[Xamarin.Android.Build.Tasks] optimize $(AssemblySearchPaths) (#2223)

jonathanpeppers · jonpryor · commit e39070277336 · 2018-09-26T11:08:16.000-04:00
Context: https://docs.microsoft.com/en-us/visualstudio/msbuild/resolveassemblyreference-task?view=vs-2017 Context: https://twitter.com/KirillOsenkov/status/1043725067081764865 @KirillOsenkov added a new analyzer to the Windows binlog viewer, noting `$(AssemblySearchPaths)` that are unused during a build. Looking at what we are using currently, it reports: Unused AssemblySearchPaths locations {AssemblyFolders} {AssemblyFoldersFromConfig:C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\AssemblyFolders.config,v9.0} {CandidateAssemblyFiles} {Registry:Software\Microsoft\MonoAndroid,v9.0,AssemblyFoldersEx} bin\Debug\ Luckily, we already had MSBuild logic in place to remove `{GAC}` from this list. But we certainly are probing search paths that are nonsensical for Xamarin.Android: - `{AssemblyFolders}`: Specifies the task will use the Visual Studio.NET 2003 finding-assemblies-from-registry scheme. - `{AssemblyFoldersFromConfig:*}`: this probes the system-wide config file in the MSBuild / Visual Studio install - `{CandidateAssemblyFiles}`: The `CandidateAssemblyFiles` property on `ResolveAssemblyReferences` is blank. Docs say: Assemblies in this list will be considered when the SearchPaths parameter contains `{CandidateAssemblyFiles}` as one of the paths to consider. - `{Registry:*}`: probe the Windows registry... - `bin\Debug` or `$(OutputPath)`: not needed, and a potential cause of confusion. This would be if there was an arbitrary extra assembly sitting in `$(OutputPath)`. And if we look further, we see odd things: Primary reference "System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e". Resolved file path is "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Control\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v1.0\System.dll". Reference found at search path location "{TargetFrameworkDirectory}". For SearchPath "{TargetFrameworkDirectory}". Considered "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Control\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v9.0\System.winmd", but it didn't exist. Considered "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Control\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v9.0\System.dll", but it didn't exist. Considered "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Control\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v9.0\System.exe", but it didn't exist. Considered "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Control\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v1.0\System.winmd", but it didn't exist. Why are we looking for `.winmd` files? This is a UWP thing... And then apparently, our build also will look for `.pri` files? Another UWP thing... AllowedRelatedFileExtensions .pdb .xml .pri .dll.config .exe.config .dll.mdb .exe.mdb So the first fix is to trim `$(AssemblySearchPaths)` to precisely what Xamarin.Android needs: <AssemblySearchPaths> {HintPathFromItem}; {TargetFrameworkDirectory}; {RawFileName}; </AssemblySearchPaths> We shouldn't be concerned about other system-wide places. Next, we should only be looking at these file extensions: <AllowedReferenceAssemblyFileExtensions> .dll; </AllowedReferenceAssemblyFileExtensions> <AllowedReferenceRelatedFileExtensions> .pdb; .xml; .dll.config; .dll.mdb; </AllowedReferenceRelatedFileExtensions> Removing `.winmd` from `$(AllowedReferenceAssemblyFileExtensions)` and `.pri` from `$(AllowedReferenceRelatedFileExtensions)`. We can also ignore `.exe*` files, since Xamarin.Android projects only use `.dll` files. This makes the log probing for `System.dll` much cleaner: Primary reference "System, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e". Resolved file path is "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Release\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v1.0\System.dll". Reference found at search path location "{TargetFrameworkDirectory}". For SearchPath "{TargetFrameworkDirectory}". Considered "C:\Users\myuser\Desktop\Git\xamarin-android\bin\Release\lib\xamarin.android\xbuild-frameworks\MonoAndroid\v9.0\System.dll", but it didn't exist. Here is the log of changes made to these properties here at MSBuild evaluation time: Property reassignment: $(AssemblySearchPaths)=" {HintPathFromItem}; {TargetFrameworkDirectory}; {RawFileName}; " (previous value: " {CandidateAssemblyFiles}; ; {HintPathFromItem}; {TargetFrameworkDirectory}; {AssemblyFoldersFromConfig:C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\AssemblyFolders.config,v9.0}; {Registry:Software\Microsoft\MonoAndroid,v9.0,AssemblyFoldersEx}; {AssemblyFolders}; {GAC}; {RawFileName}; bin\Debug\ ") at xamarin-android\bin\Release\lib\xamarin.android\xbuild\Xamarin\Android\Xamarin.Android.Common.targets (338,2) Property reassignment: $(AllowedReferenceAssemblyFileExtensions)=" .dll; " (previous value: " .winmd; .dll; .exe ") at xamarin-android\bin\Release\lib\xamarin.android\xbuild\Xamarin\Android\Xamarin.Android.Common.targets (343,2) Property reassignment: $(AllowedReferenceRelatedFileExtensions)=" .pdb; .xml; .dll.config; .dll.mdb; " (previous value: " .pdb; .xml; .pri; .dll.config; .exe.config ") at xamarin-android\bin\Release\lib\xamarin.android\xbuild\Xamarin\Android\Xamarin.Android.Common.targets (347,2) ~~ Results ~~ I timed the Xamarin.Forms Control Gallery project, since I felt this change would improve larger projects the most. Project here: https://github.com/jonathanpeppers/Xamarin.Forms/tree/msbuild-timing Before: 1106 ms ResolveAssemblies 2 calls 1401 ms ResolveAssemblyReference 18 calls After: 909 ms ResolveAssemblies 2 calls 1088 ms ResolveAssemblyReference 18 calls This seems to directly save ~500ms to these targets in incremental builds for this project. This project references ~7 other Xamarin.Android projects. ~~ Upstream ~~ On MacOS, I also see probing for `.winmd` files! Considered "xamarin-android/bin/Debug/lib/xamarin.android/xbuild-frameworks/MonoAndroid/v9.0/System.winmd", but it didn't exist. Perhaps we need some upstream changes to MSBuild as well...
diff --git a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
@@ -336,8 +336,20 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 
 <!-- Do not resolve from the GAC under any circumstances in Mobile -->
 <PropertyGroup>
-	<AssemblySearchPaths>$([System.String]::Copy('$(AssemblySearchPaths)').Replace('{GAC}',''))</AssemblySearchPaths>
-	<AssemblySearchPaths Condition="'$(MSBuildRuntimeVersion)' != ''">$(AssemblySearchPaths.Split(';'))</AssemblySearchPaths>
+	<AssemblySearchPaths>
+		{HintPathFromItem};
+		{TargetFrameworkDirectory};
+		{RawFileName};
+	</AssemblySearchPaths>
+	<AllowedReferenceAssemblyFileExtensions>
+		.dll;
+	</AllowedReferenceAssemblyFileExtensions>
+	<AllowedReferenceRelatedFileExtensions>
+		.pdb;
+		.xml;
+		.dll.config;
+		.dll.mdb;
+	</AllowedReferenceRelatedFileExtensions>
 </PropertyGroup>
 
 <Target Name="_SeparateAppExtensionReferences">
