[Xamarin.Android.Build.Tasks] fix enormous string expansion

Documentation/guides/MSBuildBestPractices.md

@@ -106,6 +106,63 @@ abbreviation could be used if the name is quite long, such as:
 [msbuild-transforms]: https://docs.microsoft.com/en-us/visualstudio/msbuild/msbuild-transforms
 [msbuild-metadata]: https://docs.microsoft.com/en-us/visualstudio/msbuild/msbuild-well-known-item-metadata
 
+## Conditions
+
+You can skip an MSBuild `<Target/>` or task with a `Condition` such
+as:
+
+```xml
+<Target Name="Foo" Condition=" '$(Bar)' == 'true' ">
+  <!-- ... -->
+</Target>
+```
+
+If you want to skip the target if an item group is empty, you might be
+tempted to do:
+
+```xml
+<Target Name="Foo" Condition=" '@(MyItems)' != '' ">
+  <!-- ... -->
+</Target>
+```
+
+If you think about what this does, it's doing a `string.Join()` on
+`@(MyItems)` to compare if it matches an empty string. Luckily MSBuild
+has a "fast path" for evaluating against an empty string, but it still
+can generate the log message:
+
+```
+Target "Foo" skipped, due to false condition; ('@(MyItems)' != '') was evaluated as ('A;B;C' != '')
+```
+
+If `@(MyItems)` was 100 full paths to files, this would be a long log
+message!
+
+The solution is you should generally do this instead:
+
+```xml
+<Target Name="Foo" Condition=" '@(MyItems->Count())' != '0' ">
+  <!-- ... -->
+</Target>
+```
+
+This causes MSBuild to always generate a reasonable log message:
+
+```
+Target "Foo" skipped, due to false condition; ('@(MyItems->Count())' != '0') was evaluated as ('100' != '0')
+```
+
+`->Count()` will return 0 even if the item group does not exist. See
+the [MSBuild Documentation][itemfunctions] for details.
+
+Some links around the logging behavior:
+
+* https://github.com/dotnet/msbuild/issues/5315
+* https://github.com/dotnet/msbuild/pull/5553
+* https://github.com/dotnet/roslyn/pull/46445
+
+[itemfunctions]: https://docs.microsoft.com/visualstudio/msbuild/item-functions
+
 ## Incremental Builds
 
 The MSBuild Github repo has some [documentation][msbuild] on this

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Aapt2.targets

@@ -194,12 +194,12 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 </Target>
 
 <Target Name="_FixupCustomViewsForAapt2"
-    Condition=" '$(_AndroidUseAapt2)' == 'True' And '@(_ProcessedCustomViews)' != '' ">
+    Condition=" '$(_AndroidUseAapt2)' == 'True' And '@(_ProcessedCustomViews->Count())' != '0' ">
   <ItemGroup>
     <_ItemsToFixup Include="@(_CompileResourcesInputs)" Condition=" '@(_ProcessedCustomViews->'%(Identity)')' == '%(Identity)' "/>
   </ItemGroup>
   <Aapt2Compile
-      Condition=" '$(AndroidUseAapt2)' == 'True' And '@(_ItemsToFixup)' != '' "
+      Condition=" '$(AndroidUseAapt2)' == 'True' And '@(_ItemsToFixup->Count())' != '0' "
       ContinueOnError="$(DesignTimeBuild)"
       DaemonMaxInstanceCount="$(Aapt2DaemonMaxInstanceCount)"
       DaemonKeepInDomain="$(_Aapt2DaemonKeepInDomain)"
@@ -212,7 +212,7 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
       ToolExe="$(Aapt2ToolExe)">
     <Output TaskParameter="CompiledResourceFlatFiles" ItemName="_UpdatedFlatFiles" />
   </Aapt2Compile>
-  <Touch Files="$(_AndroidResgenFlagFile)" AlwaysCreate="True" Condition=" '@(_UpdatedFlatFiles)' != '' " />
+  <Touch Files="$(_AndroidResgenFlagFile)" AlwaysCreate="True" Condition=" '@(_UpdatedFlatFiles->Count())' != '0' " />
 </Target>
 
 <Target Name="_CreateBaseApkWithAapt2"

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Bindings.Core.targets

@@ -38,14 +38,14 @@ It is shared between "legacy" binding projects and .NET 5 projects.
 
