Re: [PATCH v4 3/3] rebase: add a config option for --rebase-merges

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Alex,

On Wed, 22 Feb 2023, Alex Henrie wrote:

> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index b68fc2fbb7..45cf445d42 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -771,6 +771,20 @@ static int run_specific_rebase(struct rebase_options *opts)
>  	return status ? -1 : 0;
>  }
>
> +static void parse_merges_value(struct rebase_options *options, const char *value)
> +{
> +	if (value) {
> +		if (!strcmp("no-rebase-cousins", value))

If you want to support `rebase.merges=` to imply `no-rebase-cousins`, this
would be the correct place to do it:

		if (!*value || !strcmp("no-rebase-cousins", value))

> +			options->rebase_cousins = 0;
> +		else if (!strcmp("rebase-cousins", value))
> +			options->rebase_cousins = 1;
> +		else
> +			die(_("Unknown mode: %s"), value);
> +	}
> +
> +	options->rebase_merges = 1;

I would expect `options->rebase_merges = 0` if `value == NULL`. IOW I
would have expected `parse_merges_value()` to start with:

	if (!value) {
		options->rebase_merges = 0;
		return;
	}

This assumes, of course, the parse_options semantics, where a `--no-*` option
passes `NULL` as argument to the callback.

However, this is _not_ the parse_options callback, and if the (optional)
argument was not specified, we do end up with a `NULL` here in spite of
wanting to enable the rebase-merges mode.

However, a primary reason why you introduce the function is to support
config value parsing. And in config value parsing, a "maybe-bool" with a
NULL value is considered to be equivalent to `true`! (See
`git_parse_maybe_bool_text()` or
https://git-scm.com/docs/git-config#Documentation/git-config.txt-true for
details.). For example,

	[http]
		sslVerify

is equivalent to

	[http]
		sslVerify = true

But since `git_parse_maybe_bool()` already takes care of handling that
case (in which case we do not even want to call `git_parse_maybe_bool()`),
you can limit that function to handling the command-line semantics.

So with those confusingly disagreeing semantics, I see not only myself,
but other readers doing very, very well, indeed, with a code comment that
explains under what circumstances we expect this callback to be called
with `value == NULL`.

> +}
> +
>  static int rebase_config(const char *var, const char *value, void *data)
>  {
>  	struct rebase_options *opts = data;
> @@ -815,6 +829,13 @@ static int rebase_config(const char *var, const char *value, void *data)
>  		return 0;
>  	}
>
> +	if (!strcmp(var, "rebase.merges") && value && *value) {

Why do we require a non-empty `value` here?

	[rebase]
		merges

should be equivalent to `true`,

	[rebase]
		merges =

should probably be equivalent to `false`, and both are handled correctly
by `git_parse_maybe_bool()`.

> +		opts->rebase_merges = git_parse_maybe_bool(value);
> +		if (opts->rebase_merges < 0)
> +			parse_merges_value(opts, value);
> +		return 0;
> +	}
> +
>  	if (!strcmp(var, "rebase.backend")) {
>  		return git_config_string(&opts->default_backend, var, value);
>  	}
> @@ -980,6 +1001,18 @@ static int parse_opt_empty(const struct option *opt, const char *arg, int unset)
>  	return 0;
>  }
>
> +static int parse_opt_merges(const struct option *opt, const char *arg, int unset)
> +{
> +	struct rebase_options *options = opt->value;
> +
> +	if (unset)
> +		options->rebase_merges = 0;
> +	else
> +		parse_merges_value(options, arg);
> +
> +	return 0;
> +}
> +

It is kind of inelegant to require a _second_ callback for the
command-line parsing, but I guess if we want a `--no-rebase-merges` option
to override a config setting, we cannot help it.

