Improve incremental build in presence of globs

build/NuGetPackages/Microsoft.Build.Tasks.Core.nuspec

@@ -47,6 +47,8 @@
         <dependency id="System.Runtime.InteropServices.RuntimeInformation" version="4.0.0" />
         <dependency id="System.Runtime.Serialization.Primitives" version="4.1.1" />
         <dependency id="System.Runtime.Serialization.Xml" version="4.1.1" />
+        <dependency id="System.Security.Cryptography.Algorithms" version="4.2.0" />
+        <dependency id="System.Security.Cryptography.Primitives" version="4.0.0" />
         <dependency id="System.Security.Cryptography.X509Certificates" version="4.1.0" />
         <dependency id="System.Text.Encoding" version="4.0.11" />
         <dependency id="System.Text.Encoding.Extensions" version="4.0.11" />

ref/net46/Microsoft.Build.Tasks.Core/Microsoft.Build.Tasks.Core.cs

@@ -655,6 +655,15 @@ public GetSDKReferenceFiles() { }
         public string TargetSDKVersion { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public override bool Execute() { throw null; }
     }
+    public partial class Hash : Microsoft.Build.Tasks.TaskExtension
+    {
+        public Hash() { }
+        [Microsoft.Build.Framework.OutputAttribute]
+        public string HashResult { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        [Microsoft.Build.Framework.RequiredAttribute]
+        public Microsoft.Build.Framework.ITaskItem[] ItemsToHash { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        public override bool Execute() { throw null; }
+    }
     [System.Runtime.InteropServices.GuidAttribute("00020401-0000-0000-C000-000000000046")]
     [System.Runtime.InteropServices.InterfaceTypeAttribute((System.Runtime.InteropServices.ComInterfaceType)(1))]
     public partial interface IFixedTypeInfo
@@ -1177,6 +1186,7 @@ public WriteLinesToFile() { }
         public Microsoft.Build.Framework.ITaskItem File { get { throw null; } set { } }
         public Microsoft.Build.Framework.ITaskItem[] Lines { get { throw null; } set { } }
         public bool Overwrite { get { throw null; } set { } }
+        public bool WriteOnlyWhenDifferent { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public override bool Execute() { throw null; }
     }
     public partial class XamlTaskFactory : Microsoft.Build.Framework.ITaskFactory

ref/netstandard1.3/Microsoft.Build.Tasks.Core/Microsoft.Build.Tasks.Core.cs

@@ -370,6 +370,15 @@ public GetReferenceAssemblyPaths() { }
         public string TargetFrameworkMonikerDisplayName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public override bool Execute() { throw null; }
     }
+    public partial class Hash : Microsoft.Build.Tasks.TaskExtension
+    {
+        public Hash() { }
+        [Microsoft.Build.Framework.OutputAttribute]
+        public string HashResult { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        [Microsoft.Build.Framework.RequiredAttribute]
+        public Microsoft.Build.Framework.ITaskItem[] ItemsToHash { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
+        public override bool Execute() { throw null; }
+    }
     public partial class MakeDir : Microsoft.Build.Tasks.TaskExtension
     {
         public MakeDir() { }
@@ -625,6 +634,7 @@ public WriteLinesToFile() { }
         public Microsoft.Build.Framework.ITaskItem File { get { throw null; } set { } }
         public Microsoft.Build.Framework.ITaskItem[] Lines { get { throw null; } set { } }
         public bool Overwrite { get { throw null; } set { } }
+        public bool WriteOnlyWhenDifferent { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public override bool Execute() { throw null; }
     }
 }

src/XMakeTasks/FileIO/WriteLinesToFile.cs

@@ -4,12 +4,7 @@
 using System;
 using System.IO;
 using System.Text;
-using System.Diagnostics;
-using System.Collections;
-using System.Globalization;
-
 using Microsoft.Build.Framework;
-using Microsoft.Build.Utilities;
 using Microsoft.Build.Shared;
 
 namespace Microsoft.Build.Tasks
@@ -24,6 +19,9 @@ public class WriteLinesToFile : TaskExtension
         private bool _overwrite = false;
         private string _encoding = null;
 
