markdown: Remove logic for creating markdown engines for all realms.

This logic likely never ran due to a combination of bugs.

* Running `maybe_update_markdown_engines` unconditionally meant that
  `if md_engine_key in md_engines` was likely always true.
* Introduced in 65838bb: DEFAULT_MARKDOWN_KEY could never be in
  md_engines, so should we have ever reached that code path, we'd have
  tried to rebuild all markdown engines every time.

And it also wasn't clearly helpful -- because we fetch all linkifiers
for a realm on every request anyway, we don't really save database
queries by doing a bulk fetch on startup, and doing so would likely
result in a material regression to Zulip's overall startup time that
we were creating markdown engines for large numbers of realms in bulk
during process startup.

zerver/lib/markdown/__init__.py

@@ -73,7 +73,6 @@ from zerver.models import (
     UserGroup,
     UserGroupMembership,
     UserProfile,
-    all_linkifiers_for_installation,
     get_active_streams,
     linkifiers_for_realm,
 )
@@ -2373,32 +2372,22 @@ def topic_links(linkifiers_key: int, topic_name: str) -> List[Dict[str, str]]:
     return [{k: str(v) for k, v in match.items() if k != "index"} for match in matches]
 
 
-def maybe_update_markdown_engines(linkifiers_key: Optional[int], email_gateway: bool) -> None:
-    # If linkifiers_key is None, load all linkifiers
+def maybe_update_markdown_engines(linkifiers_key: int, email_gateway: bool) -> None:
     global linkifier_data
-    if linkifiers_key is None:
-        all_linkifiers = all_linkifiers_for_installation()
-        all_linkifiers[DEFAULT_MARKDOWN_KEY] = []
-        for linkifiers_key, linkifiers in all_linkifiers.items():
-            linkifier_data[linkifiers_key] = linkifiers
-            make_md_engine(linkifiers_key, email_gateway)
-        # Hack to ensure that linkifiers_key is right for mirrored Zephyrs
-        linkifier_data[ZEPHYR_MIRROR_MARKDOWN_KEY] = []
-        make_md_engine(ZEPHYR_MIRROR_MARKDOWN_KEY, False)
-    else:
-        linkifiers = linkifiers_for_realm(linkifiers_key)
-        if linkifiers_key not in linkifier_data or linkifier_data[linkifiers_key] != linkifiers:
-            # Linkifier data has changed, update `linkifier_data` and any
-            # of the existing Markdown engines using this set of linkifiers.
-            linkifier_data[linkifiers_key] = linkifiers
-            for email_gateway_flag in [True, False]:
-                if (linkifiers_key, email_gateway_flag) in md_engines:
-                    # Update only existing engines(if any), don't create new one.
-                    make_md_engine(linkifiers_key, email_gateway_flag)
 
-        if (linkifiers_key, email_gateway) not in md_engines:
-            # Markdown engine corresponding to this key doesn't exists so create one.
-            make_md_engine(linkifiers_key, email_gateway)
+    linkifiers = linkifiers_for_realm(linkifiers_key)
+    if linkifiers_key not in linkifier_data or linkifier_data[linkifiers_key] != linkifiers:
+        # Linkifier data has changed, update `linkifier_data` and any
+        # of the existing Markdown engines using this set of linkifiers.
+        linkifier_data[linkifiers_key] = linkifiers
+        for email_gateway_flag in [True, False]:
+            if (linkifiers_key, email_gateway_flag) in md_engines:
+                # Update only existing engines(if any), don't create new one.
+                make_md_engine(linkifiers_key, email_gateway_flag)
+
+    if (linkifiers_key, email_gateway) not in md_engines:
+        # Markdown engine corresponding to this key doesn't exists so create one.
+        make_md_engine(linkifiers_key, email_gateway)
 
 
 # We want to log Markdown parser failures, but shouldn't log the actual input
@@ -2578,14 +2567,7 @@ def do_convert(
 
     maybe_update_markdown_engines(linkifiers_key, email_gateway)
     md_engine_key = (linkifiers_key, email_gateway)
-
-    if md_engine_key in md_engines:
-        _md_engine = md_engines[md_engine_key]
-    else:
-        if DEFAULT_MARKDOWN_KEY not in md_engines:
-            maybe_update_markdown_engines(linkifiers_key=None, email_gateway=False)
-
-        _md_engine = md_engines[(DEFAULT_MARKDOWN_KEY, email_gateway)]
+    _md_engine = md_engines[md_engine_key]
     # Reset the parser; otherwise it will get slower over time.
     _md_engine.reset()
 

zerver/models.py

@@ -3,13 +3,11 @@ import datetime
 import re
 import secrets
 import time
-from collections import defaultdict
 from datetime import timedelta
 from typing import (
     AbstractSet,
     Any,
     Callable,
-    DefaultDict,
     Dict,
     Iterable,
     List,
@@ -938,20 +936,6 @@ def linkifiers_for_realm_remote_cache(realm_id: int) -> List[LinkifierDict]:
     return filters
 
 
-def all_linkifiers_for_installation() -> Dict[int, List[LinkifierDict]]:
-    filters: DefaultDict[int, List[LinkifierDict]] = defaultdict(list)
-    for linkifier in RealmFilter.objects.all():
-        filters[linkifier.realm_id].append(
-            LinkifierDict(
-                pattern=linkifier.pattern,
-                url_format=linkifier.url_format_string,
-                id=linkifier.id,
-            )
-        )
-
-    return filters
-
-
 def flush_linkifiers(sender: Any, **kwargs: Any) -> None:
     realm_id = kwargs["instance"].realm_id
     cache_delete(get_linkifiers_cache_key(realm_id))

zerver/tests/test_markdown.py

@@ -45,7 +45,6 @@ from zerver.lib.message import render_markdown
 from zerver.lib.request import JsonableError
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.tex import render_tex
-from zerver.lib.types import LinkifierDict
 from zerver.lib.user_groups import create_user_group
 from zerver.models import (
     MAX_MESSAGE_LENGTH,
@@ -1420,30 +1419,6 @@ class MarkdownTest(ZulipTestCase):
             ],
         )
 
-    def test_maybe_update_markdown_engines(self) -> None:
-        realm = get_realm("zulip")
-        url_format_string = r"https://trac.example.com/ticket/%(id)s"
-        linkifier = RealmFilter(
-            realm=realm, pattern=r"#(?P<id>[0-9]{2,8})", url_format_string=url_format_string
-        )
-        linkifier.save()
-
-        import zerver.lib.markdown
-
-        zerver.lib.markdown.linkifier_data = {}
-        maybe_update_markdown_engines(None, False)
-        all_linkifiers = zerver.lib.markdown.linkifier_data
-        zulip_linkifiers = all_linkifiers[realm.id]
-        self.assertEqual(len(zulip_linkifiers), 1)
-        self.assertDictEqual(
-            zulip_linkifiers[0],
-            LinkifierDict(
-                pattern="#(?P<id>[0-9]{2,8})",
-                url_format="https://trac.example.com/ticket/%(id)s",
-                id=linkifier.id,
-            ),
-        )
-
     def test_flush_linkifier(self) -> None:
         realm = get_realm("zulip")