FIX: mathtext accents

This is a follow up to matplotlib#4588

The change in ae91e9f fixed
the symbols that started with accent names, but broke all of
the other accents.

This fixes both by special casing the 8 named symbols that start with
an accent as a prefix.

ex  '\doteq' should be parsed as a single symbol, not as as two symbols
(e, q) with a dot over the e ('\dot{e}q')

Author: tacaswell

lib/matplotlib/mathtext.py

@@ -2190,6 +2190,7 @@ def __init__(self):
         p.simple           = Forward()
         p.simple_group     = Forward()
         p.single_symbol    = Forward()
+        p.snowflake        = Forward()
         p.space            = Forward()
         p.sqrt             = Forward()
         p.stackrel         = Forward()
@@ -2223,6 +2224,7 @@ def __init__(self):
         unicode_range =  "\U00000080-\U0001ffff"
         p.single_symbol <<= Regex(r"([a-zA-Z0-9 +\-*/<>=:,.;!\?&'@()\[\]|%s])|(\\[%%${}\[\]_|])" %
                                unicode_range)
+        p.snowflake     <<= Suppress(p.bslash) + oneOf(self._snowflake)
         p.symbol_name   <<= (Combine(p.bslash + oneOf(list(six.iterkeys(tex2uni)))) +
                           FollowedBy(Regex("[^A-Za-z]").leaveWhitespace() | StringEnd()))
         p.symbol        <<= (p.single_symbol | p.symbol_name).leaveWhitespace()
@@ -2297,8 +2299,10 @@ def __init__(self):
                               | Error("Expected \operatorname{value}"))
                          )
 
-        p.placeable     <<= ( p.symbol # Must be first
-                         | p.accent # Must be second
+        p.placeable     <<= ( p.snowflake # this needs to be before accent so named symbols
+                                          # that are prefixed with an accent name work
+                         | p.accent # Must be before symbol as all accents are symbols
+                         | p.symbol # Must be third to catch all named symbols and single chars not in a group
                          | p.c_over_c
                          | p.function
                          | p.group
@@ -2505,6 +2509,8 @@ def symbol(self, s, loc, toks):
                            do_kern = False)]
         return [char]
 
+    snowflake = symbol
+
     def unknown_symbol(self, s, loc, toks):
         # print "symbol", toks
         c = toks[0]
@@ -2560,9 +2566,9 @@ def c_over_c(self, s, loc, toks):
         r'bar'   : r'\combiningoverline',
         r'grave' : r'\combininggraveaccent',
         r'acute' : r'\combiningacuteaccent',
-        r'ddot'  : r'\combiningdiaeresis',
         r'tilde' : r'\combiningtilde',
         r'dot'   : r'\combiningdotabove',
+        r'ddot'  : r'\combiningdiaeresis',
         r'vec'   : r'\combiningrightarrowabove',
         r'"'     : r'\combiningdiaeresis',
         r"`"     : r'\combininggraveaccent',
@@ -2577,6 +2583,11 @@ def c_over_c(self, s, loc, toks):
 
     _wide_accents = set(r"widehat widetilde widebar".split())
 
+    # make a lambda and call it to get the namespace right
+    _snowflake = (lambda am: [p for p in tex2uni if
+                              any(p.startswith(a) and a != p for a in am)]
+                  ) (set(_accent_map))
+
     def accent(self, s, loc, toks):
         assert(len(toks)==1)
         state = self.get_state()