TYP: Make glyph indices distinct from character codes

Previously, these were both typed as `int`, which means you could mix
and match them erroneously. While the character code can't be made a
distinct type (because it's used for `chr`/`ord`), typing glyph indices
as a distinct type means these can't be fully swapped.

Unfortunately, you can still go back to the base type, so glyph indices
still work as character codes. But this is still sufficient to catch
errors such as the wrong call to `FT2Font.get_kerning` in
`_mathtext.py`.

Author: QuLogic

doc/api/next_api_changes/development/30143-ES.rst

@@ -0,0 +1,7 @@
+Glyph indices now typed distinctly from character codes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously, character codes and glyph indices were both typed as `int`, which means you
+could mix and match them erroneously. While the character code can't be made a distinct
+type (because it's used for `chr`/`ord`), typing glyph indices as a distinct type means
+these can't be fully swapped.

lib/matplotlib/_afm.py

@@ -30,9 +30,10 @@
 import inspect
 import logging
 import re
-from typing import BinaryIO, NamedTuple, TypedDict
+from typing import BinaryIO, NamedTuple, TypedDict, cast
 
 from ._mathtext_data import uni2type1
+from .ft2font import CharacterCodeType, GlyphIndexType
 
 
 _log = logging.getLogger(__name__)
@@ -197,7 +198,7 @@ class CharMetrics(NamedTuple):
     The bbox of the character (B) as a tuple (*llx*, *lly*, *urx*, *ury*)."""
 
 
-def _parse_char_metrics(fh: BinaryIO) -> tuple[dict[int, CharMetrics],
+def _parse_char_metrics(fh: BinaryIO) -> tuple[dict[CharacterCodeType, CharMetrics],
                                                dict[str, CharMetrics]]:
     """
     Parse the given filehandle for character metrics information.
@@ -218,7 +219,7 @@ def _parse_char_metrics(fh: BinaryIO) -> tuple[dict[int, CharMetrics],
     """
     required_keys = {'C', 'WX', 'N', 'B'}
 
-    ascii_d: dict[int, CharMetrics] = {}
+    ascii_d: dict[CharacterCodeType, CharMetrics] = {}
     name_d: dict[str, CharMetrics] = {}
     for bline in fh:
         # We are defensively letting values be utf8. The spec requires
@@ -409,19 +410,21 @@ def get_str_bbox_and_descent(self, s: str) -> tuple[int, int, float, int, int]:
 
         return left, miny, total_width, maxy - miny, -miny
 
-    def get_glyph_name(self, glyph_ind: int) -> str:  # For consistency with FT2Font.
+    def get_glyph_name(self,  # For consistency with FT2Font.
+                       glyph_ind: GlyphIndexType) -> str:
         """Get the name of the glyph, i.e., ord(';') is 'semicolon'."""
-        return self._metrics[glyph_ind].name
+        return self._metrics[cast(CharacterCodeType, glyph_ind)].name
 
-    def get_char_index(self, c: int) -> int:  # For consistency with FT2Font.
+    def get_char_index(self,  # For consistency with FT2Font.
+                       c: CharacterCodeType) -> GlyphIndexType:
         """
         Return the glyph index corresponding to a character code point.
 
         Note, for AFM fonts, we treat the glyph index the same as the codepoint.
         """
-        return c
+        return cast(GlyphIndexType, c)
 
-    def get_width_char(self, c: int) -> float:
+    def get_width_char(self, c: CharacterCodeType) -> float:
         """Get the width of the character code from the character metric WX field."""
         return self._metrics[c].width
 

lib/matplotlib/_mathtext.py

@@ -37,7 +37,8 @@
 
 if T.TYPE_CHECKING:
     from collections.abc import Iterable
-    from .ft2font import Glyph
+    from .ft2font import CharacterCodeType, Glyph
+
 
 ParserElement.enable_packrat()
 _log = logging.getLogger("matplotlib.mathtext")
@@ -47,7 +48,7 @@
 # FONTS
 
 
-def get_unicode_index(symbol: str) -> int:  # Publicly exported.
+def get_unicode_index(symbol: str) -> CharacterCodeType:  # Publicly exported.
     r"""
     Return the integer index (from the Unicode table) of *symbol*.
 
