From 6ee7dbef9be643dfb79b87cc9eaa35fc735cd6da Mon Sep 17 00:00:00 2001
From: Andrew Arnott <andrew.arnott@microsoft.com>
Date: Tue, 18 Oct 2022 08:07:15 -0600
Subject: [PATCH] Add `CharSet = Unicode` to `extern` methods with `char`
 parameters

Fixes #734
---
 src/Microsoft.Windows.CsWin32/Generator.cs      | 11 +++++++++--
 .../GeneratorTests.cs                           | 17 +++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.Windows.CsWin32/Generator.cs b/src/Microsoft.Windows.CsWin32/Generator.cs
index 04681130..d38b6f57 100644
--- a/src/Microsoft.Windows.CsWin32/Generator.cs
+++ b/src/Microsoft.Windows.CsWin32/Generator.cs
@@ -2300,7 +2300,7 @@ private static AttributeSyntax InterfaceType(ComInterfaceType interfaceType)
                 IdentifierName(Enum.GetName(typeof(ComInterfaceType), interfaceType)!))));
     }
 
-    private static AttributeSyntax DllImport(MethodImport import, string moduleName, string? entrypoint)
+    private static AttributeSyntax DllImport(MethodImport import, string moduleName, string? entrypoint, CharSet charSet = CharSet.Ansi)
     {
         List<AttributeArgumentSyntax> args = new();
         AttributeSyntax? dllImportAttribute = Attribute(IdentifierName("DllImport"));
@@ -2319,6 +2319,12 @@ private static AttributeSyntax DllImport(MethodImport import, string moduleName,
                     .WithNameEquals(NameEquals(nameof(DllImportAttribute.SetLastError))));
         }
 
+        if (charSet != CharSet.Ansi)
+        {
+            args.Add(AttributeArgument(MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, IdentifierName(nameof(CharSet)), IdentifierName(Enum.GetName(typeof(CharSet), charSet)!)))
+                .WithNameEquals(NameEquals(IdentifierName(nameof(DllImportAttribute.CharSet)))));
+        }
+
         dllImportAttribute = dllImportAttribute.WithArgumentList(FixTrivia(AttributeArgumentList().AddArguments(args.ToArray())));
         return dllImportAttribute;
     }
@@ -3123,6 +3129,7 @@ private void DeclareExternMethod(MethodDefinitionHandle methodDefinitionHandle)
             // If this method releases a handle, recreate the method signature such that we take the struct rather than the SafeHandle as a parameter.
             TypeSyntaxSettings typeSettings = this.MetadataIndex.ReleaseMethods.Contains(entrypoint ?? methodName) ? this.externReleaseSignatureTypeSettings : this.externSignatureTypeSettings;
             MethodSignature<TypeHandleInfo> signature = methodDefinition.DecodeSignature(SignatureHandleProvider.Instance, null);
+            bool requiresUnicodeCharSet = signature.ParameterTypes.Any(p => p is PrimitiveTypeHandleInfo { PrimitiveTypeCode: PrimitiveTypeCode.Char });
 
             CustomAttributeHandleCollection? returnTypeAttributes = this.GetReturnTypeCustomAttributes(methodDefinition);
             TypeSyntaxAndMarshaling returnType = signature.ReturnType.ToTypeSyntax(typeSettings, returnTypeAttributes, ParameterAttributes.Out);
@@ -3131,7 +3138,7 @@ private void DeclareExternMethod(MethodDefinitionHandle methodDefinitionHandle)
                 List<AttributeListSyntax>()
                     .Add(AttributeList()
                         .WithCloseBracketToken(TokenWithLineFeed(SyntaxKind.CloseBracketToken))
-                        .AddAttributes(DllImport(import, moduleName, entrypoint))),
+                        .AddAttributes(DllImport(import, moduleName, entrypoint, requiresUnicodeCharSet ? CharSet.Unicode : CharSet.Ansi))),
                 modifiers: TokenList(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.StaticKeyword), TokenWithSpace(SyntaxKind.ExternKeyword)),
                 returnType.Type.WithTrailingTrivia(TriviaList(Space)),
                 explicitInterfaceSpecifier: null!,
diff --git a/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs b/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs
index 5bcb903c..2c0cd78e 100644
--- a/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs
+++ b/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs
@@ -1307,6 +1307,23 @@ public void InOutPWSTRGetsRefSpanCharFriendlyOverload()
         Assert.Contains(generatedMethods, m => m.ParameterList.Parameters.Count == 1 && m.ParameterList.Parameters[0].Modifiers.Any(SyntaxKind.RefKeyword) && m.ParameterList.Parameters[0].Type?.ToString() == "Span<char>");
     }
 
+    [Fact]
+    public void UnicodeExtenMethodsGetCharSet()
+    {
+        const string MethodName = "VkKeyScan";
+        this.generator = this.CreateGenerator();
+        Assert.True(this.generator.TryGenerate(MethodName, CancellationToken.None));
+        this.CollectGeneratedCode(this.generator);
+        this.AssertNoDiagnostics();
+        MethodDeclarationSyntax generatedMethod = this.FindGeneratedMethod(MethodName).Single();
+        Assert.Contains(
+            generatedMethod.AttributeLists.SelectMany(al => al.Attributes),
+            a => a.Name.ToString() == "DllImport" &&
+            a.ArgumentList?.Arguments.Any(arg => arg is {
+                NameEquals.Name.Identifier.ValueText: nameof(DllImportAttribute.CharSet),
+                Expression: MemberAccessExpressionSyntax { Name: IdentifierNameSyntax { Identifier.ValueText: nameof(CharSet.Unicode) } } }) is true);
+    }
+
     [Fact]
     public void NullMethodsClass()
     {