[PATCH 3 of 3] addrevision: use general delta when the incoming base delta is bad

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1449015359 28800
#      Tue Dec 01 16:15:59 2015 -0800
# Node ID 64e48bdff2461e793c963d677407d35fc32c30a9
# Parent  49f5bfa7043ae0c797536dab93260aee92fcbaa8
# EXP-Topic generaldelta
# Available At http://hg.netv6.net/marmoute-wip/mercurial/
#              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r 64e48bdff246
addrevision: use general delta when the incoming base delta is bad

We unify the delta selection process to be a simple three options process:

- try to use the incoming delta (if lazydeltabase is on)
- try to find a suitable parents to delta against (if gd is on)
- try to delta against the tipmost revision

The first of this option that yield a valid delta will be used.

The test change in 'test-generaldelta.t' show this behavior as we use a delta
against the parent instead of a full delta when the incoming delta is not
suitable.

This as some impact on 'test-bundle.t' because a delta somewhere changes. It
does not seems to change the test semantic and have been ignored.

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1422,38 +1422,37 @@ class revlog(object):
         else:
             textlen = len(text)
 
         # should we try to build a delta?
         if prev != nullrev:
+            tested = set()
             if cachedelta and self._generaldelta and self._lazydeltabase:
                 # Assume what we received from the server is a good choice
                 # build delta will reuse the cache
                 candidatedelta = builddelta(cachedelta[0])
+                tested.add(candidatedelta[3])
                 if self._isgooddelta(candidatedelta, textlen):
                     delta = candidatedelta
-                elif prev != candidatedelta[3]:
-                    # Try against prev to hopefully save us a fulltext.
-                    delta = builddelta(prev)
-            elif self._generaldelta:
+            if delta is None and self._generaldelta:
                 parents = [p1r, p2r]
-                if not self._aggressivemergedeltas:
+                # exclude already lazy tested base if any
+                parents = [p for p in parents if p not in tested]
+                if parents and not self._aggressivemergedeltas:
                     # Pick whichever parent is closer to us (to minimize the
-                    # chance of having to build a fulltext). Since
-                    # nullrev == -1, any non-merge commit will always pick p1r.
+                    # chance of having to build a fulltext).
                     parents = [max(parents)]
+                tested.update(parents)
                 pdeltas = []
                 for p in parents:
                     pd = builddelta(p)
                     if self._isgooddelta(pd, textlen):
                         pdeltas.append(pd)
                 if pdeltas:
                     delta = min(pdeltas, key=lambda x: x[1])
-                elif prev not in parents:
-                    # Neither is good, try against prev to hopefully save us
-                    # a fulltext.
-                    delta = builddelta(prev)
-            else:
+            if delta is None and prev not in tested:
+                # other approach failed try against prev to hopefully save us a
+                # fulltext.
                 delta = builddelta(prev)
         if delta is not None:
             dist, l, data, base, chainbase, chainlen, compresseddeltalen = delta
 
         if not self._isgooddelta(delta, textlen):
diff --git a/tests/test-bundle.t b/tests/test-bundle.t
--- a/tests/test-bundle.t
+++ b/tests/test-bundle.t
@@ -264,17 +264,17 @@ Cannot produce streaming clone bundles w
   [255]
 
 packed1 is produced properly
 
   $ hg -R test debugcreatestreamclonebundle packed.hg
-  writing 2663 bytes for 6 files
+  writing 2667 bytes for 6 files
   bundle requirements: generaldelta, revlogv1
 
   $ f -B 64 --size --sha1 --hexdump packed.hg
-  packed.hg: size=2826, sha1=e139f97692a142b19cdcff64a69697d5307ce6d4
+  packed.hg: size=2830, sha1=c28255110a88ffa52ddc44985cad295b1ab349bc
   0000: 48 47 53 31 55 4e 00 00 00 00 00 00 00 06 00 00 |HGS1UN..........|
-  0010: 00 00 00 00 0a 67 00 16 67 65 6e 65 72 61 6c 64 |.....g..generald|
+  0010: 00 00 00 00 0a 6b 00 16 67 65 6e 65 72 61 6c 64 |.....k..generald|
   0020: 65 6c 74 61 2c 72 65 76 6c 6f 67 76 31 00 64 61 |elta,revlogv1.da|
   0030: 74 61 2f 61 64 69 66 66 65 72 65 6e 74 66 69 6c |ta/adifferentfil|
 
 generaldelta requirement is listed in stream clone bundles
 
diff --git a/tests/test-generaldelta.t b/tests/test-generaldelta.t
--- a/tests/test-generaldelta.t
+++ b/tests/test-generaldelta.t
@@ -103,11 +103,11 @@ delta coming from the server base delta 
   $ hg -R usegd debugindex -m
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0     104     -1       0 cef96823c800 000000000000 000000000000
        1       104      57      0       1 58ab9a8d541d cef96823c800 000000000000
        2       161      57      1       2 134fdc6fd680 cef96823c800 000000000000
-       3       218     104     -1       3 723508934dad cef96823c800 000000000000
+       3       218      57      0       3 723508934dad cef96823c800 000000000000
   $ hg -R full debugindex -m
      rev    offset  length  delta linkrev nodeid       p1           p2
        0         0     104     -1       0 cef96823c800 000000000000 000000000000
        1       104      57      0       1 58ab9a8d541d cef96823c800 000000000000
        2       161      57      0       2 134fdc6fd680 cef96823c800 000000000000