+        // Default encoding taken from System.IO.WriteAllText()
+        private static readonly Encoding s_defaultEncoding = new UTF8Encoding(false, true);
+
         /// <summary>
         /// File to write lines to.
         /// </summary>
@@ -61,6 +59,13 @@ public string Encoding
             set { _encoding = value; }
         }
 
+        /// <summary>
+        /// If true, the target file specified, if it exists, will be read first to compare against
+        /// what the task would have written. If identical, the file is not written to disk and the
+        /// timestamp will be preserved.
+        /// </summary>
+        public bool WriteOnlyWhenDifferent { get; set; }
+
 
         /// <summary>
         /// Execute the task.
@@ -83,12 +88,12 @@ public override bool Execute()
                     }
                 }
 
-                Encoding encode = null;
+                Encoding encoding = s_defaultEncoding;
                 if (_encoding != null)
                 {
                     try
                     {
-                        encode = System.Text.Encoding.GetEncoding(_encoding);
+                        encoding = System.Text.Encoding.GetEncoding(_encoding);
                     }
                     catch (ArgumentException)
                     {
@@ -97,7 +102,6 @@ public override bool Execute()
                     }
                 }
 
-
                 try
                 {
                     if (Overwrite)
@@ -110,29 +114,41 @@ public override bool Execute()
                         }
                         else
                         {
-                            // Passing a null encoding, or Encoding.Default, to WriteAllText or AppendAllText
-                            // is not the same as calling the overload that does not take encoding!
-                            // Encoding.Default is based on the current codepage, the overload without encoding is UTF8-without-BOM.
-                            if (encode == null)
+                            string contentsAsString = null;
+
+                            try
+                            {
+                                // When WriteOnlyWhenDifferent is set, read the file and if they're the same return.
+                                if (WriteOnlyWhenDifferent && FileUtilities.FileExistsNoThrow(File.ItemSpec))
+                                {
+                                    var existingContents = System.IO.File.ReadAllText(File.ItemSpec);
+                                    if (existingContents.Length == buffer.Length)
+                                    {
+                                        contentsAsString = buffer.ToString();
+                                        if (existingContents.Equals(contentsAsString))
+                                        {
+                                            Log.LogMessageFromResources(MessageImportance.Low, "WriteLinesToFile.SkippingUnchangedFile", File.ItemSpec);
+                                            return true;
+                                        }
+                                    }
+                                }
+                            }
+                            catch (IOException)
                             {
-                                System.IO.File.WriteAllText(File.ItemSpec, buffer.ToString());
+                                Log.LogMessageFromResources(MessageImportance.Low, "WriteLinesToFile.ErrorReadingFile", File.ItemSpec);
                             }
-                            else
+
+                            if (contentsAsString == null)
                             {
-                                System.IO.File.WriteAllText(File.ItemSpec, buffer.ToString(), encode);
+                                contentsAsString = buffer.ToString();
                             }
+
+                            System.IO.File.WriteAllText(File.ItemSpec, contentsAsString, encoding);
                         }
                     }
                     else
                     {
-                        if (encode == null)
-                        {
-                            System.IO.File.AppendAllText(File.ItemSpec, buffer.ToString());
-                        }
-                        else
-                        {
-                            System.IO.File.AppendAllText(File.ItemSpec, buffer.ToString(), encode);
-                        }
+                        System.IO.File.AppendAllText(File.ItemSpec, buffer.ToString(), encoding);
                     }
                 }
                 catch (Exception e) when (ExceptionHandling.IsIoRelatedException(e))

