revset: forward ordering requirement to argument of present()

present() is special in that it returns the argument set with no
modification, so the ordering requirement should be forwarded.

We could make present() fix the order like orset(), but that would be silly
because we know the extra filtering cost is unnecessary.

mercurial/revset.py

@@ -2473,7 +2473,13 def _analyze(x, order):
     elif op == 'keyvalue':
         return (op, x[1], _analyze(x[2], order))
     elif op == 'func':
-        return (op, x[1], _analyze(x[2], defineorder), order)
+        f = getsymbol(x[1])
+        d = defineorder
+        if f == 'present':
+            # 'present(set)' is known to return the argument set with no
+            # modification, so forward the current order to its argument
+            d = order
+        return (op, x[1], _analyze(x[2], d), order)
     raise ValueError('invalid operator %r' % op)
 
 def analyze(x, order=defineorder):

tests/test-revset.t

@@ -1485,7 +1485,23 ordering defined by it.
       <baseset [0, 1]>>>
   2
 
- 'present()' should do nothing other than suppressing an error:
+ because 'present()' does nothing other than suppressing an error, the
+ ordering requirement should be forwarded to the nested expression
+
+  $ try -p optimized 'present(2 + 0 + 1)'
+  * optimized:
+  (func
+    ('symbol', 'present')
+    (func
+      ('symbol', '_list')
+      ('string', '2\x000\x001')
+      define)
+    define)
+  * set:
+  <baseset [2, 0, 1]>
+  2
+  0
+  1
 
   $ try --optimize '2:0 & present(0 + 1 + 2)'
   (and
@@ -1510,15 +1526,16 ordering defined by it.
       (func
         ('symbol', '_list')
         ('string', '0\x001\x002')
-        define)
+        follow)
       follow)
     define)
   * set:
-  <baseset [0, 1, 2]>
-  0
+  <filteredset
+    <spanset- 0:2>,
+    <baseset [0, 1, 2]>>
+  2
   1
-  2
- BROKEN: should be '2 1 0'
+  0
 
  'reverse()' should take effect only if it is the outermost expression: