4 files changed, 133 insertions, 3 deletions

diff --git a/src/wix/WixToolset.Core/Preprocessor.cs b/src/wix/WixToolset.Core/Preprocessor.cs
index 486a4c8c..3abe0b5f 100644
--- a/src/wix/WixToolset.Core/Preprocessor.cs
+++ b/src/wix/WixToolset.Core/Preprocessor.cs
@@ -185,6 +185,7 @@ namespace WixToolset.Core
             }
 
             if ("=" == operation ||
+                "==" == operation ||
                 "!=" == operation ||
                 "<" == operation ||
                 "<=" == operation ||
@@ -885,6 +886,7 @@ namespace WixToolset.Core
                 // or end of string, whichever comes first
                 var space = expression.IndexOf(" ", StringComparison.Ordinal);
                 var equals = expression.IndexOf("=", StringComparison.Ordinal);
+                var doubleEquals = expression.IndexOf("==", StringComparison.Ordinal);
                 var lessThan = expression.IndexOf("<", StringComparison.Ordinal);
                 var lessThanEquals = expression.IndexOf("<=", StringComparison.Ordinal);
                 var greaterThan = expression.IndexOf(">", StringComparison.Ordinal);
@@ -903,6 +905,11 @@ namespace WixToolset.Core
                     equals = Int32.MaxValue;
                 }
 
+                if (doubleEquals == -1)
+                {
+                    doubleEquals = Int32.MaxValue;
+                }
+
                 if (lessThan == -1)
                 {
                     lessThan = Int32.MaxValue;
@@ -933,7 +940,7 @@ namespace WixToolset.Core
                     equalsNoCase = Int32.MaxValue;
                 }
 
-                closingIndex = Math.Min(space, Math.Min(equals, Math.Min(lessThan, Math.Min(lessThanEquals, Math.Min(greaterThan, Math.Min(greaterThanEquals, Math.Min(equalsNoCase, notEquals)))))));
+                closingIndex = Math.Min(space, Math.Min(equals, Math.Min(doubleEquals, Math.Min(lessThan, Math.Min(lessThanEquals, Math.Min(greaterThan, Math.Min(greaterThanEquals, Math.Min(equalsNoCase, notEquals))))))));
 