>  static void NORETURN error_on_missing_default_upstream(void)
>  {
>  	struct branch *current_branch = branch_get(NULL);
> @@ -1035,7 +1068,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  	struct object_id branch_base;
>  	int ignore_whitespace = 0;
>  	const char *gpg_sign = NULL;
> -	const char *rebase_merges = NULL;
>  	struct string_list strategy_options = STRING_LIST_INIT_NODUP;
>  	struct object_id squash_onto;
>  	char *squash_onto_name = NULL;
> @@ -1137,10 +1169,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  			   &options.allow_empty_message,
>  			   N_("allow rebasing commits with empty messages"),
>  			   PARSE_OPT_HIDDEN),
> -		{OPTION_STRING, 'r', "rebase-merges", &rebase_merges,
> -			N_("mode"),
> +		OPT_CALLBACK_F('r', "rebase-merges", &options, N_("mode"),
>  			N_("try to rebase merges instead of skipping them"),
> -			PARSE_OPT_OPTARG, NULL, (intptr_t)"no-rebase-cousins"},
> +			PARSE_OPT_OPTARG, parse_opt_merges),
>  		OPT_BOOL(0, "fork-point", &options.fork_point,
>  			 N_("use 'merge-base --fork-point' to refine upstream")),
>  		OPT_STRING('s', "strategy", &options.strategy,
> @@ -1436,14 +1467,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>  	if (options.exec.nr)
>  		imply_merge(&options, "--exec");
>
> -	if (rebase_merges) {
> -		if (!strcmp("rebase-cousins", rebase_merges))
> -			options.rebase_cousins = 1;
> -		else if (strcmp("no-rebase-cousins", rebase_merges))
> -			die(_("Unknown mode: %s"), rebase_merges);
> -		options.rebase_merges = 1;
> +	if (options.rebase_merges)
>  		imply_merge(&options, "--rebase-merges");
> -	}
>
>  	if (options.type == REBASE_APPLY) {
>  		if (ignore_whitespace)
> diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
> index c73949df18..d4b0e8fd49 100755
> --- a/t/t3430-rebase-merges.sh
> +++ b/t/t3430-rebase-merges.sh
> @@ -284,6 +284,102 @@ test_expect_success '--rebase-merges="" is invalid syntax' '
>  	test_cmp expect actual
>  '
>
> +test_expect_success 'rebase.merges="" is equivalent to not passing --rebase-merges' '
> +	test_config rebase.merges "" &&
> +	git checkout -b config-merges-blank E &&
> +	git rebase C &&
> +	test_cmp_graph C.. <<-\EOF
> +	* B
> +	* D
> +	o C
> +	EOF
> +'
> +
> +test_expect_success 'rebase.merges=rebase-cousins is equivalent to --rebase-merges=rebase-cousins' '
> +	test_config rebase.merges rebase-cousins &&
> +	git checkout -b config-rebase-cousins main &&
> +	git rebase HEAD^ &&
> +	test_cmp_graph HEAD^.. <<-\EOF
> +	*   Merge the topic branch '\''onebranch'\''
> +	|\
> +	| * D
> +	| * G
> +	|/
> +	o H
> +	EOF
> +'
> +
> +test_expect_success '--no-rebase-merges overrides rebase.merges=no-rebase-cousins' '
> +	test_config rebase.merges no-rebase-cousins &&
> +	git checkout -b override-config-no-rebase-cousins E &&
> +	git rebase --no-rebase-merges C &&
> +	test_cmp_graph C.. <<-\EOF
> +	* B
> +	* D
> +	o C
> +	EOF
> +'
> +
> +test_expect_success '--rebase-merges=no-rebase-cousins overrides rebase.merges=rebase-cousins' '
> +	test_config rebase.merges rebase-cousins &&
> +	git checkout -b override-config-rebase-cousins main &&
> +	git rebase --rebase-merges=no-rebase-cousins HEAD^ &&
> +	test_cmp_graph HEAD^.. <<-\EOF
> +	*   Merge the topic branch '\''onebranch'\''
> +	|\
> +	| * D
> +	| * G
> +	o | H
> +	|/
> +	o A
> +	EOF
> +'
> +
> +test_expect_success '--rebase-merges overrides rebase.merges=false' '
> +	test_config rebase.merges false &&
> +	git checkout -b override-config-merges-false E &&
> +	before="$(git rev-parse --verify HEAD)" &&
> +	test_tick &&
> +	git rebase --rebase-merges C &&
> +	test_cmp_rev HEAD $before
> +'
> +
> +test_expect_success '--rebase-merges does not override rebase.merges=rebase-cousins' '
> +	test_config rebase.merges rebase-cousins &&
> +	git checkout -b no-override-config-rebase-cousins main &&
> +	git rebase --rebase-merges HEAD^ &&
> +	test_cmp_graph HEAD^.. <<-\EOF
> +	*   Merge the topic branch '\''onebranch'\''
> +	|\
> +	| * D
> +	| * G
> +	|/
> +	o H
> +	EOF
> +'
> +
> +test_expect_success 'local rebase.merges=false overrides global rebase.merges=true' '
> +	test_config_global rebase.merges true &&
> +	test_config rebase.merges false &&
> +	git checkout -b override-global-config E &&
> +	git rebase C &&
> +	test_cmp_graph C.. <<-\EOF
> +	* B
> +	* D
> +	o C
> +	EOF
> +'
> +
> +test_expect_success 'local rebase.merges="" does not override global rebase.merges=true' '
> +	test_config_global rebase.merges no-rebase-cousins &&
> +	test_config rebase.merges "" &&
> +	git checkout -b no-override-global-config E &&
> +	before="$(git rev-parse --verify HEAD)" &&
> +	test_tick &&
> +	git rebase C &&
> +	test_cmp_rev HEAD $before
> +'
> +

I understand the temptation to introduce exhaustive matrices that test all
the different settings in all the different ways they can be specified.

However, I would much prefer to keep the tests succinct, not the least to
avoid the every-increasing runtime of Git's CI. It's already taking about
an order of magnitude or two too long to be reasonable.

So I'd suggest reducing the tests to a single one instead of eight: verify
that `rebase.merges=no-rebase-cousins` is heeded, and that
`--no-rebase-cousins` overrides that. That should be plenty sufficient to
prevent regressions.

Ciao,
Johannes

>  test_expect_success 'refs/rewritten/* is worktree-local' '
>  	git worktree add wt &&
>  	cat >wt/script-from-scratch <<-\EOF &&
> --
> 2.39.2
>
>