bugdown: Remove whitespace strip from inline code.

Fixes #4507

static/third/marked/lib/marked.js

@@ -445,7 +445,7 @@ var inline = {
   nolink: /^!?\[((?:\[[^\]]*\]|[^\[\]])*)\]/,
   strong: /^__([\s\S]+?)__(?!_)|^\*\*([\s\S]+?)\*\*(?!\*)/,
   em: /^\b_((?:[^_]|__)+?)_\b|^\*((?:\*\*|[\s\S])+?)\*(?!\*)/,
-  code: /^(`+)\s*([\s\S]*?[^`])\s*\1(?!`)/,
+  code: /^(`+)(\s*[\s\S]*?[^`]\s*)\1(?!`)/,
   br: /^ {2,}\n(?!\s*$)/,
   del: noop,
   emoji: noop,

zerver/fixtures/markdown_test_cases.json

@@ -25,6 +25,12 @@
       "expected_output": "<p>Hamlet once said</p>\n<div class=\"codehilite\"><pre><span></span>def func():\n    x = 1\n\n    y = 2\n\n    z = 3\n</pre></div>\n\n\n<p>And all was good.</p>",
       "text_content": "Hamlet once said\ndef func():\n    x = 1\n\n    y = 2\n\n    z = 3\n\n\n\nAnd all was good."
     },
+    {
+      "name": "inline_code_spaces",
+      "input": "` outer ` ```    space    ```",
+      "expected_output": "<p><code> outer </code> <code>    space    </code></p>",
+      "text_content": " outer      space    "
+    },
     {
       "name": "codeblock_backticks",
       "input": "\n```\nfenced code\n```\n\n```inline code```\n",

zerver/lib/bugdown/__init__.py

@@ -355,6 +355,24 @@ class InlineHttpsProcessor(markdown.treeprocessors.Treeprocessor):
                 continue
             img.set("src", get_camo_url(url))
 
+class BacktickPattern(markdown.inlinepatterns.Pattern):
+    """ Return a `<code>` element containing the matching text. """
+    def __init__(self, pattern):
+        # type: (Text) -> None
+        markdown.inlinepatterns.Pattern.__init__(self, pattern)
+        self.ESCAPED_BSLASH = '%s%s%s' % (markdown.util.STX, ord('\\'), markdown.util.ETX)
+        self.tag = 'code'
+
+    def handleMatch(self, m):
+        # type: (Match[Text]) -> Union[Text, Element]
+        if m.group(4):
+            el = markdown.util.etree.Element(self.tag)
+            # Modified to not strip whitespace
+            el.text = markdown.util.AtomicString(m.group(4))
+            return el
+        else:
+            return m.group(2).replace('\\\\', self.ESCAPED_BSLASH)
+
 class InlineInterestingLinkProcessor(markdown.treeprocessors.Treeprocessor):
     TWITTER_MAX_IMAGE_HEIGHT = 400
     TWITTER_MAX_TO_PREVIEW = 3
@@ -1346,7 +1364,7 @@ class Bugdown(markdown.Extension):
         for k in ('image_link', 'image_reference', 'automail',
                   'autolink', 'link', 'reference', 'short_reference',
                   'escape', 'strong_em', 'emphasis', 'emphasis2',
-                  'linebreak', 'strong'):
+                  'linebreak', 'strong', 'backtick'):
             del md.inlinePatterns[k]
         try:
             # linebreak2 was removed upstream in version 3.2.1, so
@@ -1357,6 +1375,12 @@ class Bugdown(markdown.Extension):
 
         md.preprocessors.add("custom_text_notifications", AlertWordsNotificationProcessor(md), "_end")
 
+        # Inline code block without whitespace stripping
+        md.inlinePatterns.add(
+            "backtick",
+            BacktickPattern(r'(?:(?<!\\)((?:\\{2})+)(?=`+)|(?<!\\)(`+)(.+?)(?<!`)\3(?!`))'),
+            "_begin")
+
         # Custom bold syntax: **foo** but not __foo__
         md.inlinePatterns.add('strong',
                               markdown.inlinepatterns.SimpleTagPattern(r'(\*\*)([^\n]+?)\2', 'strong'),