Regenerate history completion on version change.

Incrementing _USER_VERSION in the source will cause the
HistoryCompletion table to regenerate when users update.

This is currently necessary to support some recent formatting fixes, but
could be incremented again in the future for other changes.

qutebrowser/browser/history.py

@@ -30,6 +30,10 @@ from qutebrowser.utils import (utils, objreg, log, usertypes, message,
 from qutebrowser.misc import objects, sql
 
 
+# increment to indicate that HistoryCompletion must be regenerated
+_USER_VERSION = 1
+
+
 class CompletionHistory(sql.SqlTable):
 
     """History which only has the newest entry for each URL."""
@@ -48,7 +52,10 @@ class WebHistory(sql.SqlTable):
         super().__init__("History", ['url', 'title', 'atime', 'redirect'],
                          parent=parent)
         self.completion = CompletionHistory(parent=self)
+        if sql.Query('pragma user_version').run().value() < _USER_VERSION:
+            self.completion.delete_all()
         if not self.completion:
+            # either the table is out-of-date or the user wiped it manually
             self._rebuild_completion()
         self.create_index('HistoryIndex', 'url')
         self.create_index('HistoryAtimeIndex', 'atime')
@@ -83,6 +90,7 @@ class WebHistory(sql.SqlTable):
             data['title'].append(entry.title)
             data['last_atime'].append(entry.atime)
         self.completion.insert_batch(data)
+        sql.Query('pragma user_version = {}'.format(_USER_VERSION)).run()
 
     def get_recent(self):
         """Get the most recent history entries."""

tests/unit/browser/test_history.py

@@ -377,3 +377,20 @@ def test_no_rebuild_completion(hist):
 
     hist2 = history.WebHistory()
     assert list(hist2.completion) == [('example.com/1', '', 1)]
+
+
+def test_user_version(hist, monkeypatch):
+    """Ensure that completion is regenerated if user_version is incremented."""
+    hist.add_url(QUrl('example.com/1'), redirect=False, atime=1)
+    hist.add_url(QUrl('example.com/2'), redirect=False, atime=2)
+    hist.completion.delete('url', 'example.com/2')
+
+    hist2 = history.WebHistory()
+    assert list(hist2.completion) == [('example.com/1', '', 1)]
+
+    monkeypatch.setattr(history, '_USER_VERSION', history._USER_VERSION + 1)
+    hist3 = history.WebHistory()
+    assert list(hist3.completion) == [
+        ('example.com/1', '', 1),
+        ('example.com/2', '', 2),
+    ]