add [lb], [rb], and [@] tags

app/lib/babycode.py

@@ -141,6 +141,12 @@ TAGS = {
     "spoiler": tag_spoiler,
 }
 
+VOID_TAGS = {
+    'lb': lambda attr: '[',
+    'rb': lambda attr: ']',
+    '@': lambda attr: '@',
+}
+
 # [img] is considered block for the purposes of collapsing whitespace,
 # despite being potentially inline (since the resulting <img> tag is inline, but creates a block container around itself and sibling images).
 # [code] has a special case in is_inline().
@@ -260,6 +266,7 @@ def babycode_to_html(s, banned_tags=[]):
     subj = sanitize(s)
     parser = Parser(subj)
     parser.valid_bbcode_tags = allowed_tags
+    parser.void_bbcode_tags = set(VOID_TAGS)
     parser.bbcode_tags_only_text_children = TEXT_ONLY
     parser.mentions_allowed = '@mention' not in banned_tags
     parser.valid_emotes = EMOJI.keys()
@@ -296,6 +303,8 @@ def babycode_to_html(s, banned_tags=[]):
                     c = c + Markup(fold(child, _nobr, _surrounding))
                 res = TAGS[element['name']](c, element['attr'], surrounding)
                 return res
+            case "bbcode_void":
+                return VOID_TAGS[element['name']](element['attr'])
             case "link":
                 return f"<a href=\"{element['url']}\">{element['url']}</a>"
             case 'emote':

app/lib/babycode_parser.py

@@ -11,6 +11,7 @@ PAT_MENTION = r'[a-zA-Z0-9_-]'
 class Parser:
     def __init__(self, src_str):
         self.valid_bbcode_tags = {}
+        self.void_bbcode_tags = {}
         self.valid_emotes = []
         self.bbcode_tags_only_text_children = []
         self.mentions_allowed = True
@@ -228,11 +229,46 @@ class Parser:
         }
 
 
+    def parse_bbcode_void(self):
+        self.save_position()
+
+        if not self.check_char("["):
+            self.restore_position()
+            return None
+
+        name = self.match_pattern(PAT_BBCODE_TAG)
+
+        if name == "":
+            self.restore_position()
+            return None
+
+        attr = None
+
+        if self.check_char("="):
+            attr = self.match_pattern(PAT_BBCODE_ATTR)
+
+        if not self.check_char("]"):
+            self.restore_position()
+            return None
+
+        if not name in self.void_bbcode_tags:
+            self.restore_position()
+            return None
+
+        self.forget_position()
+        return {
+            'type': 'bbcode_void',
+            'name': name,
+            'attr': attr,
+        }
+
+
     def parse_element(self, siblings):
         if self.is_end_of_source():
             return None
 
         element = self.parse_emote() \
+            or self.parse_bbcode_void() \
             or self.parse_bbcode() \
             or self.parse_rule() \
             or self.parse_link() \

app/templates/guides/babycode.html

@@ -173,6 +173,19 @@
         <a class="mention display me" href="#mentions" title="@your-username">Your display name</a>
         <p>Mentioning a user does not notify them. It is simply a way to link to their profile in your posts.</p>
       </section>
+      <section class="guide-section">
+        <h2 id="void-tags">Void tags</h2>
+        <p>The special void tags <code class="inline-code">[lb]</code>, <code class="inline-code">[rb]</code>, and <code class="inline-code">[@]</code> will appear as the literal characters <code class="inline-code">[</code>, <code class="inline-code">]</code>, and <code class="inline-code">@</code> respectively. Unlike other tags, they are self-contained and have no closing equivalent.</p>
+        <ul class="guide-list">
+          {% set lbrb = "[color=red]This text will be red[/color]\n\n[lb]color=red[rb]This text won't be red[lb]/color[rb]" %}
+          <li><code class="inline-code">[lb]</code> and <code class="inline-code">[rb]</code> allow you to use square brackets without them being interpreted as Babycode:
+            {{ ("[code]" + lbrb + "[/code]") | babycode | safe }}
+            Will result in:<br>
+            {{ lbrb | babycode | safe }}
+          </li>
+          <li>The <code class="inline-code">[@]</code> tag allows you to use the @ symbol without it being turned into a mention.</li>
+        </ul>
+      </section>
     {% endset %}
     {{ sections | safe }}
   </div>