Simplify UTF8 StrPtr usage (pythonnet#2374)

* Use non-BOM encodings

* Copy potential BOM to the output of PyString_FromString

The documentation of the used `PyUnicode_DecodeUTF16` states that not
passing `*byteorder` or passing a 0 results in the first two bytes, if
they are the BOM (U+FEFF, zero-width no-break space), to be interpreted
and skipped, which is incorrect when we convert a known "non BOM"
string, which all strings from C# are.

* Default to UTF8 for StrPtr

src/embed_tests/TestPyType.cs

@@ -28,7 +28,8 @@ public void CanCreateHeapType()
             const string name = "nÁmæ";
             const string docStr = "dÁcæ";
 
-            using var doc = new StrPtr(docStr, Encodings.UTF8);
+            using var doc = new StrPtr(docStr);
+
             var spec = new TypeSpec(
                 name: name,
                 basicSize: Util.ReadInt32(Runtime.Runtime.PyBaseObjectType, TypeOffset.tp_basicsize),

src/runtime/Native/NativeTypeSpec.cs

@@ -17,7 +17,7 @@ public NativeTypeSpec(TypeSpec spec)
         {
             if (spec is null) throw new ArgumentNullException(nameof(spec));
 
-            this.Name = new StrPtr(spec.Name, Encodings.UTF8);
+            this.Name = new StrPtr(spec.Name);
             this.BasicSize = spec.BasicSize;
             this.ItemSize = spec.ItemSize;
             this.Flags = (int)spec.Flags;

src/runtime/Native/StrPtr.cs

@@ -10,6 +10,8 @@ struct StrPtr : IDisposable
         public IntPtr RawPointer { get; set; }
         unsafe byte* Bytes => (byte*)this.RawPointer;
 
+        public unsafe StrPtr(string value) : this(value, Encodings.UTF8) {}
+
         public unsafe StrPtr(string value, Encoding encoding)
         {
             if (value is null) throw new ArgumentNullException(nameof(value));

src/runtime/Runtime.cs

@@ -795,13 +795,13 @@ public static int Py_Main(int argc, string[] argv)
 
         internal static int PyRun_SimpleString(string code)
         {
-            using var codePtr = new StrPtr(code, Encodings.UTF8);
+            using var codePtr = new StrPtr(code);
             return Delegates.PyRun_SimpleStringFlags(codePtr, Utf8String);
         }
 
         internal static NewReference PyRun_String(string code, RunFlagType st, BorrowedReference globals, BorrowedReference locals)
         {
-            using var codePtr = new StrPtr(code, Encodings.UTF8);
+            using var codePtr = new StrPtr(code);
             return Delegates.PyRun_StringFlags(codePtr, st, globals, locals, Utf8String);
         }
 
@@ -813,14 +813,15 @@ internal static NewReference PyRun_String(string code, RunFlagType st, BorrowedR
         /// </summary>
         internal static NewReference Py_CompileString(string str, string file, int start)
         {
-            using var strPtr = new StrPtr(str, Encodings.UTF8);
+            using var strPtr = new StrPtr(str);
+
             using var fileObj = new PyString(file);
             return Delegates.Py_CompileStringObject(strPtr, fileObj, start, Utf8String, -1);
         }
 
         internal static NewReference PyImport_ExecCodeModule(string name, BorrowedReference code)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyImport_ExecCodeModule(namePtr, code);
         }
 
@@ -867,13 +868,13 @@ internal static bool PyObject_IsIterable(BorrowedReference ob)
 
         internal static int PyObject_HasAttrString(BorrowedReference pointer, string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyObject_HasAttrString(pointer, namePtr);
         }
 
         internal static NewReference PyObject_GetAttrString(BorrowedReference pointer, string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyObject_GetAttrString(pointer, namePtr);
         }
 
@@ -884,12 +885,12 @@ internal static NewReference PyObject_GetAttrString(BorrowedReference pointer, S
         internal static int PyObject_DelAttr(BorrowedReference @object, BorrowedReference name) => Delegates.PyObject_SetAttr(@object, name, null);
         internal static int PyObject_DelAttrString(BorrowedReference @object, string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyObject_SetAttrString(@object, namePtr, null);
         }
         internal static int PyObject_SetAttrString(BorrowedReference @object, string name, BorrowedReference value)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyObject_SetAttrString(@object, namePtr, value);
         }
 