@@ -85,7 +86,7 @@ class VectorParse(NamedTuple):
     width: float
     height: float
     depth: float
-    glyphs: list[tuple[FT2Font, float, int, float, float]]
+    glyphs: list[tuple[FT2Font, float, CharacterCodeType, float, float]]
     rects: list[tuple[float, float, float, float]]
 
 VectorParse.__module__ = "matplotlib.mathtext"
@@ -212,7 +213,7 @@ class FontInfo(NamedTuple):
     fontsize: float
     postscript_name: str
     metrics: FontMetrics
-    num: int
+    num: CharacterCodeType
     glyph: Glyph
     offset: float
 
@@ -365,7 +366,7 @@ def _get_offset(self, font: FT2Font, glyph: Glyph, fontsize: float,
         return 0.
 
     def _get_glyph(self, fontname: str, font_class: str,
-                   sym: str) -> tuple[FT2Font, int, bool]:
+                   sym: str) -> tuple[FT2Font, CharacterCodeType, bool]:
         raise NotImplementedError
 
     # The return value of _get_info is cached per-instance.
@@ -459,7 +460,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
     _slanted_symbols = set(r"\int \oint".split())
 
     def _get_glyph(self, fontname: str, font_class: str,
-                   sym: str) -> tuple[FT2Font, int, bool]:
+                   sym: str) -> tuple[FT2Font, CharacterCodeType, bool]:
         font = None
         if fontname in self.fontmap and sym in latex_to_bakoma:
             basename, num = latex_to_bakoma[sym]
@@ -551,7 +552,7 @@ class UnicodeFonts(TruetypeFonts):
     # Some glyphs are not present in the `cmr10` font, and must be brought in
     # from `cmsy10`. Map the Unicode indices of those glyphs to the indices at
     # which they are found in `cmsy10`.
-    _cmr10_substitutions = {
+    _cmr10_substitutions: dict[CharacterCodeType, CharacterCodeType] = {
         0x00D7: 0x00A3,  # Multiplication sign.
         0x2212: 0x00A1,  # Minus sign.
     }
@@ -594,11 +595,11 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
     _slanted_symbols = set(r"\int \oint".split())
 
     def _map_virtual_font(self, fontname: str, font_class: str,
-                          uniindex: int) -> tuple[str, int]:
+                          uniindex: CharacterCodeType) -> tuple[str, CharacterCodeType]:
         return fontname, uniindex
 
     def _get_glyph(self, fontname: str, font_class: str,
-                   sym: str) -> tuple[FT2Font, int, bool]:
+                   sym: str) -> tuple[FT2Font, CharacterCodeType, bool]:
         try:
             uniindex = get_unicode_index(sym)
             found_symbol = True
@@ -607,8 +608,7 @@ def _get_glyph(self, fontname: str, font_class: str,
             found_symbol = False
             _log.warning("No TeX to Unicode mapping for %a.", sym)
 
-        fontname, uniindex = self._map_virtual_font(
-            fontname, font_class, uniindex)
+        fontname, uniindex = self._map_virtual_font(fontname, font_class, uniindex)
 
         new_fontname = fontname
 
@@ -693,7 +693,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
             self.fontmap[name] = fullpath
 
     def _get_glyph(self, fontname: str, font_class: str,
-                   sym: str) -> tuple[FT2Font, int, bool]:
+                   sym: str) -> tuple[FT2Font, CharacterCodeType, bool]:
         # Override prime symbol to use Bakoma.
         if sym == r'\prime':
             return self.bakoma._get_glyph(fontname, font_class, sym)
@@ -783,7 +783,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
             self.fontmap[name] = fullpath
 
     def _map_virtual_font(self, fontname: str, font_class: str,
-                          uniindex: int) -> tuple[str, int]:
+                          uniindex: CharacterCodeType) -> tuple[str, CharacterCodeType]:
         # Handle these "fonts" that are actually embedded in
         # other fonts.
         font_mapping = stix_virtual_fonts.get(fontname)
@@ -1170,7 +1170,7 @@ def __init__(self, elements: T.Sequence[Node]):
         self.glue_sign    = 0    # 0: normal, -1: shrinking, 1: stretching
         self.glue_order   = 0    # The order of infinity (0 - 3) for the glue
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return "{}<w={:.02f} h={:.02f} d={:.02f} s={:.02f}>[{}]".format(
             super().__repr__(),
             self.width, self.height,

lib/matplotlib/_mathtext_data.py

@@ -3,9 +3,12 @@
 """
 
 from __future__ import annotations
-from typing import overload
+from typing import TypeAlias, overload
 
