FIX: correctly handle generic font families in svg text-as-text mode

tacaswell · tacaswell · commit b31ed3f51ed4 · 2022-08-16T11:40:19.000-04:00
This: - expands the generic fonts families to the user configured specific fonts in the svg output - ensures that each font family only appears once per text element in the svg output - ensures that generic families are unquoted and specific families are closes #22528 closes #23492
diff --git a/lib/matplotlib/backends/backend_svg.py b/lib/matplotlib/backends/backend_svg.py
@@ -1151,10 +1151,55 @@ def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
             weight = fm.weight_dict[prop.get_weight()]
             if weight != 400:
                 font_parts.append(f'{weight}')
+
+            # TODO lift this up and add caching
+            def _format_font_name(fn):
+                normalize_names = {
+                    'sans': 'sans-serif',
+                    'sans serif': 'sans-serif'
+                }
+                # A generic font family.  We need to do two things:
+                #  1. list all of the configured fonts with quoted names
+                #  2. append the generic name unquoted
+                if fn in fm.font_family_aliases:
+                    # fix spelling of sans-serif
+                    # we accept 3 ways CSS only supports 1
+                    fn = normalize_names.get(fn, fn)
+                    # get all of the font names and fix spelling of sans-serif
+                    # if it comes back
+                    aliases = [
+                        normalize_names.get(_, _) for _ in
+                        fm.FontManager._expand_aliases(fn)
+                    ]
+                    # make sure the generic name appears at least once
+                    aliases.append(fn)
+
+                    def unique_iter(inp):
+                        """Only return unique values."""
+                        seen = set()
+                        for i in inp:
+                            if i not in seen:
+                                seen.add(i)
+                                yield i
+
+                    return ', '.join(
+                        [
+                            # generic font families must not be quoted
+                            a if a in fm.font_family_aliases
+                            # specific font families must be quoted
+                            else repr(a)
+                            # make sure each font family only shows up once
+                            for a in unique_iter(aliases)
+                        ]
+                    )
+                # specific font families must be quoted
+                else:
+                    return repr(fn)
+
             font_parts.extend([
                 f'{_short_float_fmt(prop.get_size())}px',
-                # ensure quoting
-                f'{", ".join(repr(f) for f in prop.get_family())}',
+                # ensure quoting and expansion of font names
+                ", ".join(_format_font_name(f) for f in prop.get_family()),
             ])
             style['font'] = ' '.join(font_parts)
             if prop.get_stretch() != 'normal':
