Cleanup: Remove Mono support (#9745)

### Context

The time has come to clean up the repo and remove Mono specific code.

### Changes Made

Deleted everything Mono. No changes to any of the supported platforms.

### Testing

Existing unit tests.

Directory.Build.props

@@ -9,7 +9,7 @@
 
   <PropertyGroup>
     <Product>Microsoft® Build Tools®</Product>
-    <Configurations>Debug;Release;Debug-MONO;Release-MONO;MachineIndependent</Configurations>
+    <Configurations>Debug;Release;MachineIndependent</Configurations>
   </PropertyGroup>
 
   <PropertyGroup>
@@ -60,17 +60,6 @@
     <NoWarn>$(NoWarn);NU1507;NU1603;NU5105;1701;1702;SYSLIB0011;SYSLIB0037;SYSLIB0044;RS0016;RS0017;</NoWarn>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(Configuration)' == 'Debug-MONO'">
-    <DebugSymbols Condition="'$(DebugSymbols)' == ''">true</DebugSymbols>
-    <Optimize Condition="'$(Optimize)' == ''">false</Optimize>
-    <DefineConstants>$(DefineConstants);DEBUG</DefineConstants>
-    <MonoBuild>true</MonoBuild>
-  </PropertyGroup>
-  <PropertyGroup Condition="'$(Configuration)' == 'Release-MONO'">
-    <DebugSymbols Condition="'$(DebugSymbols)' == ''">true</DebugSymbols>
-    <Optimize Condition="'$(Optimize)' == ''">true</Optimize>
-    <MonoBuild>true</MonoBuild>
-  </PropertyGroup>
   <!-- Configuration MSBuild for portable (xcopy-install) toolsets: works on WinNT and linux/mac via Mono, isolates from machine environment:
     uses only tools installed with it, ignores Registry and GAC and Visual Studio installations to provide the same build experience on all machines -->
   <PropertyGroup Condition="'$(Configuration)' == 'MachineIndependent'">

README.md

@@ -41,7 +41,6 @@ Before you contribute, please read through the contributing and developer guides
 * **Developer Guide on:**
    - [.NET Core](documentation/wiki/Building-Testing-and-Debugging-on-.Net-Core-MSBuild.md)
    - [Full Framework](documentation/wiki/Building-Testing-and-Debugging-on-Full-Framework-MSBuild.md)
-   - [Mono](documentation/wiki/Building-Testing-and-Debugging-on-Mono-MSBuild.md)
 
 * See our [help wanted issues](https://github.com/dotnet/msbuild/issues?q=is%3Aopen+is%3Aissue+label%3A%22help+wanted%22) for a list of issues we think are great to onboard new developers.
    - **Note:** Please leave a comment asking to be assigned the issue if you want to work on it.

eng/AfterSigning.targets

@@ -10,6 +10,6 @@
         <Copy
             SourceFiles="$(ArtifactsBinDir)MSBuildTaskHost\x64\Release\net35\MSBuildTaskHost.pdb"
             DestinationFolder="$(ArtifactsSymStoreDirectory)\MSBuildTaskHost\net35\amd64"
-            Condition="'$(MSBuildRuntimeType)' != 'Core' and '$(MonoBuild)' != 'true'"/>
+            Condition="'$(MSBuildRuntimeType)' != 'Core'"/>
     </Target>
 </Project>

eng/BootStrapMSBuild.targets

@@ -2,7 +2,7 @@
 
   <!--
   Copies the binaries of MSBuild to a bootstrap folder so we can rebuild msbuild with itself.
-  On netcore and mono it performs a directory copy.
+  On netcore it performs a directory copy.
   On full framework it performs a more involved deployment.
    -->
 
@@ -11,7 +11,6 @@
     <BootstrapDestination Condition="'$(Platform)' == 'x64' or '$(Platform)' == 'arm64'">$(BootstrapDestination)$(Platform)\</BootstrapDestination>
     <BootstrapDestination>$(BootstrapDestination)$(TargetFramework.ToLowerInvariant())\MSBuild\</BootstrapDestination>
 
-    <!-- TODO: Mono build should use BootstrapNetCore logic -->
     <BootstrapDependsOn Condition="$(TargetFramework.StartsWith('net4'))">BootstrapFull</BootstrapDependsOn>
     <BootstrapDependsOn Condition="!$(TargetFramework.StartsWith('net4'))">BootstrapNetCore</BootstrapDependsOn>
 
