Use STL type for FT2Font fallback list

This allows pybind11 to generate the type hints for us, and it also
takes care of checking the list and its contents are the right type.

Author: QuLogic

lib/matplotlib/tests/test_ft2font.py

@@ -152,10 +152,10 @@ def test_ft2font_invalid_args(tmp_path):
     with pytest.raises(ValueError, match='hinting_factor must be greater than 0'):
         ft2font.FT2Font(file, 0)
 
-    with pytest.raises(TypeError, match='Fallback list must be a list'):
+    with pytest.raises(TypeError, match='incompatible constructor arguments'):
         # failing to be a list will fail before the 0
         ft2font.FT2Font(file, _fallback_list=(0,))  # type: ignore[arg-type]
-    with pytest.raises(TypeError, match='Fallback fonts must be FT2Font objects.'):
+    with pytest.raises(TypeError, match='incompatible constructor arguments'):
         ft2font.FT2Font(file, _fallback_list=[0])  # type: ignore[list-item]
 
     # kerning_factor argument.

src/ft2font_wrapper.cpp

@@ -172,7 +172,8 @@ const char *PyFT2Font_init__doc__ =
 
 static PyFT2Font *
 PyFT2Font_init(py::object filename, long hinting_factor = 8,
-               py::object fallback_list_or_none = py::none(), int kerning_factor = 0)
+               std::optional<std::vector<PyFT2Font *>> fallback_list = std::nullopt,
+               int kerning_factor = 0)
 {
     if (hinting_factor <= 0) {
         throw py::value_error("hinting_factor must be greater than 0");
@@ -192,24 +193,13 @@ PyFT2Font_init(py::object filename, long hinting_factor = 8,
     open_args.stream = &self->stream;
 
     std::vector<FT2Font *> fallback_fonts;
-    if (!fallback_list_or_none.is_none()) {
-        if (!py::isinstance<py::list>(fallback_list_or_none)) {
-            throw py::type_error("Fallback list must be a list");
-        }
-        auto fallback_list = fallback_list_or_none.cast<py::list>();
-
-        // go through fallbacks once to make sure the types are right
-        for (auto item : fallback_list) {
-            if (!py::isinstance<PyFT2Font>(item)) {
-                throw py::type_error("Fallback fonts must be FT2Font objects.");
-            }
-        }
-        // go through a second time to add them to our lists
-        for (auto item : fallback_list) {
+    if (fallback_list) {
+        // go through fallbacks to add them to our lists
+        for (auto item : *fallback_list) {
             self->fallbacks.append(item);
             // Also (locally) cache the underlying FT2Font objects. As long as
             // the Python objects are kept alive, these pointer are good.
-            FT2Font *fback = py::cast<PyFT2Font *>(item)->x;
+            FT2Font *fback = item->x;
             fallback_fonts.push_back(fback);
         }
     }