Add implicit conversions between bool and VARIANT_BOOL

Fixes #1051

Author: AArnott

src/Microsoft.Windows.CsWin32/Generator.GeneratedCode.cs

@@ -34,6 +34,11 @@ private class GeneratedCode
         /// </summary>
         private readonly Dictionary<MethodDefinitionHandle, Exception?> methodsGenerating = new();
 
+        /// <summary>
+        /// The constants that are or have been generated.
+        /// </summary>
+        private readonly Dictionary<FieldDefinitionHandle, Exception?> constantsGenerating = new();
+
         /// <summary>
         /// A collection of the names of special types we are or have generated.
         /// </summary>
@@ -303,12 +308,26 @@ internal void GenerateConstant(FieldDefinitionHandle fieldDefinitionHandle, Acti
         {
             this.ThrowIfNotGenerating();
 
-            if (this.fieldsToSyntax.ContainsKey(fieldDefinitionHandle) || this.parent?.fieldsToSyntax.ContainsKey(fieldDefinitionHandle) is true)
+            if (this.constantsGenerating.TryGetValue(fieldDefinitionHandle, out Exception? failure) || this.parent?.constantsGenerating.TryGetValue(fieldDefinitionHandle, out failure) is true)
             {
+                if (failure is object)
+                {
+                    throw new GenerationFailedException("This constant already failed in generation previously.", failure);
+                }
+
                 return;
             }
 
-            generator();
+            this.constantsGenerating.Add(fieldDefinitionHandle, null);
+            try
+            {
+                generator();
+            }
+            catch (Exception ex)
+            {
+                this.constantsGenerating[fieldDefinitionHandle] = ex;
+                throw;
+            }
         }
 
         internal void GenerateMacro(string macroName, Action generator)

src/Microsoft.Windows.CsWin32/Generator.TypeDef.cs

@@ -200,6 +200,11 @@ private StructDeclarationSyntax DeclareTypeDefStruct(TypeDefinition typeDef, Typ
                 members = AddOrReplaceMembers(members, this.ExtractMembersFromTemplate(name.Identifier.ValueText));
                 this.TryGenerateType("Windows.Win32.Foundation.PC" + name.Identifier.ValueText.Substring(1)); // the template references its constant version
                 break;
+            case "VARIANT_BOOL":
+                members = AddOrReplaceMembers(members, this.ExtractMembersFromTemplate(name.Identifier.ValueText));
+                this.TryGenerateConstant("VARIANT_TRUE", out _); // the template references its constant version
+                this.TryGenerateConstant("VARIANT_FALSE", out _); // the template references its constant version
+                break;
             case "BSTR":
             case "HRESULT":
             case "NTSTATUS":

src/Microsoft.Windows.CsWin32/templates/VARIANT_BOOL.cs

@@ -0,0 +1,6 @@
+partial struct VARIANT_BOOL
+{
+	internal VARIANT_BOOL(bool value) => this.Value = value ? VARIANT_TRUE : VARIANT_FALSE;
+	public static implicit operator bool(VARIANT_BOOL value) => value != VARIANT_FALSE;
+	public static implicit operator VARIANT_BOOL(bool value) => value ? VARIANT_TRUE : VARIANT_FALSE;
+}

test/GenerationSandbox.Tests/VARIANT_BOOLTests.cs

@@ -0,0 +1,87 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Windows.Win32.Foundation;
+
+public class VARIANT_BOOLTests
+{
+    [Fact]
+    public void Ctor_bool()
+    {
+        VARIANT_BOOL b = true;
+        bool b2 = b;
+        Assert.True(b);
+        Assert.True(b2);
+
+        Assert.False(default(VARIANT_BOOL));
+    }
+
+    [Fact]
+    public void Ctor_int()
+    {
+        Assert.Equal(2, new VARIANT_BOOL(2).Value);
+    }
+
+    [Fact]
+    public void ExplicitCast()
+    {
+        Assert.Equal(2, ((VARIANT_BOOL)2).Value);
+    }
+
+    [Theory]
+    [InlineData(3)]
+    [InlineData(-1)]
+    [InlineData(0)]
+    [InlineData(1)]
+    [InlineData(0xfff)]
+    public void LossyConversionFromBOOLtoBool(short ordinal)
+    {
+        VARIANT_BOOL nativeBool = new VARIANT_BOOL(ordinal);
+        bool managedBool = nativeBool;
+        Assert.Equal(ordinal != 0, managedBool);
+        BOOLEAN roundtrippedNativeBool = managedBool;
+        Assert.Equal(managedBool ? 1 : 0, roundtrippedNativeBool);
+    }
+
+    [Fact]
+    public void BOOLEqualsComparesExactValue()
+    {
+        VARIANT_BOOL b1 = new VARIANT_BOOL(1);
+        VARIANT_BOOL b2 = new VARIANT_BOOL(2);
+        Assert.Equal(b1, b1);
+        Assert.NotEqual(b1, b2);
+    }
+
+    [Fact]
+    public void BOOL_OverridesEqualityOperator()
+    {
+        var @true = new VARIANT_BOOL(true);
+        var @false = new VARIANT_BOOL(false);
+        Assert.True(@true == new VARIANT_BOOL(true));
+        Assert.False(@true != new VARIANT_BOOL(true));
+        Assert.True(@true != @false);
+        Assert.False(@true == @false);
+
+        var two = new VARIANT_BOOL(2);
+        Assert.False(two == @true);
+        Assert.True(two != @true);
+    }
+
+    [Fact]
+    public void LogicalOperators_And()
+    {
+        VARIANT_BOOL @true = true, @false = false;
+        Assert.False(@false && @false);
+        Assert.False(@true && @false);
+        Assert.True(@true && @true);
+    }
+
+    [Fact]
+    public void LogicalOperators_Or()
+    {
+        VARIANT_BOOL @true = true, @false = false;
+        Assert.True(@true || @false);
+        Assert.False(@false || @false);
+        Assert.True(@true || @true);
+    }
+}

test/Microsoft.Windows.CsWin32.Tests/StructTests.cs

@@ -173,6 +173,7 @@ public void SpecialStruct_ByRequest(string structName)
     [CombinatorialData]
     public void InterestingStructs(
         [CombinatorialValues(
+        "VARIANT_BOOL", // has a custom conversion to bool and relies on other members being generated
         "DRIVER_OBJECT", // has an inline array of delegates
         "DEVICE_RELATIONS", // ends with an inline "flexible" array
         "D3DHAL_CONTEXTCREATEDATA", // contains a field that is a pointer to a struct that is normally managed