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

>
> On Mon, Mar 29, 2021 at 3:44 PM ZheNing Hu <adlternative@gmail.com> wrote:
> >
> > Christian Couder <christian.couder@gmail.com> 于2021年3月29日周一 下午5:05写道：
> > >
> > > >
> > > > Yes, $ARG or $1 are always exist because of:
> > > >
> > > >                arg = xstrdup("");
> > > >
> > > > so I think maybe we don't even need this judge in `apply_command`?
> > > > +               if (arg)
> > > > +                       strvec_push(&cp.args, arg);
> > >
> > > Yeah, I haven't looked at the code, but that might be a good
> > > simplification. If you work on this, please submit it in a separate
> > > commit.
> >
> > Well, if necessary, I'll put it in another commit, maybe I should double check
> > to see if there's anything special going on.
> >
> > > > > Another way to do it would be to have another config option called
> > > > > `trailer.<token>.alwaysRunCmd` to tell if the cmd specified by
> > > > > `trailer.<token>.cmd` should be run even if no '<token>=<value>'
> > > > > argument is passed on the command line. As we are introducing
> > > > > `trailer.<token>.cmd`, it's a good time to wonder if this would be a
> > > > > better design. But this issue is quite complex, because of the fact
> > > > > that 'trailer.<token>.ifMissing' and 'trailer.<token>.ifExists' also
> > > > > take a part in deciding if the command will be run.
> > >
> > > Actually after thinking about it, I think it might be better, instead
> > > of `trailer.<token>.alwaysRunCmd`, to add something like
> > > `trailer.<token>.runMode` that could take multiple values like:
> >
> > If really can achieve it is certainly better than 'alwaysRunCmd'.
> > The following three small configuration options look delicious.
> > But I think it needs to be discussed in more detail:
> >
> > > - "beforeCLI": would make it run once, like ".command" does now before
> > > any CLI trailer are processed
> >
> > Does "beforeCLI" handle all trailers? Or is it just doing something to add empty
> > value trailers?
>
> I am not sure what you mean by "handle all trailers". What I mean is
> that it would just work like ".command" does right now before the
> "--trailers ..." options are processed.
>
> Let's suppose the "trailer.foo.command" config option is set to "bar".
> Then the "bar" command will be run just before the "--trailers ..."
> options are processed and the output of that, let's say "baz" will be
> used to add a new "foo: baz" trailer to the ouput of `git
> interpret-trailers`.
>
> For example:
>
> -------
> $ git -c trailer.foo.command='echo baz' interpret-trailers<<EOF
> EOF
>
> foo: baz
> -------
>
> In other words an empty value trailer is just a special case when the
> command that is run does not output anything. But such commands are
> expected to output something not trivial at least in some cases.
>
> See also the example in the doc that uses:
>
> $ git config trailer.sign.command 'echo "$(git config user.name)
> <$(git config user.email)>"'
>

> > > - "forEachCLIToken": would make it run once for each trailer that has
> > > the token, like ".command" also does now, the difference would be that
> > > the value for the token would be passed in the $1 argument
> >
> > This is exactly same as before.
>
> Yeah it is the same as before when the "--trailers ..." options are
> processed, but not before that.
>
> To get exactly the same as before one would need to configure both
> "beforeCLI" _and_ "forEachCLIToken", for example like this (note that
> we use "--add" when adding "forEachCLIToken"):
>
> $ git config trailer.foo.runMode beforeCLI
> $ git config --add trailer.foo.runMode forEachCLIToken
> $ git config -l | grep foo
> trailer.foo.runmode=beforeCLI
> trailer.foo.runmode=forEachCLIToken
>
> > > - "afterCLI": would make it run once after all the CLI trailers have
> > > been processed and it could pass the different values for the token if
> > > any in different arguments: $1, $2, $3, ...
> >
> > I might get a little confused here: What's the input for $1,$2,$3?
>
> The input would be the different values that are used for the token in
> the "--trailer ..." CLI arguments.
>
> For (an hypothetical) example:
>
> ------
> $ git config trailer.foo.runMode afterCLI
> $ git config trailer.foo.cmd 'echo $@'
> $ git interpret-trailers --trailer foo=a --trailer foo=b --trailer foo=c<<EOF
> EOF
>
> foo: a b c
> $ git interpret-trailers<<EOF
> EOF
>
> foo:
> ------
>
> I am not sure "afterCLI" would be useful, but we might not want to
> implement it right now. It's just an example to show that we could add
> other modes to run the configured ".cmd" (and maybe ".command" too).
>