src/XMakeTasks/Hash.cs

@@ -0,0 +1,62 @@
+using System.Security.Cryptography;
+using System.Text;
+using Microsoft.Build.Framework;
+
+namespace Microsoft.Build.Tasks
+{
+    /// <summary>
+    /// Generates a hash of a given ItemGroup items. Metadata is not considered in the hash.
+    /// <remarks>
+    /// Currently uses SHA1. Implementation subject to change between MSBuild versions. Not
+    /// intended as a cryptographic security measure, only uniqueness between build executions.
+    /// </remarks>
+    /// </summary>
+    public class Hash : TaskExtension
+    {
+        private const string ItemSeparatorCharacter = "\u2028";
+
+        /// <summary>
+        /// Items from which to generate a hash.
+        /// </summary>
+        [Required]
+        public ITaskItem[] ItemsToHash { get; set; }
+
+        /// <summary>
+        /// Hash of the ItemsToHash ItemSpec.
+        /// </summary>
+        [Output]
+        public string HashResult { get; set; }
+
+        /// <summary>
+        /// Execute the task.
+        /// </summary>
+        public override bool Execute()
+        {
+            if (ItemsToHash != null && ItemsToHash.Length > 0)
+            {
+                StringBuilder hashInput = new StringBuilder();
+
+                foreach (var item in ItemsToHash)
+                {
+                    hashInput.Append(item.ItemSpec);
+                    hashInput.Append(ItemSeparatorCharacter);
+                }
+
+                using (var sha1 = SHA1.Create())
+                {
+                    var hash = sha1.ComputeHash(Encoding.UTF8.GetBytes(hashInput.ToString()));
+                    var hashResult = new StringBuilder(hash.Length*2);
+
+                    foreach (byte b in hash)
+                    {
+                        hashResult.Append(b.ToString("x2"));
+                    }
+
+                    HashResult = hashResult.ToString();
+                }
+            }
+
+            return true;
+        }
+    }
+}

src/XMakeTasks/Microsoft.Build.Tasks.csproj

@@ -404,6 +404,7 @@
       <ExcludeFromStyleCop>true</ExcludeFromStyleCop>
     </Compile>
     <Compile Include="GetReferenceAssemblyPaths.cs" />
+    <Compile Include="Hash.cs" />
     <Compile Include="InstalledSDKResolver.cs" />
     <Compile Include="ErrorFromResources.cs" />
     <Compile Include="ExtractedClassName.cs">

src/XMakeTasks/Microsoft.Common.CurrentVersion.targets

@@ -3010,6 +3010,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       _GenerateCompileInputs;
       BeforeCompile;
       _TimeStampBeforeCompile;
+      _GenerateCompileDependencyCache;
       CoreCompile;
       _TimeStampAfterCompile;
       AfterCompile;
@@ -3164,6 +3165,31 @@ Copyright (C) Microsoft Corporation. All rights reserved.
 
   </Target>
 
+  <!--
+    ============================================================
+                                        _GenerateCompileDependencyCache
+
+    Generate a file used to track compiler dependencies between incremental build
+    executions. This handles cases where items are added or removed from a glob (e.g.
+    <Compile Include="**\*.cs" />) and can't otherwise be detected with timestamp 
+    comparisons. The file contains a hash of compiler inputs that are known to 
+    contribute to incremental build inconsistencies.
+    ============================================================
+    -->
+  <Target Name="_GenerateCompileDependencyCache" DependsOnTargets="ResolveAssemblyReferences">
+    <ItemGroup>
+      <CustomAdditionalCompileInputs Include="$(IntermediateOutputPath)CoreCompileInputs.cache" />
+      <CoreCompileCache Include="@(Compile->'%(FullPath)')" />
+      <CoreCompileCache Include="@(ReferencePath->'%(FullPath)')" />
+    </ItemGroup>
+
+    <Hash ItemsToHash="@(CoreCompileCache)">
+      <Output TaskParameter="HashResult" PropertyName="CoreCompileDependencyHash" />
+    </Hash>
+
+    <WriteLinesToFile Lines="$(CoreCompileDependencyHash)" File="$(IntermediateOutputPath)CoreCompileInputs.cache" Overwrite="True" WriteOnlyWhenDifferent="True" />
+  </Target>
+
   <!--
     ============================================================
                                         _TimeStampAfterCompile

