Improve error arising from fully commented-out TeX strings.

anntzer · anntzer · commit ae6e943f3c34 · 2020-02-05T00:11:30.000+01:00
Currently, `figtext(.5, .5, "%foo", usetex=True)` results in an obscure
exception (`FileNotFoundError: No such file or directory: blah.dvi`).

Best would be to force TeX to always generate a page even if the string
is "empty" (from TeX's PoV), but in the meantime, at least log a warning
to make the situation slightly less confusing.
diff --git a/lib/matplotlib/dviread.py b/lib/matplotlib/dviread.py
@@ -196,7 +196,15 @@ def __init__(self, filename, dpi):
         Use None to return TeX's internal units.
         """
         _log.debug('Dvi: %s', filename)
-        self.file = open(filename, 'rb')
+        try:
+            self.file = open(filename, 'rb')
+        except FileNotFoundError:
+            # This warning should go away once we fix texmanager to always
+            # create a dvi file, even if it is empty.
+            _log.warning(
+                '%s does not exist; this may arise from processing an empty '
+                'or fully commented-out TeX string.', filename)
+            raise
         self.dpi = dpi
         self.fonts = {}
         self.state = _dvistate.pre
