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.Core
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Threading;
+    using WixToolset.Data;
+    using WixToolset.Extensibility;
+    using WixToolset.Extensibility.Data;
+
+    internal class OptimizeContext : IOptimizeContext
+    {
+        internal OptimizeContext(IServiceProvider serviceProvider)
+        {
+            this.ServiceProvider = serviceProvider;
+        }
+
+        public IServiceProvider ServiceProvider { get; }
+
+        public IReadOnlyCollection<IOptimizerExtension> Extensions { get; set; }
+
+        public string IntermediateFolder { get; set; }
+
+        public IReadOnlyCollection<IBindPath> BindPaths { get; set; }
+
+        public IDictionary<string, string> BindVariables { get; set; }
+
+        public Platform Platform { get; set; }
+
+        public bool IsCurrentPlatform64Bit => this.Platform == Platform.ARM64 || this.Platform == Platform.X64;
+
+        public IReadOnlyCollection<Intermediate> Intermediates { get; set; }
+
+        public IReadOnlyCollection<Localization> Localizations { get; set; }
+
+        public CancellationToken CancellationToken { get; set; }
+    }
+}
diff --git a/src/wix/WixToolset.Core/Optimizer.cs b/src/wix/WixToolset.Core/Optimizer.cs
new file mode 100644
index 00000000..5864121e
--- /dev/null
+++ b/src/wix/WixToolset.Core/Optimizer.cs
@@ -0,0 +1,36 @@
+// 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.Core
+{
+    using System;
+    using WixToolset.Extensibility.Data;
+    using WixToolset.Extensibility.Services;
+
+    internal class Optimizer : IOptimizer
+    {
+        internal Optimizer(IServiceProvider serviceProvider)
+        {
+            this.ServiceProvider = serviceProvider;
+            this.Messaging = this.ServiceProvider.GetService<IMessaging>();
+        }
+
+        private IServiceProvider ServiceProvider { get; }
+
+        private IMessaging Messaging { get; }
+
+        public void Optimize(IOptimizeContext context)
+        {
+            foreach (var extension in context.Extensions)
+            {
+                extension.PreOptimize(context);
+            }
+
+            // TODO: Fill with useful optimization features.
+
+            foreach (var extension in context.Extensions)
+            {
+                extension.PostOptimize(context);
+            }
+        }
+    }
+}
diff --git a/src/wix/WixToolset.Core/WixToolsetServiceProvider.cs b/src/wix/WixToolset.Core/WixToolsetServiceProvider.cs
index 5620bcd2..cb8dbd87 100644
--- a/src/wix/WixToolset.Core/WixToolsetServiceProvider.cs
+++ b/src/wix/WixToolset.Core/WixToolsetServiceProvider.cs
@@ -37,6 +37,7 @@ namespace WixToolset.Core
             this.AddService<ICommandLine>((provider, singletons) => new CommandLine.CommandLine(provider));
             this.AddService<IPreprocessContext>((provider, singletons) => new PreprocessContext(provider));
             this.AddService<ICompileContext>((provider, singletons) => new CompileContext(provider));
+            this.AddService<IOptimizeContext>((provider, singletons) => new OptimizeContext(provider));
             this.AddService<ILibraryContext>((provider, singletons) => new LibraryContext(provider));
             this.AddService<ILibraryResult>((provider, singletons) => new LibraryResult());
             this.AddService<ILinkContext>((provider, singletons) => new LinkContext(provider));
@@ -58,6 +59,7 @@ namespace WixToolset.Core
 
             this.AddService<IBinder>((provider, singletons) => new Binder(provider));
             this.AddService<ICompiler>((provider, singletons) => new Compiler(provider));
+            this.AddService<IOptimizer>((provider, singletons) => new Optimizer(provider));
             this.AddService<ILayoutCreator>((provider, singletons) => new LayoutCreator(provider));
             this.AddService<IPreprocessor>((provider, singletons) => new Preprocessor(provider));
             this.AddService<ILibrarian>((provider, singletons) => new Librarian(provider));
diff --git a/src/wix/test/Example.Extension/ExampleExtensionFactory.cs b/src/wix/test/Example.Extension/ExampleExtensionFactory.cs
index 0b0fb836..16eea6dc 100644
--- a/src/wix/test/Example.Extension/ExampleExtensionFactory.cs
+++ b/src/wix/test/Example.Extension/ExampleExtensionFactory.cs
@@ -35,6 +35,10 @@ namespace Example.Extension
             {
                 extension = new ExampleCompilerExtension();
             }
+            else if (extensionType == typeof(IOptimizerExtension))
+            {
+                extension = new ExampleOptimizerExtension();
+            }
             else if (extensionType == typeof(IExtensionData))
             {
                 extension = new ExampleExtensionData();
diff --git a/src/wix/test/Example.Extension/ExampleOptimizerExtension.cs b/src/wix/test/Example.Extension/ExampleOptimizerExtension.cs
new file mode 100644
index 00000000..6a2cb91e
--- /dev/null
+++ b/src/wix/test/Example.Extension/ExampleOptimizerExtension.cs
@@ -0,0 +1,22 @@
+// 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 Example.Extension
+{
+    using System.Linq;
+    using WixToolset.Extensibility;
+    using WixToolset.Extensibility.Data;
+
+    internal class ExampleOptimizerExtension : BaseOptimizerExtension
+    {
+        public override void PostOptimize(IOptimizeContext context)
+        {
+            foreach (var intermediate in context.Intermediates)
+            {
+                foreach (var symbol in intermediate.Sections.SelectMany(s=>s.Symbols).OfType<ExampleSymbol>())
+                {
+                    symbol.Value = $"{symbol.Value} <optimized>";
+                }
+            }
+        }
+    }
+}
diff --git a/src/wix/test/WixToolsetTest.CoreIntegration/ExtensionFixture.cs b/src/wix/test/WixToolsetTest.CoreIntegration/ExtensionFixture.cs
index 710f3b8d..429226f5 100644
--- a/src/wix/test/WixToolsetTest.CoreIntegration/ExtensionFixture.cs
+++ b/src/wix/test/WixToolsetTest.CoreIntegration/ExtensionFixture.cs
@@ -24,7 +24,7 @@ namespace WixToolsetTest.CoreIntegration
             var results = build.BuildAndQuery(Build, "Wix4Example");
             WixAssert.CompareLineByLine(new[]
             {
-                "Wix4Example:Foo\tfilF5_pLhBuF5b4N9XEo52g_hUM5Lo\tBar"
+                "Wix4Example:Foo\tfilF5_pLhBuF5b4N9XEo52g_hUM5Lo\tBar <optimized>"
             }, results);
         }
 
