limit custom study to 100 tags

The hard limit from sqlite may be larger, but things slow down as more
tags are selected.

https://forums.ankiweb.net/t/unable-to-create-custom-test/10467

There are a number of things that could be improved here:

- we should show a live count so users are aware of the limit
- we should be filling in the parent tags when they're not explicitly
listed on a card
- we should reconsider disabling the 'tags to include' by default

It may make sense to defer these changes until we can move this screen
into Svelte/handle the processing in the backend.

ftl/core/errors.ftl

@@ -3,3 +3,7 @@ errors-invalid-input-details = Invalid input: { $details }
 errors-parse-number-fail = A number was invalid or out of range.
 errors-filtered-parent-deck = Filtered decks can not have child decks.
 errors-filtered-deck-required = This action can only be used on a filtered deck.
+errors-100-tags-max =
+    A maximum of 100 tags can be selected. Listing the
+    tags you want instead of the ones you don't want is usually simpler, and there
+    is no need to select child tags if you have selected a parent tag.

pylib/anki/lang.py

@@ -211,3 +211,7 @@ def is_rtl(lang: str) -> bool:
 # for testing purposes
 def without_unicode_isolation(s: str) -> str:
     return s.replace("\u2068", "").replace("\u2069", "")
+
+
+def with_collapsed_whitespace(s: str) -> str:
+    return re.sub(r"\s+", " ", s)

qt/aqt/taglimit.py

@@ -3,10 +3,11 @@
 from typing import List, Optional
 
 import aqt
+from anki.lang import with_collapsed_whitespace
 from aqt.customstudy import CustomStudy
 from aqt.main import AnkiQt
 from aqt.qt import *
-from aqt.utils import disable_help_button, restoreGeom, saveGeom
+from aqt.utils import disable_help_button, restoreGeom, saveGeom, showWarning, tr
 
 
 class TagLimit(QDialog):
@@ -73,7 +74,6 @@ class TagLimit(QDialog):
         QDialog.reject(self)
 
     def accept(self) -> None:
-        self.hide()
         # gather yes/no tags
         yes = []
         no = []
@@ -89,6 +89,10 @@ class TagLimit(QDialog):
             idx = self.dialog.inactiveList.indexFromItem(item)
             if self.dialog.inactiveList.selectionModel().isSelected(idx):
                 no.append(self.tags_list[c])
+        if (len(yes) + len(no)) > 100:
+            showWarning(with_collapsed_whitespace(tr.errors_100_tags_max()))
+            return
+        self.hide()
         # save in the deck for future invocations
         self.deck["activeTags"] = yes
         self.deck["inactiveTags"] = no