[PATCH v2 0/3] Support :(optional) filepaths

Notes:
- Based on commit 2da08f2c3d (parseopt: values of pathname type can be
  prefixed with :(optional), 2024-10-14) (broken-out/wip/optional-path)
- Rebased on v2.51.0
- I'm least sure of the 3rd patch and am happy to drop it in support of
  the first 2. I think it might be better to (a) integrate :(optional)
  support as pathspec magic and (b) use pathspec magic in parse-options
  when getting filenames. But I'm not sure, and this has other
  ramifications I'm not prepared to deal with. (For example: `git grep
  path <file>… :(optional)non-existent` could pretend like
  `non-existent` was never given?)
- The parsing is not exactly a "clean API," but I wasn't sure how to
  make it cleaner :)

Changes in v2:
- Only check for missing files, not empty files
- Move a test change to the appropriate commit
- Document optional magic in options in gitcli(1)

This series adds support for optional filepaths in config and parse-options, which supports use-cases such as missing commit templates or blame.ignoreRevsFile values without erroring.

v1: https://lore.kernel.org/git/20250501214057.371711-1-gitster@pobox.com/

Junio C Hamano (3):
  t7500: make each piece more independent
  config: values of pathname type can be prefixed with :(optional)
  parseopt: values of pathname type can be prefixed with :(optional)

 Documentation/config.adoc                 |  4 ++-
 Documentation/gitcli.adoc                 | 14 +++++++++
 config.c                                  | 16 +++++++++--
 parse-options.c                           | 31 +++++++++++++-------
 t/t7500-commit-template-squash-signoff.sh | 35 +++++++++++++++++------
 wrapper.c                                 | 13 +++++++++
 wrapper.h                                 |  4 ++-
 7 files changed, 94 insertions(+), 23 deletions(-)

Diff-intervalle contre v1 :
1:  82d283c626 ! 1:  63b2b24d42 t7500: make each piece more independent
    @@ Commit message
         Signed-off-by: Taylor Blau <me@ttaylorr.com>
     
      ## t/t7500-commit-template-squash-signoff.sh ##
    +@@ t/t7500-commit-template-squash-signoff.sh: commit_msg_is ()
    + 	(
    + 		GIT_EDITOR="echo hello >\"\$1\"" &&
    + 		export GIT_EDITOR &&
    +-		test_must_fail git commit
    ++		test_must_fail git commit --allow-empty
    + 	)
    + '
    + 
     @@ t/t7500-commit-template-squash-signoff.sh: commit_msg_is ()
      TEMPLATE="$PWD"/template
      
2:  dbafaff13b ! 2:  5c97f580a9 config: values of pathname type can be prefixed with :(optional)
    @@ Commit message
         pathname wants to signal such an optional file, it can be marked by
         prepending ":(optional)" in front of it.  Such a setting that is
         marked optional would avoid getting the command barf for a missing
    -    file, as an optional configuration setting that names a missing or
    -    an empty file is not even seen.
    +    file, as an optional configuration setting that names a missing
    +    file is not even seen.
     
         cf. <xmqq5ywehb69.fsf@gitster.g>
     
         Signed-off-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Taylor Blau <me@ttaylorr.com>
     
    - ## Documentation/config.txt ##
    -@@ Documentation/config.txt: compiled without runtime prefix support, the compiled-in prefix will be
    +
    + ## Notes ##
    +    The 2nd paragraph in this commit is wrapped strangely
    +
    +    I've kept the strange wrapping length for now, but can reflow it if
    +    desired.
    +
    + ## Documentation/config.adoc ##
    +@@ Documentation/config.adoc: compiled without runtime prefix support, the compiled-in prefix will be
      substituted instead. In the unlikely event that a literal path needs to
      be specified that should _not_ be expanded, it needs to be prefixed by
      `./`, like so: `./%(prefix)/bin`.
     -
     ++
     +If prefixed with `:(optional)`, the configuration variable is treated
    -+as if it does not exist, if the named path does not exist or names an
    -+empty file.
    ++as if it does not exist, if the named path does not exist.
      
