revset: add inspection data to max() and min() functions

We are likely to be interested in how these functions build a result set.

mercurial/revset.py

@@ -1325,12 +1325,12 b' def maxrev(repo, subset, x):'
     try:
         m = os.max()
         if m in subset:
-            return baseset([m])
+            return baseset([m], datarepr=('<max %r, %r>', subset, os))
     except ValueError:
         # os.max() throws a ValueError when the collection is empty.
         # Same as python's max().
         pass
-    return baseset()
+    return baseset(datarepr=('<max %r, %r>', subset, os))
 
 @predicate('merge()', safe=True)
 def merge(repo, subset, x):
@@ -1370,12 +1370,12 b' def minrev(repo, subset, x):'
     try:
         m = os.min()
         if m in subset:
-            return baseset([m])
+            return baseset([m], datarepr=('<min %r, %r>', subset, os))
     except ValueError:
         # os.min() throws a ValueError when the collection is empty.
         # Same as python's min().
         pass
-    return baseset()
+    return baseset(datarepr=('<min %r, %r>', subset, os))
 
 @predicate('modifies(pattern)', safe=True)
 def modifies(repo, subset, x):

tests/test-revset.t

@@ -1727,7 +1727,10 b' test nesting and variable passing'
       ('symbol', '2')
       ('symbol', '5')))
   * set:
-  <baseset [5]>
+  <baseset
+    <max
+      <fullreposet+ 0:9>,
+      <spanset+ 2:5>>>
   5
 
 test chained `or` operations are flattened at parsing phase
@@ -2005,8 +2008,40 b' issue2549 - correct optimizations'
     <not
       <baseset [2]>>>
   1
-  $ log 'max(1 or 2) and not 2'
-  $ log 'min(1 or 2) and not 1'
+  $ try 'max(1 or 2) and not 2'
+  (and
+    (func
+      ('symbol', 'max')
+      (or
+        ('symbol', '1')
+        ('symbol', '2')))
+    (not
+      ('symbol', '2')))
+  * set:
+  <filteredset
+    <baseset
+      <max
+        <fullreposet+ 0:9>,
+        <baseset [1, 2]>>>,
+    <not
+      <baseset [2]>>>
+  $ try 'min(1 or 2) and not 1'
+  (and
+    (func
+      ('symbol', 'min')
+      (or
+        ('symbol', '1')
+        ('symbol', '2')))
+    (not
+      ('symbol', '1')))
+  * set:
+  <filteredset
+    <baseset
+      <min
+        <fullreposet+ 0:9>,
+        <baseset [1, 2]>>>,
+    <not
+      <baseset [1]>>>
   $ try 'last(1 or 2, 1) and not 2'
   (and
     (func