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> Completion isn't a simple left-to-right thing. Sorry, I still don't understand why that's relavent. It's probably my fault for not being clear enough. Please

by vunie 7y ago

> Completion isn't a simple left-to-right thing. Sorry, I still don't understand why that's relavent. It's probably my fault for not being clear enough. Please be patient with me as I try to further elaborate: If the command is in charge of both generating completions and also for parsing arguments, wouldn't it be aware of all inner-dependencies between flags? Wouldn't such awareness make it possible to generate candidates based on previous flags? I'm not familiar with ffmpeg, but let's assume that there was another similar program called ggmpeg. Let's assume that it accepts the flag '--input-format' and then either the flag '--repeat-video-range' or '--repeat-image-frames', depending on whether the format is an video or an image. That is, only the following flag sequences are valid: ggmpeg --input-format=video/webm --repeat-video-range=.. ... or ggmpeg --input-format=image/png --repeat-image-frames=.. ... Let's also assume that ggmpeg signals to the shell that it is responsible for generating its own completions by passing the flag --_completion to it. Now, if the user types the following command ggmpeg --input-format=image/png --repea[CURSOR] and then presses tab, thereby invoking the shell's auto completion routine, which in turn ultimately executes "ggmpeg" "--_completion" "--input-format=image/png" "--repea" wouldn't ggmpeg have all the necessary information to only suggest '--repeat-image-frames' and not '--repeat-video-range'?

shakna 7y ago
Ok, here's a simpler example that might demonstrate why it can't always be solved. ffmpeg -i input.avi -metadata author=shakna output.mp4 What metadata keys are allowed, if at all, actually depends on the output file. If I'd chosen to make an ogv instead, then that metadata flag would become disabled, because it doesn't accept most sets of metadata. I can't complete: ffmpeg -i input.avi -metadata a[TAB] Because the entire set of CLI commands isn't simple left-to-right solveable. However, if I do: ffmpeg -i input.avi -metadata author=shakna output.mp4 output.ogv That means I'm outputting one file with metadata, output.mp4, and one file without it, output.ogv. So the flag is conditionally enabled or disabled.
- vunie 7y ago
  I can now see what you meant by completion not being left-to-right solvable. Thanks for taking the time to lay out a clear example. While completion isn't be solvable in general, surly we can agree that its usefulness (when solvable) merits making it more readily available to users. Having the shell implementation automatically deduce suggestions from the command itself (when available/possible) would go a long way towards increasing availability in my opinion.

by vunie 7y ago

shakna 7y ago

Ok, here's a simpler example that might demonstrate why it can't always be solved. ffmpeg -i input.avi -metadata author=shakna output.mp4 What metadata keys are allowed, if at all, actually depends on the output file. If I'd chosen to make an ogv instead, then that metadata flag would become disabled, because it doesn't accept most sets of metadata. I can't complete: ffmpeg -i input.avi -metadata a[TAB] Because the entire set of CLI commands isn't simple left-to-right solveable. However, if I do: ffmpeg -i input.avi -metadata author=shakna output.mp4 output.ogv That means I'm outputting one file with metadata, output.mp4, and one file without it, output.ogv. So the flag is conditionally enabled or disabled.

vunie 7y ago
I can now see what you meant by completion not being left-to-right solvable. Thanks for taking the time to lay out a clear example. While completion isn't be solvable in general, surly we can agree that its usefulness (when solvable) merits making it more readily available to users. Having the shell implementation automatically deduce suggestions from the command itself (when available/possible) would go a long way towards increasing availability in my opinion.