src/XMakeTasks/Microsoft.Common.tasks

@@ -125,6 +125,7 @@
     <UsingTask TaskName="Microsoft.Build.Tasks.GetFrameworkPath"                      AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.Build.Tasks.GetFrameworkSdkPath"                   AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.Build.Tasks.GetReferenceAssemblyPaths"             AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
+    <UsingTask TaskName="Microsoft.Build.Tasks.Hash"                                  AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.Build.Tasks.LC"                                    AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.Build.Tasks.MakeDir"                               AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />
     <UsingTask TaskName="Microsoft.Build.Tasks.Message"                               AssemblyName="Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition="'$(MSBuildAssemblyVersion)' != ''" />

src/XMakeTasks/Resources/Strings.resx

@@ -2085,6 +2085,14 @@
     <value>MSB3491: Could not write lines to file "{0}". {1}</value>
     <comment>{StrBegin="MSB3491: "}</comment>
   </data>
+  <data name="WriteLinesToFile.ErrorReadingFile">
+    <value>MSB3492: Could not read existing file "{0}" to determine whether its contents are up to date. Overwriting it.</value>
+    <comment>{StrBegin="MSB3491: "}</comment>
+  </data>
+  <data name="WriteLinesToFile.SkippingUnchangedFile">
+    <value>MSB3493: </value>
+    <comment>{StrBegin="Skipping write to file "{0}" because content would not change."}</comment>
+  </data>
   <!--
         The GetReferenceAssemblyPaths message bucket is: MSB3642 - MSB3646.
         If this bucket overflows, pls. contact 'vsppbdev'.

src/XMakeTasks/UnitTests/Hash_Tests.cs

@@ -0,0 +1,59 @@
+using Microsoft.Build.Framework;
+using Microsoft.Build.UnitTests;
+using Microsoft.Build.Utilities;
+using Xunit;
+
+namespace Microsoft.Build.Tasks.UnitTests
+{
+    public class Hash_Tests
+    {
+        [Fact]
+        public void HashTaskTest()
+        {
+            // This hash was pre-computed. If the implementation changes it may need to be adjusted.
+            var expectedHash = "5593e2db83ac26117cd95ed8917f09b02a02e2a0";
+
+            var actualHash = ExecuteHashTask(new ITaskItem[]
+            {
+                new TaskItem("Item1"), new TaskItem("Item2"), new TaskItem("Item3")
+            });
+            Assert.Equal(expectedHash, actualHash);
+
+            // Try again to ensure the same hash
+            var actualHash2 = ExecuteHashTask(new ITaskItem[]
+            {
+                new TaskItem("Item1"), new TaskItem("Item2"), new TaskItem("Item3")
+            });
+            Assert.Equal(expectedHash, actualHash2);
+        }
+
+        [Fact]
+        public void HashTaskEmptyInputTest()
+        {
+            // Hash should be valid for empty item
+            var emptyItemHash = ExecuteHashTask(new ITaskItem[] {new TaskItem("")});
+            Assert.False(string.IsNullOrWhiteSpace(emptyItemHash));
+            Assert.NotEmpty(emptyItemHash);
+
+            // Hash should be null for null ItemsToHash or array of length 0
+            var nullItemsHash = ExecuteHashTask(null);
+            Assert.Null(nullItemsHash);
+
+            var zeroLengthItemsHash = ExecuteHashTask(new ITaskItem[0]);
+            Assert.Null(zeroLengthItemsHash);
+        }
+
+        private string ExecuteHashTask(ITaskItem[] items)
+        {
+            var hashTask = new Hash
+            {
+                BuildEngine = new MockEngine(),
+                ItemsToHash = items
+            };
+
+            Assert.True(hashTask.Execute());
+
+            return hashTask.HashResult;
+        }
+    }
+}

src/XMakeTasks/UnitTests/Microsoft.Build.Tasks.UnitTests.csproj

@@ -62,6 +62,7 @@
     <Compile Include="FindInList_Tests.cs" />
     <Compile Include="FindUnderPath_Tests.cs" />
     <Compile Include="GenerateBindingRedirects_Tests.cs" />
+    <Compile Include="Hash_Tests.cs" />
     <Compile Include="GenerateResource_Tests.cs" />
     <Compile Include="GetReferencePaths_Tests.cs" />
     <Compile Include="DirectoryBuildProjectImportTestBase.cs" />