Add support for strikethrough in markdown

Fixes #304

app/__init__.py

@@ -25,18 +25,14 @@ from flask_flatpages import FlatPages
 from flask_babel import Babel
 from flask_login import logout_user, current_user, LoginManager
 import os, redis
+from app.markdown import init_markdown, MARKDOWN_EXTENSIONS, MARKDOWN_EXTENSION_CONFIG
+
 
 app = Flask(__name__, static_folder="public/static")
 app.config["FLATPAGES_ROOT"] = "flatpages"
 app.config["FLATPAGES_EXTENSION"] = ".md"
-app.config["FLATPAGES_MARKDOWN_EXTENSIONS"] = ["fenced_code", "tables", "codehilite", 'toc']
-app.config["FLATPAGES_EXTENSION_CONFIG"] = {
-	"fenced_code": {},
-	"tables": {},
-	"codehilite": {
-		"guess_lang": False,
-	}
-}
+app.config["FLATPAGES_MARKDOWN_EXTENSIONS"] = MARKDOWN_EXTENSIONS
+app.config["FLATPAGES_EXTENSION_CONFIG"] = MARKDOWN_EXTENSION_CONFIG
 app.config.from_pyfile(os.environ["FLASK_CONFIG"])
 
 r = redis.Redis.from_url(app.config["REDIS_URL"])
@@ -55,6 +51,7 @@ gravatar = Gravatar(app,
 		force_lower=False,
 		use_ssl=True,
 		base_url=None)
+init_markdown(app)
 
 login_manager = LoginManager()
 login_manager.init_app(app)
@@ -69,8 +66,7 @@ if not app.debug and app.config["MAIL_UTILS_ERROR_SEND_TO"]:
 	app.logger.addHandler(build_handler(app))
 
 
-from app.utils.markdown import init_app
-init_app(app)
+
 
 # @babel.localeselector
 # def get_locale():

app/blueprints/admin/email.py

@@ -21,7 +21,7 @@ from flask_wtf import FlaskForm
 from wtforms import *
 from wtforms.validators import *
 
-from app.utils.markdown import render_markdown
+from app.markdown import render_markdown
 from app.models import *
 from app.tasks.emails import send_user_email
 from app.utils import rank_required, addAuditLog

app/blueprints/api/endpoints.py

@@ -19,7 +19,7 @@ from flask_login import current_user, login_required
 from sqlalchemy.sql.expression import func
 
 from app import csrf
-from app.utils.markdown import render_markdown
+from app.markdown import render_markdown
 from app.models import Tag, PackageState, PackageType, Package, db, PackageRelease, Permission, ForumTopic, MinetestRelease, APIToken, PackageScreenshot, License, ContentWarning, User
 from app.querybuilder import QueryBuilder
 from app.utils import is_package_page, get_int_or_abort

app/markdown.py

@@ -6,6 +6,9 @@ from bleach.linkifier import LinkifyFilter
 from bs4 import BeautifulSoup
 from markdown import Markdown
 from flask import Markup
+from markdown.extensions import Extension
+from markdown.inlinepatterns import SimpleTagInlineProcessor
+
 
 # Based on
 # https://github.com/Wenzil/mdx_bleach/blob/master/mdx_bleach/whitelist.py
@@ -25,7 +28,7 @@ ALLOWED_TAGS = [
 	"a",
 	"img",
 	"table", "thead", "tbody", "tr", "th", "td",
-	"div", "span",
+	"div", "span", "del", "s",
 ]
 
 ALLOWED_CSS = [
@@ -68,11 +71,30 @@ def render_markdown(source):
 	return cleaner.clean(html)
 
 
-def init_app(app):
+class DelInsExtension(Extension):
+	def extendMarkdown(self, md):
+		del_proc = SimpleTagInlineProcessor(r'(\~\~)(.+?)(\~\~)', 'del')
+		md.inlinePatterns.register(del_proc, 'del', 200)
+
+		ins_proc = SimpleTagInlineProcessor(r'(\+\+)(.+?)(\+\+)', 'ins')
+		md.inlinePatterns.register(ins_proc, 'ins', 200)
+
+
+MARKDOWN_EXTENSIONS = ["fenced_code", "tables", "codehilite", "toc", DelInsExtension()]
+MARKDOWN_EXTENSION_CONFIG = {
+	"fenced_code": {},
+	"tables": {},
+	"codehilite": {
+		"guess_lang": False,
+	}
+}
+
+
+def init_markdown(app):
 	global md
 
-	md = Markdown(extensions=app.config["FLATPAGES_MARKDOWN_EXTENSIONS"],
-			extension_configs=app.config["FLATPAGES_EXTENSION_CONFIG"],
+	md = Markdown(extensions=MARKDOWN_EXTENSIONS,
+			extension_configs=MARKDOWN_EXTENSION_CONFIG,
 			output_format="html5")
 
 	@app.template_filter()

app/template_filters.py

@@ -6,7 +6,7 @@ from flask_babel import format_timedelta, gettext
 from urllib.parse import urlparse
 from datetime import datetime as dt
 
-from .utils.markdown import get_headings
+from app.markdown import get_headings
 
 
 @app.context_processor