Backport PR #9203: Latextools: Make latex_to_png_mpl not fail on errors

- Also make make both `latex_to_foo` functions to return None on failure.
- This will help to solve the errors qtconsole is having to handle Latex (as reported in jupyter/qtconsole#56)

IPython/lib/latextools.py

@@ -1,199 +1,205
 # -*- coding: utf-8 -*-
 """Tools for handling LaTeX."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 from io import BytesIO, open
 import os
 import tempfile
 import shutil
 import subprocess
 
 from IPython.utils.process import find_cmd, FindCmdError
 from traitlets.config import get_config
 from traitlets.config.configurable import SingletonConfigurable
 from traitlets import List, Bool, Unicode
 from IPython.utils.py3compat import cast_unicode, cast_unicode_py2 as u, PY3
 
 try: # Py3
     from base64 import encodebytes
 except ImportError: # Py2
     from base64 import encodestring as encodebytes
 
 
 class LaTeXTool(SingletonConfigurable):
     """An object to store configuration of the LaTeX tool."""
     def _config_default(self):
         return get_config()
     
     backends = List(
         Unicode(), ["matplotlib", "dvipng"],
         help="Preferred backend to draw LaTeX math equations. "
         "Backends in the list are checked one by one and the first "
         "usable one is used.  Note that `matplotlib` backend "
         "is usable only for inline style equations.  To draw  "
         "display style equations, `dvipng` backend must be specified. ",
         # It is a List instead of Enum, to make configuration more
         # flexible.  For example, to use matplotlib mainly but dvipng
         # for display style, the default ["matplotlib", "dvipng"] can
         # be used.  To NOT use dvipng so that other repr such as
         # unicode pretty printing is used, you can use ["matplotlib"].
         config=True)
 
     use_breqn = Bool(
         True,
         help="Use breqn.sty to automatically break long equations. "
         "This configuration takes effect only for dvipng backend.",
         config=True)
 
     packages = List(
         ['amsmath', 'amsthm', 'amssymb', 'bm'],
         help="A list of packages to use for dvipng backend. "
         "'breqn' will be automatically appended when use_breqn=True.",
         config=True)
 
     preamble = Unicode(
         help="Additional preamble to use when generating LaTeX source "
         "for dvipng backend.",
         config=True)
 
 
 def latex_to_png(s, encode=False, backend=None, wrap=False):
     """Render a LaTeX string to PNG.
 
     Parameters
     ----------
     s : text
         The raw string containing valid inline LaTeX.
     encode : bool, optional
         Should the PNG data base64 encoded to make it JSON'able.
     backend : {matplotlib, dvipng}
         Backend for producing PNG data.
     wrap : bool
         If true, Automatically wrap `s` as a LaTeX equation.
 
     None is returned when the backend cannot be used.
 
     """
     s = cast_unicode(s)
     allowed_backends = LaTeXTool.instance().backends
     if backend is None:
         backend = allowed_backends[0]
     if backend not in allowed_backends:
         return None
     if backend == 'matplotlib':
         f = latex_to_png_mpl
     elif backend == 'dvipng':
         f = latex_to_png_dvipng
     else:
         raise ValueError('No such backend {0}'.format(backend))
     bin_data = f(s, wrap)
     if encode and bin_data:
         bin_data = encodebytes(bin_data)
     return bin_data
 
 
 def latex_to_png_mpl(s, wrap):
     try:
         from matplotlib import mathtext
+        from pyparsing import ParseFatalException
     except ImportError:
         return None
-    
+
     # mpl mathtext doesn't support display math, force inline
     s = s.replace('$$', '$')
     if wrap:
         s = u'${0}$'.format(s)
-    
-    mt = mathtext.MathTextParser('bitmap')
-    f = BytesIO()
-    mt.to_png(f, s, fontsize=12)
-    return f.getvalue()
+
+    try:
+        mt = mathtext.MathTextParser('bitmap')
+        f = BytesIO()
+        mt.to_png(f, s, fontsize=12)
+        return f.getvalue()
+    except (ValueError, RuntimeError, ParseFatalException):
+        return None
 
 
 def latex_to_png_dvipng(s, wrap):
     try:
         find_cmd('latex')
         find_cmd('dvipng')
     except FindCmdError:
         return None
     try:
         workdir = tempfile.mkdtemp()
         tmpfile = os.path.join(workdir, "tmp.tex")
         dvifile = os.path.join(workdir, "tmp.dvi")
         outfile = os.path.join(workdir, "tmp.png")
 
         with open(tmpfile, "w", encoding='utf8') as f:
             f.writelines(genelatex(s, wrap))
 
         with open(os.devnull, 'wb') as devnull:
             subprocess.check_call(
                 ["latex", "-halt-on-error", "-interaction", "batchmode", tmpfile],
                 cwd=workdir, stdout=devnull, stderr=devnull)
 
             subprocess.check_call(
                 ["dvipng", "-T", "tight", "-x", "1500", "-z", "9",
                  "-bg", "transparent", "-o", outfile, dvifile], cwd=workdir,
                 stdout=devnull, stderr=devnull)
 
         with open(outfile, "rb") as f:
             return f.read()
+    except subprocess.CalledProcessError:
+        return None
     finally:
         shutil.rmtree(workdir)
 
 
 def kpsewhich(filename):
     """Invoke kpsewhich command with an argument `filename`."""
     try:
         find_cmd("kpsewhich")
         proc = subprocess.Popen(
             ["kpsewhich", filename],
             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         (stdout, stderr) = proc.communicate()
         return stdout.strip().decode('utf8', 'replace')
     except FindCmdError:
         pass
 
 
 def genelatex(body, wrap):
     """Generate LaTeX document for dvipng backend."""
     lt = LaTeXTool.instance()
     breqn = wrap and lt.use_breqn and kpsewhich("breqn.sty")
     yield u(r'\documentclass{article}')
     packages = lt.packages
     if breqn:
         packages = packages + ['breqn']
     for pack in packages:
         yield u(r'\usepackage{{{0}}}'.format(pack))
     yield u(r'\pagestyle{empty}')
     if lt.preamble:
         yield lt.preamble
     yield u(r'\begin{document}')
     if breqn:
         yield u(r'\begin{dmath*}')
         yield body
         yield u(r'\end{dmath*}')
     elif wrap:
         yield u'$${0}$$'.format(body)
     else:
         yield body
     yield u'\end{document}'
 
 
 _data_uri_template_png = u"""<img src="data:image/png;base64,%s" alt=%s />"""
 
 def latex_to_html(s, alt='image'):
     """Render LaTeX to HTML with embedded PNG data using data URIs.
 
     Parameters
     ----------
     s : str
         The raw string containing valid inline LateX.
     alt : str
         The alt text to use for the HTML.
     """
     base64_data = latex_to_png(s, encode=True).decode('ascii')
     if base64_data:
         return _data_uri_template_png  % (base64_data, alt)