Gracefully handle unspecified args with ArgParser

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="96" height="96"hspace="10"> Issue by sethladd
Originally opened as dart-lang/sdk#14786

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It would be nice to have an option in ArgParser to ignore unspecified args.

Use Case:

Build system specifies its own options.
Build system uses another library that specifies its options.

I want to pass args to both the main build system and the included library:

build.dart --my-option --deploy

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Well, I found this in the API docs:

By default, the parse() method stops as soon as it reaches -- by itself or anything that the parser doesn't recognize as an option, flag, or option value. If arguments still remain, they go into ArgResults.rest.

Which looks like it can help me today.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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After playing around the -- doesn't help me because the tools generate the command-line, and they don't put their args after --.

So I think I need a "ignore unspecified args" option for ArgParser.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Will you accept a patch for such a feature?

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cc @munificent.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="48" height="48"hspace="10"> Comment by munificent

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Args has an option now to ignore unspecified arguments, but not unrecognized options. The former lets you have options that appear after non-option arguments. For example:

$ myapp some/file.txt --option

Args can skip over some/file.txt and parse --option. But it doesn't do that for things that look like options (i.e. a leading "-").

I'd be fine with a patch for the latter too, provided it was an opt-in feature. I'm thinking add a "ignoreUnknownOptions" argument to parse().

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Thanks Bob. ignoreUnknownOptions as an opt-IN would work. Good to know you'd accept a patch. :)

[DartBot]

<img src="https://avatars.githubusercontent.com/u/3276024?v=3" align="left" width="48" height="48"hspace="10"> Comment by anders-sandholm

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Removed Library-Args label.
Added Pkg-Args label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Now at #107

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Added MovedToGithub label.