From c4a5afcf24769ec9adde99bc80f1ed33c9ee5e78 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 10 Feb 2019 19:14:26 +0530
Subject: [PATCH] Allow loading builtin markdown extensions without relying on
 pkg_resources

---
 src/calibre/ebooks/txt/processor.py | 22 ++++++++++++++++++++--
 src/calibre/test_build.py           |  2 +-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/calibre/ebooks/txt/processor.py b/src/calibre/ebooks/txt/processor.py
index b2a6292748..7a729f859e 100644
--- a/src/calibre/ebooks/txt/processor.py
+++ b/src/calibre/ebooks/txt/processor.py
@@ -103,10 +103,28 @@ DEFAULT_MD_EXTENSIONS = ('footnotes', 'tables', 'toc')
 
 
 def create_markdown_object(extensions):
+    # Need to load markdown extensions without relying on pkg_resources
+    import importlib
     from calibre.ebooks.markdown import Markdown
+    from markdown import Extension
+
+    class NotBrainDeadMarkdown(Markdown):
+        def build_extension(self, ext_name, configs):
+            if '.' in ext_name or ':' in ext_name:
+                return Markdown.build_extension(self, ext_name, configs)
+            ext_name = 'markdown.extensions.' + ext_name
+            module = importlib.import_module(ext_name)
+            if hasattr(module, 'makeExtension'):
+                return module.makeExtension(**configs)
+            for name, x in vars(module).items():
+                if type(x) is type and issubclass(x, Extension) and x is not Extension:
+                    return x(**configs)
+            raise ImportError('No extension class in {}'.format(ext_name))
+
     from calibre.ebooks.conversion.plugins.txt_input import MD_EXTENSIONS
-    extensions = [x.lower() for x in extensions if x.lower() in MD_EXTENSIONS]
-    md = Markdown(extensions=extensions)
+    extensions = [x.lower() for x in extensions]
+    extensions = [x for x in extensions if x in MD_EXTENSIONS]
+    md = NotBrainDeadMarkdown(extensions=extensions)
     return md
 
 
diff --git a/src/calibre/test_build.py b/src/calibre/test_build.py
index 64470fa025..f450e91744 100644
--- a/src/calibre/test_build.py
+++ b/src/calibre/test_build.py
@@ -271,7 +271,7 @@ class BuildTest(unittest.TestCase):
     def test_markdown(self):
         from calibre.ebooks.txt.processor import create_markdown_object
         from calibre.ebooks.conversion.plugins.txt_input import MD_EXTENSIONS
-        create_markdown_object(MD_EXTENSIONS)
+        create_markdown_object(sorted(MD_EXTENSIONS))
         from calibre.library.comments import sanitize_comments_html
         sanitize_comments_html(b'''<script>moo</script>xxx<img src="http://moo.com/x.jpg">''')