@@ -72,10 +71,8 @@
       <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\Tracker*.exe" />
       <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\FileTracker*.dll" />
       <SdkResolverFiles Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Bin\SdkResolvers\Microsoft.DotNet.MSBuildSdkResolver\**\*.*" />
-      <NuGetSdkResolverManifest Include= "$(RepoRoot)src\MSBuild\SdkResolvers\VS\Microsoft.Build.NuGetSdkResolver.xml" Condition="'$(MonoBuild)' != 'true'" />
-      <NuGetSdkResolverManifest Include= "$(RepoRoot)src\MSBuild\SdkResolvers\Standalone\Microsoft.Build.NuGetSdkResolver.xml" Condition="'$(MonoBuild)' == 'true'" />
+      <NuGetSdkResolverManifest Include="$(RepoRoot)src\MSBuild\SdkResolvers\VS\Microsoft.Build.NuGetSdkResolver.xml" />
       <InstalledSdks Include="$(DOTNET_INSTALL_DIR)\sdk\$(DotNetCliVersion)\Sdks\**\*.*" />
-      <InstalledSdks Include="$(MSBuildBinPath)\Sdks\**\*" Condition="'$(MonoBuild)' == 'true'" />
 
       <InstalledStaticAnalysisTools Include="$(VsInstallRoot)\Team Tools\Static Analysis Tools\**\*.*" />
 
@@ -140,11 +137,6 @@
 
     <Copy SourceFiles="@(InstalledSdks)"
           DestinationFiles="@(InstalledSdks -> '$(BootstrapDestination)Sdks\%(RecursiveDir)%(Filename)%(Extension)')"
-          Condition="'$(MonoBuild)' != 'true'"
-          SkipUnchangedFiles="true" />
-    <Copy SourceFiles="@(InstalledSdks)"
-          DestinationFiles="@(InstalledSdks -> '$(BootstrapDestination)$(TargetMSBuildToolsVersion)\Bin\Sdks\%(RecursiveDir)%(Filename)%(Extension)')"
-          Condition="'$(MonoBuild)' == 'true'"
           SkipUnchangedFiles="true" />
 
     <Copy SourceFiles="@(InstalledStaticAnalysisTools)"
@@ -155,14 +147,9 @@
           DestinationFiles="@(InstalledNuGetFiles->'$(BootstrapDestination)Microsoft\NuGet\%(Filename)%(Extension)')"
           SkipUnchangedFiles="true" />
 
-    <Copy Condition="'$(MonoBuild)' != 'true'"
-          SourceFiles="@(_NuGetRuntimeDependencies)"
+    <Copy SourceFiles="@(_NuGetRuntimeDependencies)"
           DestinationFolder="$(BootstrapDestination)..\Common7\IDE\CommonExtensions\Microsoft\NuGet\"
           SkipUnchangedFiles="true" />
-    <Copy Condition="'$(MonoBuild)' == 'true'"
-          SourceFiles="@(_NuGetRuntimeDependencies)"
-          DestinationFolder="$(BootstrapDestination)$(TargetMSBuildToolsVersion)\Bin"
-          SkipUnchangedFiles="true" />
 
     <Copy SourceFiles="@(NuGetSdkResolverManifest)"
           DestinationFolder="$(BootstrapDestination)$(TargetMSBuildToolsVersion)\Bin\SdkResolvers\Microsoft.Build.NuGetSdkResolver"

eng/Versions.props

@@ -10,10 +10,9 @@
     <!-- Workaround for https://github.com/dotnet/roslyn/issues/35793 -->
     <SemanticVersioningV1>true</SemanticVersioningV1>
     <MicroBuildPluginsSwixBuildVersion>1.1.87</MicroBuildPluginsSwixBuildVersion>
-    <MonoBuild Condition="'$(Configuration)' == 'Debug-MONO' or '$(Configuration)' == 'Release-MONO'">true</MonoBuild>
   </PropertyGroup>
   <!-- Repo Toolset Features -->
-  <PropertyGroup Condition="'$(MonoBuild)' != 'true'">
+  <PropertyGroup>
     <UsingToolIbcOptimization>true</UsingToolIbcOptimization>
     <!-- Force a specific compiler version because record changes cause genapi output to flip-flop -->
     <UsingToolMicrosoftNetCompilers>true</UsingToolMicrosoftNetCompilers>

eng/cibuild_bootstrapped_msbuild.ps1

@@ -80,13 +80,6 @@ try {
     $buildToolPath = Join-Path $bootstrapRoot "net472\MSBuild\Current\Bin\MSBuild.exe"
     $buildToolCommand = "";
     $buildToolFramework = "net472"
-
-    if ($configuration -eq "Debug-MONO" -or $configuration -eq "Release-MONO")
-    {
-      # Copy MSBuild.dll to MSBuild.exe so we can run it without a host
-      $sourceDll = Join-Path $bootstrapRoot "net472\MSBuild\Current\Bin\MSBuild.dll"
-      Copy-Item -Path $sourceDll -Destination $msbuildToUse
-    }
   }
   else
   {

eng/cibuild_bootstrapped_msbuild.sh

@@ -44,15 +44,6 @@ PerfLogDir="$ArtifactsDir/log/$configuration/PerformanceLogs"
 . "$ScriptRoot/common/tools.sh"
 InitializeDotNetCli true
 
