highlight: eagerly discover plugin lexers while demandimport is off

Since highlight is only relevant for servers, it seems worthwhile to
just trigger this eagerly, which avoids really weird traceback
problems caused by demandimport messing with some of the lexer plugins.

Differential Revision: https://phab.mercurial-scm.org/D1619

hgext/highlight/highlight.py

@@ -1,89 +1,93 b''
 # highlight.py - highlight extension implementation file
 #
 #  Copyright 2007-2009 Adam Hupp <[e-mail]> and others
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 #
 # The original module was split in an interface and an implementation
 # file to defer pygments loading and speedup extension setup.
 
 from __future__ import absolute_import
 
 from mercurial import demandimport
 demandimport.ignore.extend(['pkgutil', 'pkg_resources', '__main__'])
 
 from mercurial import (
     encoding,
     util,
 )
 
 with demandimport.deactivated():
     import pygments
     import pygments.formatters
     import pygments.lexers
+    import pygments.plugin
     import pygments.util
 
+    for unused in pygments.plugin.find_plugin_lexers():
+        pass
+
 highlight = pygments.highlight
 ClassNotFound = pygments.util.ClassNotFound
 guess_lexer = pygments.lexers.guess_lexer
 guess_lexer_for_filename = pygments.lexers.guess_lexer_for_filename
 TextLexer = pygments.lexers.TextLexer
 HtmlFormatter = pygments.formatters.HtmlFormatter
 
 SYNTAX_CSS = ('\n<link rel="stylesheet" href="{url}highlightcss" '
               'type="text/css" />')
 
 def pygmentize(field, fctx, style, tmpl, guessfilenameonly=False):
 
     # append a <link ...> to the syntax highlighting css
     old_header = tmpl.load('header')
     if SYNTAX_CSS not in old_header:
         new_header = old_header + SYNTAX_CSS
         tmpl.cache['header'] = new_header
 
     text = fctx.data()
     if util.binary(text):
         return
 
     # str.splitlines() != unicode.splitlines() because "reasons"
     for c in "\x0c\x1c\x1d\x1e":
         if c in text:
             text = text.replace(c, '')
 
     # Pygments is best used with Unicode strings:
     # <http://pygments.org/docs/unicode/>
     text = text.decode(encoding.encoding, 'replace')
 
     # To get multi-line strings right, we can't format line-by-line
     try:
         lexer = guess_lexer_for_filename(fctx.path(), text[:1024],
                                          stripnl=False)
     except (ClassNotFound, ValueError):
         # guess_lexer will return a lexer if *any* lexer matches. There is
         # no way to specify a minimum match score. This can give a high rate of
         # false positives on files with an unknown filename pattern.
         if guessfilenameonly:
             return
 
         try:
             lexer = guess_lexer(text[:1024], stripnl=False)
         except (ClassNotFound, ValueError):
             # Don't highlight unknown files
             return
 
     # Don't highlight text files
     if isinstance(lexer, TextLexer):
         return
 
     formatter = HtmlFormatter(nowrap=True, style=style)
 
     colorized = highlight(text, lexer, formatter)
     coloriter = (s.encode(encoding.encoding, 'replace')
                  for s in colorized.splitlines())
 
     tmpl.filters['colorize'] = lambda x: next(coloriter)
 
     oldl = tmpl.cache[field]
     newl = oldl.replace('line|escape', 'line|colorize')
     tmpl.cache[field] = newl