Partial fix for Matplotlib 3.9's test suite.

Author: anntzer

Diff for: ext/_mplcairo.cpp

@@ -1588,10 +1588,12 @@ void GraphicsContextRenderer::draw_text(
                   next_glyphs_pos = glyphs_pos + cluster.num_glyphs;
       for (auto j = glyphs_pos; j < next_glyphs_pos; ++j) {
         if (!gac.glyphs[j].index) {
-          auto missing =
-            py::cast(s.substr(bytes_pos, cluster.num_bytes))
-            .attr("encode")("ascii", "namereplace");
-          warn_on_missing_glyph(missing.cast<std::string>());
+          auto missing = py::cast(s.substr(bytes_pos, cluster.num_bytes));
+          warn_on_missing_glyph(  // Format forced by test_mathtext_ticks.
+            "{} ({})"_format(
+              py::module::import("builtins").attr("ord")(missing),
+              missing.attr("encode")("ascii", "namereplace").attr("decode")())
+            .cast<std::string>());
         }
       }
       bytes_pos = next_bytes_pos;

Diff for: ext/_util.cpp

@@ -903,8 +903,8 @@ void warn_on_missing_glyph(std::string s)
 {
   PY_CHECK(
     PyErr_WarnEx,
-    nullptr,
-    "Requested glyph ({}) missing from current font."_format(s)
+    PyExc_UserWarning,
+    "Glyph {} missing from current font."_format(s)
     .cast<std::string>().c_str(),
     1);
 }