treemanifest: allow hybrid repos to make treeonly commits

If a hybrid repo pulls in a treeonly commit from a treeonly client, it
previously couldn't commit on top of it because it tried to read the flat
manifest. This patch makes it possible for the hybrid repo to make a treeonly
commit if it is committing on top of a treeonly commit (i.e. where the manifest
only exists in the tree store, not in the flat manifest revlog).

This makes it easier for multiple types of repositories to interact, and to flip
back and forth between treeonly and non-treeonly as we migrate.

Differential Revision: https://phab.mercurial-scm.org/D1304

fastmanifest/implementation.py

@@ -1016,11 +1016,19 @@ class manifestfactory(object):
         return node
 
     def ctxwrite(self, orig, mfctx, transaction, link, p1, p2, added, removed):
-        node = orig(mfctx, transaction, link, p1, p2, added, removed)
-
+        mfl = mfctx._manifestlog
         treeenabled = self.ui.configbool("fastmanifest", "usetree")
+        if (supportsctree and treeenabled and
+            p1 not in mfl._revlog.nodemap and
+            not mfl.datastore.getmissing([('', p1)])):
+            # If p1 is not in the flat manifest but is in the tree store, then
+            # this is a commit on top of a tree only commit and we should then
+            # produce a treeonly commit.
+            node = None
+        else:
+            node = orig(mfctx, transaction, link, p1, p2, added, removed)
+
         if supportsctree and treeenabled:
-            mfl = mfctx._manifestlog
             datastore = mfl.datastore
             opener = mfctx._revlog().opener
 
@@ -1082,13 +1090,25 @@ class manifestfactory(object):
                     transaction.addabort('treepack', abort)
                     transaction.addpending('treepack', writepending)
 
-                dpack = treemanifest.InterceptedMutableDataPack(
-                        transaction.treedatapack,
-                        node, p1)
-                hpack = treemanifest.InterceptedMutableHistoryPack(
-                        transaction.treehistpack, node, p1)
+                # If the manifest was already committed as a flat manifest, use
+                # its node.
+                if node is not None:
+                    dpack = treemanifest.InterceptedMutableDataPack(
+                            transaction.treedatapack,
+                            node, p1)
+                    hpack = treemanifest.InterceptedMutableHistoryPack(
+                            transaction.treehistpack, node, p1)
+                else:
+                    dpack = transaction.treedatapack
+                    hpack = transaction.treehistpack
+
                 newtreeiter = newtree.finalize(tree)
                 for nname, nnode, ntext, np1text, np1, np2 in newtreeiter:
+                    # If the node wasn't set by a flat manifest, use the tree
+                    # root node.
+                    if node is None and nname == '':
+                        node = nnode
+
                     # Not using deltas, since there aren't any other trees in
                     # this pack it could delta against.
                     dpack.add(nname, nnode, revlog.nullid, ntext)

tests/test-treemanifest-treeonly.t

@@ -254,6 +254,28 @@ Test histedit treeonly commits
   |
   ~
 
+Test turning treeonly off and making sure we can still commit on top of treeonly
+commits
+  $ echo >> subdir/x
+  $ hg debugindex -m --config treemanifest.treeonly=False | tail -1
+       2       102      51     -1       2 0427baa4e948 85b359fdb09e 000000000000
+  $ hg commit -m 'treeonly from hybrid repo' --config treemanifest.treeonly=False
+  $ hg log -r . -T '{desc}\n' --stat
+  treeonly from hybrid repo
+   subdir/x |  1 +
+   1 files changed, 1 insertions(+), 0 deletions(-)
+  
+  $ hg log -r . -T '{desc}\n' --stat --config treemanifest.treeonly=False
+  treeonly from hybrid repo
+   subdir/x |  1 +
+   1 files changed, 1 insertions(+), 0 deletions(-)
+  
+  $ hg debugindex -m --config treemanifest.treeonly=False | tail -1
+       2       102      51     -1       2 0427baa4e948 85b359fdb09e 000000000000
+  $ hg strip -r . --config fbamend.safestrip=False
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  saved backup bundle to $TESTTMP/client/.hg/strip-backup/87da9865954c-3cfa5389-backup.hg (glob)
+
 Test peer-to-peer push/pull of tree only commits
   $ cd ..
   $ clearcache