[PATCH] Rename/copy detection fix.

The rename/copy detection logic in earlier round was only good
enough to show patch output and discussion on the mailing list
about the diff-raw format updates revealed many problems with
it.  This patch fixes all the ones known to me, without making
things I want to do later impossible, mostly related to patch
reordering.

 (1) Earlier rename/copy detector determined which one is rename
     and which one is copy too early, which made it impossible
     to later introduce diffcore transformers to reorder
     patches.  This patch fixes it by moving that logic to the
     very end of the processing.

 (2) Earlier output routine diff_flush() was pruning all the
     "no-change" entries indiscriminatingly.  This was done due
     to my false assumption that one of the requirements in the
     diff-raw output was not to show such an entry (which
     resulted in my incorrect comment about "diff-helper never
     being able to be equivalent to built-in diff driver").  My
     special thanks go to Linus for correcting me about this.
     When we produce diff-raw output, for the downstream to be
     able to tell renames from copies, sometimes it _is_
     necessary to output "no-change" entries, and this patch
     adds diffcore_prune() function for doing it.

 (3) Earlier diff_filepair structure was trying to be not too
     specific about rename/copy operations, but the purpose of
     the structure was to record one or two paths, which _was_
     indeed about rename/copy.  This patch discards xfrm_msg
     field which was trying to be generic for this wrong reason,
     and introduces a couple of fields (rename_score and
     rename_rank) that are explicitly specific to rename/copy
     logic.  One thing to note is that the information in a
     single diff_filepair structure _still_ does not distinguish
     renames from copies, and it is deliberately so.  This is to
     allow patches to be reordered in later stages.

 (4) This patch also adds some tests about diff-raw format
     output and makes sure that necessary "no-change" entries
     appear on the output.

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

2 files changed, 97 insertions, 11 deletions

diff --git a/t/t4003-diff-rename-1.sh b/t/t4003-diff-rename-1.sh
index 167d0b95b5..999ee6054e 100644
--- a/t/t4003-diff-rename-1.sh
+++ b/t/t4003-diff-rename-1.sh
@@ -11,7 +11,8 @@ test_description='More rename detection
 test_expect_success \
     'prepare reference tree' \
     'cat ../../COPYING >COPYING &&
-    git-update-cache --add COPYING &&
+     echo frotz >rezrov &&
+    git-update-cache --add COPYING rezrov &&
     tree=$(git-write-tree) &&
     echo $tree'
 
@@ -22,9 +23,10 @@ test_expect_success \
     rm -f COPYING &&
     git-update-cache --add --remove COPYING COPYING.?'
 
-# tree has COPYING.  work tree has COPYING.1 and COPYING.2,
-# both are slightly edited.  So we say you copy-and-edit one,
-# and rename-and-edit the other.
+# tree has COPYING and rezrov.  work tree has COPYING.1 and COPYING.2,
+# both are slightly edited, and unchanged rezrov.  So we say you
+# copy-and-edit one, and rename-and-edit the other.  We do not say
+# anything about rezrov.
 
 GIT_DIFF_OPTS=--unified=0 git-diff-cache -M -p $tree |
 sed -e 's/\([0-9][0-9]*\)/#/g' >current &&
@@ -64,9 +66,10 @@ test_expect_success \
     'mv COPYING.2 COPYING &&
      git-update-cache --add --remove COPYING COPYING.1 COPYING.2'
 
-# tree has COPYING.  work tree has COPYING and COPYING.1,
-# both are slightly edited.  So we say you edited one,
-# and copy-and-edit the other.
+# tree has COPYING and rezrov.  work tree has COPYING and COPYING.1,
+# both are slightly edited, and unchanged rezrov.  So we say you
+# edited one, and copy-and-edit the other.  We do not say
+# anything about rezrov.
 
