[PATCH] Finish making --emu23 equivalent to pure 2-way merge.

This adds #3ALT rule (and #2ALT rule for symmetry) to the
read-tree 3-way merge logic that collapses paths that are added
only in one branch and not in the other internally.

This makes --emu23 to succeed in the last remaining case where
the pure 2-way merge succeeded and earlier one failed.  Running
diff between t1001 and t1005 test scripts shows that the only
difference between the two is that --emu23 can leave the states
into separate stages so that the user can use usual 3-way merge
resolution techniques to carry forward the local changes when
pure 2-way merge would have refused to run.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 36 insertions, 16 deletions

diff --git a/t/t1000-read-tree-m-3way.sh b/t/t1000-read-tree-m-3way.sh
index 92833fe95..3d9b3ac9b 100755
--- a/t/t1000-read-tree-m-3way.sh
+++ b/t/t1000-read-tree-m-3way.sh
@@ -75,13 +75,13 @@ In addition:
 . ../lib-read-tree-m-3way.sh
 
 ################################################################
-# Trivial "majority when 3 stages exist" merge plus #5ALT trivial
-# merge.
+# Trivial "majority when 3 stages exist" merge plus #2ALT, #3ALT
+# and #5ALT trivial merges.
 
 cat >expected <<\EOF
 100644 X 2	AA
 100644 X 3	AA
-100644 X 2	AN
+100644 X 0	AN
 100644 X 1	DD
 100644 X 3	DF
 100644 X 2	DF/DF
@@ -96,7 +96,7 @@ cat >expected <<\EOF
 100644 X 2	MM
 100644 X 3	MM
 100644 X 0	MN
-100644 X 3	NA
+100644 X 0	NA
 100644 X 1	ND
 100644 X 2	ND
 100644 X 0	NM
@@ -107,7 +107,7 @@ cat >expected <<\EOF
 100644 X 3	TT
 100644 X 2	Z/AA
 100644 X 3	Z/AA
-100644 X 2	Z/AN
+100644 X 0	Z/AN
 100644 X 1	Z/DD
 100644 X 1	Z/DM
 100644 X 3	Z/DM
@@ -119,7 +119,7 @@ cat >expected <<\EOF
 100644 X 2	Z/MM
 100644 X 3	Z/MM
 100644 X 0	Z/MN
-100644 X 3	Z/NA
+100644 X 0	Z/NA
 100644 X 1	Z/ND
 100644 X 2	Z/ND
 100644 X 0	Z/NM
@@ -233,23 +233,31 @@ test_expect_failure \
      git-update-cache --add XX &&
      git-read-tree -m $tree_O $tree_A $tree_B"
 
-test_expect_failure \
-    '2 - must not have an entry not in A.' \
+test_expect_success \
+    '2 - must match B in !O && !A && B case.' \
+    "rm -f .git/index NA &&
+     cp .orig-B/NA NA &&
+     git-update-cache --add NA &&
+     git-read-tree -m $tree_O $tree_A $tree_B"
+
+test_expect_success \
+    '2 - matching B alone is OK in !O && !A && B case.' \
     "rm -f .git/index NA &&
      cp .orig-B/NA NA &&
      git-update-cache --add NA &&
+     echo extra >>NA &&
      git-read-tree -m $tree_O $tree_A $tree_B"
 
 test_expect_success \
-    '3 - must match and be up-to-date in !O && A && !B case.' \
+    '3 - must match A in !O && A && !B case.' \
     "rm -f .git/index AN &&
      cp .orig-A/AN AN &&
      git-update-cache --add AN &&
      git-read-tree -m $tree_O $tree_A $tree_B &&
      check_result"
 
-test_expect_failure \
-    '3 (fail) - must match and be up-to-date in !O && A && !B case.' \
+test_expect_success \
+    '3 - matching A alone is OK in !O && A && !B case.' \
     "rm -f .git/index AN &&
      cp .orig-A/AN AN &&
      git-update-cache --add AN &&
@@ -257,7 +265,7 @@ test_expect_failure \
      git-read-tree -m $tree_O $tree_A $tree_B"
 
 test_expect_failure \
-    '3 (fail) - must match and be up-to-date in !O && A && !B case.' \
+    '3 (fail) - must match A in !O && A && !B case.' \
     "rm -f .git/index AN &&
      cp .orig-A/AN AN &&
      echo extra >>AN &&
diff --git a/t/t1005-read-tree-m-2way-emu23.sh b/t/t1005-read-tree-m-2way-emu23.sh
index 495642e08..bb955ed39 100644
--- a/t/t1005-read-tree-m-2way-emu23.sh
+++ b/t/t1005-read-tree-m-2way-emu23.sh
@@ -80,6 +80,17 @@ test_expect_success \
      git-ls-tree $treeM &&
      git-diff-tree $treeH $treeM'
 
+# "read-tree -m H I+H M" but I is empty so this is "read-tree -m H H M".
+#
+# bozbar [O && A && B && O==A && O!=B (#14) ==> B] take M by read-tree
+# frotz  [!O && !A && B (#2) ==> B]                take M by read-tree
+# nitfol [O && A && B && O==A && O==B (#15) ==> B] take M by read-tree
+# rezrov [O && A && !B && O==A (#10) ==> no merge] removed by script
+#
+# Earlier one did not have #2ALT so taking M was done by the script,
+# which also updated the work tree and making frotz clean.  With #2ALT,
+# this is resolved by read-tree itself and the path is left dirty
+# because we are not testing "read-tree -u --emu23".
 test_expect_success \
     '1, 2, 3 - no carry forward' \
     'rm -f .git/index &&
@@ -87,7 +98,7 @@ test_expect_success \
      git-ls-files --stage >1-3.out &&
      diff -u M.out 1-3.out &&
      check_cache_at bozbar dirty &&
-     check_cache_at frotz clean && # different from pure 2-way
+     check_cache_at frotz dirty && # same as pure 2-way again.
      check_cache_at nitfol dirty'
 
 echo '+100644 X 0	yomin' >expected
@@ -103,8 +114,8 @@ test_expect_success \
      check_cache_at yomin clean'
 
 # "read-tree -m H I+H M" where !H && !M; so (I+H) not being up-to-date
-# should not matter, but without #3ALT this does not work.
-: test_expect_success \
+# should not matter.  Thanks to #3ALT, this is now possible.
+test_expect_success \
     '5 - carry forward local addition.' \
     'rm -f .git/index &&
      echo yomin >yomin &&
@@ -218,6 +229,7 @@ test_expect_success \
 # This is different from straight 2-way merge in that it leaves
 # three stages of bozbar in the index file without failing, so
 # the user can run git-diff-stages to examine the situation.
+# With #2ALT, frotz is resolved internally.
 test_expect_success \
     '16 - conflicting local change.' \
     'rm -f .git/index &&
@@ -228,7 +240,7 @@ test_expect_success \
 100644 X 1	bozbar
 100644 X 2	bozbar
 100644 X 3	bozbar
-100644 X 3	frotz
+100644 X 0	frotz
 100644 X 0	nitfol
 100644 X 1	rezrov
 100644 X 2	rezrov