[PATCH] read-tree: save more user hassles during fast-forward.

This implements the "never lose the current cache information or
the work tree state, but favor a successful merge over merge
failure" principle in the fast-forward two-tree merge operation.

It comes with a set of tests to cover all the cases described in
the case matrix found in the new documentation.

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

4 files changed, 698 insertions, 13 deletions

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index cbde13dba..6440c4b41 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -53,6 +53,80 @@ the stuff that really changed.
 This is used to avoid unnecessary false hits when "git-diff-files" is
 run after git-read-tree.
 
+
+Two Tree Merge
+~~~~~~~~~~~~~~
+
+Typically, this is invoked as "git-read-tree -m $H $M", where $H
+is the head commit of the current repository, and $M is the head
+of a foreign tree, which is simply ahead of $H (i.e. we are in a
+fast forward situation).
+
+When two trees are specified, the user is telling git-read-tree
+the following:
+
+    (1) The current index and work tree is derived from $H, but
+        the user may have local changes in them since $H;
+
+    (2) The user wants to fast-forward to $M.
+
+In this case, the "git-read-tree -m $H $M" command makes sure
+that no local change is lost as the result of this "merge".
+Here are the "carry forward" rules:
+
+        I (index)           H        M        Result
+       -------------------------------------------------------
+      0 nothing             nothing  nothing  (does not happen)
+      1 nothing             nothing  exists   use M
+      2 nothing             exists   nothing  remove path from cache
+      3 nothing             exists   exists   use M
+
+        clean I==H  I==M
+       ------------------
+      4 yes   N/A   N/A     nothing  nothing  keep index
+      5 no    N/A   N/A     nothing  nothing  keep index
+
+      6 yes   N/A   yes     nothing  exists   keep index
+      7 no    N/A   yes     nothing  exists   keep index
+      8 yes   N/A   no      nothing  exists   fail
+      9 no    N/A   no      nothing  exists   fail
+
+     10 yes   yes   N/A     exists   nothing  remove path from cache
+     11 no    yes   N/A     exists   nothing  fail
+     12 yes   no    N/A     exists   nothing  fail
+     13 no    no    N/A     exists   nothing  fail
+
+        clean (H=M)
+       ------
+     14 yes                 exists   exists   keep index
+     15 no                  exists   exists   keep index
+
+        clean I==H  I==M (H!=M)
+       ------------------
+     16 yes   no    no      exists   exists   fail
+     17 no    no    no      exists   exists   fail
+     18 yes   no    yes     exists   exists   keep index
+     19 no    no    yes     exists   exists   keep index
+     20 yes   yes   no      exists   exists   use M
+     21 no    yes   no      exists   exists   fail
+
+In all "keep index" cases, the cache entry stays as in the
+original index file.  If the entry were not up to date,
+git-read-tree keeps the copy in the work tree intact when
+operating under the -u flag.
+
+When this form of git-read-tree returns successfully, you can
+see what "local changes" you made are carried forward by running
+"git-diff-cache --cached $M".  Note that this does not
+necessarily match "git-diff-cache --cached $H" would have
+produced before such a two tree merge.  This is because of cases
+18 and 19 --- if you already had the changes in $M (e.g. maybe
+you picked it up via e-mail in a patch form), "git-diff-cache
+--cached $H" would have told you about the change before this
+merge, but it would not show in "git-diff-cache --cached $M"
+output after two-tree merge.
+
+
 3-Way Merge
 ~~~~~~~~~~~
 Each "index" entry has two bits worth of "stage" state. stage 0 is the
diff --git a/read-tree.c b/read-tree.c
index 2fb27e974..8eb243212 100644
--- a/read-tree.c
+++ b/read-tree.c
@@ -155,28 +155,51 @@ static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **ds
 /*
  * Two-way merge.
  *
- * The rule is: 
- *  - every current entry has to match the old tree
- *  - if the current entry matches the new tree, we leave it
- *    as-is. Otherwise we require that it be up-to-date.