-latex_to_bakoma = {
+from .ft2font import CharacterCodeType
+
+
+latex_to_bakoma: dict[str, tuple[str, CharacterCodeType]] = {
     '\\__sqrt__'                 : ('cmex10', 0x70),
     '\\bigcap'                   : ('cmex10', 0x5c),
     '\\bigcup'                   : ('cmex10', 0x5b),
@@ -241,7 +244,7 @@
 
 # Automatically generated.
 
-type12uni = {
+type12uni: dict[str, CharacterCodeType] = {
     'aring'          : 229,
     'quotedblright'  : 8221,
     'V'              : 86,
@@ -475,7 +478,7 @@
 #  for key in sd:
 #      print("{0:24} : {1: <s},".format("'" + key + "'", sd[key]))
 
-tex2uni = {
+tex2uni: dict[str, CharacterCodeType] = {
     '#'                      : 0x23,
     '$'                      : 0x24,
     '%'                      : 0x25,
@@ -1113,8 +1116,9 @@
 # Each element is a 4-tuple of the form:
 #   src_start, src_end, dst_font, dst_start
 
-_EntryTypeIn = tuple[str, str, str, str | int]
-_EntryTypeOut = tuple[int, int, str, int]
+_EntryTypeIn: TypeAlias = tuple[str, str, str, str | CharacterCodeType]
+_EntryTypeOut: TypeAlias = tuple[CharacterCodeType, CharacterCodeType, str,
+                                 CharacterCodeType]
 
 _stix_virtual_fonts: dict[str, dict[str, list[_EntryTypeIn]] | list[_EntryTypeIn]] = {
     'bb': {
@@ -1735,7 +1739,7 @@ def _normalize_stix_fontcodes(d):
 del _stix_virtual_fonts
 
 # Fix some incorrect glyphs.
-stix_glyph_fixes = {
+stix_glyph_fixes: dict[CharacterCodeType, CharacterCodeType] = {
     # Cap and Cup glyphs are swapped.
     0x22d2: 0x22d3,
     0x22d3: 0x22d2,

lib/matplotlib/_text_helpers.py

@@ -7,14 +7,14 @@
 import dataclasses
 
 from . import _api
-from .ft2font import FT2Font, Kerning, LoadFlags
+from .ft2font import FT2Font, GlyphIndexType, Kerning, LoadFlags
 
 
 @dataclasses.dataclass(frozen=True)
 class LayoutItem:
     ft_object: FT2Font
     char: str
-    glyph_idx: int
+    glyph_idx: GlyphIndexType
     x: float
     prev_kern: float
 

lib/matplotlib/dviread.pyi

@@ -8,6 +8,9 @@ from collections.abc import Generator
 from typing import NamedTuple
 from typing_extensions import Self  # < Py 3.11
 
+from .ft2font import GlyphIndexType
+
+
 class _dvistate(Enum):
     pre = ...
     outer = ...
@@ -41,9 +44,9 @@ class Text(NamedTuple):
     @property
     def font_effects(self) -> dict[str, float]: ...
     @property
-    def index(self) -> int: ...  # type: ignore[override]
+    def index(self) -> GlyphIndexType: ...  # type: ignore[override]
     @property
-    def glyph_name_or_index(self) -> int | str: ...
+    def glyph_name_or_index(self) -> GlyphIndexType | str: ...
 
