Use documented invalid handles when SafeHandle is null

Also throw when the handle is not optional, but null is provided.

Fixes #755

Author: AArnott

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -1756,7 +1756,7 @@ internal void RequestMacro(MethodDeclarationSyntax macro)
             // Collect all the known invalid values for this handle.
             // If no invalid values are given (e.g. BSTR), we'll just assume 0 is invalid.
             HashSet<IntPtr> invalidHandleValues = this.GetInvalidHandleValues(((HandleTypeHandleInfo)releaseMethodParameterTypeHandleInfo).Handle);
-            long preferredInvalidValue = invalidHandleValues.Contains(new IntPtr(-1)) ? -1 : invalidHandleValues.FirstOrDefault().ToInt64();
+            IntPtr preferredInvalidValue = GetPreferredInvalidHandleValue(invalidHandleValues);
 
             CustomAttributeHandleCollection? atts = this.GetReturnTypeCustomAttributes(releaseMethodDef);
             TypeSyntaxAndMarshaling releaseMethodReturnType = releaseMethodSignature.ReturnType.ToTypeSyntax(this.externSignatureTypeSettings, atts);
@@ -1767,7 +1767,7 @@ internal void RequestMacro(MethodDeclarationSyntax macro)
 
             MemberAccessExpressionSyntax thisHandle = MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, ThisExpression(), IdentifierName("handle"));
             ExpressionSyntax intptrZero = DefaultExpression(IntPtrTypeSyntax);
-            ExpressionSyntax invalidHandleIntPtr = ObjectCreationExpression(IntPtrTypeSyntax).AddArgumentListArguments(Argument(LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(preferredInvalidValue))));
+            ExpressionSyntax invalidHandleIntPtr = IntPtrExpr(preferredInvalidValue);
 
             // private static readonly IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);
             IdentifierNameSyntax invalidValueFieldName = IdentifierName("INVALID_HANDLE_VALUE");
@@ -2249,6 +2249,8 @@ protected virtual void Dispose(bool disposing)
 
     private static SyntaxToken TokenWithLineFeed(SyntaxKind syntaxKind) => SyntaxFactory.Token(TriviaList(), syntaxKind, TriviaList(LineFeed));
 
+    private static IntPtr GetPreferredInvalidHandleValue(HashSet<IntPtr> invalidHandleValues) => invalidHandleValues.Contains(new IntPtr(-1)) ? new IntPtr(-1) : invalidHandleValues.FirstOrDefault();
+
     private static bool RequiresUnsafe(TypeSyntax? typeSyntax) => typeSyntax is PointerTypeSyntax || typeSyntax is FunctionPointerTypeSyntax;
 
     private static string GetClassNameForModule(string moduleName) =>
@@ -2622,6 +2624,9 @@ private static Guid DecodeGuidFromAttribute(CustomAttribute guidAttribute)
 
     private static bool IsHresult(TypeHandleInfo? typeHandleInfo) => typeHandleInfo is HandleTypeHandleInfo handleInfo && handleInfo.IsType("HRESULT");
 
+    private static ExpressionSyntax IntPtrExpr(IntPtr value) => ObjectCreationExpression(IntPtrTypeSyntax).AddArgumentListArguments(
+        Argument(LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(value.ToInt64()))));
+
     private T AddApiDocumentation<T>(string api, T memberDeclaration)
         where T : MemberDeclarationSyntax
     {
@@ -4717,6 +4722,22 @@ private IEnumerable<MethodDeclarationSyntax> DeclareFriendlyOverloads(MethodDefi
                 leadingStatements.Add(LocalDeclarationStatement(VariableDeclaration(externParam.Type).AddVariables(
                     VariableDeclarator(typeDefHandleName.Identifier))));
 
+                // throw new ArgumentNullException(nameof(hTemplateFile));
+                StatementSyntax nullHandleStatement = ThrowStatement(ObjectCreationExpression(IdentifierName(nameof(ArgumentNullException))).WithArgumentList(ArgumentList().AddArguments(Argument(NameOfExpression(IdentifierName(externParam.Identifier.ValueText))))));
+                if (isOptional)
+                {
+                    HashSet<IntPtr> invalidValues = this.GetInvalidHandleValues(parameterHandleTypeInfo.Handle);
+                    if (invalidValues.Count > 0)
+                    {
+                        // (HANDLE)new IntPtr(-1);
+                        IntPtr invalidValue = GetPreferredInvalidHandleValue(invalidValues);
+                        ExpressionSyntax invalidExpression = CastExpression(externParam.Type, IntPtrExpr(invalidValue));
+
+                        // hTemplateFileLocal = invalid-handle-value;
+                        nullHandleStatement = ExpressionStatement(AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, typeDefHandleName, invalidExpression));
+                    }
+                }
+
                 // if (hTemplateFile is object)
                 leadingStatements.Add(IfStatement(
                     BinaryExpression(SyntaxKind.IsExpression, origName, PredefinedType(Token(SyntaxKind.ObjectKeyword))),
@@ -4734,7 +4755,7 @@ private IEnumerable<MethodDeclarationSyntax> DeclareFriendlyOverloads(MethodDefi
                                 InvocationExpression(MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, origName, IdentifierName(nameof(SafeHandle.DangerousGetHandle))), ArgumentList())))
                         .WithOperatorToken(TokenWithSpaces(SyntaxKind.EqualsToken)))),
                     //// else hTemplateFileLocal = default;
-                    ElseClause(ExpressionStatement(AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, typeDefHandleName, DefaultExpression(externParam.Type.WithoutTrailingTrivia())).WithOperatorToken(TokenWithSpaces(SyntaxKind.EqualsToken))))));
+                    ElseClause(nullHandleStatement)));
 
                 // if (hTemplateFileAddRef)
                 //     hTemplateFile.DangerousRelease();

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

@@ -297,6 +297,7 @@ public void InterestingAPIs(
             "PZZWSTR",
             "PCZZSTR",
             "PCZZWSTR",
+            "NCryptImportKey", // friendly overload takes SafeHandle backed by a UIntPtr instead of IntPtr
             "IUIAutomation", // non-preservesig retval COM method with a array size index parameter
             "IHTMLWindow2", // contains properties named with C# reserved keywords
             "CreateFile", // built-in SafeHandle use
@@ -2653,7 +2654,7 @@ internal static unsafe Microsoft.Win32.SafeHandles.SafeFileHandle CreateFile(str
 						hTemplateFileLocal = (winmdroot.Foundation.HANDLE)hTemplateFile.DangerousGetHandle();
 					}}
 					else
-						hTemplateFileLocal = default(winmdroot.Foundation.HANDLE);
+						hTemplateFileLocal= new winmdroot.Foundation.HANDLE (new IntPtr(-1L));
 					winmdroot.Foundation.HANDLE __result = PInvoke.CreateFile(lpFileNameLocal, dwDesiredAccess, dwShareMode, lpSecurityAttributes.HasValue ? &lpSecurityAttributesLocal : null, dwCreationDisposition, dwFlagsAndAttributes, hTemplateFileLocal);
 					return new Microsoft.Win32.SafeHandles.SafeFileHandle(__result, ownsHandle: true);
 				}}