rebase: protect against diff.renames configuration

We currently do not disable diff.renames configuration while rebase
internally runs "format-patch" to feed "am -3".

The end user configuration for "diff" should not affect the result
produced by the higher level command that is related to "diff" only
because internally it is implemented in terms of it.

For that matter, I have a feeling that format-patch should not even look
at diff.renames, but we seem to have been doing this for a long time so
there is no easy way to fix this thinko.

In any case, here is a much straightforward fix for "rebase".

[jn: with test case from David]

Reported-by: David D. Kilzer <ddkilzer@kilzer.net>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase.sh

@@ -543,7 +543,7 @@ fi
 if test -z "$do_merge"
 then
 	git format-patch -k --stdout --full-index --ignore-if-in-upstream \
-		$root_flag "$revisions" |
+		--no-renames $root_flag "$revisions" |
 	git am $git_am_opt --rebasing --resolvemsg="$RESOLVEMSG" &&
 	move_to_original_branch
 	ret=$?

t/t3400-rebase.sh

@@ -19,7 +19,16 @@ test_expect_success 'prepare repository with topic branches' '
 	echo First >A &&
 	git update-index --add A &&
 	git commit -m "Add A." &&
-	git checkout -b my-topic-branch &&
+	git checkout -b force-3way &&
+	echo Dummy >Y &&
+	git update-index --add Y &&
+	git commit -m "Add Y." &&
+	git checkout -b filemove &&
+	git reset --soft master &&
+	mkdir D &&
+	git mv A D/A &&
+	git commit -m "Move A." &&
+	git checkout -b my-topic-branch master &&
 	echo Second >B &&
 	git update-index --add B &&
 	git commit -m "Add B." &&
@@ -128,6 +137,19 @@ test_expect_success 'rebase a single mode change' '
 	GIT_TRACE=1 git rebase master
 '
 
+test_expect_success 'rebase is not broken by diff.renames' '
+	git config diff.renames copies &&
+	test_when_finished "git config --unset diff.renames" &&
+	git checkout filemove &&
+	GIT_TRACE=1 git rebase force-3way
+'
+
+test_expect_success 'setup: recover' '
+	test_might_fail git rebase --abort &&
+	git reset --hard &&
+	git checkout modechange
+'
+
 test_expect_success 'Show verbose error when HEAD could not be detached' '
 	>B &&
 	test_must_fail git rebase topic 2>output.err >output.out &&