CsWin32Generator should allow newer language versions (#1517)

* Add test for invalid language version

* Allow for newer language versions.

Author: jevansaks

src/CsWin32Generator/Program.cs

@@ -173,8 +173,8 @@ public async Task<int> Main(
         {
             if (!LanguageVersionFacts.TryParse(languageVersionString, out this.languageVersion))
             {
-                this.ReportError($"Invalid language version: {languageVersionString}");
-                return 1;
+                // Assume any language version we haven't seen is C# 13 (the newest that we need).
+                this.languageVersion = LanguageVersion.CSharp13;
             }
         }
 

test/CsWin32Generator.Tests/CsWin32GeneratorTests.cs

@@ -122,6 +122,14 @@ public async Task TestPlatformCaseSensitivity(string platform)
         await this.InvokeGeneratorAndCompile($"{nameof(this.TestPlatformCaseSensitivity)}_{platform}");
     }
 
+    [Fact]
+    public async Task CanGenerateWithNewerLanguageVersion()
+    {
+        this.languageVersionOverride = "20";
+        this.nativeMethods.Add("SHGetFileInfo");
+        await this.InvokeGeneratorAndCompileFromFact();
+    }
+
     [Fact]
     public async Task TestGenerateCoCreateableClass()
     {

test/CsWin32Generator.Tests/CsWin32GeneratorTestsBase.cs

@@ -31,6 +31,7 @@ public partial class CsWin32GeneratorTestsBase : GeneratorTestBase
     protected string assemblyName = "TestAssembly";
     protected string? keyFile;
     protected string platform = "x64";
+    protected string? languageVersionOverride;
     protected int expectedExitCode = 0;
     protected string? tfm;
     protected string[]? win32winmdPaths;
@@ -141,7 +142,11 @@ protected async Task InvokeGenerator(string outputPath, string testCase, TestOpt
             args.AddRange(["--key-file", this.keyFile]);
         }
 
-        if (this.parseOptions.LanguageVersion is LanguageVersion version && version < LanguageVersion.CSharp13)
+        if (this.languageVersionOverride is not null)
+        {
+            args.AddRange(["--language-version", this.languageVersionOverride]);
+        }
+        else if (this.parseOptions.LanguageVersion is LanguageVersion version && version < LanguageVersion.CSharp13)
         {
             args.AddRange(["--language-version", LanguageVersionFacts.ToDisplayString(version)]);
         }