phabricator: record all local commits used to create a Differential revision

Arcanist records all of the commits that it squashes into a single review, and
that info will be helpful when adding similar functionality.  This info is used
when submitting an updated review, so that the extension can recalculate the old
diff and see if a new one is necessary, or if it is just a property update.  It
also shows on the `commits` tab in the `Revision Contents` section.

When submitting in the usual 1:1 commit to review mode, the wire protocol is
unchanged.

The content of `hg:meta` is a bit odd, but such is the problem when folding
several commits.  The choice for the parent node is obvious, but the `node`
value uses the tip commit because that seems more natural, and is used elsewhere
to look up the previous diff when updating.  The rest of the attributes follow
from there.

Differential Revision: https://phab.mercurial-scm.org/D8308

hgext/phabricator.py

@@ -968,42 +968,49 b' def creatediff(basectx, ctx):'
     return diff
 
 
-def writediffproperties(ctx, diff):
-    """write metadata to diff so patches could be applied losslessly"""
+def writediffproperties(ctxs, diff):
+    """write metadata to diff so patches could be applied losslessly
+
+    ``ctxs`` is the list of commits that created the diff, in ascending order.
+    The list is generally a single commit, but may be several when using
+    ``phabsend --fold``.
+    """
     # creatediff returns with a diffid but query returns with an id
     diffid = diff.get(b'diffid', diff.get(b'id'))
+    basectx = ctxs[0]
+    tipctx = ctxs[-1]
+
     params = {
         b'diff_id': diffid,
         b'name': b'hg:meta',
         b'data': templatefilters.json(
             {
-                b'user': ctx.user(),
-                b'date': b'%d %d' % ctx.date(),
-                b'branch': ctx.branch(),
-                b'node': ctx.hex(),
-                b'parent': ctx.p1().hex(),
+                b'user': tipctx.user(),
+                b'date': b'%d %d' % tipctx.date(),
+                b'branch': tipctx.branch(),
+                b'node': tipctx.hex(),
+                b'parent': basectx.p1().hex(),
             }
         ),
     }
-    callconduit(ctx.repo().ui, b'differential.setdiffproperty', params)
+    callconduit(basectx.repo().ui, b'differential.setdiffproperty', params)
 
+    commits = {}
+    for ctx in ctxs:
+        commits[ctx.hex()] = {
+            b'author': stringutil.person(ctx.user()),
+            b'authorEmail': stringutil.email(ctx.user()),
+            b'time': int(ctx.date()[0]),
+            b'commit': ctx.hex(),
+            b'parents': [ctx.p1().hex()],
+            b'branch': ctx.branch(),
+        }
     params = {
         b'diff_id': diffid,
         b'name': b'local:commits',
-        b'data': templatefilters.json(
-            {
-                ctx.hex(): {
-                    b'author': stringutil.person(ctx.user()),
-                    b'authorEmail': stringutil.email(ctx.user()),
-                    b'time': int(ctx.date()[0]),
-                    b'commit': ctx.hex(),
-                    b'parents': [ctx.p1().hex()],
-                    b'branch': ctx.branch(),
-                },
-            }
-        ),
+        b'data': templatefilters.json(commits),
     }
-    callconduit(ctx.repo().ui, b'differential.setdiffproperty', params)
+    callconduit(basectx.repo().ui, b'differential.setdiffproperty', params)
 
 
 def createdifferentialrevision(
@@ -1049,7 +1056,7 b' def createdifferentialrevision('
         # pushers could know the correct node metadata.
         assert olddiff
         diff = olddiff
-    writediffproperties(ctx, diff)
+    writediffproperties([ctx], diff)
 
     # Set the parent Revision every time, so commit re-ordering is picked-up
     if parentrevphid:
@@ -1289,7 +1296,9 b' def phabsend(ui, repo, *revs, **opts):'
                     # If it fails just warn and keep going, otherwise the DREV
                     # associations will be lost
                     try:
-                        writediffproperties(unfi[newnode], diffmap[old.node()])
+                        writediffproperties(
+                            [unfi[newnode]], diffmap[old.node()]
+                        )
                     except util.urlerr.urlerror:
                         ui.warnnoi18n(
                             b'Failed to update metadata for D%d\n' % drevid