outgoing: add a simple fastpath when there is no common

outgoing: add a simple fastpath when there is no common

This further speed up case like `hg bundle --all` for larger repository.

### data-env-vars.name            = mozilla-try-2023-03-22-zstd-sparse-revlog
  # benchmark.name                = hg.command.bundle
  # bin-env-vars.hg.flavor        = default
  # bin-env-vars.hg.py-re2-module = default
  # benchmark.variants.revs       = all
  # benchmark.variants.type       = none-streamv2
before: 316.749699
after:  311.165461   (-1.76%, -5.58)


There is further work to be done in this area like not doing any outgoing
computation in the stream case for example. however the recent changes already
gives use a large win for a small amount of local work.

### benchmark.name                = hg.command.bundle
  # bin-env-vars.hg.flavor        = default
  # bin-env-vars.hg.py-re2-module = default
  # benchmark.variants.revs       = all
  # benchmark.variants.type       = none-streamv2
 ## data-env-vars.name            = mercurial-public-2024-03-22-zstd-sparse-revlog
pre-%ln-change: 1.263859
the-%ln-change: 0.700229  (-44.60%, -0.56)
prev-changeset: 0.496050  (-60.75%, -0.77)
this-changeset: 0.495243  (-60.81%, -0.77)
 ## data-env-vars.name            = tryton-public-2024-03-22-zstd-sparse-revlog
pre-%ln-change: 2.975765
the-%ln-change: 1.870798  (-37.13%, -1.10)
prev-changeset: 1.461583  (-50.88%, -1.51)
this-changeset: 1.469185  (-50.63%, -1.51)
 ## data-env-vars.name            = pypy-2024-03-22-zstd-sparse-revlog
pre-%ln-change: 4.540080
the-%ln-change: 3.401700  (-25.07%, -1.14)
prev-changeset: 2.915810  (-35.78%, -1.62)
this-changeset: 2.911643  (-35.87%, -1.63)
 ## data-env-vars.name            = heptapod-public-2024-03-25-zstd-sparse-revlog
pre-%ln-change: 10.138396
the-%ln-change: 7.750458  (-23.55%, -2.39)
prev-changeset: 6.665565  (-34.25%, -3.47)
this-changeset: 6.672078  (-34.19%, -3.47)
 ## data-env-vars.name            = mozilla-try-2023-03-22-zstd-sparse-revlog
pre-%ln-change: 399.484481
the-%ln-change: 346.508952 (-13.26%, -52.98)
prev-changeset: 316.749699 (-20.71%, -82.73)
this-changeset: 311.165461 (-22.11%, -88.32)

--- a/mercurial/discovery.py	Tue Apr 09 22:36:35 2024 +0200
+++ b/mercurial/discovery.py	Tue Apr 09 22:37:15 2024 +0200
@@ -104,16 +104,28 @@
             m = 'commonheads and missingroots arguments are mutually exclusive'
             raise error.ProgrammingError(m)
         cl = repo.changelog
+        unfi = repo.unfiltered()
+        ucl = unfi.changelog
+        to_node = ucl.node
         missing = None
         common = None
+        arg_anc = ancestorsof
         if ancestorsof is None:
             ancestorsof = cl.heads()
-        if missingroots:
+
+        # XXX-perf: do we need all this to be node-list? They would be simpler
+        # as rev-num sets (and smartset)
+        if missingroots == [nodemod.nullrev] or missingroots == []:
+            commonheads = [repo.nullid]
+            common = set()
+            if arg_anc is None:
+                missing = [to_node(r) for r in cl]
+            else:
+                missing_rev = repo.revs('::%ln', missingroots, ancestorsof)
+                missing = [to_node(r) for r in missing_rev]
+        elif missingroots is not None:
             # TODO remove call to nodesbetween.
             missing_rev = repo.revs('%ln::%ln', missingroots, ancestorsof)
-            unfi = repo.unfiltered()
-            ucl = unfi.changelog
-            to_node = ucl.node
             ancestorsof = [to_node(r) for r in ucl.headrevs(missing_rev)]
             parent_revs = ucl.parentrevs
             common_legs = set()