# HG changeset patch
# User Mike Hommey <mh@glandium.org>
# Date 1452567607 18000
# Node ID 7a678a12a5cfab1c0d24ce1f47b211ededa7d500
# Parent  ed8012a0b60a508b40fd21cb9966440968a02d54
mdiff: don't emit a diff header for empty trivial deltas

An empty trivial delta, coded as (0, 0, 0) makes the delta application
do nothing, but still takes 12 bytes, while skipping it altogether works
as much, without taking any space at all.

diff -r ed8012a0b60a -r 7a678a12a5cf mercurial/mdiff.py
--- a/mercurial/mdiff.py	Mon Jan 11 09:49:48 2016 -0800
+++ b/mercurial/mdiff.py	Mon Jan 11 22:00:07 2016 -0500
@@ -376,7 +376,7 @@
     return [(d[0], d[2], d[1] - d[0]) for d in bdiff.blocks(a, b)]
 
 def trivialdiffheader(length):
-    return struct.pack(">lll", 0, 0, length)
+    return struct.pack(">lll", 0, 0, length) if length else ''
 
 def replacediffheader(oldlen, newlen):
     return struct.pack(">lll", 0, oldlen, newlen)
diff -r ed8012a0b60a -r 7a678a12a5cf tests/test-clonebundles.t
--- a/tests/test-clonebundles.t	Mon Jan 11 09:49:48 2016 -0800
+++ b/tests/test-clonebundles.t	Mon Jan 11 22:00:07 2016 -0500
@@ -131,7 +131,7 @@
 changes. If this output changes, we could break old clients.
 
   $ f --size --hexdump partial.hg
-  partial.hg: size=208
+  partial.hg: size=207
   0000: 48 47 31 30 47 5a 78 9c 63 60 60 98 17 ac 12 93 |HG10GZx.c``.....|
   0010: f0 ac a9 23 45 70 cb bf 0d 5f 59 4e 4a 7f 79 21 |...#Ep..._YNJ.y!|
   0020: 9b cc 40 24 20 a0 d7 ce 2c d1 38 25 cd 24 25 d5 |..@$ ...,.8%.$%.|
@@ -143,8 +143,8 @@
   0080: 41 d6 24 59 18 a4 a4 9a a6 18 1a 5b 98 9b 5a 98 |A.$Y.......[..Z.|
   0090: 9a 18 26 9b a6 19 98 1a 99 99 26 a6 18 9a 98 24 |..&.......&....$|
   00a0: 26 59 a6 25 5a 98 a5 18 a6 24 71 41 35 b1 43 dc |&Y.%Z....$qA5.C.|
-  00b0: 96 b0 83 f7 e9 45 8b d2 56 c7 a3 1f 82 52 d7 8a |.....E..V....R..|
-  00c0: 78 ed fc d5 76 f1 36 95 dc 05 07 00 ad 39 5e d3 |x...v.6......9^.|
+  00b0: 16 b2 83 f7 e9 45 8b d2 56 c7 a3 1f 82 52 d7 8a |.....E..V....R..|
+  00c0: 78 ed fc d5 76 f1 36 35 dc 05 00 36 ed 5e c7    |x...v.65...6.^.|
 
   $ echo "http://localhost:$HGPORT1/partial.hg" > server/.hg/clonebundles.manifest
   $ hg clone -U http://localhost:$HGPORT partial-bundle
@@ -189,11 +189,11 @@
 by old clients.
 
   $ f --size --hexdump full.hg
-  full.hg: size=408
+  full.hg: size=406
   0000: 48 47 32 30 00 00 00 0e 43 6f 6d 70 72 65 73 73 |HG20....Compress|
   0010: 69 6f 6e 3d 47 5a 78 9c 63 60 60 90 e5 76 f6 70 |ion=GZx.c``..v.p|
   0020: f4 73 77 75 0f f2 0f 0d 60 00 02 46 06 76 a6 b2 |.swu....`..F.v..|
-  0030: d4 a2 e2 cc fc 3c 03 23 06 06 e6 7d 40 b1 4d c1 |.....<.#...}@.M.|
+  0030: d4 a2 e2 cc fc 3c 03 23 06 06 e6 65 40 b1 4d c1 |.....<.#...e@.M.|
   0040: 2a 31 09 cf 9a 3a 52 04 b7 fc db f0 95 e5 a4 f4 |*1...:R.........|
   0050: 97 17 b2 c9 0c 14 00 02 e6 d9 99 25 1a a7 a4 99 |...........%....|
   0060: a4 a4 1a 5b 58 a4 19 27 9b a4 59 a4 1a 59 a4 99 |...[X..'..Y..Y..|
@@ -212,10 +212,10 @@
   0130: 34 31 c5 d0 c4 24 31 c9 32 2d d1 c2 2c c5 30 25 |41...$1.2-..,.0%|
   0140: 09 e4 ee 85 8f 85 ff 88 ab 89 36 c7 2a c4 47 34 |..........6.*.G4|
   0150: fe f8 ec 7b 73 37 3f c3 24 62 1d 8d 4d 1d 9e 40 |...{s7?.$b..M..@|
-  0160: 06 3b 10 14 36 a4 38 10 04 d8 21 01 5a b2 83 f7 |.;..6.8...!.Z...|
+  0160: 06 3b 10 14 36 a4 38 10 04 d8 21 01 9a b1 83 f7 |.;..6.8...!.....|
   0170: e9 45 8b d2 56 c7 a3 1f 82 52 d7 8a 78 ed fc d5 |.E..V....R..x...|
-  0180: 76 f1 36 25 81 49 c0 ad 30 c0 0e 49 8f 54 b7 9e |v.6%.I..0..I.T..|
-  0190: d4 1c 09 00 bb 8d f0 bd                         |........|
+  0180: 76 f1 36 25 81 89 c7 ad ec 90 34 48 75 2b 89 49 |v.6%......4Hu+.I|
+  0190: bf 00 d6 97 f0 8d                               |......|
 
   $ echo "http://localhost:$HGPORT1/full.hg" > server/.hg/clonebundles.manifest
   $ hg clone -U http://localhost:$HGPORT full-bundle
diff -r ed8012a0b60a -r 7a678a12a5cf tests/test-debugbundle.t
--- a/tests/test-debugbundle.t	Mon Jan 11 09:49:48 2016 -0800
+++ b/tests/test-debugbundle.t	Mon Jan 11 22:00:07 2016 -0500
@@ -11,8 +11,8 @@
   uncompressed size of bundle content:
        332 (changelog)
        282 (manifests)
-       105  b
-       105  c
+        93  b
+        93  c
 
 Terse output:
 
@@ -34,9 +34,9 @@
   ae25a31b30b3490a981e7b96a3238cc69583fda1 686dbf0aeca417636fa26a9121c681eabbb15a20 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 686dbf0aeca417636fa26a9121c681eabbb15a20 55
   
   b
-  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 12
+  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 0
   
   c
-  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0000000000000000000000000000000000000000 12
+  b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0000000000000000000000000000000000000000 0
 
   $ cd ..