From cf759a6fe8b8b17dbcac706636daee300205d892 Mon Sep 17 00:00:00 2001
From: Matteo Nastasi <nastasi@openquake.org>
Date: Thu, 28 Sep 2017 16:56:54 +0200
Subject: [PATCH] move syntax_highlight doc filter in compatibility module and
 define it conditionally

---
 rest_framework/compat.py                      | 27 +++++++++++++
 rest_framework/templatetags/rest_framework.py | 38 +++----------------
 2 files changed, 32 insertions(+), 33 deletions(-)

diff --git a/rest_framework/compat.py b/rest_framework/compat.py
index e0f718ced..115011fd3 100644
--- a/rest_framework/compat.py
+++ b/rest_framework/compat.py
@@ -273,6 +273,32 @@ except ImportError:
     def pygments_css(style):
         return None
 
+if markdown is not None and pygments is not None:
+    class CodeBlockPreprocessor(Preprocessor):
+        pattern = re.compile(
+            r'^\s*@@ (.+?) @@\s*(.+?)^\s*@@', re.M|re.S)
+
+        formatter = HtmlFormatter()
+
+        def run(self, lines):
+            def repl(m):
+                try:
+                    lexer = get_lexer_by_name(m.group(1))
+                except (ValueError, NameError):
+                    lexer = TextLexer()
+                code = m.group(2).replace('\t','    ')
+                code = pygments.highlight(code, lexer, self.formatter)
+                code = code.replace('\n\n', '\n&nbsp;\n').replace('\n', '<br />').replace('\\@','@')
+                return '\n\n%s\n\n' % code
+            ret = self.pattern.sub(repl, "\n".join(lines))
+            return ret.split("\n")
+
+    def md_filter_add_syntax_highlight(md):
+        md.preprocessors.add('highlight', CodeBlockPreprocessor(), "_begin")
+        return True
+else:
+    def md_filter_add_syntax_highlight(md):
+        return False
 
 try:
     import pytz
@@ -374,3 +400,4 @@ def include(module, namespace=None, app_name=None):
         return include(module, namespace, app_name)
     else:
         return include((module, app_name), namespace)
+
diff --git a/rest_framework/templatetags/rest_framework.py b/rest_framework/templatetags/rest_framework.py
index 0f355ac0d..7002f0b9f 100644
--- a/rest_framework/templatetags/rest_framework.py
+++ b/rest_framework/templatetags/rest_framework.py
@@ -11,7 +11,8 @@ from django.utils.html import escape, format_html, smart_urlquote
 from django.utils.safestring import SafeData, mark_safe
 
 from rest_framework.compat import (
-    NoReverseMatch, markdown, pygments_highlight, reverse, template_render
+    NoReverseMatch, markdown, pygments_highlight, reverse, template_render,
+    md_filter_add_syntax_highlight,
 )
 from rest_framework.renderers import HTMLFormRenderer
 from rest_framework.utils.urls import replace_query_param
@@ -66,44 +67,15 @@ def form_for_link(link):
     return mark_safe(coreschema.render_to_form(schema))
 
 
-from markdown.preprocessors import Preprocessor
-from pygments.formatters import HtmlFormatter
-from pygments.lexers import get_lexer_by_name, TextLexer
-from pygments import highlight
-import pygments
-import re
-
-# starting from this blogpost and modified to support current markdown extensions API
-# https://zerokspot.com/weblog/2008/06/18/syntax-highlighting-in-markdown-with-pygments/
-class CodeBlockPreprocessor(Preprocessor):
-    pattern = re.compile(
-        r'^\s*@@ (.+?) @@\s*(.+?)^\s*@@', re.M|re.S)
-
-    formatter = HtmlFormatter()
-
-    def run(self, lines):
-        def repl(m):
-            try:
-                lexer = get_lexer_by_name(m.group(1))
-            except (ValueError, NameError):
-                lexer = TextLexer()
-            code = m.group(2).replace('\t','    ')
-            code = pygments.highlight(code, lexer, self.formatter)
-            code = code.replace('\n\n', '\n&nbsp;\n').replace('\n', '<br />').replace('\\@','@')
-            return '\n\n%s\n\n' % code
-        # import ipdb ; ipdb.set_trace()
-        ret = self.pattern.sub(repl, "\n".join(lines))
-        return ret.split("\n")
-
-
 @register.simple_tag
 def render_markdown(markdown_text):
     if not markdown:
         return markdown_text
     md = markdown.Markdown()
-    md.preprocessors.add('highlight', CodeBlockPreprocessor(), "_begin")
 
-    a = md.convert(markdown_text)
+    # add pygments syntax highlight if pygments package is available
+    md_filter_add_syntax_highlight(md)
+
     return mark_safe(md.convert(markdown_text))