docutils: Warn about long lines

README.rst

@@ -123,6 +123,13 @@ See |help(docutils)|_ for more information.  The ``.. coq::`` directive accepts
 
 To ensure that Coq blocks render properly, you'll need to tell your blogging platform to include ``alectryon.css``.  Using a git submodule or vendoring a copy of Alectryon is an easy way to ensure that this stylesheet is accessible to your blogging software.
 
+By default, Alectryon will raise warnings for lines over 72 characters.  You can change the threshold or silence the warnings by adjusting ``alectryon.docutils.LONG_LINE_THRESHOLD``.  With `Pelican <https://github.com/getpelican/pelican>`_, use the following snippet to make warnings non-fatal::
+
+   DOCUTILS_SETTINGS = {
+       'halt_level': 3, # Error
+       'warning_stream': None # stderr
+   }
+
 .. |help(docutils)| replace:: ``help(alectryon.docutils)``
 .. _help(docutils): alectryon/docutils.py
 

alectryon/core.py

@@ -380,3 +380,13 @@ def group_whitespace_with_code(fragments):
         else:
             grouped.append(fr)
     return grouped
+
+def find_long_lines(fragments, threshold):
+    prefix = ""
+    for fr in fragments:
+        suffix = "".join(w.contents for w in getattr(fr, "wsp", ()))
+        lines = (prefix + fr.contents + suffix).split("\n")
+        for line in lines:
+            if len(line) > threshold:
+                yield line
+        prefix = lines[-1]

alectryon/docutils.py

@@ -47,7 +47,7 @@
 from docutils.parsers.rst import directives, roles, Directive
 from docutils.transforms import Transform
 
-from .core import annotate, group_whitespace_with_code, process_io_annotations
+from .core import annotate, group_whitespace_with_code, process_io_annotations, find_long_lines
 from .html import HtmlWriter
 from .pygments import highlight
 
@@ -63,6 +63,8 @@ class alectryon_pending_toggle(Special, Invisible, Element):
 Display all goals and responses
 </label>""".replace('\n', '')
 
+LONG_LINE_THRESHOLD = 72
+
 class AlectryonTransform(Transform):
     default_priority = 995
     auto_toggle = True
@@ -74,6 +76,14 @@ def set_fragment_annots(fragments, options):
                 if hasattr(fr, 'annots') and not fr.annots:
                     fr.annots.add('all')
 
+    def check_for_long_lines(self, node, fragments):
+        if LONG_LINE_THRESHOLD is None:
+            return
+        for line in find_long_lines(fragments, threshold=LONG_LINE_THRESHOLD):
+            msg = "Long line: {!r} ({} characters)".format(line, len(line))
+            self.document.reporter.warning(msg, base_node=node)
+            return
+
     def apply_coq(self):
         writer = HtmlWriter(highlight)
         nodes = list(self.document.traverse(alectryon_pending))
@@ -85,6 +95,7 @@ def apply_coq(self):
             else:
                 classes = ("alectryon-floating",)
                 fragments = group_whitespace_with_code(process_io_annotations(fragments))
+                self.check_for_long_lines(node, fragments)
                 AlectryonTransform.set_fragment_annots(fragments, options)
                 html = writer.gen_fragments_html(fragments, classes=classes).render(pretty=False)
                 node.replace_self(raw(node['content'], html, format='html'))