phases: use revision number in new_heads

All graph operations will be done using revision numbers, so passing nodes only
means they will eventually get converted to revision numbers internally.

As part of an effort to align the code on using revision number we make the
`phases.newheads` function operated on revision number, taking them as input
and using them in returns, instead of the node-id it used to consume and
produce.

This is part of multiple changesets effort to translate more part of the logic,
but is done step by step to facilitate the identification of issue that might
arise in mercurial core and extensions.

To make the change simpler to handle for third party extensions, we also rename
the function, using a more modern form. This will help detecting the different
between the node-id version and the rev-num version.

I also take this as an opportunity to add some comment about possible
performance improvement for the future. They don't matter too much now, but they
are worse exploring in a while.

mercurial/discovery.py

@@ -190,7 +190,12 b' def findcommonoutgoing('
         if len(missing) == len(allmissing):
             ancestorsof = onlyheads
         else:  # update missing heads
-            ancestorsof = phases.newheads(repo, onlyheads, excluded)
+            to_rev = repo.changelog.index.rev
+            to_node = repo.changelog.node
+            excluded_revs = [to_rev(r) for r in excluded]
+            onlyheads_revs = [to_rev(r) for r in onlyheads]
+            new_heads = phases.new_heads(repo, onlyheads_revs, excluded_revs)
+            ancestorsof = [to_node(r) for r in new_heads]
         og.ancestorsof = ancestorsof
     if portable:
         # recompute common and ancestorsof as if -r<rev> had been given for

mercurial/phases.py

@@ -109,6 +109,7 b' import weakref'
 from typing import (
     Any,
     Callable,
+    Collection,
     Dict,
     Iterable,
     List,
@@ -127,7 +128,6 b' from .node import ('
 )
 from . import (
     error,
-    pycompat,
     requirements,
     smartset,
     txnutil,
@@ -1125,9 +1125,11 b' def analyzeremotephases(repo, subset, ro'
             msg = _(b'ignoring unexpected root from remote: %i %s\n')
             repo.ui.warn(msg % (phase, nhex))
     # compute heads
+    subset_revs = [to_rev(n) for n in subset]
+    public_heads = new_heads(repo, subset_revs, draft_roots)
     draft_nodes = [to_node(r) for r in draft_roots]
-    publicheads = newheads(repo, subset, draft_nodes)
-    return publicheads, draft_nodes
+    public_nodes = [to_node(r) for r in public_heads]
+    return public_nodes, draft_nodes
 
 
 class remotephasessummary:
@@ -1152,7 +1154,11 b' class remotephasessummary:'
         self.draftheads = [c.node() for c in dheads]
 
 
-def newheads(repo, heads, roots):
+def new_heads(
+    repo,
+    heads: Collection[int],
+    roots: Collection[int],
+) -> Collection[int]:
     """compute new head of a subset minus another
 
     * `heads`: define the first subset
@@ -1161,16 +1167,15 b' def newheads(repo, heads, roots):'
     # phases > dagop > patch > copies > scmutil > obsolete > obsutil > phases
     from . import dagop
 
-    repo = repo.unfiltered()
-    cl = repo.changelog
-    rev = cl.index.get_rev
     if not roots:
         return heads
-    if not heads or heads == [repo.nullid]:
+    if not heads or heads == [nullrev]:
         return []
     # The logic operated on revisions, convert arguments early for convenience
-    new_heads = {rev(n) for n in heads if n != repo.nullid}
-    roots = [rev(n) for n in roots]
+    # PERF-XXX: maybe heads could directly comes as a set without impacting
+    # other user of that value
+    new_heads = set(heads)
+    new_heads.discard(nullrev)
     # compute the area we need to remove
     affected_zone = repo.revs(b"(%ld::%ld)", roots, new_heads)
     # heads in the area are no longer heads
@@ -1188,7 +1193,9 b' def newheads(repo, heads, roots):'
         pruned = dagop.reachableroots(repo, candidates, prunestart)
         new_heads.difference_update(pruned)
 
-    return pycompat.maplist(cl.node, sorted(new_heads))
+    # PERF-XXX: do we actually need a sorted list here? Could we simply return
+    # a set?
+    return sorted(new_heads)
 
 
 def newcommitphase(ui: "uimod.ui") -> int: