[PATCH v3 0/1] cat-file: add mailmap subcommand to --batch-command

git-cat-file(1)'s --batch-command works with the --use-mailmap option, but this option needs to be set when the process is created. This means we cannot change this option mid-operation.

At GitLab, Gitaly keeps interacting with a long-lived git-cat-file process and it would be useful if --batch-command supported toggling mailmap dynamically on an existing process.

This patch adds a `mailmap` subcommand to --batch-command that accepts a boolean argument and toggles mailmap dynamically for subsequent commands.

The series is based on top of 5361983c07 (The 22nd batch, 2026-03-21).

CI: https://gitlab.com/gitlab-org/git/-/pipelines/2419600519

Changes in v3:
- Use "keeps interacting with a long-lived git-cat-file process" wording
  in the commit message and cover letter.
- Drop the `Suggested-by` trailer.
- Avoid style-only churn in the `commands[]` table by keeping existing
  initializer style and only adding the new command entry.
- Introduce a `load_mailmap()` helper used by both startup and
  `parse_cmd_mailmap()`.
- Parse `mailmap <bool>` using `git_parse_maybe_bool()` instead of
  handling only `yes`/`no`.
- Update docs to describe `mailmap <bool>` and reference Git's boolean
  syntax from `git-config(1)`.
- Add tests for startup option interaction (`--mailmap`/`--no-mailmap`),
  accepted boolean values (`true`/`false`), and invalid boolean input.
- Link to v2: https://public-inbox.org/git/20260329082804.53400-1-siddharthasthana31@gmail.com/
- Link to v1: https://public-inbox.org/git/a4ec7bfa-f16b-4505-9b37-d3dd137e93cb@gmail.com/T/#m5c62fb6ad0fbcc99a706dba4c78b66359c247acd

Thanks, Siddharth

---
Siddharth Asthana (1):
  cat-file: add mailmap subcommand to --batch-command

 Documentation/git-cat-file.adoc |   7 +++
 builtin/cat-file.c              |  32 ++++++++++--
 t/t4203-mailmap.sh              | 105 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 140 insertions(+), 4 deletions(-)

Range-diff versus v2:

1:  936ca27419 ! 1:  df446d7ca3 cat-file: add mailmap subcommand to --batch-command
    @@ Commit message
         but this option needs to be set when the process is created. This means
         we cannot change this option mid-operation.
     
    -    At GitLab, Gitaly caches git-cat-file processes and it would be useful
    -    if --batch-command supported toggling mailmap dynamically with existing
    -    processes.
    +    At GitLab, Gitaly keeps interacting with a long-lived git-cat-file
    +    process and it would be useful if --batch-command supported toggling
    +    mailmap dynamically on an existing process.
     
    -    Add a `mailmap` subcommand to --batch-command that takes a single
    -    argument: `yes` to enable mailmap and `no` to disable it. When enabled,
    -    mailmap data is loaded from disk on first use and kept in memory so that
    -    toggling back on does not require reloading.
    +    Add a `mailmap` subcommand to --batch-command that takes a boolean
    +    argument. The command now uses `git_parse_maybe_bool()` and supports all
    +    standard Git boolean values. Mailmap data is loaded lazily and kept in
    +    memory, while a helper centralizes the one-time load path used both at
    +    startup and from the batch-command handler.
    +
    +    Extend tests to cover runtime toggling, startup option interactions
    +    (`--mailmap`/`--no-mailmap`), accepted boolean forms, and invalid values.
     
    -    Suggested-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Siddharth Asthana <siddharthasthana31@gmail.com>
     
      ## Documentation/git-cat-file.adoc ##
    @@ Documentation/git-cat-file.adoc: flush::
      	is used, no output will come until a `flush` is issued. When `--buffer`
      	is not used, commands are flushed each time without issuing `flush`.
     +
    -+mailmap <yes|no>::
    -+	Enable or disable mailmap for subsequent `contents` and `info`
    -+	commands. When `yes` is given, mailmap data is loaded from disk on
    -+	first use and kept in memory; passing `yes` again does not reload it.
    -+	When `no` is given, mailmap is disabled but the data stays in memory
    -+	so that a later `mailmap yes` does not need to reload it from disk.
    ++mailmap <bool>::
    ++	Enable or disable mailmap for subsequent commands.
    +++
    ++The `<bool>` argument accepts the same boolean values as
    ++linkgit:git-config[1]. When enabled, mailmap data is loaded on first
    ++use and kept in memory until the process exits.
      --
     
      ## builtin/cat-file.c ##
    +@@ builtin/cat-file.c: static int use_mailmap;
     +
     +static void load_mailmap(void)
     +{
     +	if (mailmap.strdup_strings)
     +		return;
     +
     +	read_mailmap(the_repository, &mailmap);
     +}
     +
     @@ builtin/cat-file.c: static void parse_cmd_info(struct batch_options *opt,
      	batch_one_object(line, output, opt, data);
      }
    @@ builtin/cat-file.c: static void parse_cmd_info(struct batch_options *opt,
     +{
    -+	if (!strcmp(line, "yes")) {
    -+		if (!mailmap_loaded) {
    -+			read_mailmap(the_repository, &mailmap);
    -+			mailmap_loaded = 1;
    -+		}
    -+		use_mailmap = 1;
    -+	} else if (!strcmp(line, "no")) {
    -+		use_mailmap = 0;
    -+	} else {
    -+		die(_("mailmap: unknown argument '%s', expected 'yes' or 'no'"), line);
    -+	}
    ++	int value = git_parse_maybe_bool(line);
    ++
    ++	if (value < 0)
    ++		die(_("mailmap: invalid boolean '%s'"), line);
    ++
    ++	if (value > 0)
    ++		load_mailmap();
    ++	use_mailmap = value;
     +}
     +
    @@ builtin/cat-file.c: static const struct parse_cmd {
    -+	{ "use-mailmap", parse_cmd_use_mailmap, 0 },
    -+	{ "no-use-mailmap", parse_cmd_disable_mailmap, 0 },
    ++	{ "mailmap", parse_cmd_mailmap, 1 },
     +};
     
     @@ builtin/cat-file.c: int cmd_cat_file(int argc,
      	if (use_mailmap)
    -+		read_mailmap(the_repository, &mailmap);
    ++		load_mailmap();

base-commit: 5361983c075154725be47b65cca9a2421789e410