Support line breaks for FEEL statements

[MaxTru]

Is your feature request related to a problem? Please describe.

When writing FEEL expressions, it often is handy to split them across multiple lines.

For example:

myVariable = null
or
myVariable > 5

rather than

myVariable = null or myVariable > 5

which is hard to read.

• In particular in the Web Modeler, where the prop panel can not be extended, but this is a different topic.

When writing multiline statements, the modeler explicitly persists the lineBreaks. E.g.,:

"=myVariable = null 
or 
myVariable > 5"

According to my local testing, this works just fine with the Engine.

However, the Modeler itself will expliticly complain, that this statement is not valid.

Describe the solution you'd like

• Explicitly test that multi-line FEEL is accepted by the engine (my fuzzy testing reveiled: yes). Potentially agree this as interface with engine.
• Adjust linting and code support for FEEL to accept multi-line statements

Describe alternatives you've considered

• Keep as is (this would make sense if multi-line is explicitly discouraged

Additional context

[nikku]

Thanks for opening this issue. What you found is a grammar bug.

The same statement works properly, if indented or wrapped in brackets:

(
  myVariable = null 
  or
  myVariable > 5
)

[nikku]

Moving this back to backlog for the time being. I was not able to follow-up.

[nikku]

I'm taking a timeboxed stab at this.

[nikku]

I made significant progress on this issue today but was not able to fully complete it.

Under the hood this is actually a non-trivial topic. For historical reasons, being tricked by old versions of the DMN spec lezer-feel would recognize a list of expressions, rather than a single expression. Newlines would sometimes confuse the parse as it needs to always decide if this is a continuation of an existing expression or the start of a new expression.

The solution we chose is to put the parser in full DMN FEEL 1.5 compat mode, parsing single expressions only (nikku/lezer-feel@6389057#diff-3410025680394470cd4d356b9dad20b8a39c090592049243a50866cb6d556677, https://github.com/nikku/lezer-feel/blob/master/CHANGELOG.md#100). This implied downstream changes in all supporting libraries.

What is missing is integration into our editing stack:

• feel-lint (Lezer feel bump feel-lint#1)
• feel-editor (Bump feel feel-editor#40)
• properties-panel (Bump feel editor properties-panel#254)
• bpmn-js-properties-panel

[nikku]

Fixed upstream via bpmn-io/properties-panel#254.