Expand MSBuild property containing the name of other property - msbuild

Question

Let's say I have property $(Foo), that is defined as a result of some function, that returns the string value $(Bar). Is it possible to expand it somehow, so that $(Foo) will be expanded to the value of $(Bar)?
Given example project:
<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<Bar>Bar Value</Bar>
<Foo>$([System.String]::Concat("$(","Bar",")"))</Foo>
<Baz>$(Foo)</Baz>
<Qux>$(Bar)</Qux>
</PropertyGroup>
<Target Name="Test">
<Message Text="Foo == $(Foo)" />
<Message Text="Baz == $(Baz)" />
<Message Text="Qux == $(Qux)" />
</Target>
</Project>
Here's what I have:
S:\>msbuild Test.proj /t:Test /nologo
Build started 18.09.2013 17:52:14.
Project "S:\Test.proj" on node 1 (Test target(s)).
Test:
Foo == $(Bar)
Baz == $(Bar)
Qux == Bar Value
Done Building Project "S:\Test.proj" (Test target(s)).
Build succeeded.
0 Warning(s)
0 Error(s)
So, $(Qux), which is defined to $(Bar) directly, is expanded correctly, but $(Foo) and $(Baz) are not. Is it possible to expand them too?
S:\>msbuild /version
Microsoft (R) Build Engine version 4.0.30319.17929
[Microsoft .NET Framework, version 4.0.30319.18052]
Copyright (C) Microsoft Corporation. All rights reserved.
4.0.30319.17929

Answer 1

You want to simulate something like $($(Foo)) that is invalid syntax for MsBuild. But you can simulate this behavior by using items and by dynamically creating items in targets. You can’t do it in the "global scope" because of Property and Item evaluation order.
So you have to do it in some targets.
Here is sample that sets property by means of InitialTargets.
<?xml version="1.0" encoding="utf-8"?>
<Project InitialTargets="MyPropertiesSetup" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<Bar>Bar Value</Bar>
<!-- A value of Foo property specifies the name of the property it takes value from. -->
<Foo>Bar</Foo>
<Baz></Baz>
<Qux>$(Bar)</Qux>
</PropertyGroup>
<Target Name="Test">
<Message Text="Foo == $(Foo)" />
<Message Text="Baz == $(Baz)" />
<Message Text="Qux == $(Qux)" />
</Target>
<Target Name="MyPropertiesSetup">
<ItemGroup>
<_Foo Include="$(Foo)" />
<_Baz Include="%(_Foo.Identity)" />
</ItemGroup>
<PropertyGroup>
<Foo>$(%(_Foo.Identity))</Foo>
<Baz>$(%(_Baz.Identity))</Baz>
</PropertyGroup>
</Target>
</Project>
If you can use item for values instead properties, there is more elegant way do it (MSBuild Trickery #68 - #($(CanYouDoThis)):
<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<Foo>Bar</Foo>
<Foo2>Bar2</Foo2>
</PropertyGroup>
<ItemGroup>
<Bar Include="Bar Value" />
<Bar2 Include="Bar2 Value" />
</ItemGroup>
<Target Name="Test">
<Message Text="Foo == '#($(Foo))'" />
<Message Text="Foo2 == '#($(Foo2))'" />
</Target>
</Project>