From b8b3d77cf57fd2bd0317611739c491d4d9a8166b Mon Sep 17 00:00:00 2001
From: Oscar Gustafsson <oscar.gustafsson@gmail.com>
Date: Sun, 9 Jan 2022 14:25:51 +0100
Subject: [PATCH] mathtext now supports units for the third genfrac argument

---
 .../mathtext_genfrac_supports_unit.rst        | 11 +++++
 lib/matplotlib/_mathtext.py                   | 43 ++++++++++++++++---
 2 files changed, 49 insertions(+), 5 deletions(-)
 create mode 100644 doc/users/next_whats_new/mathtext_genfrac_supports_unit.rst

diff --git a/doc/users/next_whats_new/mathtext_genfrac_supports_unit.rst b/doc/users/next_whats_new/mathtext_genfrac_supports_unit.rst
new file mode 100644
index 000000000000..f1738a0fac00
--- /dev/null
+++ b/doc/users/next_whats_new/mathtext_genfrac_supports_unit.rst
@@ -0,0 +1,11 @@
+``mathtext`` now supports units for the bar thickness ``\genfrac`` argument
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This follows the standard LaTeX version where units are required.
+
+.. code-block:: python
+
+import matplotlib.pyplot as plt
+
+plt.text(0.5, 0.5, r'$\genfrac{(}{)}{0.5cm}{0}{foo}{bar}$')
+plt.draw()
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
index c58340c3804e..973361817a7a 100644
--- a/lib/matplotlib/_mathtext.py
+++ b/lib/matplotlib/_mathtext.py
@@ -1958,6 +1958,7 @@ def __init__(self):
         p.customspace      = Forward()
         p.end_group        = Forward()
         p.float_literal    = Forward()
+        p.float_with_wo_unit = Forward()
         p.font             = Forward()
         p.frac             = Forward()
         p.dfrac            = Forward()
@@ -1995,6 +1996,7 @@ def __init__(self):
         p.symbol_name      = Forward()
         p.token            = Forward()
         p.underset         = Forward()
+        p.unit             = Forward()
         p.unknown_symbol   = Forward()
 
         # Set names on everything -- very useful for debugging
@@ -2004,6 +2006,10 @@ def __init__(self):
 
         p.float_literal <<= Regex(r"[-+]?([0-9]+\.?[0-9]*|\.[0-9]+)")
         p.int_literal   <<= Regex("[-+]?[0-9]+")
+        p.unit          <<= Regex("(pt|mm|cm|in|em|mu|"
+                                  "sp|bp|dd|pc|nc|nd|cc)")
+        p.float_with_wo_unit <<= Group((p.float_literal + p.unit) |
+                                       p.float_literal)
 
         p.lbrace        <<= Literal('{').suppress()
         p.rbrace        <<= Literal('}').suppress()
@@ -2093,7 +2099,7 @@ def __init__(self):
                 + (p.lbrace
                    + Optional(p.ambi_delim | p.right_delim_safe, default='')
                    + p.rbrace)
-                + (p.lbrace + p.float_literal + p.rbrace)
+                + (p.lbrace + p.float_with_wo_unit + p.rbrace)
                 + p.simple_group + p.required_group + p.required_group)
                | Error("Expected "
                        r"\genfrac{ldelim}{rdelim}{rulesize}{style}{num}{den}"))
@@ -2322,6 +2328,22 @@ def _make_space(self, percentage):
         r'\!':         -0.16667,  # -3/18 em = -3 mu
     }
 
+    _unit_multipliers = {
+         # pt|mm|cm|in|mu|sp|bp|dd|pc|nc|nd|cc
+        "pt": 1,
+        'mm': 7227/2540,
+        'cm': 7227/254,
+        'in': 7227/100,
+        'mu': 7227/2540000,
+        'sp': 1/65536,
+        'bp': 803/800,
+        'dd': 1238/1157,
+        'pc': 12,
+        'nc': 1370/107,
+        'nd': 685/642,
+        'cc': 14856/1157
+        }
+
     def space(self, s, loc, toks):
         tok, = toks
         num = self._space_widths[tok]
@@ -2741,7 +2763,7 @@ def _genfrac(self, ldelim, rdelim, rule, style, num, den):
         thickness = state.font_output.get_underline_thickness(
             state.font, state.fontsize, state.dpi)
 
-        rule = float(rule)
+        rule = self._get_float_with_unit(rule, state.fontsize)
 
         if style is not self._MathStyle.DISPLAYSTYLE:
             num.shrink()
@@ -2786,7 +2808,7 @@ def frac(self, s, loc, toks):
         thickness = state.font_output.get_underline_thickness(
             state.font, state.fontsize, state.dpi)
         (num, den), = toks
-        return self._genfrac('', '', thickness, self._MathStyle.TEXTSTYLE,
+        return self._genfrac('', '', [thickness], self._MathStyle.TEXTSTYLE,
                              num, den)
 
     def dfrac(self, s, loc, toks):
@@ -2794,14 +2816,25 @@ def dfrac(self, s, loc, toks):
         thickness = state.font_output.get_underline_thickness(
             state.font, state.fontsize, state.dpi)
         (num, den), = toks
-        return self._genfrac('', '', thickness, self._MathStyle.DISPLAYSTYLE,
+        return self._genfrac('', '', [thickness], self._MathStyle.DISPLAYSTYLE,
                              num, den)
 
     def binom(self, s, loc, toks):
         (num, den), = toks
-        return self._genfrac('(', ')', 0.0, self._MathStyle.TEXTSTYLE,
+        return self._genfrac('(', ')', [0.0], self._MathStyle.TEXTSTYLE,
                              num, den)
 
+    def _get_float_with_unit(self, val, fontsize):
+        ret = float(val[0])
+        if len(val) == 2:
+            if val[1].lower() == 'em':
+                # "1 em is a distance equal to the type size"
+                ret = ret*fontsize
+            else:
+                # Remaining units
+                ret = ret*self._unit_multipliers[val[1]]
+        return ret
+
     def _genset(self, s, loc, toks):
         (annotation, body), = toks
         state = self.get_state()