From 3d9bb3e218b44980cc93a192db61b06152acf7bb Mon Sep 17 00:00:00 2001
From: kasperk81 <83082615+kasperk81@users.noreply.github.com>
Date: Thu, 7 Nov 2024 02:09:59 +0200
Subject: [PATCH] Make MaxSupportedLangVersion calculation dynamic

Uses historical trend to calculate language version based on the
.NET version, removing hardcoded mappings. Ensures
future .NET versions automatically align with expected C# version.
---
 .../MSBuildTask/Microsoft.CSharp.Core.targets | 29 ++++++-------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/src/Compilers/Core/MSBuildTask/Microsoft.CSharp.Core.targets b/src/Compilers/Core/MSBuildTask/Microsoft.CSharp.Core.targets
index ad407778bafb0..8810b43f2482e 100644
--- a/src/Compilers/Core/MSBuildTask/Microsoft.CSharp.Core.targets
+++ b/src/Compilers/Core/MSBuildTask/Microsoft.CSharp.Core.targets
@@ -7,31 +7,20 @@
     <!-- .NETCoreApp < 3.0, .NETStandard < 2.1, or any other target framework -->
     <_MaxSupportedLangVersion Condition="('$(TargetFrameworkIdentifier)' != '.NETCoreApp' OR '$(_TargetFrameworkVersionWithoutV)' &lt; '3.0') AND
                                          ('$(TargetFrameworkIdentifier)' != '.NETStandard' OR '$(_TargetFrameworkVersionWithoutV)' &lt; '2.1')">7.3</_MaxSupportedLangVersion>
-    
+
     <!-- .NETCoreApp < 5.0, .NETStandard == 2.1 -->
     <_MaxSupportedLangVersion Condition="(('$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' &lt; '5.0') OR
                                           ('$(TargetFrameworkIdentifier)' == '.NETStandard' AND '$(_TargetFrameworkVersionWithoutV)' == '2.1')) AND
                                           '$(_MaxSupportedLangVersion)' == ''">8.0</_MaxSupportedLangVersion>
 
-    <!-- .NETCoreApp == 5.0 -->
-    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' == '5.0' AND
-                                         '$(_MaxSupportedLangVersion)' == ''">9.0</_MaxSupportedLangVersion>
-
-    <!-- .NETCoreApp == 6.0 -->
-    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' == '6.0' AND
-                                         '$(_MaxSupportedLangVersion)' == ''">10.0</_MaxSupportedLangVersion>
-
-    <!-- .NETCoreApp == 7.0 -->
-    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' == '7.0' AND
-                                         '$(_MaxSupportedLangVersion)' == ''">11.0</_MaxSupportedLangVersion>
-
-    <!-- .NETCoreApp == 8.0 -->
-    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' == '8.0' AND
-                                         '$(_MaxSupportedLangVersion)' == ''">12.0</_MaxSupportedLangVersion>
-
-    <!-- .NETCoreApp == 9.0 -->
-    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(_TargetFrameworkVersionWithoutV)' == '9.0' AND
-                                         '$(_MaxSupportedLangVersion)' == ''">13.0</_MaxSupportedLangVersion>
+    <!-- 
+      Automatically calculate the maximum supported C# language version based on the .NET Target Framework.
+      - Pattern: .NET 5.0 uses C# 9.0, .NET 6.0 uses C# 10.0, and so on.
+      - Starting from C# 9.0 for .NET 5.0, we add the difference between the major .NET version and 5 
+        to determine the correct language version.
+    -->
+    <_MaxSupportedLangVersion Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND
+                                         '$(_MaxSupportedLangVersion)' == ''">$([MSBuild]::Add(9, $([MSBuild]::Subtract($(_TargetFrameworkVersionWithoutV), 5)))).0</_MaxSupportedLangVersion>
 
     <MaxSupportedLangVersion>$(_MaxSupportedLangVersion)</MaxSupportedLangVersion>
     <LangVersion Condition="'$(LangVersion)' == '' AND '$(_MaxSupportedLangVersion)' != ''">$(_MaxSupportedLangVersion)</LangVersion>