TST: add type checking and tests for fallback list

tacaswell · tacaswell · commit 755b8ff5d7fa · 2022-07-07T17:05:31.000-04:00
diff --git a/lib/matplotlib/tests/test_font_manager.py b/lib/matplotlib/tests/test_font_manager.py
@@ -347,3 +347,16 @@ def test_get_font_names():
     assert set(available_fonts) == set(mpl_font_names)
     assert len(available_fonts) == len(mpl_font_names)
     assert available_fonts == mpl_font_names
+
+
+def test_fallback_errors():
+    file_name = findfont('DejaVu Sans')
+
+    with pytest.raises(TypeError, match="Fallback list must be a list"):
+        # failing to be a list will fail before the 0
+        ft2font.FT2Font(file_name, _fallback_list=(0,))
+
+    with pytest.raises(
+            TypeError, match="Fallback fonts must be FT2Font objects."
+    ):
+        ft2font.FT2Font(file_name, _fallback_list=[0])
diff --git a/src/ft2font_wrapper.cpp b/src/ft2font_wrapper.cpp
@@ -372,19 +372,33 @@ static int PyFT2Font_init(PyFT2Font *self, PyObject *args, PyObject *kwds)
     open_args.flags = FT_OPEN_STREAM;
     open_args.stream = &self->stream;
 
-    if (fallback_list && PyList_Check(fallback_list)) {
-        Py_ssize_t size = PyList_Size(fallback_list);
-
+    if (fallback_list) {
+	 if (!PyList_Check(fallback_list)) {
+	      PyErr_SetString(PyExc_TypeError, "Fallback list must be a list");
+	      goto exit;
+	 }
+	 Py_ssize_t size = PyList_Size(fallback_list);
+
+	 // go through fallbacks once to make sure the types are right
+	 for (Py_ssize_t i = 0; i < size; ++i) {
+	      // this returns a borrowed reference
+	      PyObject* item = PyList_GetItem(fallback_list, i);
+	      if (!PyObject_IsInstance(item, PyObject_Type(reinterpret_cast<PyObject *>(self)))) {
+		   PyErr_SetString(PyExc_TypeError, "Fallback fonts must be FT2Font objects.");
+		   goto exit;
+	      }
+        }
+        // go through a second time to add them to our lists
         for (Py_ssize_t i = 0; i < size; ++i) {
             // this returns a borrowed reference
             PyObject* item = PyList_GetItem(fallback_list, i);
-            // Increase the ref count, we will undo this in dealloc
-            // this makes sure things do not get gc'd under us!
+            // Increase the ref count, we will undo this in dealloc this makes
+            // sure things do not get gc'd under us!
             Py_INCREF(item);
             self->fallbacks.push_back(item);
-            // TODO: check whether item is actually an FT2Font
+            // Also (locally) cache the underlying FT2Font objects. As long as
+            // the Python objects are kept alive, these pointer are good.
             FT2Font *fback = reinterpret_cast<PyFT2Font *>(item)->x;
-            // Also (locally) cache the underlying FT2Font objects
             fallback_fonts.push_back(fback);
         }
 