+ * The rule is to "carry forward" what is in the index without losing
+ * information across a "fast forward", favoring a successful merge
+ * over a merge failure when it makes sense.  For details of the
+ * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
+ *
  */
 static int twoway_merge(struct cache_entry **src, struct cache_entry **dst)
 {
-	struct cache_entry *old = src[0];
-	struct cache_entry *a = src[1], *b = src[2];
+	struct cache_entry *current = src[0];
+	struct cache_entry *oldtree = src[1], *newtree = src[2];
 
 	if (src[3])
 		return -1;
 
-	if (old) {
-		if (!a || !same(old, a))
+	if (current) {
+		if ((!oldtree && !newtree) || /* 4 and 5 */
+		    (!oldtree && newtree &&
+		     same(current, newtree)) || /* 6 and 7 */
+		    (oldtree && newtree &&
+		     same(oldtree, newtree)) || /* 14 and 15 */
+		    (oldtree && newtree &&
+		     !same(oldtree, newtree) && /* 18 and 19*/
+		     same(current, newtree))) {
+			*dst++ = current;
+			return 1;
+		}
+		else if (oldtree && !newtree && same(current, oldtree)) {
+			/* 10 or 11 */
+			verify_uptodate(current);
+			return 0;
+		}
+		else if (oldtree && newtree &&
+			 same(current, oldtree) && !same(current, newtree)) {
+			/* 20 or 21 */
+			verify_uptodate(current);
+			return merged_entry(newtree, NULL, dst);
+		}
+		else
+			/* all other failures */
 			return -1;
 	}
-	if (b)
-		return merged_entry(b, old, dst);
-	if (old)
-		verify_uptodate(old);
-	return 0;
+	else if (newtree)
+		return merged_entry(newtree, NULL, dst);
+	else
+		return 0;
 }
 
 /*
diff --git a/t/t1001-read-tree-m-2way.sh b/t/t1001-read-tree-m-2way.sh
new file mode 100755
index 000000000..33041f3cc
--- /dev/null
+++ b/t/t1001-read-tree-m-2way.sh
@@ -0,0 +1,281 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Junio C Hamano
+#
+
+test_description='Two way merge with read-tree -m $H $M
+
+This test tries two-way merge (aka fast forward with carry forward).
+
+There is the head (called H) and another commit (called M), which is
+simply ahead of H.  The index and the work tree contains a state that
+is derived from H, but may also have local changes.  This test checks
+all the combinations described in the two-tree merge "carry forward"
+rules, found in <Documentation/git-rev-tree.txt>.
+
+In the test, these paths are used:
+        bozbar  - in H, stays in M, modified from bozbar to gnusto
+        frotz   - not in H added in M
+        nitfol  - in H, stays in M unmodified
+        rezrov  - in H, deleted in M
+        yomin   - not in H nor M
+'
+. ./test-lib.sh
+
+_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
+_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
+compare_change () {
+	sed >current \
+	    -e '/^--- /d; /^+++ /d; /^@@ /d;' \
+	    -e 's/^\(.[0-7][0-7][0-7][0-7][0-7][0-7]\) '"$_x40"' /\1 X /' "$1"
+	diff -u expected current
+}
+
+check_cache_at () {
+	clean_if_empty=`git-diff-files "$1"`
+	case "$clean_if_empty" in
+	'')  echo "$1: clean" ;;
+	?*)  echo "$1: dirty" ;;
+	esac
+	case "$2,$clean_if_empty" in
+	clean,)		:     ;;
+	clean,?*)	false ;;
+	dirty,)		false ;;
+	dirty,?*)	:     ;;
+	esac
+}
+
+test_expect_success \
+    setup \
+    'echo frotz >frotz &&
+     echo nitfol >nitfol &&
+     echo bozbar >bozbar &&
+     echo rezrov >rezrov &&
+     echo yomin >yomin &&
+     git-update-cache --add nitfol bozbar rezrov &&
+     treeH=`git-write-tree` &&
+     echo treeH $treeH &&
+     git-ls-tree $treeH &&
+
+     echo gnusto >bozbar &&
+     git-update-cache --add frotz bozbar --force-remove rezrov &&
+     git-ls-files --stage >M.out &&
+     treeM=`git-write-tree` &&
+     echo treeM $treeM &&
+     git-ls-tree $treeM &&
+     git-diff-tree $treeH $treeM'
+
+test_expect_success \
+    '1, 2, 3 - no carry forward' \
+    'rm -f .git/index &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >1-3.out &&
+     cmp M.out 1-3.out &&
+     check_cache_at bozbar dirty &&
+     check_cache_at frotz dirty &&
+     check_cache_at nitfol dirty'
+
+echo '+100644 X 0	yomin' >expected
+
+test_expect_success \
+    '4 - carry forward local addition.' \
+    'rm -f .git/index &&
+     git-update-cache --add yomin &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >4.out || exit
+     diff --unified=0 M.out 4.out >4diff.out
+     compare_change 4diff.out expected &&
+     check_cache_at yomin clean'
+
+test_expect_success \
+    '5 - carry forward local addition.' \
+    'rm -f .git/index &&
+     echo yomin >yomin &&
+     git-update-cache --add yomin &&
