msbuild Directory.build.props cascade per project? - msbuild

Question

Executive Summary: I want to set properties in property groups based on conditions that are present only late in the build pipeline and am looking for a way to solve this earlier.
I have a fairly simple Directory.build.props file
<Project>
<PropertyGroup>
<MyMode>Default</MyMode>
</PropertyGroup>
<!-- This one overrides the default group above -->
<PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
<MyMode>Changed to Debug</MyMode>
</PropertyGroup>
<!-- This one is not applied -->
<PropertyGroup Condition=" '$(TargetFrameworkVersion)' == 'v4.7.2' ">
<MyMode>Framework</MyMode>
</PropertyGroup>
<Target Name="Stats" AfterTargets="Build">
<Message Importance="High" Text="::::: Mode set to $(MyMode)" />
<Message Importance="High" Text="::::: Target Framework set to $(TargetFrameworkVersion)" />
</Target>
</Project>
And a simple project structure
E:.
│ Directory.build.props
│ MSBuild_Test.sln
│
├───ConsoleAppNet
│ App.config
│ ConsoleAppNet.csproj
│ Program.cs
│
└───MSBuild_Test
Class1.cs
LibStandard.csproj
LibStandard is a .net standard library, ConsoleAppNet is a .net framework project which also has a build dependency to LibStandard
When I execute the msbuild script above I get this output
LibStandard -> E:\temp\MSBuild_Test\MSBuild_Test\bin\Debug\netstandard2.0\LibStandard.dll
::::: Mode set to Changed to Debug
::::: Target Framework set to v2.0
ConsoleAppNet -> E:\temp\MSBuild_Test\ConsoleAppNet\bin\Debug\ConsoleAppNet.exe
::::: Mode set to Changed to Debug
::::: Target Framework set to v4.7.2
As you can see, the console output should have triggered the property group with the condition resulting in MyMode being Framework, but it did not work out. This one was never matched:
<PropertyGroup Condition=" '$(TargetFrameworkVersion)' == 'v4.7.2' ">
<MyMode>Framework</MyMode>
</PropertyGroup>
Is there a good way to apply PropertyGroups during load based on the condition above?
I am aware that I can place PropertyGroup overrides in a Target, e.g.:
<Target Name="TooLate" BeforeTargets="BeforeBuild" Condition=" '$(TargetFrameworkVersion' == 'v4.7.2' ">
<PropertyGroup >
<MyMode>Framework</MyMode>
</PropertyGroup>
</Target>
and it also gets executed correctly but at this point in time I cannot set important other variables.
My intention is to redirect output directories based on different conditions. When I set $(OutputPath) in a target, it is already too late. The project ignores this output for the entire build of this project:
<Target Name="TooLate" BeforeTargets="BeforeBuild" Condition=" '$(TargetFrameworkVersion)' == 'v4.7.2' ">
<PropertyGroup >
<OutputPath>New_Output_Directory</OutputPath>
</PropertyGroup>
</Target>
I can even echo the OutputPath variable and it points to the correct value but the build uses the old value and not redirecting the output.

Answer 1

High five me, I found the solution for all the coming up Samuels asking about the same issue.
Quick answer
At the time of import of the Directory.build.props no other properties (e.g TargetFramework) are already imported and will default to empty. This is why the checks on them fail. Use Directory.build.targets instead!
Directory.build.props imported very early, allowing you to set properties at the beginning
Directory.build.targets imported very late, allowing you to customize the build chain
Resources
Here are some very useful pages regarding msbuild
Explanation of available targets
How to customize your build
Explanation
Here is a quote from the paragraph on the customization page (so long the current documents are alive ...)
Import order
Directory.Build.props is imported very early in
Microsoft.Common.props, and properties defined later are unavailable
to it. So, avoid referring to properties that are not yet defined (and
will evaluate to empty).
Directory.Build.targets is imported from Microsoft.Common.targets
after importing .targets files from NuGet packages. So, it can
override properties and targets defined in most of the build logic,
but sometimes you may need to customize the project file after the
final import.
By reading this the implication is somewhat fuzzy about the targets but Directory.Build.targets is the best place to override properties and use conditional checks.