Subject: Re: [PATCH v5 1/5] rebase -i: add --ignore-whitespace flag

From: Đoàn Trần Công Danh <[email-masked]>
Date: Fri, 26 Jun 2020 20:37:14 +0700

On 2020-06-26 10:55:24+0100, Phillip Wood <[email-masked]> wrote:
> From: Rohit Ashiwal <[email-masked]>
> 
> Rebase is implemented with two different backends - 'apply' and
> 'merge' each of which support a different set of options. In
> particular the apply backend supports a number of options implemented
> by 'git am' that are not implemented in the merge backend. This means
> that the available options are different depending on which backend is
> used which is confusing. This patch adds support for the
> --ignore-whitespace option to the merge backend. This option treats
> lines with only whitespace changes as unchanged and is implemented in
> the merge backend by translating it to -Xignore-space-change.
> 
> Signed-off-by: Rohit Ashiwal <[email-masked]>
> Signed-off-by: Phillip Wood <[email-masked]>
> ---
>  Documentation/git-rebase.txt           | 19 +++++++-
>  builtin/rebase.c                       | 16 +++++--
>  t/t3422-rebase-incompatible-options.sh |  1 -
>  t/t3436-rebase-more-options.sh         | 60 ++++++++++++++++++++++++++
>  4 files changed, 90 insertions(+), 6 deletions(-)
>  create mode 100755 t/t3436-rebase-more-options.sh
> 
> diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
> index f7a6033607..b003784f01 100644
> --- a/Documentation/git-rebase.txt
> +++ b/Documentation/git-rebase.txt
> @@ -422,8 +422,23 @@ your branch contains commits which were dropped, this option can be used
>  with `--keep-base` in order to drop those commits from your branch.
>  
>  --ignore-whitespace::
> +	Ignore whitespace differences when trying to reconcile
> +differences. Currently, each backend implements an approximation of
> +this behavior:
> ++
> +apply backend: When applying a patch, ignore changes in whitespace in
> +context lines. Unfortunately, this means that if the "old" lines being
> +replaced by the patch differ only in whitespace from the existing
> +file, you will get a merge conflict instead of a successful patch
> +application.
> ++
> +merge backend: Treat lines with only whitespace changes as unchanged
> +when merging. Unfortunately, this means that any patch hunks that were
> +intended to modify whitespace and nothing else will be dropped, even
> +if the other side had no changes that conflicted.
> +
>  --whitespace=<option>::
> -	These flags are passed to the 'git apply' program
> +	This flag is passed to the 'git apply' program
>  	(see linkgit:git-apply[1]) that applies the patch.
>  	Implies --apply.
>  +
> @@ -572,7 +587,6 @@ The following options:
>   * --apply
>   * --committer-date-is-author-date
>   * --ignore-date
> - * --ignore-whitespace
>   * --whitespace
>   * -C
>  
> @@ -598,6 +612,7 @@ In addition, the following pairs of options are incompatible:
>   * --preserve-merges and --signoff
>   * --preserve-merges and --rebase-merges
>   * --preserve-merges and --empty=
> + * --preserve-merges and --ignore-whitespace
>   * --keep-base and --onto
>   * --keep-base and --root
>  
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index 27a07d4e78..810c9b7779 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -126,6 +126,7 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
>  	replay.reschedule_failed_exec = opts->reschedule_failed_exec;
>  	replay.gpg_sign = xstrdup_or_null(opts->gpg_sign_opt);
>  	replay.strategy = opts->strategy;
> +
>  	if (opts->strategy_opts)
>  		parse_strategy_opts(&replay, opts->strategy_opts);
>  
> @@ -1466,6 +1467,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  	struct strbuf revisions = STRBUF_INIT;
>  	struct strbuf buf = STRBUF_INIT;
>  	struct object_id merge_base;
> +	int ignore_whitespace = 0;
>  	enum action action = ACTION_NONE;
>  	const char *gpg_sign = NULL;
>  	struct string_list exec = STRING_LIST_INIT_NODUP;
> @@ -1495,16 +1497,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  			PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
>  		OPT_BOOL(0, "signoff", &options.signoff,
>  			 N_("add a Signed-off-by: line to each commit")),
> -		OPT_PASSTHRU_ARGV(0, "ignore-whitespace", &options.git_am_opts,
> -				  NULL, N_("passed to 'git am'"),
> -				  PARSE_OPT_NOARG),
>  		OPT_PASSTHRU_ARGV(0, "committer-date-is-author-date",
>  				  &options.git_am_opts, NULL,
>  				  N_("passed to 'git am'"), PARSE_OPT_NOARG),
>  		OPT_PASSTHRU_ARGV(0, "ignore-date", &options.git_am_opts, NULL,
>  				  N_("passed to 'git am'"), PARSE_OPT_NOARG),
>  		OPT_PASSTHRU_ARGV('C', NULL, &options.git_am_opts, N_("n"),
>  				  N_("passed to 'git apply'"), 0),
> +		OPT_BOOL(0, "ignore-whitespace", &ignore_whitespace,
> +			 N_("ignore changes in whitespace")),
>  		OPT_PASSTHRU_ARGV(0, "whitespace", &options.git_am_opts,
>  				  N_("action"), N_("passed to 'git apply'"), 0),
>  		OPT_BIT('f', "force-rebase", &options.flags,
> @@ -1850,6 +1851,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  		imply_merge(&options, "--rebase-merges");
>  	}
>  
> +	if (options.type == REBASE_APPLY) {
> +		if (ignore_whitespace)
> +			argv_array_push (&options.git_am_opts,
> +					 "--ignore-whitespace");
> +	} else if (ignore_whitespace) {
> +			string_list_append (&strategy_options,
> +					    "ignore-space-change");
> +	}
> +