+     echo yomin yomin >yomin &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >5.out || exit
+     diff --unified=0 M.out 5.out >5diff.out
+     compare_change 5diff.out expected &&
+     check_cache_at yomin dirty'
+
+test_expect_success \
+    '6 - local addition already has the same.' \
+    'rm -f .git/index &&
+     git-update-cache --add frotz &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >6.out &&
+     diff --unified=0 M.out 6.out &&
+     check_cache_at frotz clean'
+
+test_expect_success \
+    '7 - local addition already has the same.' \
+    'rm -f .git/index &&
+     echo frotz >frotz &&
+     git-update-cache --add frotz &&
+     echo frotz frotz >frotz &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >7.out &&
+     diff --unified=0 M.out 7.out &&
+     check_cache_at frotz dirty'
+
+test_expect_success \
+    '8 - conflicting addition.' \
+    'rm -f .git/index &&
+     echo frotz frotz >frotz &&
+     git-update-cache --add frotz &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '9 - conflicting addition.' \
+    'rm -f .git/index &&
+     echo frotz frotz >frotz &&
+     git-update-cache --add frotz &&
+     echo frotz >frotz &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '10 - path removed.' \
+    'rm -f .git/index &&
+     echo rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >10.out &&
+     cmp M.out 10.out'
+
+test_expect_success \
+    '11 - dirty path removed.' \
+    'rm -f .git/index &&
+     echo rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     echo rezrov rezrov >rezrov &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '12 - unmatching local changes being removed.' \
+    'rm -f .git/index &&
+     echo rezrov rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '13 - unmatching local changes being removed.' \
+    'rm -f .git/index &&
+     echo rezrov rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     echo rezrov >rezrov &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+cat >expected <<EOF
+-100644 X 0	nitfol
++100644 X 0	nitfol
+EOF
+
+test_expect_success \
+    '14 - unchanged in two heads.' \
+    'rm -f .git/index &&
+     echo nitfol nitfol >nitfol &&
+     git-update-cache --add nitfol &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >14.out || exit
+     diff --unified=0 M.out 14.out >14diff.out
+     compare_change 14diff.out expected &&
+     check_cache_at nitfol clean'
+
+test_expect_success \
+    '15 - unchanged in two heads.' \
+    'rm -f .git/index &&
+     echo nitfol nitfol >nitfol &&
+     git-update-cache --add nitfol &&
+     echo nitfol nitfol nitfol >nitfol &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >15.out || exit
+     diff --unified=0 M.out 15.out >15diff.out
+     compare_change 15diff.out expected &&
+     check_cache_at nitfol dirty'
+
+test_expect_success \
+    '16 - conflicting local change.' \
+    'rm -f .git/index &&
+     echo bozbar bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '17 - conflicting local change.' \
+    'rm -f .git/index &&
+     echo bozbar bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     echo bozbar bozbar bozbar >bozbar &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '18 - local change already having a good result.' \
+    'rm -f .git/index &&
+     echo gnusto >bozbar &&
+     git-update-cache --add bozbar &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >18.out &&
+     diff --unified=0 M.out 18.out &&
+     check_cache_at bozbar clean'
+
+test_expect_success \
+    '19 - local change already having a good result, further modified.' \
+    'rm -f .git/index &&
+     echo gnusto >bozbar &&
+     git-update-cache --add bozbar &&
+     echo gnusto gnusto >bozbar &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >19.out &&
+     diff --unified=0 M.out 19.out &&
+     check_cache_at bozbar dirty'
+
+test_expect_success \
+    '20 - no local change, use new tree.' \
+    'rm -f .git/index &&
+     echo bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     git-read-tree -m $treeH $treeM &&
+     git-ls-files --stage >20.out &&
+     diff --unified=0 M.out 20.out &&
+     check_cache_at bozbar dirty'
+
+test_expect_success \
+    '21 - no local change, dirty cache.' \
+    'rm -f .git/index &&
+     echo bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     echo gnusto gnusto >bozbar &&
+     if git-read-tree -m $treeH $treeM; then false; else :; fi'
+
+# Also make sure we did not break DF vs DF/DF case.
