[Feature Request]: Add a Defined('propname') condition

Summary

The proposal is about adding a Defined('propname') condition in addition to available ones. The condition returns true if the property is present among project properties. More specifically it should evaluate to true if Microsoft.Build.Evaluation.Project.GetProperty(name) returns a non null value.

Background and Motivation

I’m trying to add preprocessor definitions and conditionally exclude files in a CSharp project, based on these definitions. A documented approach, which basically suggest to to use regex directly on $(DefineConstants), becomes unworkable for me even for simple use cases.

Most build systems provides the following facilities to ease such tasks:

• Coercion of strings to boolean (eg. CMake)
• Check for definition of external properties.

MSBuild provides none of the above two. The current approach I’m using is defining externally some FEATURE_A=1, FEATURE_B=1, etc. properties (1 is just an arbitrary value), then using these conditionals in the CSharp project:

  <ItemGroup Condition="$(FEATURE_A) == ''">
    <None Include="FeatureA\*.cs" />
    <Compile Remove="FeatureA\*.cs" />
  </ItemGroup>

Proposed Feature

Since I’m not seeing MSBuild to implement coercion of properties to booleans, I suggest adding a Defined('propname') condition that will allow to implement other commonly used approaches when conditionally including/excluding stuff in msbuild projects. The example above would become:

  <ItemGroup Condition="!Defined('FEATURE_A')">
    <None Include="FeatureA\*.cs" />
    <Compile Remove="FeatureA\*.cs" />
  </ItemGroup>

This both allows to avoid defining properties with arbitrarily values and makes the condition much more readable.

Alternative Designs

No response

[AR-May]

Team triage: we would like to collect community interest for this issue.

[jrdodds]

Instead of being limited to a Condition attribute, I’d like to see this implemented as an MSBuild property function.

e.g.

$([MSBuild]::IsPropertyDefined(string propertyName))