 GIT_DIFF_OPTS=--unified=0 git-diff-cache -C -p $tree |
 sed -e 's/\([0-9][0-9]*\)/#/g' >current
@@ -103,10 +106,11 @@ test_expect_success \
     'cat ../../COPYING >COPYING &&
      git-update-cache --add --remove COPYING COPYING.1'
 
-# tree has COPYING.  work tree has the same COPYING and COPYING.1,
-# but COPYING is not edited.  We say you copy-and-edit COPYING.1;
-# this is only possible because -C mode now reports the unmodified
-# file to the diff-core.
+# tree has COPYING and rezrov.  work tree has COPYING and COPYING.1,
+# but COPYING is not edited.  We say you copy-and-edit COPYING.1; this
+# is only possible because -C mode now reports the unmodified file to
+# the diff-core.  Unchanged rezrov, although being fed to
+# git-diff-cache as well, should not be mentioned.
 
 GIT_DIFF_OPTS=--unified=0 git-diff-cache -C -p $tree |
 sed -e 's/\([0-9][0-9]*\)/#/g' >current
diff --git a/t/t4005-diff-rename-2.sh b/t/t4005-diff-rename-2.sh
new file mode 100644
index 0000000000..90f4f4c295
--- /dev/null
+++ b/t/t4005-diff-rename-2.sh
@@ -0,0 +1,82 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Junio C Hamano
+#
+
+test_description='Same rename detection as t4003 but testing diff-raw.
+
+'
+. ./test-lib.sh
+
+test_expect_success \
+    'prepare reference tree' \
+    'cat ../../COPYING >COPYING &&
+     echo frotz >rezrov &&
+    git-update-cache --add COPYING rezrov &&
+    tree=$(git-write-tree) &&
+    echo $tree'
+
+test_expect_success \
+    'prepare work tree' \
+    'sed -e 's/HOWEVER/However/' <COPYING >COPYING.1 &&
+    sed -e 's/GPL/G.P.L/g' <COPYING >COPYING.2 &&
+    rm -f COPYING &&
+    git-update-cache --add --remove COPYING COPYING.?'
+
+# tree has COPYING and rezrov.  work tree has COPYING.1 and COPYING.2,
+# both are slightly edited, and unchanged rezrov.  We say COPYING.1
+# and COPYING.2 are based on COPYING, and do not say anything about
+# rezrov.
+
+git-diff-cache -M $tree >current
+
+cat >expected <<\EOF
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0603b3238a076dc6c8022aedc6648fa523a17178	COPYING	COPYING.1
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 06c67961bbaed34a127f76d261f4c0bf73eda471	COPYING	COPYING.2
+EOF
+
+test_expect_success \
+    'validate output from rename/copy detection' \
+    'diff -u current expected'
+
+test_expect_success \
+    'prepare work tree again' \
+    'mv COPYING.2 COPYING &&
+     git-update-cache --add --remove COPYING COPYING.1 COPYING.2'
+
+# tree has COPYING and rezrov.  work tree has COPYING and COPYING.1,
+# both are slightly edited, and unchanged rezrov.  We say COPYING.1
+# is based on COPYING and COPYING is still there, and do not say anything
+# about rezrov.
+
+git-diff-cache -C $tree >current
+cat >expected <<\EOF
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0603b3238a076dc6c8022aedc6648fa523a17178	COPYING	COPYING.1
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 06c67961bbaed34a127f76d261f4c0bf73eda471	COPYING	COPYING
+EOF
+
+test_expect_success \
+    'validate output from rename/copy detection' \
+    'diff -u current expected'
+
+test_expect_success \
+    'prepare work tree once again' \
+    'cat ../../COPYING >COPYING &&
+     git-update-cache --add --remove COPYING COPYING.1'
+
+# tree has COPYING and rezrov.  work tree has the same COPYING and
+# copy-edited COPYING.1, and unchanged rezrov.  We should see
+# unmodified COPYING in the output, so that downstream diff-helper can
+# notice.  We should not say anything about rezrov.
+
+git-diff-cache -C $tree >current
+cat >expected <<\EOF
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0603b3238a076dc6c8022aedc6648fa523a17178	COPYING	COPYING.1
+:100644 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 6ff87c4664981e4397625791c8ea3bbb5f2279a3	COPYING	COPYING
+EOF
+
+test_expect_success \
+    'validate output from rename/copy detection' \
+    'diff -u current expected'
+
+test_done