revset: handle wdir() in `roots()`

This is already handled in `heads()`, and both are needed to determine if a set
is contiguous.

I'm guessing the `0 <= p` check was to try to filter out the null revision, but
it looks like that comes through in the corner case of a new repo with no
commits.  But that was already the case, as shown by the tests.

Before (on a clone of hg):

    $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'roots(all())'
    ! wall 0.059301 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)

After:

    $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'roots(all())'
    ! wall 0.059387 comb 0.060000 user 0.060000 sys 0.000000 (best of 100)

mercurial/revset.py

@@ -2342,9 +2342,14 b' def roots(repo, subset, x):'
     parents = repo.changelog.parentrevs
 
     def filter(r):
-        for p in parents(r):
-            if 0 <= p and p in s:
-                return False
+        try:
+            for p in parents(r):
+                if 0 <= p and p in s:
+                    return False
+        except error.WdirUnsupported:
+            for p in repo[None].parents():
+                if p.rev() in s:
+                    return False
         return True
 
     return subset & s.filter(filter, condrepr=b'<roots>')

tests/test-revset2.t

@@ -1481,6 +1481,13 b' prepare repository that has "default" br'
   $ hg init namedbranch
   $ cd namedbranch
 
+  $ log 'roots(.)'
+  -1
+  $ log 'roots(. or wdir())'
+  -1
+  $ log 'roots(wdir())'
+  2147483647
+
   $ echo default0 >> a
   $ hg ci -Aqm0
   $ echo default1 >> a
@@ -1498,6 +1505,11 b' prepare repository that has "default" br'
   $ echo default5 >> a
   $ hg ci -m5
 
+  $ log 'roots(. or wdir())'
+  5
+  $ log 'roots(wdir())'
+  2147483647
+
 "null" revision belongs to "default" branch (issue4683)
 
   $ log 'branch(null)'