Hm, I've just noticed this by now.
Would it's better if we rewrite it as:

	if (ignore_whitespace) {
		if (options.type == REBASE_APPLY)
			argv_array_push(&options.git_am_opts,
					"--ignore-whitespace");
		else
			string_list_append(&strategy_options,
					   "ignore-space-change");
	}

Ah, the incoming patches will add more conditions into the:

	if (options.type == REBASE_APPLY)

I'm still not convinced, though.

Anyway, IIRC, --ignore-whitespace and --ignore-space-change has the
same meaning, I think it's better to use the same option for both
legs, no?

I can understand the decision to use --ignore-whitespace as keeping
the pass-through behavior of old code, but I think future maintenance
is more important than that.

I've tried changing ignore-whitespace to ignore-space-change and run
make test

It looks good to me (aka nothing failed _in my machine_),
4/5 and 5/5 is not applied, though.

>  	if (strategy_options.nr) {
>  		int i;
>  
> diff --git a/t/t3422-rebase-incompatible-options.sh b/t/t3422-rebase-incompatible-options.sh
> index 50e7960702..55ca46786d 100755
> --- a/t/t3422-rebase-incompatible-options.sh
> +++ b/t/t3422-rebase-incompatible-options.sh
> @@ -61,7 +61,6 @@ test_rebase_am_only () {
>  }
>  
>  test_rebase_am_only --whitespace=fix
> -test_rebase_am_only --ignore-whitespace
>  test_rebase_am_only --committer-date-is-author-date
>  test_rebase_am_only -C4
>  
> diff --git a/t/t3436-rebase-more-options.sh b/t/t3436-rebase-more-options.sh
> new file mode 100755
> index 0000000000..4f8a6e51c9
> --- /dev/null
> +++ b/t/t3436-rebase-more-options.sh
> @@ -0,0 +1,60 @@
> +#!/bin/sh
> +#
> +# Copyright (c) 2019 Rohit Ashiwal
> +#
> +
> +test_description='tests to ensure compatibility between am and interactive backends'
> +
> +. ./test-lib.sh
> +
> +. "$TEST_DIRECTORY"/lib-rebase.sh
> +
> +# This is a special case in which both am and interactive backends
> +# provide the same output. It was done intentionally because
> +# both the backends fall short of optimal behaviour.
> +test_expect_success 'setup' '
> +	git checkout -b topic &&
> +	test_write_lines "line 1" "	line 2" "line 3" >file &&
> +	git add file &&
> +	git commit -m "add file" &&
> +
> +	test_write_lines "line 1" "new line 2" "line 3" >file &&
> +	git commit -am "update file" &&
> +	git tag side &&
> +
> +	git checkout --orphan master &&
> +	test_write_lines "line 1" "        line 2" "line 3" >file &&
> +	git commit -am "add file" &&
> +	git tag main
> +'
> +
> +test_expect_success '--ignore-whitespace works with apply backend' '
> +	test_must_fail git rebase --apply main side &&
> +	git rebase --abort &&
> +	git rebase --apply --ignore-whitespace main side &&
> +	git diff --exit-code side
> +'
> +
> +test_expect_success '--ignore-whitespace works with merge backend' '
> +	test_must_fail git rebase --merge main side &&
> +	git rebase --abort &&
> +	git rebase --merge --ignore-whitespace main side &&
> +	git diff --exit-code side
> +'
> +
> +test_expect_success '--ignore-whitespace is remembered when continuing' '
> +	(
> +		set_fake_editor &&
> +		FAKE_LINES="break 1" git rebase -i --ignore-whitespace \
> +			main side &&
> +		git rebase --continue
> +	) &&
> +	git diff --exit-code side
> +'
> +
> +# This must be the last test in this file
> +test_expect_success '$EDITOR and friends are unchanged' '
> +	test_editor_unchanged
> +'
> +
> +test_done
> -- 
> 2.27.0
> 

-- 
Danh