Merge pull request #640 from elachlan/NullFieldOnHandles

Add Null static field to handles
microsoft · Aug 9, 2022 · 2dc756c · 2dc756c
2 parents 2b98859 + bbaa6e1
commit 2dc756c
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Showing 2 changed files with 25 additions and 0 deletions.
diff --git a/src/Microsoft.Windows.CsWin32/Generator.cs b/src/Microsoft.Windows.CsWin32/Generator.cs
@@ -3885,6 +3885,12 @@ private IEnumerable<MemberDeclarationSyntax> CreateCommonTypeDefMembers(Identifi
         // If this typedef struct represents a pointer, add an IsNull property.
         if (fieldType is IdentifierNameSyntax { Identifier: { Value: nameof(IntPtr) or nameof(UIntPtr) } })
         {
+            // internal static HWND Null => default;
+            yield return PropertyDeclaration(structName.WithTrailingTrivia(TriviaList(Space)), "Null")
+                .WithExpressionBody(ArrowExpressionClause(LiteralExpression(SyntaxKind.DefaultLiteralExpression)))
+                .AddModifiers(TokenWithSpace(this.Visibility), TokenWithSpace(SyntaxKind.StaticKeyword))
+                .WithSemicolonToken(SemicolonWithLineFeed);
+
             // internal static bool IsNull => value == default;
             yield return PropertyDeclaration(PredefinedType(TokenWithSpace(SyntaxKind.BoolKeyword)), "IsNull")
                 .AddModifiers(TokenWithSpace(this.Visibility))

diff --git a/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs b/test/Microsoft.Windows.CsWin32.Tests/GeneratorTests.cs
@@ -587,6 +587,17 @@ public void HandleStructsHaveIsNullProperty(string handleName)
         this.AssertGeneratedMember(handleName, "IsNull", "internal bool IsNull => Value == default;");
     }
 
+    [Theory]
+    [InlineData("HANDLE")]
+    [InlineData("HGDIOBJ")]
+    [InlineData("HINSTANCE")]
+    public void HandleStructsHaveStaticNullMember(string handleName)
+    {
+        // A null HGDIOBJ has a specific meaning beyond just the concept of an invalid handle:
+        // https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-selectobject#return-value
+        this.AssertGeneratedMember(handleName, "Null", $"internal static {handleName} Null => default;");
+    }
+
     [Theory]
     [InlineData("HANDLE")]
     [InlineData("HGDIOBJ")]
@@ -1970,6 +1981,8 @@ namespace Foundation
 			internal readonly IntPtr Value;
 			internal HWND(IntPtr value) => this.Value = value;
 
+			internal static HWND Null => default;
+
 			internal bool IsNull => Value == default;
 			public static implicit operator IntPtr(HWND value) => value.Value;
 			public static explicit operator HWND(IntPtr value) => new HWND(value);
@@ -2076,6 +2089,8 @@ namespace Graphics.Gdi
 			internal readonly IntPtr Value;
 			internal HDC(IntPtr value) => this.Value = value;
 
+			internal static HDC Null => default;
+
 			internal bool IsNull => Value == default;
 			public static implicit operator IntPtr(HDC value) => value.Value;
 			public static explicit operator HDC(IntPtr value) => new HDC(value);
@@ -2118,6 +2133,8 @@ namespace Foundation
 			internal readonly IntPtr Value;
 			internal HWND(IntPtr value) => this.Value = value;
 
+			internal static HWND Null => default;
+
 			internal bool IsNull => Value == default;
 			public static implicit operator IntPtr(HWND value) => value.Value;
 			public static explicit operator HWND(IntPtr value) => new HWND(value);
@@ -2459,6 +2476,8 @@ namespace Foundation
 			internal readonly IntPtr Value;
 			internal HANDLE(IntPtr value) => this.Value = value;
 
+			internal static HANDLE Null => default;
+
 			internal bool IsNull => Value == default;
 			public static implicit operator IntPtr(HANDLE value) => value.Value;
 			public static explicit operator HANDLE(IntPtr value) => new HANDLE(value);