@@ -92,7 +92,7 @@ namespace WixToolsetTest.CoreIntegration
                 var example = section.Symbols.Where(t => t.Definition.Type == SymbolDefinitionType.MustBeFromAnExtension).Single();
                 WixAssert.StringEqual("Foo", example.Id?.Id);
                 WixAssert.StringEqual("filF5_pLhBuF5b4N9XEo52g_hUM5Lo", example[0].AsString());
-                WixAssert.StringEqual("Bar", example[1].AsString());
+                WixAssert.StringEqual("Bar <optimized>", example[1].AsString());
             }
         }
 
diff --git a/src/wix/test/WixToolsetTest.CoreIntegration/TestData/ExampleExtension/Decompiled-Expected.xml b/src/wix/test/WixToolsetTest.CoreIntegration/TestData/ExampleExtension/Decompiled-Expected.xml
index 42ececb1..0375b3b6 100644
--- a/src/wix/test/WixToolsetTest.CoreIntegration/TestData/ExampleExtension/Decompiled-Expected.xml
+++ b/src/wix/test/WixToolsetTest.CoreIntegration/TestData/ExampleExtension/Decompiled-Expected.xml
@@ -5,7 +5,7 @@
     <StandardDirectory Id="ProgramFilesFolder">
       <Directory Id="INSTALLFOLDER" ShortName="oekcr5lq" Name="MsiPackage">
         <Component Id="filF5_pLhBuF5b4N9XEo52g_hUM5Lo" Guid="{GUID}" Bitness="always32">
-          <Example Id="Foo" Value="Bar" xmlns="http://www.example.com/scheams/v1/wxs" />
+          <Example Id="Foo" Value="Bar &lt;optimized&gt;" xmlns="http://www.example.com/scheams/v1/wxs" />
           <File Id="filF5_pLhBuF5b4N9XEo52g_hUM5Lo" Name="example.txt" KeyPath="yes" Source="PFiles\MsiPackage\example.txt" />
         </Component>
       </Directory>
diff --git a/src/wix/test/WixToolsetTest.CoreIntegration/WixlibFixture.cs b/src/wix/test/WixToolsetTest.CoreIntegration/WixlibFixture.cs
index 76326741..0cd8a542 100644
--- a/src/wix/test/WixToolsetTest.CoreIntegration/WixlibFixture.cs
+++ b/src/wix/test/WixToolsetTest.CoreIntegration/WixlibFixture.cs
@@ -288,7 +288,7 @@ namespace WixToolsetTest.CoreIntegration
 
                 var example = section.Symbols.Where(t => t.Definition.Type == SymbolDefinitionType.MustBeFromAnExtension).Single();
                 WixAssert.StringEqual("Foo", example.Id?.Id);
-                WixAssert.StringEqual("Bar", example[1].AsString());
+                WixAssert.StringEqual("Bar <optimized>", example[1].AsString());
             }
         }
 
@@ -351,7 +351,7 @@ namespace WixToolsetTest.CoreIntegration
                 var examples = section.Symbols.Where(t => t.Definition.Type == SymbolDefinitionType.MustBeFromAnExtension).ToArray();
                 WixAssert.CompareLineByLine(new[] { "Foo", "Other" }, examples.Select(t => t.Id?.Id).ToArray());
                 WixAssert.CompareLineByLine(new[] { "filF5_pLhBuF5b4N9XEo52g_hUM5Lo", "filvxdStJhRE_M5kbpLsTZJXbs34Sg" }, examples.Select(t => t[0].AsString()).ToArray());
-                WixAssert.CompareLineByLine(new[] { "Bar", "Value" }, examples.Select(t => t[1].AsString()).ToArray());
+                WixAssert.CompareLineByLine(new[] { "Bar <optimized>", "Value <optimized>" }, examples.Select(t => t[1].AsString()).ToArray());
             }
         }
     }