Changes in qgis_process that might be useful

[paleolimbot]

@nyalldawson You said to flag you if there's anything from the QGIS end that could make this better! I've spent a bit of time on this and have some ideas...it works fantastically and consistently (as far as I can tell) on multiple platforms!

The only three things I can think of:

• The ability for providers to work out-of-the-box in a headless state would be helpful for testing! There's an open issue with a workaround ( qgis_process: processing plugin not loaded / reduced list of algorithms on freshly installed systems and headless servers qgis/QGIS#37989 ), but locating the QGIS3.ini file on multiple platforms/distros is hard and probably better left to QGIS, if that's at all possible.
• JSON IO would be useful (JSON args through stdin and JSON output on stdout)...there's a few things like commas in fillenames that will break e.g., multilayer input/output, and my current approach for getting argument metadata is basically regex matching on the helpfile (which will eventually break if it isn't wrong already!). I also worry about encoding issues but I do seem to be able to get back an é from INPUT -> OUTPUT, so maybe that's not an issue. Again, maybe this is really hard, but eventually my regexes are going to break.
• Documentation of how string values are parsed would be really top-notch ( New standalone console tool for running processing algorithms (Request in QGIS) qgis/QGIS-Documentation#5803 ). I can help with this one since I've spent a lot of time guessing but I don't know where to begin (what do I fork? what file do I create!?)

Thanks for PRing a great tool into QGIS and let me know what I can do to help!

[nyalldawson]

Documentation of how string values are parsed would be really top-notch ( qgis/QGIS-Documentation#5803 ). I can help with this one since I've spent a lot of time guessing but I don't know where to begin (what do I fork? what file do I create!?)

The new json output includes this type of information

    "DISTANCE": {
      "default_value": 10,
      "description": "Distance",
      "is_advanced": false,
      "is_destination": false,
      "name": "DISTANCE",
      "optional": false,
      "raw_definition": {
        "data_type": 1,
        "default": 10,
        "default_unit": 9,
        "description": "Distance",
        "flags": 0,
        "help": null,
        "max": 1.7976931348623157e+308,
        "metadata": {},
        "min": -1.7976931348623157e+308,
        "name": "DISTANCE",
        "parameter_type": "distance",
        "parent": "INPUT"
      },
      "type": {
        "acceptable_values": [
          "A numeric value"
        ],
        "description": "A numeric parameter representing a distance measure.",
        "id": "distance",
        "metadata": {},
        "name": "Distance"
      }
    },

Specifically, the acceptable_values list here gives a breakdown of the different string inputs which are acceptable for each parameter.

Does that help?

[paleolimbot]

That's brilliant! Thank you! After I've finished the type handling here I'll take a stab at forking the QGIS docs and adding any bits that are missing.

[nyalldawson]

The ability for providers to work out-of-the-box in a headless state would be helpful for testing! There's an open issue with a workaround ( qgis/QGIS#37989 ), but locating the QGIS3.ini file on multiple platforms/distros is hard and probably better left to QGIS, if that's at all possible.

Fixed in qgis/QGIS#39324