Correctly read the 'style' argument while processing 'genfrac'. (matplotlib#23034)

* Correctly read the 'style' argument while processing 'genfrac'.

* Default to text style if style not specified.

* Hard-coded enumerations. Support script_stype and script_script_style.

* Automatically convert style number to enumerated type.

* Used double quotes for strings.

* Verify that genfrac's displaystyle == dfrac.

* Use rcParams instead of rcParamsDefault in the test.

The test changes the DPI of the figure, but compares images after saving them, so rcParams['savefig.dpi'] is more appropriate.

Author: tfpf

lib/matplotlib/_mathtext.py

@@ -1634,10 +1634,10 @@ class Parser:
     """
 
     class _MathStyle(enum.Enum):
-        DISPLAYSTYLE = enum.auto()
-        TEXTSTYLE = enum.auto()
-        SCRIPTSTYLE = enum.auto()
-        SCRIPTSCRIPTSTYLE = enum.auto()
+        DISPLAYSTYLE = 0
+        TEXTSTYLE = 1
+        SCRIPTSTYLE = 2
+        SCRIPTSCRIPTSTYLE = 3
 
     _binary_operators = set(
       '+ * - \N{MINUS SIGN}'
@@ -1725,6 +1725,9 @@ def set_names_and_parse_actions():
         p.float_literal  = Regex(r"[-+]?([0-9]+\.?[0-9]*|\.[0-9]+)")
         p.space          = oneOf(self._space_widths)("space")
 
+        p.style_literal  = oneOf(
+            [str(e.value) for e in self._MathStyle])("style_literal")
+
         p.single_symbol  = Regex(
             r"([a-zA-Z0-9 +\-*/<>=:,.;!\?&'@()\[\]|%s])|(\\[%%${}\[\]_|])" %
             "\U00000080-\U0001ffff"  # unicode range
@@ -1799,7 +1802,7 @@ def set_names_and_parse_actions():
             "{" + Optional(p.delim)("ldelim") + "}"
             + "{" + Optional(p.delim)("rdelim") + "}"
             + "{" + p.float_literal("rulesize") + "}"
-            + p.optional_group("style")
+            + "{" + Optional(p.style_literal)("style") + "}"
             + p.required_group("num")
             + p.required_group("den"))
 
@@ -2324,7 +2327,7 @@ def _genfrac(self, ldelim, rdelim, rule, style, num, den):
         state = self.get_state()
         thickness = state.get_current_underline_thickness()
 
-        if style is not self._MathStyle.DISPLAYSTYLE:
+        for _ in range(style.value):
             num.shrink()
             den.shrink()
         cnum = HCentered([num])
@@ -2358,10 +2361,13 @@ def _genfrac(self, ldelim, rdelim, rule, style, num, den):
             return self._auto_sized_delimiter(ldelim, result, rdelim)
         return result
 
+    def style_literal(self, s, loc, toks):
+        return self._MathStyle(int(toks["style_literal"]))
+
     def genfrac(self, s, loc, toks):
         return self._genfrac(
             toks.get("ldelim", ""), toks.get("rdelim", ""),
-            toks["rulesize"], toks["style"],
+            toks["rulesize"], toks.get("style", self._MathStyle.TEXTSTYLE),
             toks["num"], toks["den"])
 
     def frac(self, s, loc, toks):

lib/matplotlib/tests/test_mathtext.py

@@ -367,6 +367,16 @@ def test_inverted_delimiters(fig_test, fig_ref):
     fig_ref.text(.5, .5, r"$)($", math_fontfamily="dejavusans")
 
 
+@check_figures_equal(extensions=["png"])
+def test_genfrac_displaystyle(fig_test, fig_ref):
+    fig_test.text(0.1, 0.1, r"$\dfrac{2x}{3y}$")
+
+    thickness = _mathtext.TruetypeFonts.get_underline_thickness(
+        None, None, fontsize=mpl.rcParams["font.size"],
+        dpi=mpl.rcParams["savefig.dpi"])
+    fig_ref.text(0.1, 0.1, r"$\genfrac{}{}{%f}{0}{2x}{3y}$" % thickness)
+
+
 def test_mathtext_fallback_valid():
     for fallback in ['cm', 'stix', 'stixsans', 'None']:
         mpl.rcParams['mathtext.fallback'] = fallback