chore: Centralize TFM definitions in Directory.Build.props with platform-specific handling (#103)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: glennawatson <[email protected]>

Author: Copilot

src/Directory.Build.props

@@ -31,6 +31,23 @@
     <AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>
   </PropertyGroup>
 
+  <!-- Define Target Framework Monikers (TFMs) -->
+  <PropertyGroup>
+    <!-- Cross-platform TFMs that work on all platforms -->
+    <NetCoreTargetFrameworks>netstandard2.0;net8.0;net9.0;net10.0</NetCoreTargetFrameworks>
+    
+    <!-- Windows-only .NET Framework TFMs - only included on Windows builds -->
+    <NetFrameworkTargetFrameworks Condition="$([MSBuild]::IsOsPlatform('Windows'))">net462;net472</NetFrameworkTargetFrameworks>
+    
+    <!-- Library projects: netstandard2.0, net462, net472, net8.0, net9.0, net10.0 -->
+    <LibraryTargetFrameworks>$(NetCoreTargetFrameworks)</LibraryTargetFrameworks>
+    <LibraryTargetFrameworks Condition="'$(NetFrameworkTargetFrameworks)' != ''">$(LibraryTargetFrameworks);$(NetFrameworkTargetFrameworks)</LibraryTargetFrameworks>
+    
+    <!-- Test projects: net8.0, net9.0, net10.0, net462, net472 (no netstandard) -->
+    <TestTargetFrameworks>net8.0;net9.0;net10.0</TestTargetFrameworks>
+    <TestTargetFrameworks Condition="'$(NetFrameworkTargetFrameworks)' != ''">$(TestTargetFrameworks);$(NetFrameworkTargetFrameworks)</TestTargetFrameworks>
+  </PropertyGroup>
+
   <ItemGroup Condition="'$(IsTestProject)' != 'true'">
     <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" />
   </ItemGroup>

src/ReactiveUI.Extensions.Tests/ReactiveUI.Extensions.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-      <TargetFrameworks>net8.0;net9.0;net10.0</TargetFrameworks>
+      <TargetFrameworks>$(TestTargetFrameworks)</TargetFrameworks>
       <IsPackable>false</IsPackable>
       <ImplicitUsings>enable</ImplicitUsings>
       <Nullable>enable</Nullable>

src/ReactiveUI.Extensions/ReactiveUI.Extensions.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net8.0;net9.0;net10.0</TargetFrameworks>
+    <TargetFrameworks>$(LibraryTargetFrameworks)</TargetFrameworks>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>