-if [ $host_type = "mono" ] ; then
-  export _InitializeBuildTool="msbuild"
-  export _InitializeBuildToolCommand=""
-  export _InitializeBuildToolFramework="net472"
-
-  configuration="$configuration-MONO"
-  extra_properties=" /p:DeterministicSourcePaths=false"
-fi
-
 if [[ $build_stage1 == true ]];
 then
 	/bin/bash "$ScriptRoot/common/build.sh" --restore --build --ci --configuration $configuration /p:CreateBootstrap=true $properties $extra_properties || exit $?
@@ -65,18 +56,6 @@ then
   _InitializeBuildTool="$_InitializeDotNetCli/dotnet"
   _InitializeBuildToolCommand="$bootstrapRoot/net8.0/MSBuild/MSBuild.dll"
   _InitializeBuildToolFramework="net8.0"
-elif [ $host_type = "mono" ]
-then
-  export _InitializeBuildTool="mono"
-  export _InitializeBuildToolCommand="$bootstrapRoot/net472/MSBuild/Current/Bin/MSBuild.dll"
-  export _InitializeBuildToolFramework="net472"
-
-  # FIXME: remove this once we move to a newer version of Arcade with a fix for $MonoTool
-  # https://github.com/dotnet/arcade/commit/f6f14c169ba19cd851120e0d572cd1c5619205b3
-  export MonoTool=`which mono`
-
-  extn_path="$bootstrapRoot/net472/MSBuild/Current/Bin/Extensions"
-  extra_properties=" /p:MSBuildExtensionsPath=$extn_path /p:MSBuildExtensionsPath32=$extn_path /p:MSBuildExtensionsPath64=$extn_path /p:DeterministicSourcePaths=false"
 else
   echo "Unsupported hostType ($host_type)"
   exit 1

src/Build.UnitTests/BackEnd/BuildManager_Tests.cs

@@ -325,8 +325,6 @@ public void VerifyEnvironmentSavedBetweenCalls()
         /// </summary>
 #if RUNTIME_TYPE_NETCORE
         [Theory(Skip = "https://github.com/dotnet/msbuild/issues/1975")]
-#elif MONO
-        [Theory(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
 #else
         [Theory(Skip = "https://github.com/dotnet/msbuild/issues/2057")]
 #endif
@@ -403,11 +401,7 @@ public void ShutdownNodesAfterParallelBuild(int numberOfParallelProjectsToBuild,
         /// <summary>
         /// A simple successful build, out of process only.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void SimpleBuildOutOfProcess()
         {
             RunOutOfProcBuild(_ => _env.SetEnvironmentVariable("MSBUILDNOINPROCNODE", "1"));
@@ -416,11 +410,7 @@ public void SimpleBuildOutOfProcess()
         /// <summary>
         /// A simple successful build, out of process only. Triggered by setting build parameters' DisableInProcNode to true.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void DisableInProcNode()
         {
             RunOutOfProcBuild(buildParameters => buildParameters.DisableInProcNode = true);
@@ -466,11 +456,7 @@ private void RunOutOfProcBuild(Action<BuildParameters> buildParametersModifier)
             Assert.NotEqual(Process.GetCurrentProcess().Id, processId); // "Build is expected to be out-of-proc. In fact it was in-proc."
         }
 
