space buttons by at least a day

when a card has a low interval like 1, you can end up with next times of
2,2,3, which some users think is a bug. change the code to yield 2,3,4
instead.

anki/sched.py

@@ -820,21 +820,23 @@ did = ? and queue = 2 and due <= ? limit ?""",
         delay = self._daysLate(card)
         conf = self._revConf(card)
         fct = card.factor / 1000.0
+        ivl2 = self._constrainedIvl((card.ivl + delay/4) * 1.2, conf, card.ivl)
+        ivl3 = self._constrainedIvl((card.ivl + delay/2) * fct, conf, ivl2)
+        ivl4 = self._constrainedIvl(
+            (card.ivl + delay) * fct * conf['ease4'], conf, ivl3)
         if ease == 2:
-            interval = (card.ivl + delay/4) * 1.2
+            interval = ivl2
         elif ease == 3:
-            interval = (card.ivl + delay/2) * fct
+            interval = ivl3
         elif ease == 4:
-            interval = (card.ivl + delay) * fct * conf['ease4']
-        # apply interval factor adjustment
-        interval = self._ivlWithFactor(conf, interval)
-        # must be at least one day greater than previous interval; two if easy
-        interval = max(card.ivl + (2 if ease==4 else 1), int(interval))
+            interval = ivl4
         # interval capped?
         return min(interval, conf['maxIvl'])
 
-    def _ivlWithFactor(self, conf, ivl):
-        return ivl * conf.get('ivlFct', 1)
+    def _constrainedIvl(self, ivl, conf, prev):
+        "Integer interval after interval factor and prev+1 constraints applied."
+        new = ivl * conf.get('ivlFct', 1)
+        return int(max(new, prev+1))
 
     def _daysLate(self, card):
         "Number of days later than scheduled."

tests/test_sched.py

@@ -346,6 +346,26 @@ def test_reviews():
     c.load()
     assert c.queue == -1
 
+def test_button_spacing():
+    d = getEmptyDeck()
+    f = d.newNote()
+    f['Front'] = u"one"
+    d.addNote(f)
+    # 1 day ivl review card due now
+    c = f.cards()[0]
+    c.type = 2
+    c.queue = 2
+    c.due = d.sched.today
+    c.reps = 1
+    c.ivl = 1
+    c.startTimer()
+    c.flush()
+    d.reset()
+    ni = d.sched.nextIvlStr
+    assert ni(c, 2) == "2 days"
+    assert ni(c, 3) == "3 days"
+    assert ni(c, 4) == "4 days"
+
 def test_overdue_lapse():
     # disabled in commit 3069729776990980f34c25be66410e947e9d51a2
     return