Support \sqrt[not-a-number]{...}.

Author: anntzer

lib/matplotlib/_mathtext.py

@@ -2158,7 +2158,8 @@ def __init__(self):
 
         p.sqrt <<= Group(
             Suppress(Literal(r"\sqrt"))
-            - ((Optional(p.lbracket + p.int_literal + p.rbracket, default=None)
+            - ((Group(Optional(
+                p.lbracket + OneOrMore(~p.rbracket + p.token) + p.rbracket))
                 + p.required_group)
                | Error("Expected \\sqrt{value}"))
         )
@@ -2864,10 +2865,10 @@ def sqrt(self, s, loc, toks):
 
         # Add the root and shift it upward so it is above the tick.
         # The value of 0.6 is a hard-coded hack ;)
-        if root is None:
+        if not root:
             root = Box(check.width * 0.5, 0., 0.)
         else:
-            root = Hlist([Char(x, state) for x in root])
+            root = Hlist(root)
             root.shrink()
             root.shrink()
 

lib/matplotlib/tests/baseline_images/test_mathtext/mathtext1_dejavusans_00.png

@@ -114,6 +114,7 @@
 # default) and only png outputs, in order to minimize the size of baseline
 # images.
 lightweight_math_tests = [
+    r'$\sqrt[ab]{123}$',  # github issue #8665
 ]
 
 digits = "0123456789"