 class Dvi:
     file: io.BufferedReader

lib/matplotlib/ft2font.pyi

@@ -1,14 +1,21 @@
 from enum import Enum, Flag
 import sys
-from typing import BinaryIO, Literal, TypedDict, final, overload, cast
+from typing import BinaryIO, Literal, NewType, TypeAlias, TypedDict, final, overload, cast
 from typing_extensions import Buffer  # < Py 3.12
 
 import numpy as np
 from numpy.typing import NDArray
 
+
 __freetype_build_type__: str
 __freetype_version__: str
 
+# We can't change the type hints for standard library chr/ord, so character codes are a
+# simple type alias.
+CharacterCodeType: TypeAlias = int
+# But glyph indices are internal, so use a distinct type hint.
+GlyphIndexType = NewType('GlyphIndexType', int)
+
 class FaceFlags(Flag):
     SCALABLE = cast(int, ...)
     FIXED_SIZES = cast(int, ...)
@@ -202,13 +209,13 @@ class FT2Font(Buffer):
     ) -> None: ...
     def draw_glyphs_to_bitmap(self, antialiased: bool = ...) -> None: ...
     def get_bitmap_offset(self) -> tuple[int, int]: ...
-    def get_char_index(self, codepoint: int) -> int: ...
-    def get_charmap(self) -> dict[int, int]: ...
+    def get_char_index(self, codepoint: CharacterCodeType) -> GlyphIndexType: ...
+    def get_charmap(self) -> dict[CharacterCodeType, GlyphIndexType]: ...
     def get_descent(self) -> int: ...
-    def get_glyph_name(self, index: int) -> str: ...
+    def get_glyph_name(self, index: GlyphIndexType) -> str: ...
     def get_image(self) -> NDArray[np.uint8]: ...
-    def get_kerning(self, left: int, right: int, mode: Kerning) -> int: ...
-    def get_name_index(self, name: str) -> int: ...
+    def get_kerning(self, left: GlyphIndexType, right: GlyphIndexType, mode: Kerning) -> int: ...
+    def get_name_index(self, name: str) -> GlyphIndexType: ...
     def get_num_glyphs(self) -> int: ...
     def get_path(self) -> tuple[NDArray[np.float64], NDArray[np.int8]]: ...
     def get_ps_font_info(
@@ -230,8 +237,8 @@ class FT2Font(Buffer):
     @overload
     def get_sfnt_table(self, name: Literal["pclt"]) -> _SfntPcltDict | None: ...
     def get_width_height(self) -> tuple[int, int]: ...
-    def load_char(self, charcode: int, flags: LoadFlags = ...) -> Glyph: ...
-    def load_glyph(self, glyphindex: int, flags: LoadFlags = ...) -> Glyph: ...
+    def load_char(self, charcode: CharacterCodeType, flags: LoadFlags = ...) -> Glyph: ...
+    def load_glyph(self, glyphindex: GlyphIndexType, flags: LoadFlags = ...) -> Glyph: ...
     def select_charmap(self, i: int) -> None: ...
     def set_charmap(self, i: int) -> None: ...
     def set_size(self, ptsize: float, dpi: float) -> None: ...

lib/matplotlib/tests/test_ft2font.py

@@ -1,6 +1,7 @@
 import itertools
 import io
 from pathlib import Path
+from typing import cast
 
 import numpy as np
 import pytest
@@ -235,7 +236,7 @@ def enc(name):
     assert unic == after
 
     # This is just a random sample from FontForge.
-    glyph_names = {
+    glyph_names = cast(dict[str, ft2font.GlyphIndexType], {
         'non-existent-glyph-name': 0,
         'plusminus': 115,
         'Racute': 278,
@@ -247,7 +248,7 @@ def enc(name):
         'uni2A02': 4464,
         'u1D305': 5410,
         'u1F0A1': 5784,
-    }
+    })
     for name, index in glyph_names.items():
         assert font.get_name_index(name) == index
         if name == 'non-existent-glyph-name':

src/ft2font_wrapper.cpp

@@ -1772,5 +1772,8 @@ PYBIND11_MODULE(ft2font, m, py::mod_gil_not_used())
 
     m.attr("__freetype_version__") = version_string;
     m.attr("__freetype_build_type__") = FREETYPE_BUILD_TYPE;
+    auto py_int = py::module_::import("builtins").attr("int");
+    m.attr("CharacterCodeType") = py_int;
+    m.attr("GlyphIndexType") = py_int;
     m.def("__getattr__", ft2font__getattr__);
 }