bisect: --command without --noupdate should flag the parent rev it tested

14913fcb30c6 not only introduced the 'bisect(current)' revset predicate, it
also changed how the 'current' revision is used in combination with --command.
The new behaviour might be ok for --noupdate where the working directory and
its revision shouldn't be used, but it also did that when --command is used to
run a command on the currently checked out revision then it could register the
test result on the wrong revision.

An example:

Before, bisect with --command could use the wrong revision when recording the
test result:

  $ hg up -qr 0
  $ hg bisect --command "python \"$TESTTMP/script.py\" and some parameters"
  changeset 31:58c80a7c8a40: bad
  abort: inconsistent state, 31:58c80a7c8a40 is good and bad

Now it works as before and as expected and uses the working directory revision
for the --command result:

  $ hg up -qr 0
  $ hg bisect --command "python \"$TESTTMP/script.py\" and some parameters"
  changeset 0:b99c7b9c8e11: bad
  ...

mercurial/commands.py

@@ -667,12 +667,13 b' def bisect(ui, repo, rev=None, extra=Non'
 
     if command:
         changesets = 1
-        try:
-            node = state['current'][0]
-        except LookupError:
-            if noupdate:
+        if noupdate:
+            try:
+                node = state['current'][0]
+            except LookupError:
                 raise util.Abort(_('current bisect revision is unknown - '
                                    'start a new bisect to fix'))
+        else:
             node, p2 = repo.dirstate.parents()
             if p2 != nullid:
                 raise util.Abort(_('current bisect revision is a merge'))

tests/test-bisect.t

@@ -461,11 +461,14 b' test bisecting command'
   > EOF
   $ chmod +x script.py
   $ hg bisect -r
-  $ hg bisect --good tip
-  $ hg bisect --bad 0
-  Testing changeset 15:e7fa0811edb0 (31 changesets remaining, ~4 tests)
-  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg up -qr tip
   $ hg bisect --command "python \"$TESTTMP/script.py\" and some parameters"
+  changeset 31:58c80a7c8a40: good
+  abort: cannot bisect (no known bad revisions)
+  [255]
+  $ hg up -qr 0
+  $ hg bisect --command "python \"$TESTTMP/script.py\" and some parameters"
+  changeset 0:b99c7b9c8e11: bad
   changeset 15:e7fa0811edb0: good
   changeset 7:03750880c6b5: good
   changeset 3:b53bea5e2fcb: bad
@@ -516,6 +519,39 b" ensure that we still don't have a workin"
   $ hg parents
 
 
+test the same case, this time with updating
+
+  $ cat > script.sh <<'EOF'
+  > #!/bin/sh
+  > test -n "$HG_NODE" || (echo HG_NODE missing; exit 127)
+  > current="`hg log -r \"bisect(current)\" --template {node}`"
+  > test "$current" = "$HG_NODE" || (echo current is bad: $current; exit 127)
+  > rev="`hg log -r . --template {rev}`"
+  > test "$rev" -ge 6
+  > EOF
+  $ chmod +x script.sh
+  $ hg bisect -r
+  $ hg up -qr tip
+  $ hg bisect --command "sh \"$TESTTMP/script.sh\" and some params"
+  changeset 31:58c80a7c8a40: good
+  abort: cannot bisect (no known bad revisions)
+  [255]
+  $ hg up -qr 0
+  $ hg bisect --command "sh \"$TESTTMP/script.sh\" and some params"
+  changeset 0:b99c7b9c8e11: bad
+  changeset 15:e7fa0811edb0: good
+  changeset 7:03750880c6b5: good
+  changeset 3:b53bea5e2fcb: bad
+  changeset 5:7874a09ea728: bad
+  changeset 6:a3d5c6fdf0d3: good
+  The first good revision is:
+  changeset:   6:a3d5c6fdf0d3
+  user:        test
+  date:        Thu Jan 01 00:00:06 1970 +0000
+  summary:     msg 6
+  
+
+
 Check that bisect does not break on obsolete changesets
 =========================================================