[PATCH v4 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/2455043368

Changes in v4:
- Reword commit message: describe boolean support without mentioning
  internal function names, following Junio's suggestion.
- Add an in-code comment explaining why `mailmap.strdup_strings` can be
  used as the "already loaded" check in `load_mailmap()`.
- Drop local `value` variable in `parse_cmd_mailmap()` and assign
  directly to `use_mailmap`.
- Fix documentation syntax: place the closing backtick before `::`
  and break the description into a `;;` sub-list for `true`/`false`
  effects.
- Link to v3: https://lore.kernel.org/git/xmqqv7dyoei6.fsf@gitster.g/T/#m0a109f3eb5129e619ecec5f2d58ead0c5a49a4f3
- Link to v2: https://lore.kernel.org/git/xmqqv7dyoei6.fsf@gitster.g/T/#m445eab3b309bded92d1b130d225b882c73988ff2
- 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 |  12 +++++
 builtin/cat-file.c              |  37 ++++++++++++--
 t/t4203-mailmap.sh              | 105 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 150 insertions(+), 4 deletions(-)

Range-diff versus v3:

1:  dbc1a003a5 ! 1:  25ebffe39e cat-file: add mailmap subcommand to --batch-command
    @@ Commit message
         mailmap dynamically on an existing process.
     
         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.
    +    argument (usual ways you can specify a boolean value like 'yes', 'true',
    +    etc., are supported). 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.
    @@ 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 <bool>::
    -+	Enable or disable mailmap for subsequent commands.
    ++`mailmap (<bool>)`::
    ++	Enable or disable mailmap for subsequent commands. The `<bool>`
    ++	argument accepts the same boolean values as linkgit:git-config[1].
    ++	Possible effects are:
     ++
    -+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.
    ++`true`;;
    ++	Mailmap data is loaded on first use and kept in memory until the
    ++	process exits. Passing `true` again does not reload the data.
    ++`false`;;
    ++	Mailmap replacements are disabled for subsequent commands, but data
    ++	already loaded stays in memory.
      --
      +
      
    @@ builtin/cat-file.c: static int use_mailmap;
      
      static char *replace_idents_using_mailmap(char *, size_t *);
      
    ++/*
    ++ * The mailmap is initialized with .strdup_strings set to 0,
    ++ * but read_mailmap() sets the bit to 1 (this is true even when
    ++ * not a single mailmap entry is read), so it can be used for
    ++ * lazy loading.
    ++ */
     +static void load_mailmap(void)
     +{
     +	if (mailmap.strdup_strings)
    @@ builtin/cat-file.c: static void parse_cmd_info(struct batch_options *opt,
     +			      struct strbuf *output UNUSED,
     +			      struct expand_data *data UNUSED)
     +{
    -+	int value = git_parse_maybe_bool(line);
    ++	use_mailmap = git_parse_maybe_bool(line);
     +
    -+	if (value < 0)
    ++	if (use_mailmap < 0)
     +		die(_("mailmap: invalid boolean '%s'"), line);
     +
    -+	if (value > 0)
    ++	if (use_mailmap)
     +		load_mailmap();
    -+	use_mailmap = value;
     +}
     +
      static void dispatch_calls(struct batch_options *opt,

base-commit: 5361983c075154725be47b65cca9a2421789e410