Allow specifying user command-line arguments in an order-independent manner

[Calinou]

Describe the project you are working on

The Godot editor 🙂

Describe the problem or limitation you are having in your project

There are two types of command line arguments supported by Godot:

• Engine command line arguments such as -e and --fullscreen. These can be read using OS.get_cmdline_args(), which does not return user command line arguments.
• User command line arguments, which are specified after -- or ++. These can be read using OS.get_cmdline_user_args(), which does not return engine command line arguments.

See #2797 for context on why this separation was made in 4.0.

This system works well for most cases (it follows the standard UNIX command line scheme where -- on its own is a delimiter for arguments to be passed to a subprogram). However, it has its limitations. One of these limitations is that you can only pass user command line arguments at the end of the command line. This strict ordering can be a problem for plugins that wish to pass user command line arguments when running a project, as evidenced in godotengine/godot#107671 (review).

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Allow specifying user command-line arguments in an order-independent manner. The current approach to specifying user command line arguments would remain supported.

A common approach popularized by id Tech and Source is to use - for engine command line arguments, and + for game-specific (user) command line arguments:

-novid -nojoy +map de_dust2

This approach uses prefixes to distinguish between engine and user command line arguments, which means no delimiter like -- is needed.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

OS.get_cmdline_user_args() would now return arguments that are placed before --/++ if they start with a +. For arguments that you explicitly want to remain as engine arguments (such as file names), this can be bypassed by putting the value in quotes.

The prefix remains as-is in the returned array of values, so it's up to the script reading the arguments to handle any style differences here (e.g. if you wish to allow both + and -- prefixes for user arguments, but only + would be usable before the --/++ separator).

Conversely, OS.get_cmdline_args() would not return arguments that are placed before --/++ if they start with a +.

The following command lines are all valid:

godot --fullscreen -- --level=1
# Engine arguments: ["--fullscreen"]
# User arguments: ["--level=1"]

godot --fullscreen +level=1
# Engine arguments: ["--fullscreen"]
# User arguments: ["+level=1"]

godot +level=1 --fullscreen
# Engine arguments: ["--fullscreen"]
# User arguments: ["+level=1"]

godot +level=1 --fullscreen -- --level=1
# Engine arguments: ["--fullscreen"]
# User arguments: ["+level=1", "--level=1"]
# (It's up to the script to handle conflicts/priority of arguments.)

If this enhancement will not be used often, can it be worked around with a few lines of script?

No.

Is there a reason why this should be core and not an add-on in the asset library?

This is about improving the flexibility of the command line. Also, command line argument parsing happens in main.cpp, which can't be overridden by add-ons since it's very early in the Godot initialization stage.