                 if (Int32.MaxValue == closingIndex)
                 {
@@ -944,7 +951,7 @@ namespace WixToolset.Core
                 if (0 == closingIndex)
                 {
                     // Length 2 operators
-                    if (closingIndex == lessThanEquals || closingIndex == greaterThanEquals || closingIndex == notEquals || closingIndex == equalsNoCase)
+                    if (closingIndex == doubleEquals || closingIndex == lessThanEquals || closingIndex == greaterThanEquals || closingIndex == notEquals || closingIndex == equalsNoCase)
                     {
                         closingIndex = 2;
                     }
@@ -1096,7 +1103,7 @@ namespace WixToolset.Core
             {
                 leftValue = leftValue.Trim();
                 rightValue = rightValue.Trim();
-                if ("=" == operation)
+                if ("=" == operation || "==" == operation)
                 {
                     if (leftValue == rightValue)
                     {
diff --git a/src/wix/test/WixToolsetTest.Core/PreprocessorFixture.cs b/src/wix/test/WixToolsetTest.Core/PreprocessorFixture.cs
new file mode 100644
index 00000000..b3ad0803
--- /dev/null
+++ b/src/wix/test/WixToolsetTest.Core/PreprocessorFixture.cs
@@ -0,0 +1,79 @@
+// 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.Core
+{
+    using System;
+    using System.IO;
+    using System.Xml;
+    using WixBuildTools.TestSupport;
+    using WixToolset.Core;
+    using WixToolset.Extensibility.Data;
+    using WixToolset.Extensibility.Services;
+    using Xunit;
+
+    public class PreprocessorFixture
+    {
+        [Fact]
+        public void CanPreprocessWithSingleEquals()
+        {
+            var input = String.Join(Environment.NewLine,
+                "<Wix>",
+                "<?define A=0?>",
+                "<?if $(A)=\"0\" ?>",
+                "  <Package />",
+                "<?endif?>",
+                "</Wix>"
+            );
+            var expected = new[]
+            {
+                "<Wix>",
+                "  <Package />",
+                "</Wix>"
+            };
+
+            var result = PreprocessFromString(input);
+
+            var actual = result.Document.ToString().Split("\r\n");
+            WixAssert.CompareLineByLine(expected, actual);
+        }
+
+        [Fact]
+        public void CanPreprocessWithDoubleEquals()
+        {
+            var input = String.Join(Environment.NewLine,
+                "<Wix>",
+                "<?define A=0?>",
+                "<?if $(A)==\"0\" ?>",
+                "  <Fragment />",
+                "<?endif?>",
+                "</Wix>"
+            );
+            var expected = new[]
+            {
+                "<Wix>",
+                "  <Fragment />",
+                "</Wix>"
+            };
+
+            var result = PreprocessFromString(input);
+
+            var actual = result.Document.ToString().Split("\r\n");
+            WixAssert.CompareLineByLine(expected, actual);
+        }
+
+        private static IPreprocessResult PreprocessFromString(string xml)
+        {
+            using var stringReader = new StringReader(xml);
+            using var xmlReader = XmlReader.Create(stringReader);
+
+            var sp = WixToolsetServiceProviderFactory.CreateServiceProvider();
+
+            var context = sp.GetService<IPreprocessContext>();
+            context.SourcePath = @"path\provided\for\testing\purposes\only.wxs";
+
+            var preprocessor = context.ServiceProvider.GetService<IPreprocessor>();
+            var result = preprocessor.Preprocess(context, xmlReader);
+            return result;
+        }
+    }
+}
diff --git a/src/wix/test/WixToolsetTest.Core/WixToolsetTest.Core.csproj b/src/wix/test/WixToolsetTest.Core/WixToolsetTest.Core.csproj
new file mode 100644
index 00000000..3b0259cb
--- /dev/null
+++ b/src/wix/test/WixToolsetTest.Core/WixToolsetTest.Core.csproj
@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- 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. -->
+
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <DebugType>embedded</DebugType>
+    <SignOutput>false</SignOutput>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\WixToolset.Core\WixToolset.Core.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="WixBuildTools.TestSupport" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit" />
+    <PackageReference Include="xunit.runner.visualstudio" PrivateAssets="All" />
+  </ItemGroup>
+</Project>
diff --git a/src/wix/wix.sln b/src/wix/wix.sln
index 15ee82e4..81faf8be 100644
--- a/src/wix/wix.sln
+++ b/src/wix/wix.sln
@@ -52,6 +52,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "WixToolsetTest.BuildTasks",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "pack-wix", "pack-wix\pack-wix.csproj", "{CE489499-60E1-4883-B72A-CA8F95DBA073}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "WixToolsetTest.Core", "test\WixToolsetTest.Core\WixToolsetTest.Core.csproj", "{392817AE-4493-4BED-A7FD-2399379E1B1C}"
+EndProject
 Global
         GlobalSection(SolutionConfigurationPlatforms) = preSolution
                 Debug|Any CPU = Debug|Any CPU
@@ -448,6 +450,22 @@ Global
                 {CE489499-60E1-4883-B72A-CA8F95DBA073}.Release|x64.Build.0 = Release|Any CPU
                 {CE489499-60E1-4883-B72A-CA8F95DBA073}.Release|x86.ActiveCfg = Release|Any CPU
                 {CE489499-60E1-4883-B72A-CA8F95DBA073}.Release|x86.Build.0 = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|ARM64.ActiveCfg = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|ARM64.Build.0 = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|x64.ActiveCfg = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|x64.Build.0 = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|x86.ActiveCfg = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Debug|x86.Build.0 = Debug|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|Any CPU.Build.0 = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|ARM64.ActiveCfg = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|ARM64.Build.0 = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|x64.ActiveCfg = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|x64.Build.0 = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|x86.ActiveCfg = Release|Any CPU
+                {392817AE-4493-4BED-A7FD-2399379E1B1C}.Release|x86.Build.0 = Release|Any CPU
         EndGlobalSection
         GlobalSection(SolutionProperties) = preSolution
                 HideSolutionNode = FALSE
@@ -463,6 +481,7 @@ Global
                 {9D788104-2636-4E4C-891C-08FF05FEC31E} = {1284331E-BC6C-426D-AAAF-140C0174F875}
                 {93645356-5D5F-45DE-AC7F-252D35E1ACE5} = {1284331E-BC6C-426D-AAAF-140C0174F875}
                 {A05698E0-30D9-4B36-8F3B-585A99D67118} = {1284331E-BC6C-426D-AAAF-140C0174F875}
+                {392817AE-4493-4BED-A7FD-2399379E1B1C} = {1284331E-BC6C-426D-AAAF-140C0174F875}
         EndGlobalSection
         GlobalSection(ExtensibilityGlobals) = postSolution
                 SolutionGuid = {BB8820D5-723D-426D-B4A0-4D221603C5FA}