Don't emit unnecessary unchecked scope for native-int literals

sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.Predicates.cs

@@ -946,6 +946,19 @@ private bool IsUnchecked(string targetTypeName, Stmt stmt)
                 targetTypeName = transparentStruct.Name;
             }
         }
+        else
+        {
+            // The platform-dependent narrowing that could overflow on a 32-bit target only happens
+            // when the generator emits the explicit `(nint)`/`(nuint)` cast, which it only does for
+            // `VarDecl` initializers (see `UncheckStmt`). Outside of that context an expression keeps
+            // its natural C# type and never needs an `unchecked` scope, so evaluate native-sized
+            // integer targets against their widest equivalent.
+            targetTypeName = targetTypeName switch {
+                "nint" or "IntPtr" => "long",
+                "nuint" or "UIntPtr" => "ulong",
+                _ => targetTypeName,
+            };
+        }
 
         switch (stmt.StmtClass)
         {

tests/ClangSharp.PInvokeGenerator.UnitTests/Baseline/Baselines/C/CLongDefinesRegressionTestUnix.CSharp.Latest.Unix.cs

@@ -5,7 +5,7 @@ public static unsafe partial class Methods
         [return: NativeTypeName("_Bool")]
         public static bool SDL_size_add_check_overflow([NativeTypeName("size_t")] nuint a, [NativeTypeName("size_t")] nuint b, [NativeTypeName("size_t *")] nuint* ret)
         {
-            if (b > unchecked(18446744073709551615U) - a)
+            if (b > (18446744073709551615U) - a)
             {
                 return (0) != 0;
             }

tests/ClangSharp.PInvokeGenerator.UnitTests/CTest.cs

@@ -382,7 +382,7 @@ public Task CLongDefinesTestUnix()
     public Task CLongDefinesRegressionTestUnix()
     {
         // This test is to catch a potential regression when changing how native integers are handled
-        // Specifically, (18446744073709551615U) became unchecked(18446744073709551615U)
+        // Specifically, (18446744073709551615U) must not be wrapped in an unnecessary unchecked scope
 
         // Macro values are taken from the Linux headers when using Clang
         // Some values are substituted for simplicity
@@ -406,9 +406,8 @@ bool SDL_size_add_check_overflow(size_t a, size_t b, size_t *ret)
 }
 ";
 
-        // The expected below currently does not represent the ideal behavior.
-        // Ideally, the unchecked keywork is removed as it is unnecessary.
-        // This issue is tracked here: https://github.com/dotnet/ClangSharp/issues/709
+        // The unnecessary unchecked scope around the `ulong` literal is now elided; see
+        // https://github.com/dotnet/ClangSharp/issues/709
         return ValidateGeneratedCSharpLatestUnixBaselineAsync(inputContents, commandLineArgs: DefaultCClangCommandLineArgs, language: "c", languageStandard: DefaultCStandard);
     }