+test_expect_success \
+    'DF vs DF/DF case setup.' \
+    'rm -f .git/index &&
+     echo DF >DF &&
+     git-update-cache --add DF &&
+     treeDF=`git-write-tree` &&
+     echo treeDF $treeDF &&
+     git-ls-tree $treeDF &&
+
+     rm -f DF &&
+     mkdir DF &&
+     echo DF/DF >DF/DF &&
+     git-update-cache --add --remove DF DF/DF &&
+     treeDFDF=`git-write-tree` &&
+     echo treeDFDF $treeDFDF &&
+     git-ls-tree $treeDFDF &&
+     git-ls-files --stage >DFDF.out'
+
+test_expect_success \
+    'DF vs DF/DF case test.' \
+    'rm -f .git/index &&
+     rm -fr DF &&
+     echo DF >DF &&
+     git-update-cache --add DF &&
+     git-read-tree -m $treeDF $treeDFDF &&
+     git-ls-files --stage >DFDFcheck.out &&
+     diff --unified=0 DFDF.out DFDFcheck.out &&
+     check_cache_at DF/DF dirty'
+
+test_done
diff --git a/t/t1002-read-tree-m-u-2way.sh b/t/t1002-read-tree-m-u-2way.sh
new file mode 100755
index 000000000..75a4eaaf2
--- /dev/null
+++ b/t/t1002-read-tree-m-u-2way.sh
@@ -0,0 +1,307 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Junio C Hamano
+#
+
+test_description='Two way merge with read-tree -m -u $H $M
+
+This is identical to t1001, but uses -u to update the work tree as well.
+
+'
+. ./test-lib.sh
+
+_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
+_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
+compare_change () {
+	sed >current \
+	    -e '/^--- /d; /^+++ /d; /^@@ /d;' \
+	    -e 's/^\(.[0-7][0-7][0-7][0-7][0-7][0-7]\) '"$_x40"' /\1 X /' "$1"
+	diff -u expected current
+}
+
+check_cache_at () {
+	clean_if_empty=`git-diff-files "$1"`
+	case "$clean_if_empty" in
+	'')  echo "$1: clean" ;;
+	?*)  echo "$1: dirty" ;;
+	esac
+	case "$2,$clean_if_empty" in
+	clean,)		:     ;;
+	clean,?*)	false ;;
+	dirty,)		false ;;
+	dirty,?*)	:     ;;
+	esac
+}
+
+test_expect_success \
+    setup \
+    'echo frotz >frotz &&
+     echo nitfol >nitfol &&
+     echo bozbar >bozbar &&
+     echo rezrov >rezrov &&
+     echo yomin >yomin &&
+     git-update-cache --add nitfol bozbar rezrov &&
+     treeH=`git-write-tree` &&
+     echo treeH $treeH &&
+     git-ls-tree $treeH &&
+
+     echo gnusto >bozbar &&
+     git-update-cache --add frotz bozbar --force-remove rezrov &&
+     git-ls-files --stage >M.out &&
+     treeM=`git-write-tree` &&
+     echo treeM $treeM &&
+     git-ls-tree $treeM &&
+     sha1sum bozbar frotz nitfol >M.sha1 &&
+     git-diff-tree $treeH $treeM'
+
+test_expect_success \
+    '1, 2, 3 - no carry forward' \
+    'rm -f .git/index &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >1-3.out &&
+     cmp M.out 1-3.out &&
+     sha1sum -c M.sha1 &&
+     check_cache_at bozbar clean &&
+     check_cache_at frotz clean &&
+     check_cache_at nitfol clean'
+
+echo '+100644 X 0	yomin' >expected
+
+test_expect_success \
+    '4 - carry forward local addition.' \
+    'rm -f .git/index &&
+     git-update-cache --add yomin &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >4.out || exit
+     diff --unified=0 M.out 4.out >4diff.out
+     compare_change 4diff.out expected &&
+     check_cache_at yomin clean &&
+     sha1sum -c M.sha1 &&
+     echo yomin >yomin1 &&
+     diff yomin yomin1 &&
+     rm -f yomin1'
+
+test_expect_success \
+    '5 - carry forward local addition.' \
