Fixing some tests and simplify when casts are inserted for character literals

sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.VisitStmt.cs

@@ -188,9 +188,29 @@ namespace ClangSharp
                     }
                     else
                     {
-                        var isPreviousExplicitCast = IsPrevContextStmt<ExplicitCastExpr>(out _);
+                        var castType = "";
 
-                        if (!isPreviousExplicitCast)
+                        if (IsPrevContextStmt<ImplicitCastExpr>(out var implicitCastExpr))
+                        {
+                            // C# characters are effectively `ushort` while C defaults to "char" which is 
+                            // most typically `sbyte`. Due to this we need to insert a correct implicit
+                            // cast to ensure things are correctly handled here.
+
+                            var castExprTypeName = GetRemappedTypeName(implicitCastExpr, context: null, implicitCastExpr.Type, out _, skipUsing: true);
+
+                            if (!IsUnsigned(castExprTypeName))
+                            {
+                                castType = "sbyte";
+                            }
+                            else if (implicitCastExpr.Type.Handle.NumBits < 16)
+                            {
+                                // Cast to byte if the target type is less 
+
+                                castType = "byte";
+                            }
+                        }
+
+                        if (castType != "")
                         {
                             outputBuilder.Write("(sbyte)(");
                         }
@@ -199,7 +219,7 @@ namespace ClangSharp
                         outputBuilder.Write(EscapeCharacter((char)characterLiteral.Value));
                         outputBuilder.Write('\'');
 
-                        if (!isPreviousExplicitCast)
+                        if (castType != "")
                         {
                             outputBuilder.Write(')');
                         }

sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.cs

@@ -1494,7 +1494,7 @@ namespace ClangSharp
                     {
                         if (_config.GenerateUnixTypes)
                         {
-                            goto case CXTypeKind.CXType_Int;
+                            goto case CXTypeKind.CXType_UInt;
                         }
                         else
                         {

tests/ClangSharp.PInvokeGenerator.UnitTests/Base/FunctionDeclarationDllImportTest.cs

@@ -50,7 +50,7 @@ namespace ClangSharp.UnitTests
         [InlineData("unsigned short", "7", true, "ushort", "7")]
         [InlineData("unsigned int", "8", true, "uint", "8")]
         [InlineData("unsigned long long", "9", true, "ulong", "9")]
-        [InlineData("unsigned short", "'A'", true, "ushort", "(byte)('A')")]
+        [InlineData("unsigned short", "'A'", true, "ushort", "'A'")]
         public abstract Task OptionalParameterTest(string nativeType, string nativeInit, bool expectedNativeTypeNameAttr, string expectedManagedType, string expectedManagedInit);
 
         [Theory]

tests/ClangSharp.PInvokeGenerator.UnitTests/CSharpCompatibleUnix/VarDeclarationTest.cs

@@ -186,7 +186,7 @@ namespace ClangSharp.Test
     public static partial class Methods
     {{
         [NativeTypeName(""#define MyMacro1 (long)0x80000000L"")]
-        public const IntPtr MyMacro1 = (IntPtr)(0x80000000);
+        public const IntPtr MyMacro1 = unchecked((nint)(0x80000000));
 
         [NativeTypeName(""#define MyMacro2 (int)0x80000000"")]
         public const int MyMacro2 = unchecked((int)(0x80000000));
@@ -227,7 +227,7 @@ namespace ClangSharp.Test
     public static partial class Methods
     {{
         [NativeTypeName(""#define MyMacro3 MyMacro2(3)"")]
-        public const int MyMacro3 = unchecked((int)(((UIntPtr)(1) << 31) | ((UIntPtr)(2) << 16) | ((UIntPtr)(3))));
+        public const int MyMacro3 = unchecked((int)(((nuint)(1) << 31) | ((nuint)(2) << 16) | ((nuint)(3))));
     }}
 }}
 ";

tests/ClangSharp.PInvokeGenerator.UnitTests/XmlCompatibleUnix/VarDeclarationTest.cs

@@ -224,7 +224,11 @@ const GUID IID_IUnknown = {{ 0x00000000, 0x0000, 0x0000, {{ 0xC0, 0x00, 0x00, 0x
       <constant name=""MyMacro1"" access=""public"">
         <type primitive=""True"">IntPtr</type>
         <value>
-          <code>(IntPtr)(<value>0x80000000</value>)</code>
+          <unchecked>
+            <value>
+              <code>(nint)(<value>0x80000000</value>)</code>
+            </value>
+          </unchecked>
         </value>
       </constant>
       <constant name=""MyMacro2"" access=""public"">
@@ -285,7 +289,7 @@ const GUID IID_IUnknown = {{ 0x00000000, 0x0000, 0x0000, {{ 0xC0, 0x00, 0x00, 0x
         <type primitive=""True"">int</type>
         <value>
           <unchecked>
-            <code>((int)(((UIntPtr)(1) &lt;&lt; 31) | ((UIntPtr)(2) &lt;&lt; 16) | ((UIntPtr)(3))))</code>
+            <code>((int)(((nuint)(1) &lt;&lt; 31) | ((nuint)(2) &lt;&lt; 16) | ((nuint)(3))))</code>
           </unchecked>
         </value>
       </constant>