Re: [PATCH 1/3] merge: allow reading the merge commit message from a file

[Junio C Hamano <gitster@pobox.com>]

"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> This is consistent with `git commit` which, like `git merge`, supports
> passing the commit message via `-m <msg>` and, unlike `git merge` before
> this patch, via `-F <file>`.
>
> It is useful to allow this for scripted use, or for the upcoming patch
> to allow (re-)creating octopus merges in `git rebase --rebase-merges`.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  Documentation/git-merge.txt | 10 +++++++++-
>  builtin/merge.c             | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/git-merge.txt b/Documentation/git-merge.txt
> index 6a5c00e2c..537dca7fa 100644
> --- a/Documentation/git-merge.txt
> +++ b/Documentation/git-merge.txt
> @@ -12,7 +12,7 @@ SYNOPSIS
>  'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
>  	[-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
>  	[--[no-]allow-unrelated-histories]
> -	[--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
> +	[--[no-]rerere-autoupdate] [-m <msg>] [-F <file>] [<commit>...]
>  'git merge' --abort
>  'git merge' --continue
>  
> @@ -75,6 +75,14 @@ The 'git fmt-merge-msg' command can be
>  used to give a good default for automated 'git merge'
>  invocations. The automated message can include the branch description.
>  
> +-F <file>::
> +--file=<file>::
> +	Read the commit message to be used for the merge commit (in
> +	case one is created).
> ++
> +If `--log` is specified, a shortlog of the commits being merged
> +will be appended to the specified message.
> +
>  --[no-]rerere-autoupdate::
>  	Allow the rerere mechanism to update the index with the
>  	result of auto-conflict resolution if possible.
> diff --git a/builtin/merge.c b/builtin/merge.c
> index 4a4c09496..b0e907751 100644
> --- a/builtin/merge.c
> +++ b/builtin/merge.c
> @@ -111,6 +111,35 @@ static int option_parse_message(const struct option *opt,
>  	return 0;
>  }
>  
> +static int option_read_message(struct parse_opt_ctx_t *ctx,
> +			       const struct option *opt, int unset)
> +{
> +	struct strbuf *buf = opt->value;
> +	const char *arg;
> +
> +	if (unset)
> +		BUG("-F cannot be negated");

The message "-F cannot be negated" looks as if it is pointing out a
mistake by the end user, and does not mesh well with the real reason
why this is BUG() and is not die().

I understand that this is BUG() not die() because options[] array
tells this callback not to be called with unset by having the
PARSE_OPT_NONEG bit there.

> +	if (ctx->opt) {
> +		arg = ctx->opt;
> +		ctx->opt = NULL;
> +	} else if (ctx->argc > 1) {
> +		ctx->argc--;
> +		arg = *++ctx->argv;
> +	} else
> +		return opterror(opt, "requires a value", 0);
> +
> +	if (buf->len)
> +		strbuf_addch(buf, '\n');

Do we assume that buf, if it is not empty, is properly terminated
with LF already?  I am wondering if the real reason we do these two
lines is to make sure we have a separating blank line between what
is already there (if there already is something) and what we add, in
which case the above would want to say

	if (buf->len) {
		strbuf_complete_line(buf);
		strbuf_addch(buf, '\n');
	}

instead.

> +	if (ctx->prefix && !is_absolute_path(arg))
> +		arg = prefix_filename(ctx->prefix, arg);
> +	if (strbuf_read_file(buf, arg, 0) < 0)
> +		return error(_("could not read file '%s'"), arg);
> +	have_message = 1;

A similar question is what we would want to do when the file ends
with an incomplete line.  With "--log", we would be appending more
stuff to buf, and we'd want to complete such an incomplete line
before that happens, either here or in the code immediately before
"--log" is processed.

> +
> +	return 0;
> +}
> +
>  static struct strategy *get_strategy(const char *name)
>  {
>  	int i;
> @@ -228,6 +257,9 @@ static struct option builtin_merge_options[] = {
>  	OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
>  		N_("merge commit message (for a non-fast-forward merge)"),
>  		option_parse_message),
> +	{ OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
> +		N_("read message from file"), PARSE_OPT_NONEG,
> +		(parse_opt_cb *) option_read_message },
>  	OPT__VERBOSITY(&verbosity),
>  	OPT_BOOL(0, "abort", &abort_current_merge,
>  		N_("abort the current in-progress merge")),