+    'rm -f .git/index &&
+     echo yomin >yomin &&
+     git-update-cache --add yomin &&
+     echo yomin yomin >yomin &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >5.out || exit
+     diff --unified=0 M.out 5.out >5diff.out
+     compare_change 5diff.out expected &&
+     check_cache_at yomin dirty &&
+     sha1sum -c M.sha1 &&
+     : dirty index should have prevented -u from checking it out.
+     echo yomin yomin >yomin1 &&
+     diff yomin yomin1 &&
+     rm -f yomin1'
+
+test_expect_success \
+    '6 - local addition already has the same.' \
+    'rm -f .git/index &&
+     git-update-cache --add frotz &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >6.out &&
+     diff --unified=0 M.out 6.out &&
+     check_cache_at frotz clean &&
+     sha1sum -c M.sha1 &&
+     echo frotz >frotz1 &&
+     diff frotz frotz1 &&
+     rm -f frotz1'
+
+test_expect_success \
+    '7 - local addition already has the same.' \
+    'rm -f .git/index &&
+     echo frotz >frotz &&
+     git-update-cache --add frotz &&
+     echo frotz frotz >frotz &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >7.out &&
+     diff --unified=0 M.out 7.out &&
+     check_cache_at frotz dirty &&
+     if sha1sum -c M.sha1; then false; else :; fi &&
+     : dirty index should have prevented -u from checking it out.
+     echo frotz frotz >frotz1 &&
+     diff frotz frotz1 &&
+     rm -f frotz1'
+
+test_expect_success \
+    '8 - conflicting addition.' \
+    'rm -f .git/index &&
+     echo frotz frotz >frotz &&
+     git-update-cache --add frotz &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '9 - conflicting addition.' \
+    'rm -f .git/index &&
+     echo frotz frotz >frotz &&
+     git-update-cache --add frotz &&
+     echo frotz >frotz &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '10 - path removed.' \
+    'rm -f .git/index &&
+     echo rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >10.out &&
+     cmp M.out 10.out &&
+     sha1sum -c M.sha1'
+
+test_expect_success \
+    '11 - dirty path removed.' \
+    'rm -f .git/index &&
+     echo rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     echo rezrov rezrov >rezrov &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '12 - unmatching local changes being removed.' \
+    'rm -f .git/index &&
+     echo rezrov rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '13 - unmatching local changes being removed.' \
+    'rm -f .git/index &&
+     echo rezrov rezrov >rezrov &&
+     git-update-cache --add rezrov &&
+     echo rezrov >rezrov &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+cat >expected <<EOF
+-100644 X 0	nitfol
++100644 X 0	nitfol
+EOF
+
+test_expect_success \
+    '14 - unchanged in two heads.' \
+    'rm -f .git/index &&
+     echo nitfol nitfol >nitfol &&
+     git-update-cache --add nitfol &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >14.out || exit
+     diff --unified=0 M.out 14.out >14diff.out
+     compare_change 14diff.out expected &&
+     check_cache_at nitfol clean &&
+     grep -v nitfol M.sha1 | sha1sum -c &&
+     if sha1sum -c M.sha1; then false; else :; fi &&
+     echo nitfol nitfol >nitfol1 &&
+     diff nitfol nitfol1 &&
+     rm -f nitfol1'
+
+test_expect_success \
+    '15 - unchanged in two heads.' \
+    'rm -f .git/index &&
