New blocktype FilePicker and abort mechanism (UAC-7-11 of #123)

[schlingling]

Introduces a new blocktype FilePicker and abort mechanism if an parent block emits a null value.

Part of RFC0002 mobility-extension.

Implements following UACs of #123:

• [UAC-11] New blocktype FilePicker is implemented in std-extension..

I was not sure, how to register the new Block properly, so i will register it later.

[rhazn]

I left one comment, once that is fixed this is fine to merge.

[georg-schwarz]

Please add documentation to the added BlockMetaInformation subclasses on the docs fields after a rebase. You can get inspiration from the existing blocks. You will get documentation when hovering over the FilePicker block type in the VSCode plugin out of the box ;-)

[schlingling]

added doc to FilePicker @georg-schwarz. Thanks for already adding the docs to my HttpExtractor and ArchiveInterpreter :)

[schlingling]

I left one comment, once that is fixed this is fine to merge.

@rhazn: I implemented the changes discussed in slack (return null value in filepicker)

[rhazn]

Approved from my side, please wait for felix to have a look at the one comment I tagged him in.

[rhazn]

This is not a correct description.

[schlingling]

damn, copy/paste-error, sorry! Will change it.

[rhazn]

This is an interesting question for @felix-oq as well I think.

I see:

• Blocks could return combined types, e.g. FILE | NONE and we abort execution on NONE, this is the view "A block always has an output if it gets executed"
• Blocks could return their output as FILE and also return nothing (in the typescript interpreters case null), this is the view "A block generates zero or more outputs on any input"

I personally think generating zero or more outputs for any input is the best. I know it from observables, it is very helpful later on because in a lot of cases you might want to generate multiple values for one input.

While the best way to implement that would be with the actual 0 to n outputs, I think a first iteration with 1 output or null for 0 outputs is fine.

So in summary, I like the usage of returning FILE or null here and would keep it but please, @felix-oq have a look and share your opinion as well.

[schlingling]

Makes sense for me, will wait for felix, thanks for your input!

[felix-oq]

Sounds good, we can do it like that 👍