Replace deprecated Py_UNICODE APIs to support Python 3.12

Fixes #18

This is the minimum to let it build on Python 3.12, but I am not sure if it's the most efficient way.

.github/workflows/wheels.yml

@@ -22,11 +22,8 @@ jobs:
       # Skip
       #
       # * Python 3.6 on all platforms,
-      # * Python 3.12 on all platforms, and
       # * PyPy on Windows.
-      #
-      # TODO: Activate Python 3.12 when issue 18 is resolved.
-      CIBW_SKIP: cp36-* cp312-* pp*-win_amd64
+      CIBW_SKIP: cp36-* pp*-win_amd64
     steps:
       - uses: actions/checkout@v2
         with:

src/openstep_plist/_test.pyx

@@ -10,79 +10,78 @@ from .parser cimport (
     parse_plist_string as _parse_plist_string,
 )
 from .util cimport (
-    PY_NARROW_UNICODE,
     tounicode,
     is_valid_unquoted_string_char as _is_valid_unquoted_string_char,
 )
 from .writer cimport string_needs_quotes as _string_needs_quotes
+from cpython.mem cimport PyMem_Free
 from cpython.unicode cimport (
-    PyUnicode_FromUnicode, PyUnicode_AS_UNICODE, PyUnicode_GET_SIZE,
+    PyUnicode_AsUCS4Copy, PyUnicode_GET_LENGTH,
 )
 
 
 cdef class ParseContext:
 
     cdef unicode s
     cdef ParseInfo pi
+    cdef Py_UCS4 *buf
     cdef object dict_type
 
-    @classmethod
-    def fromstring(
-            ParseContext cls,
-            string,
-            Py_ssize_t offset=0,
-            dict_type=dict,
-            bint use_numbers=False
+    def __cinit__(
+        self,
+        string,
+        Py_ssize_t offset=0,
+        dict_type=dict,
+        bint use_numbers=False
     ):
-        cdef ParseContext self = ParseContext.__new__(cls)
         self.s = tounicode(string)
-        cdef Py_ssize_t length = PyUnicode_GET_SIZE(self.s)
-        cdef Py_UNICODE* buf = PyUnicode_AS_UNICODE(self.s)
+        cdef Py_ssize_t length = PyUnicode_GET_LENGTH(self.s)
+        self.buf = PyUnicode_AsUCS4Copy(self.s)
+        if not self.buf:
+            raise MemoryError()
         self.dict_type = dict_type
         self.pi = ParseInfo(
-            begin=buf,
-            curr=buf + offset,
-            end=buf + length,
+            begin=self.buf,
+            curr=self.buf + offset,
+            end=self.buf + length,
             dict_type=<void*>dict_type,
             use_numbers=use_numbers,
         )
-        return self
 
+    def __dealloc__(self):
+        PyMem_Free(self.buf)
 
-def is_narrow_unicode():
-    return PY_NARROW_UNICODE
 
-
-def is_valid_unquoted_string_char(Py_UNICODE c):
+def is_valid_unquoted_string_char(Py_UCS4 c):
     return _is_valid_unquoted_string_char(c)
 
 
 def line_number_strings(s, offset=0):
-    cdef ParseContext ctx = ParseContext.fromstring(s, offset)
+    cdef ParseContext ctx = ParseContext(s, offset)
     return _line_number_strings(&ctx.pi)
 
 
 def advance_to_non_space(s, offset=0):
-    cdef ParseContext ctx = ParseContext.fromstring(s, offset)
+    cdef ParseContext ctx = ParseContext(s, offset)
     eof = not _advance_to_non_space(&ctx.pi)
     return None if eof else s[ctx.pi.curr - ctx.pi.begin]
 
 
 def get_slashed_char(s, offset=0):
-    cdef ParseContext ctx = ParseContext.fromstring(s, offset)
+    cdef ParseContext ctx = ParseContext(s, offset)
     return _get_slashed_char(&ctx.pi)
 
 
 def parse_unquoted_plist_string(s):
-    cdef ParseContext ctx = ParseContext.fromstring(s)
+    cdef ParseContext ctx = ParseContext(s)
     return _parse_unquoted_plist_string(&ctx.pi)
 
 
 def parse_plist_string(s, required=True):
-    cdef ParseContext ctx = ParseContext.fromstring(s)
+    cdef ParseContext ctx = ParseContext(s)
     return _parse_plist_string(&ctx.pi, required=required)
 
 
 def string_needs_quotes(s):
-    cdef ParseContext ctx = ParseContext.fromstring(s)
+    cdef ParseContext ctx = ParseContext(s)
     return _string_needs_quotes(ctx.pi.begin, len(s))

src/openstep_plist/parser.pxd

@@ -5,9 +5,9 @@ from libcpp.vector cimport vector
 
 
 ctypedef struct ParseInfo:
-    const Py_UNICODE *begin
-    const Py_UNICODE *curr
-    const Py_UNICODE *end
+    const Py_UCS4 *begin
+    const Py_UCS4 *curr
+    const Py_UCS4 *end
     void *dict_type
     bint use_numbers
 
@@ -22,10 +22,10 @@ cdef uint32_t line_number_strings(ParseInfo *pi)
 cdef bint advance_to_non_space(ParseInfo *pi)
 
 
-cdef Py_UNICODE get_slashed_char(ParseInfo *pi)
+cdef Py_UCS4 get_slashed_char(ParseInfo *pi)
 
 
-cdef unicode parse_quoted_plist_string(ParseInfo *pi, Py_UNICODE quote)
+cdef unicode parse_quoted_plist_string(ParseInfo *pi, Py_UCS4 quote)
 
 
 cdef enum UnquotedType:
@@ -34,7 +34,7 @@ cdef enum UnquotedType:
     UNQUOTED_FLOAT = 2
 
 
-cdef UnquotedType get_unquoted_string_type(const Py_UNICODE *buf, Py_ssize_t length)
+cdef UnquotedType get_unquoted_string_type(const Py_UCS4 *buf, Py_ssize_t length)
 
 
 cdef object parse_unquoted_plist_string(ParseInfo *pi, bint ensure_string=*)