From 2ac0d6273fa6618e1a8783e07e2363b3abba1f2a Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Sat, 15 Feb 2020 21:36:40 +0000 Subject: [PATCH] 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 Signed-off-by: Junio C Hamano --- Documentation/git-rebase.txt | 13 ++++++++++++- builtin/rebase.c | 4 ++-- t/t5520-pull.sh | 10 ++++++---- t/t9106-git-svn-commit-diff-clobber.sh | 3 ++- 4 files changed, 22 insertions(+), 8 deletions(-) diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt index 93092da3bf6ab2..fbac1cf38dd251 100644 --- a/Documentation/git-rebase.txt +++ b/Documentation/git-rebase.txt @@ -315,7 +315,7 @@ See also INCOMPATIBLE OPTIONS below. --merge:: Use merging strategies to rebase. When the recursive (default) merge strategy is used, this allows rebase to be aware of renames on the - upstream side. + upstream side. This is the default. + Note that a rebase merge works by replaying each commit from the working branch on top of the branch. Because of this, when a merge @@ -683,6 +683,17 @@ accident of implementation rather than by design. Both backends should have the same behavior, though it is not clear which one is correct. +Interruptability +~~~~~~~~~~~~~~~~ + +The am backend has safety problems with an ill-timed interrupt; if the +user presses Ctrl-C at the wrong time to try to abort the rebase, the +rebase can enter a state where it cannot be aborted with a subsequent +`git rebase --abort`. The interactive backend does not appear to +suffer from the same shortcoming. (See +https://lore.kernel.org/git/20200207132152.GC2868@szeder.dev/ for +details.) + Miscellaneous differences ~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/builtin/rebase.c b/builtin/rebase.c index f0a862f41b5c4c..db8fd699d79c51 100644 --- a/builtin/rebase.c +++ b/builtin/rebase.c @@ -101,7 +101,7 @@ struct rebase_options { #define REBASE_OPTIONS_INIT { \ .type = REBASE_UNSPECIFIED, \ .empty = EMPTY_UNSPECIFIED, \ - .default_backend = "am", \ + .default_backend = "merge", \ .flags = REBASE_NO_QUIET, \ .git_am_opts = ARGV_ARRAY_INIT, \ .git_format_patch_opt = STRBUF_INIT \ @@ -1917,7 +1917,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix) if (options.type == REBASE_UNSPECIFIED) { if (!strcmp(options.default_backend, "merge")) - options.type = REBASE_MERGE; + imply_interactive(&options, "--merge"); else if (!strcmp(options.default_backend, "am")) options.type = REBASE_AM; else diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh index 3fff6a06fa8fed..4f9e7f7ff6b022 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 ) ' diff --git a/t/t9106-git-svn-commit-diff-clobber.sh b/t/t9106-git-svn-commit-diff-clobber.sh index dbe8deac0d2f28..aec45bca3b7b6f 100755 --- a/t/t9106-git-svn-commit-diff-clobber.sh +++ b/t/t9106-git-svn-commit-diff-clobber.sh @@ -92,7 +92,8 @@ test_expect_success 'multiple dcommit from git svn will not clobber svn' " test_expect_success 'check that rebase really failed' ' - test -d .git/rebase-apply + git status >output && + grep currently.rebasing output ' test_expect_success 'resolve, continue the rebase and dcommit' "