> > Is users more interested in dealing with trailers value or a line of the
> > trailer?
>
> I am not sure what you mean here. If "a line of the trailer" means a
> trailer that is already in the input file that is passed to `git
> interpret-trailers`, and if "trailers value" means a "--trailer ..."
> argument, then I would say that users could be interested in dealing
> with both.
>

> It's true that right now the command configured by a ".command" is not
> run when `git interpret-trailers` processes in input file that
> contains a trailer with the corresponding token. So new values for
> ".runMode" could be implemented to make that happen.
>

> > > > But as you said, to disable the automatic addition in the original .command
> > > > and use the new .alwaysRunCmd, I’m afraid there are a lot of things to consider.
> > > > Perhaps future series of patches can be considered to do it.
> > >
> > > Yeah, support for `trailer.<token>.runMode` might be added in
> > > different commits at least and possibly later in a different patch
> > > series. There are the following issues to resolve, though, if we want
> > > to focus only on a new ".cmd" config option:
> > >
> > > - how and when should it run by default,
> >
> > Do you mean that ".cmd" can get rid of the ".command" auto-add problem
> > in this patch series?
>
> I am not sure what you mean with "auto-add". Do you mean that fact
> that the ".command" runs once before the CLI "--trailer ..." options
> are processed?
>

> > This might be a good idea if I can add the three modes you mentioned above
> > in the later patch series.
>
> I like that your are interested in improving trailer handling in Git,
> but I must say that if you intend to apply for the GSoC, you might
> want to work on your application document first, as it will need to be
> discussed on the mailing list too and it will take some time. You are
> also free to work on this too, but that shouldn't be your priority.
>

> By the way if this (or another Git related) subject is more
> interesting to you than the project ideas we propose on
> https://git.github.io/SoC-2021-Ideas/, then you are welcome to write a
> proposal about working on this (improving trailer handling) rather
> than on a project idea from that page. You might want to make sure
> that some people would be willing to (co-)mentor you working on it
> though.
>

> [...]
>
> > > Another way to work on all this, would be to first work on adding
> > > support for `trailer.<token>.runMode` and on improving existing
> > > documentation, and then to add ".cmd", which could then by default use
> > > a different ".runMode" than ".command".
> >
> > I think the task can be put off until April.
> > Deal with the easier ".cmd" first.
>
> Ok for me, but see above about GSoC application.
>
>
> > > > > > This, too, but until ".command" is removed, wouldn't it be better
> > > > > > for readers to keep both variants, as the distinction between $ARG
> > > > > > and $1 needs to be illustrated?
> > > >
> > > > So the correct solution should be to keep the original .command Examples,
> > > > and then give the .cmd examples again.
> > >
> > > Maybe we could take advantage of ".cmd" to show other nice
> > > possibilities to use all of this. Especially if support for `git
> > > commit --trailer ...` is already merged, we might be able to use it in
> > > those examples, or perhaps add some examples to the git commit doc.
> >
> > Oh, the 'commit --trailer' may still be queuing, It may take a while.
>
> You might want to check if it needs another reroll or if there are
> other reasons (like no reviews) why it's not listed in the last
> "What's cooking ..." email from Junio. If you think it is ready and
> has been forgotten, you can ping reviewers (including me), to ask them
> to review it one more time, or Junio if the last version you sent has
> already been reviewed.