[PATCH v4] [GSOC]trailer: pass arg as positional parameter

From: ZheNing Hu <adlternative@gmail.com>

The `trailer.<token>.command` configuration variable specifies a command (run via the shell, so it does not have to be a single name of or path to the command, but can be a shell script), and the first occurrence of substring $ARG is replaced with the value given to the `interpret-trailer` command for the token. This has two downsides:

* The use of $ARG in the mechanism misleads the users that
the value is passed in the shell variable, and tempt them
to use $ARG more than once, but that would not work, as
the second and subsequent $ARG are not replaced.

* Because $ARG is textually replaced without regard to the
shell language syntax, even '$ARG' (inside a single-quote
pair), which a user would expect to stay intact, would be
replaced, and worse, if the value had an unmatching single
quote (imagine a name like "O'Connor", substituted into
NAME='$ARG' to make it NAME='O'Connor), it would result in
a broken command that is not syntactically correct (or
worse).

Introduce a new `trailer.<token>.cmd` configuration that takes higher precedence to deprecate and eventually remove `trailer.<token>.command`, which passes the value as a parameter to the command. Instead of "$ARG", the users will refer to the value as positional argument, $1, in their scripts.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
    [GSOC]trailer: pass arg as positional parameter
    
    In https://lore.kernel.org/git/xmqqv99i4ck2.fsf@gitster.g/ Junio and
    Christian talked about the problem of using strbuf_replace() to replace
    $ARG.
    
    Now pass trailer value as $1 to the trailer command with another
    trailer.<token>.cmd config.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-913%2Fadlternative%2Ftrailer-pass-ARG-env-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-913/adlternative/trailer-pass-ARG-env-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/913

Range-diff vs v3:

 1:  b268ecd7b395 ! 1:  e2bbdcb943c2 [GSOC]trailer: pass arg as positional parameter
     @@ Metadata
       ## Commit message ##
          [GSOC]trailer: pass arg as positional parameter
      
     -    Original implementation of `trailer.<token>.command` use
     -    `strbuf_replace` to replace $ARG in command with the <value>
     -    of the trailer, but it have a problem: `strbuf_replace`
     -    replace the $ARG only once, If the user's trailer command
     -    have used more than one $ARG, the remaining replacement will
     -    fail.
     +    The `trailer.<token>.command` configuration variable
     +    specifies a command (run via the shell, so it does not have
     +    to be a single name of or path to the command, but can be a
     +    shell script), and the first occurrence of substring $ARG is
     +    replaced with the value given to the `interpret-trailer`
     +    command for the token.  This has two downsides:
      
     -    If directly modify the implementation of the original
     -    `trailer.<token>.command`, The user’s previous `'$ARG'` in
     -    trailer command will not be replaced. So now add new config
     -    "trailer.<token>.cmd", pass trailer's value as positional
     -    parameter 1 to the user's command, the user can use $1 as
     -    trailer's value, to implement original variable replacement.
     +    * The use of $ARG in the mechanism misleads the users that
     +    the value is passed in the shell variable, and tempt them
     +    to use $ARG more than once, but that would not work, as
     +    the second and subsequent $ARG are not replaced.
      
     -    If the user has these two configuration: "trailer.<token>.cmd"
     -    and "trailer.<token>.command", "cmd" will execute and "command"
     -    will not executed.
     +    * Because $ARG is textually replaced without regard to the
     +    shell language syntax, even '$ARG' (inside a single-quote
     +    pair), which a user would expect to stay intact, would be
     +    replaced, and worse, if the value had an unmatching single
     +    quote (imagine a name like "O'Connor", substituted into
     +    NAME='$ARG' to make it NAME='O'Connor), it would result in
     +    a broken command that is not syntactically correct (or
     +    worse).
      
     -    Original `trailer.<token>.command` can still be used until git
     -    completely abandoned it.
     +    Introduce a new `trailer.<token>.cmd` configuration that
     +    takes higher precedence to deprecate and eventually remove
     +    `trailer.<token>.command`, which passes the value as a
     +    parameter to the command.  Instead of "$ARG", the users will
     +    refer to the value as positional argument, $1, in their
     +    scripts.
      
     +    Helped-by: Junio C Hamano <gitster@pobox.com>
          Signed-off-by: ZheNing Hu <adlternative@gmail.com>
      
       ## Documentation/git-interpret-trailers.txt ##
     @@ Documentation/git-interpret-trailers.txt: also be executed for each of these arg
       the command.
       
