Improve <LangVersion> selection (#3240)

paulmedynski · web-flow · commit 2772a8c36a24 · 2025-05-06T08:02:05.000-03:00
* User Story 33639: Remove &lt;LangVersion&gt; from build config

- Testing conditional &lt;LangVersion&gt; for .NET Framework only.

* User Story 33639: Remove &lt;LangVersion&gt; from build config

- Now choosing the natrual C# language version for .NET versions.
- Explictily setting C# 13 for non-.NET targets (Framework, Standard, etc).
diff --git a/src/Directory.Build.props b/src/Directory.Build.props
@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="Current" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <LangVersion>9.0</LangVersion>
     <TargetsWindows Condition="'$(OS)' == 'Windows_NT' AND '$(OSGroup)' == ''">true</TargetsWindows>
     <TargetsWindows Condition="'$(OS)' != 'Windows_NT' AND '$(OSGroup)' == ''">false</TargetsWindows>
     <TargetsWindows Condition="'$(OSGroup)' == 'Windows_NT'">true</TargetsWindows>
@@ -113,4 +112,25 @@
   <PropertyGroup>
     <AddSyntheticProjectReferencesForSolutionDependencies>false</AddSyntheticProjectReferencesForSolutionDependencies>
   </PropertyGroup>
+
+  <!--
+    For non-.NET, we explicitly set the C# language version to 13.  This matches
+    the language version used by the .NET 9 SDK, and provides helpful modern
+    language features.  While this isn't strictly supported by .NET in general,
+    it works well in practice.  There are very few C# language features that
+    depend on SDK APIs, and we avoid them.
+
+    For .NET, we omit this property entirely, which results in the SDK choosing
+    the C# language version that matches the .NET version.
+
+    Details here:
+
+    https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-versioning
+
+    https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/configure-language-version
+  -->
+  <PropertyGroup
+    Condition="'$([MSBuild]::GetTargetFrameworkIdentifier($(TargetFramework)))' != '.NETCoreApp'">
+    <LangVersion>13.0</LangVersion>
+  </PropertyGroup>
 </Project>