@@ -1071,7 +1072,7 @@ internal static bool PyBool_CheckExact(BorrowedReference ob)
 
         internal static NewReference PyLong_FromString(string value, int radix)
         {
-            using var valPtr = new StrPtr(value, Encodings.UTF8);
+            using var valPtr = new StrPtr(value);
             return Delegates.PyLong_FromString(valPtr, IntPtr.Zero, radix);
         }
 
@@ -1274,7 +1275,7 @@ internal static NewReference EmptyPyBytes()
         internal static NewReference PyByteArray_FromStringAndSize(IntPtr strPtr, nint len) => Delegates.PyByteArray_FromStringAndSize(strPtr, len);
         internal static NewReference PyByteArray_FromStringAndSize(string s)
         {
-            using var ptr = new StrPtr(s, Encodings.UTF8);
+            using var ptr = new StrPtr(s);
             return PyByteArray_FromStringAndSize(ptr.RawPointer, checked((nint)ptr.ByteCount));
         }
 
@@ -1302,7 +1303,7 @@ internal static IntPtr PyBytes_AsString(BorrowedReference ob)
 
         internal static NewReference PyUnicode_InternFromString(string s)
         {
-            using var ptr = new StrPtr(s, Encodings.UTF8);
+            using var ptr = new StrPtr(s);
             return Delegates.PyUnicode_InternFromString(ptr);
         }
 
@@ -1377,7 +1378,7 @@ internal static bool PyDict_Check(BorrowedReference ob)
 
         internal static BorrowedReference PyDict_GetItemString(BorrowedReference pointer, string key)
         {
-            using var keyStr = new StrPtr(key, Encodings.UTF8);
+            using var keyStr = new StrPtr(key);
             return Delegates.PyDict_GetItemString(pointer, keyStr);
         }
 
@@ -1393,7 +1394,7 @@ internal static BorrowedReference PyDict_GetItemString(BorrowedReference pointer
         /// </summary>
         internal static int PyDict_SetItemString(BorrowedReference dict, string key, BorrowedReference value)
         {
-            using var keyPtr = new StrPtr(key, Encodings.UTF8);
+            using var keyPtr = new StrPtr(key);
             return Delegates.PyDict_SetItemString(dict, keyPtr, value);
         }
 
@@ -1402,7 +1403,7 @@ internal static int PyDict_SetItemString(BorrowedReference dict, string key, Bor
 
         internal static int PyDict_DelItemString(BorrowedReference pointer, string key)
         {
-            using var keyPtr = new StrPtr(key, Encodings.UTF8);
+            using var keyPtr = new StrPtr(key);
             return Delegates.PyDict_DelItemString(pointer, keyPtr);
         }
 
@@ -1517,7 +1518,7 @@ internal static bool PyIter_Check(BorrowedReference ob)
 
         internal static NewReference PyModule_New(string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyModule_New(namePtr);
         }
 
@@ -1531,7 +1532,7 @@ internal static NewReference PyModule_New(string name)
         /// <returns>Return -1 on error, 0 on success.</returns>
         internal static int PyModule_AddObject(BorrowedReference module, string name, StolenReference value)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             IntPtr valueAddr = value.DangerousGetAddressOrNull();
             int res = Delegates.PyModule_AddObject(module, namePtr, valueAddr);
             // We can't just exit here because the reference is stolen only on success.
@@ -1549,7 +1550,7 @@ internal static int PyModule_AddObject(BorrowedReference module, string name, St
 
         internal static NewReference PyImport_ImportModule(string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyImport_ImportModule(namePtr);
         }
 
@@ -1558,7 +1559,7 @@ internal static NewReference PyImport_ImportModule(string name)
 
         internal static BorrowedReference PyImport_AddModule(string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PyImport_AddModule(namePtr);
         }
 
@@ -1586,13 +1587,13 @@ internal static void PySys_SetArgvEx(int argc, string[] argv, int updatepath)
 
         internal static BorrowedReference PySys_GetObject(string name)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PySys_GetObject(namePtr);
         }
 
         internal static int PySys_SetObject(string name, BorrowedReference ob)
         {
-            using var namePtr = new StrPtr(name, Encodings.UTF8);
+            using var namePtr = new StrPtr(name);
             return Delegates.PySys_SetObject(namePtr, ob);
         }
 
@@ -1691,7 +1692,7 @@ internal static IntPtr PyMem_Malloc(long size)
 
         internal static void PyErr_SetString(BorrowedReference ob, string message)
         {
-            using var msgPtr = new StrPtr(message, Encodings.UTF8);
+            using var msgPtr = new StrPtr(message);
             Delegates.PyErr_SetString(ob, msgPtr);
         }