      +trailer.<token>.cmd::
     -+	Similar to 'trailer.<token>.command'. But the difference is that
     -+	`$1` is used in the command to replace the value of the trailer
     -+	instead of the original `$ARG`, which means that we can pass the
     -+	trailer value multiple times in the command.
     -+	E.g. `git config trailer.sign.cmd "test -n \"$1\" && echo \"$1\" || true "`.
     -+	If the user has these two configuration: "trailer.<token>.cmd"
     -+	and "trailer.<token>.command", "cmd" will be executed and "command"
     -+	will not be executed.
     ++	The command specified by this configuration variable is run
     ++	with a single parameter, which is the <value> part of an
     ++	existing trailer with the same <token>.  The output from the
     ++	command is then used as the value for the <token> in the
     ++	resulting trailer.
     ++	The command is expected to replace `trailer.<token>.cmd`.
     ++	When both .cmd and .command are given for the same <token>,
     ++        .cmd is used and .command is ignored.
      +
       EXAMPLES
       --------
       
     +@@ Documentation/git-interpret-trailers.txt: $ git format-patch -1
     + $ git interpret-trailers --trailer 'Cc: Alice <alice@example.com>' --trailer 'Reviewed-by: Bob <bob@example.com>' 0001-foo.patch >0001-bar.patch
     + ------------
     + 
     +-* Configure a 'sign' trailer with a command to automatically add a
     ++* Configure a 'sign' trailer with a cmd to automatically add a
     +   'Signed-off-by: ' with the author information only if there is no
     +   'Signed-off-by: ' already, and show how it works:
     + +
     +@@ Documentation/git-interpret-trailers.txt: $ git interpret-trailers --trailer 'Cc: Alice <alice@example.com>' --trailer 'Re
     + $ git config trailer.sign.key "Signed-off-by: "
     + $ git config trailer.sign.ifmissing add
     + $ git config trailer.sign.ifexists doNothing
     +-$ git config trailer.sign.command 'echo "$(git config user.name) <$(git config user.email)>"'
     ++$ git config trailer.sign.cmd 'echo "$(git config user.name) <$(git config user.email)>"'
     + $ git interpret-trailers <<EOF
     + > EOF
     + 
     +@@ Documentation/git-interpret-trailers.txt: subject
     + Fix #42
     + ------------
     + 
     +-* Configure a 'see' trailer with a command to show the subject of a
     ++* Configure a 'see' trailer with a cmd to show the subject of a
     +   commit that is related, and show how it works:
     + +
     + ------------
     + $ git config trailer.see.key "See-also: "
     + $ git config trailer.see.ifExists "replace"
     + $ git config trailer.see.ifMissing "doNothing"
     +-$ git config trailer.see.command "git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \$ARG"
     ++$ git config trailer.see.cmd "test -n \"\$1\" && git log -1 --oneline --format=\"%h (%s)\" --abbrev-commit --abbrev=14 \"\$1\"|| true "
     + $ git interpret-trailers <<EOF
     + > subject
     + > 
      
       ## t/t7513-interpret-trailers.sh ##
      @@ t/t7513-interpret-trailers.sh: test_expect_success 'setup a commit' '
     @@ trailer.c: static int check_if_different(struct trailer_item *in_tok,
       }
       
      -static char *apply_command(const char *command, const char *arg)
     -+static char *apply_command(const char *command, const char *cmd_, const char *arg)
     ++static char *apply_command(struct conf_info *conf, const char *arg)
       {
       	struct strbuf cmd = STRBUF_INIT;
       	struct strbuf buf = STRBUF_INIT;
     @@ trailer.c: static int check_if_different(struct trailer_item *in_tok,
      -		strbuf_replace(&cmd, TRAILER_ARG_STRING, arg);
      -
      -	strvec_push(&cp.args, cmd.buf);
     -+	if (cmd_) {
     -+		strbuf_addstr(&cmd, cmd_);
     ++	if (conf->cmd) {
     ++		strbuf_addstr(&cmd, conf->cmd);
      +		strvec_push(&cp.args, cmd.buf);
      +		if (arg)
      +			strvec_push(&cp.args, arg);
     -+	} else if (command) {
     -+		strbuf_addstr(&cmd, command);
     ++	} else if (conf->command) {
     ++		strbuf_addstr(&cmd, conf->command);
      +		strvec_push(&cp.args, cmd.buf);
      +		if (arg)
      +			strbuf_replace(&cmd, TRAILER_ARG_STRING, arg);
     @@ trailer.c: static void apply_item_command(struct trailer_item *in_tok, struct ar
       				arg = xstrdup("");
       		}
      -		arg_tok->value = apply_command(arg_tok->conf.command, arg);
     -+		arg_tok->value = apply_command(arg_tok->conf.command, arg_tok->conf.cmd, arg);
     ++		arg_tok->value = apply_command(&arg_tok->conf, arg);
       		free((char *)arg);
       	}
       }

 Documentation/git-interpret-trailers.txt | 18 +++++++---
 t/t7513-interpret-trailers.sh            | 43 +++++++++++++++++++++++-
 trailer.c                                | 37 ++++++++++++++------
 3 files changed, 82 insertions(+), 16 deletions(-)