Don't fail silently when trying to load a world without -f about gz-sim

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Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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This happens to me all the time, you forgot the -f before the file path.

I think we have to handle this case better.

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Original comment by Michael Grey (Bitbucket: mxgrey, GitHub: mxgrey).

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Thanks, that was the issue! 😅

Is there a particular reason we don't support the world file as a positional argument like the old Gazebo? If we want to commit to no longer supporting that, then we should at least update the help text, which currently says the command signature is:

`ign-gazebo` [options] <world_file>

which implies that you're required to pass a world file at the end as a positional argument (<argument_name> in angle brackets at the end of the command signature usually implies a mandatory positional argument, so we should use brackets [argument_name] for optional arguments).

Additionally, we could print console warnings if users pass in unexpected arguments or neglect to load a world at startup.

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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+1 to all your suggestions

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Original comment by Michael Grey (Bitbucket: mxgrey, GitHub: mxgrey).

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Do you think it would be better to make the world_file argument an optional positional argument to match previous Gazebos, or keep it as a flagged option like it currently is?

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Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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I have no preference, but if I remember correctly, @nkoenig had a reason to add a flag initially.

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Original comment by Michael Grey (Bitbucket: mxgrey, GitHub: mxgrey).

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I feel like an optional positional argument makes the most sense since it matches typical Unix conventions the closest, but I'll hold off on submitting any changes until we hear from Nate.

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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• changed title from "Nothing shows up in the rendering?" to "Don't fail silently when trying to load a world without -f"

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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See pull request #298

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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• changed state from "new" to "resolved"