smartset: micro optimize spanset.slice() to narrow range accordingly

-1ms isn't significant, but seems not bad.

  revset  #0: limit(0:9999, 100, 9000)
  6) 0.001145
  7) 0.000214
  revset  #3: last(0:9999, 100)
  6) 0.000197
  7) 0.000171

mercurial/smartset.py

@@ -1056,6 +1056,18 b' class _spanset(abstractsmartset):'
             return x
         return None
 
+    def _slice(self, start, stop):
+        if self._hiddenrevs:
+            # unoptimized since all hidden revisions in range has to be scanned
+            return super(_spanset, self)._slice(start, stop)
+        if self._ascending:
+            x = min(self._start + start, self._end)
+            y = min(self._start + stop, self._end)
+        else:
+            x = max(self._end - stop, self._start)
+            y = max(self._end - start, self._start)
+        return _spanset(x, y, self._ascending, self._hiddenrevs)
+
     def __repr__(self):
         d = {False: '-', True: '+'}[self._ascending]
         return '<%s%s %d:%d>' % (type(self).__name__.lstrip('_'), d,

tests/test-revset.t

@@ -1080,13 +1080,54 b' Test smartset.slice() by first/last()'
   * set:
   <baseset+ []>
 
+ (using spanset)
+
+  $ hg debugrevspec --no-show-revs -s 0:7
+  * set:
+  <spanset+ 0:8>
+  $ log 'limit(0:7, 3, 4)'
+  4
+  5
+  6
+  $ log 'limit(7:0, 3, 4)'
+  3
+  2
+  1
+  $ log 'limit(0:7, 3, 6)'
+  6
+  7
+  $ log 'limit(7:0, 3, 6)'
+  1
+  0
+  $ log 'last(0:7, 2)'
+  6
+  7
+  $ hg debugrevspec -s 'limit(0:7, 3, 6)'
+  * set:
+  <spanset+ 6:8>
+  6
+  7
+  $ hg debugrevspec -s 'limit(0:7, 3, 9)'
+  * set:
+  <spanset+ 8:8>
+  $ hg debugrevspec -s 'limit(7:0, 3, 6)'
+  * set:
+  <spanset- 0:2>
+  1
+  0
+  $ hg debugrevspec -s 'limit(7:0, 3, 9)'
+  * set:
+  <spanset- 0:0>
+  $ hg debugrevspec -s 'limit(0:7, 0)'
+  * set:
+  <spanset+ 0:0>
+
 Test order of first/last revisions
 
   $ hg debugrevspec -s 'first(4:0, 3) & 3:'
   * set:
   <filteredset
-    <baseset slice=0:3
-      <spanset- 0:5>>,
+    <spanset- 2:5>,
     <spanset+ 3:10>>
   4
   3
@@ -1095,16 +1136,14 b' Test order of first/last revisions'
   * set:
   <filteredset
     <spanset+ 3:10>,
-    <baseset slice=0:3
-      <spanset- 0:5>>>
+    <spanset- 2:5>>
   3
   4
 
   $ hg debugrevspec -s 'last(4:0, 3) & :1'
   * set:
   <filteredset
-    <baseset slice=0:3
-      <spanset+ 0:5>>,
+    <spanset- 0:3>,
     <spanset+ 0:2>>
   1
   0
@@ -1113,8 +1152,7 b' Test order of first/last revisions'
   * set:
   <filteredset
     <spanset+ 0:2>,
-    <baseset slice=0:3
-      <spanset+ 0:5>>>
+    <spanset+ 0:3>>
   0
   1