+     echo nitfol nitfol >nitfol &&
+     git-update-cache --add nitfol &&
+     echo nitfol nitfol nitfol >nitfol &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >15.out || exit
+     diff --unified=0 M.out 15.out >15diff.out
+     compare_change 15diff.out expected &&
+     check_cache_at nitfol dirty &&
+     grep -v nitfol M.sha1 | sha1sum -c &&
+     if sha1sum -c M.sha1; then false; else :; fi &&
+     echo nitfol nitfol nitfol >nitfol1 &&
+     diff nitfol nitfol1 &&
+     rm -f nitfol1'
+
+test_expect_success \
+    '16 - conflicting local change.' \
+    'rm -f .git/index &&
+     echo bozbar bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '17 - conflicting local change.' \
+    'rm -f .git/index &&
+     echo bozbar bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     echo bozbar bozbar bozbar >bozbar &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+test_expect_success \
+    '18 - local change already having a good result.' \
+    'rm -f .git/index &&
+     echo gnusto >bozbar &&
+     git-update-cache --add bozbar &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >18.out &&
+     diff --unified=0 M.out 18.out &&
+     check_cache_at bozbar clean &&
+     sha1sum -c M.sha1'
+
+test_expect_success \
+    '19 - local change already having a good result, further modified.' \
+    'rm -f .git/index &&
+     echo gnusto >bozbar &&
+     git-update-cache --add bozbar &&
+     echo gnusto gnusto >bozbar &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >19.out &&
+     diff --unified=0 M.out 19.out &&
+     check_cache_at bozbar dirty &&
+     grep -v bozbar M.sha1 | sha1sum -c &&
+     if sha1sum -c M.sha1; then false; else :; fi &&
+     echo gnusto gnusto >bozbar1 &&
+     diff bozbar bozbar1 &&
+     rm -f bozbar1'
+
+test_expect_success \
+    '20 - no local change, use new tree.' \
+    'rm -f .git/index &&
+     echo bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     git-read-tree -m -u $treeH $treeM &&
+     git-ls-files --stage >20.out &&
+     diff --unified=0 M.out 20.out &&
+     check_cache_at bozbar clean &&
+     sha1sum -c M.sha1'
+
+test_expect_success \
+    '21 - no local change, dirty cache.' \
+    'rm -f .git/index &&
+     echo bozbar >bozbar &&
+     git-update-cache --add bozbar &&
+     echo gnusto gnusto >bozbar &&
+     if git-read-tree -m -u $treeH $treeM; then false; else :; fi'
+
+# Also make sure we did not break DF vs DF/DF case.
+test_expect_success \
+    'DF vs DF/DF case setup.' \
+    'rm -f .git/index &&
+     echo DF >DF &&
+     git-update-cache --add DF &&
+     treeDF=`git-write-tree` &&
+     echo treeDF $treeDF &&
+     git-ls-tree $treeDF &&
+
+     rm -f DF &&
+     mkdir DF &&
+     echo DF/DF >DF/DF &&
+     git-update-cache --add --remove DF DF/DF &&
+     treeDFDF=`git-write-tree` &&
+     echo treeDFDF $treeDFDF &&
+     git-ls-tree $treeDFDF &&
+     git-ls-files --stage >DFDF.out'
+
+test_expect_success \
+    'DF vs DF/DF case test.' \
+    'rm -f .git/index &&
+     rm -fr DF &&
+     echo DF >DF &&
+     git-update-cache --add DF &&
+     git-read-tree -m -u $treeDF $treeDFDF &&
+     git-ls-files --stage >DFDFcheck.out &&
+     diff --unified=0 DFDF.out DFDFcheck.out &&
+     check_cache_at DF/DF clean'
+
+test_done