Label Expressions not handled (but relationship type expressions are)

[flaar94]

Hi,

First of all, thanks for all your work! This plugin is a real lifesaver when working with complicated neo4j queries.

I have noticed that it doesn't seem to support most label expressions for cypher (https://neo4j.com/docs/cypher-manual/current/patterns/reference/#label-expressions), even when the corresponding expression is supported for relationship type expressions. In particular '|', eg:
MATCH (:Person|Company) is marked as incorrect while something like MATCH ()-[:WORKS_FOR|OWNS]->() is handled correctly. The other one I noticed is '!' like MATCH (:!Company) doesn't work for either labels or relationship types, but I don't use that one very often. The docs claim the syntax for labels and types are the same, so I hope it wouldn't be too much work to fix the former issue since it's apparently already done for relationship types

Anyways, Thank you!

[flaar94]

Glancing around the code, I'm guessing the main relevant parts are

graphdb-intellij-plugin/language/cypher/src/main/java/com/albertoventurini/graphdbplugin/language/cypher/lexer/Cypher.bnf

Line 496 in f9fe9e5

NodeLabel ::= ":" LabelName

graphdb-intellij-plugin/language/cypher/src/main/java/com/albertoventurini/graphdbplugin/language/cypher/lexer/Cypher.bnf

Line 525 in f9fe9e5

NodeLabels ::= NodeLabel+

graphdb-intellij-plugin/language/cypher/src/main/java/com/albertoventurini/graphdbplugin/language/cypher/lexer/Cypher.bnf

Line 312 in f9fe9e5

NodePattern ::= "(" Variable? NodeLabels? Properties? Where? ")" {pin=1}

I'm not very good at Java, but it seems like you could mostly copy how relationshipType is doing it and replace

NodePattern ::= "(" Variable? NodeLabels? Properties? Where? ")" {pin=1}

With something like

NodePattern ::= "(" Variable? LabelExpression? Properties? Where? ")" {pin=1} 
LabelExpression ::= ":" "!"? LabelName ( ( "|" | ":" ) "!"? LabelName)* {pin=1}

Looking at it, I notice that relationshipTypes doesn't handle expressions like [:WORKS_FOR:OWNS] either, so this might fix that? I'm not really sure what that pin is doing though. It's still a subset of the label-expression syntax, but seems to take care of most simple uses without getting recursive. NodeLabels is used in SET, so I'm guessing you probably shouldn't change it, although it's also used in this line:

graphdb-intellij-plugin/language/cypher/src/main/java/com/albertoventurini/graphdbplugin/language/cypher/lexer/Cypher.bnf

Line 352 in f9fe9e5

private Expression2 ::= Expression1 (PropertyLookup | NodeLabels)*

Anyways, not sure if any of that is helpful at all since I only have a superficial grasp of what is going on here