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void RequestedResultsAreSatisfied()
         {
             const string contents = @"
@@ -689,8 +675,6 @@ public void MsBuildForwardAllPropertiesFromChildLaunchChildNode()
         /// </summary>
 #if RUNTIME_TYPE_NETCORE
         [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1976")]
-#elif MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
 #else
         [Fact]
 #endif
@@ -742,8 +726,6 @@ public void OutOfProcNodeForwardCertainproperties()
         /// </summary>
 #if RUNTIME_TYPE_NETCORE
         [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1976")]
-#elif MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
 #else
         [Fact]
 #endif
@@ -811,11 +793,7 @@ public void OutOfProcNodeForwardCertainpropertiesAlsoGetResultsFromCache()
         /// Make sure when if the environment variable MsBuildForwardPropertiesFromChild is set to empty and
         /// we launch a child node that we get no properties
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void ForwardNoPropertiesLaunchChildNode()
         {
             string contents = CleanupFileContents(@"
@@ -855,8 +833,6 @@ public void ForwardNoPropertiesLaunchChildNode()
         /// </summary>
 #if RUNTIME_TYPE_NETCORE
         [Fact(Skip = "https://github.com/dotnet/msbuild/issues/933")]
-#elif MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
 #else
         [Fact]
 #endif
@@ -916,11 +892,7 @@ public override bool Execute()
         /// When a child node is launched by default we should not send any properties.
         /// we launch a child node that we get no properties
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void ForwardNoPropertiesLaunchChildNodeDefault()
         {
             string contents = CleanupFileContents(@"
@@ -2139,11 +2111,7 @@ public void Regress251333()
         /// <summary>
         /// Verify that disabling the in-proc node doesn't cause projects which don't require it to fail.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void Regress239661()
         {
             string contents = CleanupFileContents(@"
@@ -2201,11 +2169,7 @@ public void ExplicitInprocAffinityGetsOverruledByDisableInprocNode()
         /// <summary>
         /// Ensures that properties and items are transferred to the out-of-proc node when an instance is used to start the build.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void ProjectInstanceTransfersToOOPNode()
         {
             string contents = CleanupFileContents(@"
@@ -2266,11 +2230,7 @@ public void ProjectInstanceTransfersToOOPNode()
         /// <summary>
         /// Ensures that a limited set of properties are transferred from a project instance to an OOP node.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void ProjectInstanceLimitedTransferToOOPNode()
         {
             string contents = CleanupFileContents(@"
@@ -2566,8 +2526,6 @@ public void NonOverlappingEnusingTrypointTargetsShouldNotInfluenceEachOthersResu
         /// </summary>
 #if RUNTIME_TYPE_NETCORE
         [Fact(Skip = "https://github.com/dotnet/msbuild/issues/933")]
-#elif MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
 #else
         [Fact]
 #endif
@@ -2665,11 +2623,7 @@ public void Regress473114()
         /// second request will bail out where the first request did, as though it had
         /// executed the target, rather than skipping and continuing.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void VerifyMultipleRequestForSameProjectWithErrors_Simple()
         {
             var projA = _env.CreateFile(".proj").Path;
@@ -2748,11 +2702,7 @@ public void VerifyMultipleRequestForSameProjectWithErrors_Simple()
         /// expected in the first request, but be skipped by the second (since if it's "skipping
         /// unsuccessful", it can assume that all other OnError targets have also already been run)
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void VerifyMultipleRequestForSameProjectWithErrors_OnErrorChain()
         {
             var projA = _env.CreateFile(".proj").Path;
@@ -2867,11 +2817,7 @@ public void VerifyMultipleRequestForSameProjectWithErrors_OnErrorChain()
         /// they're marked as ContinueOnError=ErrorAndContinue, then we won't bail, but
         /// will continue executing (on the first request) or skipping (on the second)
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void VerifyMultipleRequestForSameProjectWithErrors_ErrorAndContinue()
         {
             var projA = _env.CreateFile(".proj").Path;
@@ -2957,11 +2903,7 @@ public void VerifyMultipleRequestForSameProjectWithErrors_ErrorAndContinue()
         /// This test verifies that if the errors are in AfterTargets, we still
         /// exit as though the target that those targets run after has already run.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1240")]
-#else
         [Fact]
-#endif
         public void VerifyMultipleRequestForSameProjectWithErrors_AfterTargets()
         {
             var projA = _env.CreateFile(".proj").Path;
@@ -3244,11 +3186,7 @@ public void TestSimultaneousSubmissionsWithLegacyThreadingData_P2P()
         /// submissions aren't restricted to running strictly serially by the single in-proc
         /// node.
         /// </summary>
-#if MONO
-        [Fact(Skip = "https://github.com/dotnet/msbuild/issues/1245")]
-#else
         [Fact]
-#endif
         public void TestSimultaneousSubmissionsWithLegacyThreadingData_P2P_MP()
         {
             string projectContent1 = @"<Project ToolsVersion=`msbuilddefaulttoolsversion` xmlns=`msbuildnamespace`>

src/Build.UnitTests/Evaluation/ProjectRootElementCache_Tests.cs

@@ -79,7 +79,7 @@ public void AddEntry()
         /// <summary>
         /// Tests that a strong reference is held to a single item
         /// </summary>
-        [WindowsFullFrameworkOnlyFact(additionalMessage: "This test fails on .NET Core and Mono: https://github.com/dotnet/msbuild/issues/282")]
+        [WindowsFullFrameworkOnlyFact(additionalMessage: "This test fails on .NET Core: https://github.com/dotnet/msbuild/issues/282")]
         public void AddEntryStrongReference()
         {
             string projectPath = NativeMethodsShared.IsUnixLike ? "/foo" : "c:\\foo";