      Variables
      ~~~~~~~~~
    @@ config.c: int git_config_string(char **dest, const char *var, const char *value)
     +	if (!path)
      		die(_("failed to expand user dir in: '%s'"), value);
     +
    -+	if (is_optional && is_empty_or_missing_file(path)) {
    ++	if (is_optional && is_missing_file(path)) {
     +		free(path);
     +		return 0;
     +	}
    @@ t/t7500-commit-template-squash-signoff.sh: commit_msg_is ()
      # From now on we'll use a template file that exists.
      TEMPLATE="$PWD"/template
      
    +
    + ## wrapper.c ##
    +@@ wrapper.c: int xgethostname(char *buf, size_t len)
    + 	return ret;
    + }
    + 
    ++int is_missing_file(const char *filename)
    ++{
    ++	struct stat st;
    ++
    ++	if (stat(filename, &st) < 0) {
    ++		if (errno == ENOENT)
    ++			return 1;
    ++		die_errno(_("could not stat %s"), filename);
    ++	}
    ++
    ++	return 0;
    ++}
    ++
    + int is_empty_or_missing_file(const char *filename)
    + {
    + 	struct stat st;
    +
    + ## wrapper.h ##
    +@@ wrapper.h: void write_file_buf(const char *path, const char *buf, size_t len);
    + __attribute__((format (printf, 2, 3)))
    + void write_file(const char *path, const char *fmt, ...);
    + 
    +-/* Return 1 if the file is empty or does not exists, 0 otherwise. */
    ++/* Return 1 if the file does not exist, 0 otherwise. */
    ++int is_missing_file(const char *filename);
    ++/* Return 1 if the file is empty or does not exist, 0 otherwise. */
    + int is_empty_or_missing_file(const char *filename);
    + 
    + enum fsync_action {
3:  2da08f2c3d ! 3:  5f7057c236 parseopt: values of pathname type can be prefixed with :(optional)
    @@ Commit message
         Signed-off-by: Junio C Hamano <gitster@pobox.com>
         Signed-off-by: Taylor Blau <me@ttaylorr.com>
     
    + ## Documentation/gitcli.adoc ##
    +@@ Documentation/gitcli.adoc: $ git describe --abbrev=10 HEAD  # correct
    + $ git describe --abbrev 10 HEAD  # NOT WHAT YOU MEANT
    + ----------------------------
    + 
    ++
    ++Magic filename options
    ++~~~~~~~~~~~~~~~~~~~~~~
    ++Options that take a filename allow a prefix `:(optional)`. For example:
    ++
    ++----------------------------
    ++git commit -F :(optional)COMMIT_EDITMSG
    ++# if COMMIT_EDITMSG does not exist, equivalent to
    ++git commit
    ++----------------------------
    ++
    ++Like with configuration values, if the named file is missing Git behaves as if
    ++the option was not given at all. See "Values" in linkgit:git-config[1].
    ++
    + NOTES ON FREQUENTLY CONFUSED OPTIONS
    + ------------------------------------
    + 
    +
      ## parse-options.c ##
     @@ parse-options.c: static enum parse_opt_result do_get_value(struct parse_opt_ctx_t *p,
      {
    - 	const char *s, *arg;
    + 	const char *arg;
      	const int unset = flags & OPT_UNSET;
     -	int err;
      
    @@ t/t7500-commit-template-squash-signoff.sh: commit_msg_is ()
      test_expect_success 'nonexistent template file in config should return error' '
      	test_config commit.template "$PWD"/notexist &&
      	(
    - 		GIT_EDITOR="echo hello >\"\$1\"" &&
    - 		export GIT_EDITOR &&
    --		test_must_fail git commit
    -+		test_must_fail git commit --allow-empty
    - 	)
    - '
    - 

base-commit: c44beea485f0f2feaf460e2ac87fdd5608d63cf0