How to pass ItemGroup with metadata between targets? - msbuild

Question

From my understanding, using DependsOnTargets is necessary to pass ItemGroup between targets. I am not sure if there are other ways to pass targets without DependsOnTargets.
I have tested that ItemGroup cannot pass from CallTarget or MSBuild task. A workaround solution is convert the ItemGroup to property (flatten it) and use Properties to pass over.
I define a ItemGroup of File. The File has Value metadata. I would like to execute target and remove one File item for each recursive loop. Here is my script:
<Target Name="MyGroup">
<ItemGroup>
<File Include="5">
<Value>5a</Value>
</File>
<File Include="4">
<Value>4a</Value>
</File>
<File Include="3">
<Value>3a</Value>
</File>
<File Include="2">
<Value>2a</Value>
</File>
<File Include="1">
<Value>1a</Value>
</File>
</ItemGroup>
</Target>
<Target Name="Recursive" DependsOnTargets="MyGroup" Condition="$(Value) > 0">
<ItemGroup>
<File Remove="$(Value)" />
</ItemGroup>
<PropertyGroup>
<Value>$([MSBuild]::Subtract($(Value), 1))</Value>
</PropertyGroup>
<Message Text="File: #(File->'%(Value)') Value=$(Value)" Importance="High" />
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=$(Value)"/>
</Target>
<Target Name="Build" DependsOnTargets="MyGroup">
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=5" />
</Target>
The output is:
File: 4a;3a;2a;1a Value=4
File: 5a;3a;2a;1a Value=3
File: 5a;4a;2a;1a Value=2
File: 5a;4a;3a;1a Value=1
File: 5a;4a;3a;2a Value=0
I expect the output to be:
File: 4a;3a;2a;1a Value=4
File: 3a;2a;1a Value=3
File: 2a;1a Value=2
File: 1a Value=1
File: Value=0
Is there a solution?

Answer 1

Not really, you are trying to circumvent idea of msbuild to build target only once (unless inputs\outputs changes).
And you can't pass itemgroups between MSBuild contexts (when you call MSBuild task - new context is created). Also in your script - ItemGroup is scoped to target - you need to define it globally so it'll be available to other targets.
What you can do is:
Define Global property Value with condition to use the one passed to script if exists.
Change ItemGroup from MyGroup target to global scope.
Define conditions on each element of itemgroup to be emitted depending on the value of Value property
e.g. your script will be something like this:
<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<Value Condition="$(Value) == ''">5</Value>
</PropertyGroup>
<ItemGroup>
<File Include="5" Condition="$(Value) >5">
<Value>5a</Value>
</File>
<File Include="4" Condition="$(Value) >4">
<Value>4a</Value>
</File>
<File Include="3" Condition="$(Value) >3">
<Value>3a</Value>
</File>
<File Include="2" Condition="$(Value) >2">
<Value>2a</Value>
</File>
<File Include="1" Condition="$(Value) >1">
<Value>1a</Value>
</File>
</ItemGroup>
<Target Name="Recursive" Condition="$(Value) >0">
<PropertyGroup>
<Value>$([MSBuild]::Subtract($(Value), 1))</Value>
</PropertyGroup>
<Message Text="File: #(File->'%(Value)') Value=$(Value)" Importance="High" />
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=$(Value)"/>
</Target>
<Target Name="Build">
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=5" />
</Target>
</Project>
As Alexey Shcherbak points out, we can't pass ItemGroup from MSBuild task. I resolve my problem by introducing a new property Done to keep a list of item that has processed.
<Target Name="MyGroup">
<ItemGroup>
<File Include="5">
<Value>5a</Value>
</File>
<File Include="4">
<Value>4a</Value>
</File>
<File Include="3">
<Value>3a</Value>
</File>
<File Include="2">
<Value>2a</Value>
</File>
<File Include="1">
<Value>1a</Value>
</File>
</ItemGroup>
</Target>
<Target Name="Recursive" DependsOnTargets="MyGroup" Condition="$(Value) > 0" >
<ItemGroup>
<File Remove="$(Value)" />
<File Remove="$(Done)" />
</ItemGroup>
<Message Text="File: #(File->'%(Value)') Value=$(Value)" Importance="High" />
<PropertyGroup>
<Done>$(Done);$(Value)</Done>
<Value>$([MSBuild]::Subtract($(Value), 1))</Value>
</PropertyGroup>
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=$(Value);Done=$(Done)" />
</Target>
<Target Name="Build" DependsOnTargets="MyGroup">
<MSBuild Projects="$(MSBuildProjectFile)" Targets="Recursive" Properties="Value=5" />
</Target>