   <Target Name="ExportJarToXml"
       DependsOnTargets="$(ExportJarToXmlDependsOnTargets)"
-      Condition=" '$(UsingAndroidNETSdk)' != 'true' Or '@(InputJar)' != '' Or '@(EmbeddedJar)' != '' ">
+      Condition=" '$(UsingAndroidNETSdk)' != 'true' Or '@(InputJar->Count())' != '0' Or '@(EmbeddedJar->Count())' != '0' ">
     <PropertyGroup>
       <AllowUnsafeBlocks Condition=" '$(AllowUnsafeBlocks)' != 'true' ">true</AllowUnsafeBlocks>
     </PropertyGroup>
   </Target>
 
   <Target Name="GenerateBindings"
-      Condition=" '$(UsingAndroidNETSdk)' != 'true' Or '@(InputJar)' != '' Or '@(EmbeddedJar)' != '' "
+      Condition=" '$(UsingAndroidNETSdk)' != 'true' Or '@(InputJar->Count())' != '0' Or '@(EmbeddedJar->Count())' != '0' "
       DependsOnTargets="ExportJarToXml;_ResolveMonoAndroidSdks"
       Inputs="$(ApiOutputFile);@(TransformFile);@(ReferencePath);@(ReferenceDependencyPaths);$(MSBuildAllProjects)"
       Outputs="$(_GeneratorStampFile)">

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Bindings.Documentation.targets

@@ -57,7 +57,7 @@ This file is only used by binding projects. .NET 5 can eventually use it, once `
   </Target>
 
   <Target Name="BuildDocumentation"
-      Condition=" '@(JavaDocIndex)' != '' And '$(_JavadocSupported)' == 'True' "
+      Condition=" '@(JavaDocIndex->Count())' != '0' And '$(_JavadocSupported)' == 'True' "
       Inputs="@(JavaDocIndex);@(IntermediateAssembly->'$(IntermediateOutputPath)%(filename).xml')"
       Outputs="@(IntermediateAssembly->'$(OutputPath)%(filename).xml')">
     <MDoc

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Wear.targets

@@ -18,7 +18,7 @@ This file is only used by "legacy" Xamarin.Android projects.
   </PropertyGroup>
 
   <Target Name="_PrepareWearApplication"
-      Condition=" $(AndroidApplication) And '@(_AppExtensionReference)' != '' "
+      Condition=" $(AndroidApplication) And '@(_AppExtensionReference->Count())' != '0' "
       DependsOnTargets="_ValidateAndroidPackageProperties">
     <ParseAndroidWearProjectAndManifest ProjectFiles="@(_AppExtensionReference)">
       <Output TaskParameter="ApplicationManifestFile" PropertyName="BundledWearApplicationManifestFile" />

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -754,7 +754,7 @@ because xbuild doesn't support framework reference assemblies.
 		Files="@(Content)"
 		Code="XA0101"
 		Text="%40(Content) build action is not supported"
-		Condition=" '@(Content)' != '' "
+		Condition=" '@(Content->Count())' != '0' "
 	/>
 </Target>
 
@@ -1008,7 +1008,7 @@ because xbuild doesn't support framework reference assemblies.
 	<RemoveUnknownFiles Files="@(_AndroidResourceDest)" Directory="$(MonoAndroidResDirIntermediate)" RemoveDirectories="true">
 		<Output ItemName="_AndroidResourceDestRemovedFiles" TaskParameter="RemovedFiles" />
 	</RemoveUnknownFiles>
-	<Touch Files="$(_AndroidResFlagFile)" AlwaysCreate="True" Condition=" !Exists ('$(_AndroidResFlagFile)') Or  '@(_ModifiedResources)' != '' Or '@(_AndroidResourceDestRemovedFiles)' != '' " />
+	<Touch Files="$(_AndroidResFlagFile)" AlwaysCreate="True" Condition=" !Exists ('$(_AndroidResFlagFile)') Or  '@(_ModifiedResources->Count())' != '0' Or '@(_AndroidResourceDestRemovedFiles->Count())' != '0' " />
 	<ItemGroup>
 		<FileWrites Include="$(_AndroidResFlagFile)" />
 	</ItemGroup>
@@ -1032,7 +1032,7 @@ because xbuild doesn't support framework reference assemblies.
 </Target>
 
 <Target Name="_FindLayoutsForBinding"
-    Condition=" '$(Language)' == 'C#' And ('$(AndroidGenerateLayoutBindings)' == 'True' Or '@(AndroidBoundLayout)' != '') ">
+    Condition=" '$(Language)' == 'C#' And ('$(AndroidGenerateLayoutBindings)' == 'True' Or '@(AndroidBoundLayout->Count())' != '0') ">
   <FindLayoutsToBind
       GenerateLayoutBindings="$(AndroidGenerateLayoutBindings)"
       BoundLayouts="@(AndroidBoundLayout)"
@@ -1068,18 +1068,18 @@ because xbuild doesn't support framework reference assemblies.
 </Target>
 
