[PATCH v5 0/3] builtin/tag.c: add --trailer option

5th follow-up patch taking welcome feedback from Patrick and JCH. Net new changes include suggested tweaks in documentation, error messaging, code formatting, and patch description.

Since git-tag --list --format="%(trailers)" can interpret trailers from annotated tag messages, it seems natural to support --trailer when writing a new tag message.

git-commit accomplishes this by taking --trailer arguments and passing them to git-interpret-trailer. This patch series refactors that logic and uses it to implement --trailer on git-tag.

John Passaro (3):
  builtin/commit: use ARGV macro to collect trailers
  builtin/commit: refactor --trailer logic
  builtin/tag: add --trailer option

 Documentation/git-tag.txt |  16 +++++-
 builtin/commit.c          |  20 +------
 builtin/tag.c             |  38 ++++++++++---
 t/t7004-tag.sh            | 114 ++++++++++++++++++++++++++++++++++++++
 trailer.c                 |  12 ++++
 trailer.h                 |   9 +++
 6 files changed, 181 insertions(+), 28 deletions(-)

base-commit: d4cc1ec35f3bcce816b69986ca41943f6ce21377
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1723%2Fjpassaro%2Fjp%2Ftag-trailer-arg-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1723/jpassaro/jp/tag-trailer-arg-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/1723

Range-diff vs v4:

 1:  ce047c58aa8 ! 1:  85f45a57f35 builtin/commit.c: remove bespoke option callback
     @@ Metadata
      Author: John Passaro <john.a.passaro@gmail.com>
      
       ## Commit message ##
     -    builtin/commit.c: remove bespoke option callback
     +    builtin/commit: use ARGV macro to collect trailers
      
     -    Replace git-commit's bespoke callback for --trailer with the standard
     -    OPT_PASSTHRU_ARGV macro. The bespoke callback was only adding its values
     -    to a strvec and sanity-checking that `unset` is always false; both of
     -    these are already implemented in the parse-option API.
     +    Replace git-commit's callback for --trailer with the standard
     +    OPT_PASSTHRU_ARGV macro. The callback only adds its values to a strvec
     +    and sanity-checking that `unset` is always false; both of these are
     +    already implemented in the parse-option API.
      
          Signed-off-by: John Passaro <john.a.passaro@gmail.com>
      
 2:  8f53a54bbfe ! 2:  75bb5cc0e8a builtin/commit.c: refactor --trailer logic
     @@ Metadata
      Author: John Passaro <john.a.passaro@gmail.com>
      
       ## Commit message ##
     -    builtin/commit.c: refactor --trailer logic
     +    builtin/commit: refactor --trailer logic
      
          git-commit adds user trailers to the commit message by passing its
          `--trailer` arguments to a child process running `git-interpret-trailers
     @@ trailer.c: void trailer_iterator_release(struct trailer_iterator *iter)
       	strbuf_release(&iter->key);
       }
      +
     -+int amend_file_with_trailers(const char *path, const struct strvec *trailer_args) {
     ++int amend_file_with_trailers(const char *path, const struct strvec *trailer_args)
     ++{
      +	struct child_process run_trailer = CHILD_PROCESS_INIT;
      +
      +	run_trailer.git_cmd = 1;
 3:  f1d68337eda ! 3:  d8b3f6229bc builtin/tag.c: add --trailer option
     @@ Metadata
      Author: John Passaro <john.a.passaro@gmail.com>
      
       ## Commit message ##
     -    builtin/tag.c: add --trailer option
     +    builtin/tag: add --trailer option
      
     -    git-tag currently supports interpreting trailers from an annotated tag
     -    message, using --list --format="%(trailers)". However, to add a trailer
     -    to a tag message, you must do so using `-F` or by editing the message.
     +    git-tag supports interpreting trailers from an annotated tag message,
     +    using --list --format="%(trailers)". However, the available methods to
     +    add a trailer to a tag message (namely -F or --editor) are not as
     +    ergonomic.
      
          In a previous patch, we moved git-commit's implementation of its
          --trailer option to the trailer.h API. Let's use that new function to
     @@ Documentation/git-tag.txt: This option is only applicable when listing tags with
       
      +--trailer <token>[(=|:)<value>]::
      +	Specify a (<token>, <value>) pair that should be applied as a
     -+	trailer. (e.g. `git tag --trailer "Signed-off-by:T A Ger \
     -+	<tagger@example.com>" --trailer "Helped-by:C O Mitter \
     -+	<committer@example.com>"` will add the "Signed-off-by" trailer
     -+	and the "Helped-by" trailer to the tag message.)
     ++	trailer. (e.g. `git tag --trailer "Custom-Key: value"`
     ++	will add a "Custom-Key" trailer to the tag message.)
      +	The `trailer.*` configuration variables
      +	(linkgit:git-interpret-trailers[1]) can be used to define if
      +	a duplicated trailer is omitted, where in the run of trailers
      +	each trailer would appear, and other details.
     -+	The trailers can be seen in `git tag --list` using
     ++	The trailers can be extracted in `git tag --list`, using
      +	`--format="%(trailers)"` placeholder.
      +
       -e::
     @@ builtin/tag.c: static void create_tag(const struct object_id *object, const char
      +			}
      +		} else if (trailer_args->nr) {
      +			strbuf_reset(buf);
     -+			if (strbuf_read_file(buf, path, 0) < 0) {
     -+				fprintf(stderr,
     -+					_("Please supply the message using either -m or -F option.\n"));
     -+				exit(1);
     -+			}
     ++			if (strbuf_read_file(buf, path, 0) < 0)
     ++				die_errno(_("failed to read '%s'"), path);
       		}
       	}