proposal: read arguments from a file

[nodirt]

Proposal:

Add DefaultApplication.AllowArgsInFIle or something like that (name suggestions are welcome). If true

• extra text is printed in usage that subcommand and its arguments can be passed through a file
• if first argument starts with @, treat the rest of the argument as a path to the file that contains command line arguments. There must be no other arguments besides @file.

This is needed on Windows where the command line length limit is low.

@maruel @vadimsht

[danjacques]

What format do you think we should use? In other applications, we've used JSON w/ a top-level list of strings. It's nice b/c it has editor support and built-in parsing, but it is a bit overkill for args :)

[nodirt]

I kind of forgot that it is the shell that splits a string to args. Yeah I guess JSON array could work.

[maruel]

run_isolated.py was changed last week to support this, but via a flag.

[nodirt]

looks like run_isolated.py uses -a luci/luci-py@b57b137#diff-6d1960f366ecaec9365dfdd290ae8d6fR397

We discussed this with @danjacques offline and think that we should also add a flag (off by default) to print the contents of the file.

Overall I am thinking of changing the proposal a bit. Instead of adding special @ syntax, add CmdFromFile global variable that is a subcommand and has flag -print-command. I don't know how this command should be called, no good name comes to mind. Ideas?

In that case opt-in would be inclusion of CmdFromFile to list of application commands. This is consistent with CmdHelp.

[maruel]

I don't mind either way, I'm fine with @ syntax. Whatever that works.

[nodirt]

@danjacques says that since this runs another subcommand, it has to be more special that a "subcommand" concept and thus @ or flag -a or -subcommand-argument-file is better than CmdFromFile. -subcommand-argument-file is a bit long to me, so I return to preferring @file or @file -print-command

Help could look like

MyApp

Usage: myapp [command] [arguments]
       myapp @filename [-print-command]

@filename is path to a file that contains a JSON array with command and its arguments.
If -print-command is specified, the the command in @filename is printed to stdout.

Commands:
  mysubcommand

Use "myapp help [command]" for more information about the command.

This looks simple enough to me