rebase: change the default backend from "am" to "merge"

The am-backend drops information and thus limits what we can do:

  * lack of full tree information from the original commits means we
    cannot do directory rename detection and warn users that they might
    want to move some of their new files that they placed in old
    directories to prevent their becoming orphaned.[1]
  * reduction in context from only having a few lines beyond those
    changed means that when context lines are non-unique we can apply
    patches incorrectly.[2]
  * lack of access to original commits means that conflict marker
    annotation has less information available.
  * the am backend has safety problems with an ill-timed interrupt.

Also, the merge/interactive backend have far more abilities, appear to
currently have a slight performance advantage[3] and have room for more
optimizations than the am backend[4] (and work is underway to take
advantage of some of those possibilities).

[1] https://lore.kernel.org/git/xmqqh8jeh1id.fsf@gitster-ct.c.googlers.com/
[2] https://lore.kernel.org/git/CABPp-BGiu2nVMQY_t-rnFR5GQUz_ipyEE8oDocKeO+h+t4Mn4A@mail.gmail.com/
[3] https://public-inbox.org/git/CABPp-BF=ev03WgODk6TMQmuNoatg2kiEe5DR__gJ0OTVqHSnfQ@mail.gmail.com/
[4] https://lore.kernel.org/git/CABPp-BGh7yW69QwxQb13K0HM38NKmQif3A6C6UULEKYnkEJ5vA@mail.gmail.com/

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 3fff6a06fa..4f9e7f7ff6 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -340,7 +340,7 @@ test_expect_success '--rebase with conflicts shows advice' '
 	test_tick &&
 	git commit -m "Create conflict" seq.txt &&
 	test_must_fail git pull --rebase . seq 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success 'failed --rebase shows advice' '
@@ -354,7 +354,7 @@ test_expect_success 'failed --rebase shows advice' '
 	git checkout -f -b fails-to-rebase HEAD^ &&
 	test_commit v2-without-cr file "2" file2-lf &&
 	test_must_fail git pull --rebase . diverging 2>err >out &&
-	test_i18ngrep "Resolve all conflicts manually" out
+	test_i18ngrep "Resolve all conflicts manually" err
 '
 
 test_expect_success '--rebase fails with multiple branches' '
@@ -774,8 +774,10 @@ test_expect_success 'git pull --rebase does not reapply old patches' '
 	(
 		cd dst &&
 		test_must_fail git pull --rebase &&
-		find .git/rebase-apply -name "000*" >patches &&
-		test_line_count = 1 patches
+		cat .git/rebase-merge/done .git/rebase-merge/git-rebase-todo >work &&
+		grep -v -e \# -e ^$ work >patches &&
+		test_line_count = 1 patches &&
+		rm -f work
 	)
 '