downgrade manually

- A regular collection open/close no longer goes through the
upgrade/downgrade steps each time. This avoids wasted cycles, and will
become more important in the future when decks and note types are
split into separate tables.
- Added a downgrade button to the profiles screen to downgrade all
profiles and close the app.
- Downgrading is still automatic when exporting/doing a full sync.

qt/aqt/main.py

@@ -214,6 +214,7 @@ class AnkiQt(QMainWindow):
         f.delete_2.clicked.connect(self.onRemProfile)
         f.profiles.currentRowChanged.connect(self.onProfileRowChange)
         f.statusbar.setVisible(False)
+        f.downgrade_button.clicked.connect(self._on_downgrade)
         # enter key opens profile
         QShortcut(QKeySequence("Return"), d, activated=self.onOpenProfile)  # type: ignore
         self.refreshProfilesList()
@@ -343,6 +344,18 @@ close the profile or restart Anki."""
 
         self.onOpenProfile()
 
+    def _on_downgrade(self):
+        self.progress.start()
+        profiles = self.pm.profiles()
+        def downgrade():
+            self.pm.downgrade(profiles)
+        def on_done(future):
+            self.progress.finish()
+            future.result()
+            showInfo("Profiles can now be opened with an older version of Anki.")
+            self.profileDiag.close()
+        self.taskman.run_in_background(downgrade, on_done)
+
     def loadProfile(self, onsuccess: Optional[Callable] = None) -> None:
         self.maybeAutoSync()
 
@@ -440,8 +453,6 @@ close the profile or restart Anki."""
     # Collection load/unload
     ##########################################################################
 
-    downgrade_on_close = True
-
     def loadCollection(self) -> bool:
         try:
             self._loadCollection()
@@ -452,7 +463,7 @@ close the profile or restart Anki."""
             # clean up open collection if possible
             if self.col:
                 try:
-                    self.col.close(save=False, downgrade=self.downgrade_on_close)
+                    self.col.close(save=False, downgrade=False)
                 except:
                     pass
                 self.col = None
@@ -507,7 +518,7 @@ close the profile or restart Anki."""
         except:
             corrupt = True
         try:
-            self.col.close(downgrade=self.downgrade_on_close)
+            self.col.close(downgrade=False)
         except Exception as e:
             print(e)
             corrupt = True

qt/aqt/profiles.py

@@ -11,13 +11,14 @@ import locale
 import pickle
 import random
 import shutil
-from typing import Any, Dict, Optional
+from typing import Any, Dict, Optional, List
 
 from send2trash import send2trash
 
 import anki.lang
 import aqt.forms
 import aqt.sound
+from anki import Collection
 from anki.db import DB
 from anki.lang import _, without_unicode_isolation
 from anki.utils import intTime, isMac, isWin
@@ -275,6 +276,21 @@ and no other programs are accessing your profile folders, then try again."""
     def collectionPath(self):
         return os.path.join(self.profileFolder(), "collection.anki2")
 
+    # Downgrade
+    ######################################################################
+
+    def downgrade(self, profiles=List[str]):
+        for name in profiles:
+            path = os.path.join(self.base, name, "collection.anki2")
+            if not os.path.exists(path):
+                continue
+            with DB(path) as db:
+                if db.scalar("select ver from col") == 11:
+                    # nothing to do
+                    continue
+            c = Collection(path)
+            c.close(save=False, downgrade=True)
+
     # Helpers
     ######################################################################
 

qt/designer/profiles.ui

@@ -88,6 +88,13 @@
           </property>
          </widget>
         </item>
+        <item>
+         <widget class="QPushButton" name="downgrade_button">
+          <property name="text">
+           <string notr="true">Downgrade &amp;&amp; Quit</string>
+          </property>
+         </widget>
+        </item>
        </layout>
       </item>
      </layout>