 <Target Name="_IncludeLayoutBindingSources" DependsOnTargets="_GenerateLayoutBindings" Condition=" '$(Language)' == 'C#' ">
-	<ItemGroup Condition=" '@(_LayoutForBinding)' != '' ">
+	<ItemGroup Condition=" '@(_LayoutForBinding->Count())' != '0' ">
 		<Compile Include="$(MSBuildThisFileDirectory)\LayoutBinding$(DefaultLanguageSourceExtension)" />
 	</ItemGroup>
 
-	<ItemGroup Condition=" '@(_LayoutForBinding)' != '' ">
+	<ItemGroup Condition=" '@(_LayoutForBinding->Count())' != '0' ">
 		<Compile Include="$(MonoAndroidCodeBehindDir)\%(_LayoutForBinding.LayoutBindingFileName)"
 			Condition="Exists ('$(MonoAndroidCodeBehindDir)\%(_LayoutForBinding.LayoutBindingFileName)')"/>
 		<FileWrites Include="$(MonoAndroidCodeBehindDir)\%(_LayoutForBinding.LayoutBindingFileName)"
 			    Condition="Exists ('$(MonoAndroidCodeBehindDir)\%(_LayoutForBinding.LayoutBindingFileName)')"/>
 	</ItemGroup>
 
-	<ItemGroup Condition=" '@(_LayoutPartialClass)' != '' ">
+	<ItemGroup Condition=" '@(_LayoutPartialClass->Count())' != '0' ">
 	        <Compile Include="$(MonoAndroidCodeBehindDir)\%(_LayoutPartialClass.LayoutPartialClassFileName)"
 			Condition="Exists ('$(MonoAndroidCodeBehindDir)\%(_LayoutPartialClass.LayoutPartialClassFileName)')"/>
 		<FileWrites Include="$(MonoAndroidCodeBehindDir)\%(_LayoutPartialClass.LayoutPartialClassFileName)"
@@ -1218,7 +1218,7 @@ because xbuild doesn't support framework reference assemblies.
 </PropertyGroup>
 
 <Target Name="UpdateAndroidInterfaceProxies"
-	Condition="@(AndroidInterfaceDescription) != ''"
+	Condition=" '@(AndroidInterfaceDescription->Count())' != '0' "
 	DependsOnTargets="$(CoreResolveReferencesDependsOn);_RunManagedAidlTool;_AddManagedAidlOutputsToCompile" />
 
 <Target Name="_RunManagedAidlTool">

src/Xamarin.Android.Build.Tasks/Xamarin.Android.EmbeddedResource.targets

@@ -94,7 +94,7 @@ This file is used by all project types, including binding projects.
   </Target>
 
   <Target Name="_CreateNativeLibraryArchive"
-      Condition=" '$(AndroidApplication)' != 'true' And '@(EmbeddedNativeLibrary)' != '' "
+      Condition=" '$(AndroidApplication)' != 'true' And '@(EmbeddedNativeLibrary->Count())' != '0' "
       Inputs="@(EmbeddedNativeLibrary)"
       Outputs="$(IntermediateOutputPath)__AndroidNativeLibraries__.zip">
     <CreateNativeLibraryArchive

src/Xamarin.Android.Build.Tasks/Xamarin.Android.PCLSupport.targets

@@ -39,7 +39,7 @@
 			If $(_HasReferenceToSystemRuntime) is true, then the facades are going to be expanded anyway, so don't run this.
 		-->
 		<GetDependsOnNETStandard
-				Condition="'$(_HasReferenceToSystemRuntime)' != 'true' and '$(_IsXBuild)' != 'true' and '$(DependsOnNETStandard)' == '' and '@(_XACandidateNETStandardReferences)' != ''"
+				Condition="'$(_HasReferenceToSystemRuntime)' != 'true' and '$(_IsXBuild)' != 'true' and '$(DependsOnNETStandard)' == '' and '@(_XACandidateNETStandardReferences->Count())' != '0'"
 				References="@(_XACandidateNETStandardReferences)">
 			<Output TaskParameter="DependsOnNETStandard" PropertyName="_XADependsOnNETStandard" />
 		</GetDependsOnNETStandard>