LexerNoViableAltException but script still runs

[awgymer]

Bug report

I am playing around with the syntax trying to understand the language server better and I managed to generate a possible lexical error in nextflow which shows an error but still runs as the user might expect. Unclear whether this is actually a bug, edge-case, or something else

Expected behavior and actual behavior

Either the script doesn't compile, or the error is not raised.

Steps to reproduce the problem

x = [z: 4]

println "$x\ some more"

Note the space after the \.

Using a \ produces a script compilation error with cause: Unexpected character: '"' in the following other cases:

"a\ b"
"\ a"
"a \ "
" \ a"

Program output

N E X T F L O W   ~  version 24.10.3

Launching `./test.nf` [backstabbing_maxwell] DSL2 - revision: 008f33b6cc

unknown recognition error type: groovyjarjarantlr4.v4.runtime.LexerNoViableAltException
[z:4] some more

Environment

• Nextflow version: 24.10.3
• Java version: openjdk version "17.0.10" 2024-01-16
• Operating system: macOS
• Bash version: GNU bash, version 3.2.57

[bentsherman]

This error is very deep, it's coming from ANTLR: https://github.com/tunnelvisionlabs/antlr4/blob/master/runtime/Java/src/org/antlr/v4/runtime/DefaultErrorStrategy.java#L148

I have never figured out why it happens or if/when it's a problem. I just added a warning for it here in the docs. Interesting to see that it can happen with other kinds of escapes.

[awgymer]

Yeah it's kind of bizarre, it gets thrown by groovyc too but obviously still compiles and runs "fine" (at least in these cases, I guess its an issue for nextflow multiline bash code in the script section?).

[bentsherman]

I think ANTLR encounters a parsing error, then encounters an error while trying to report the parsing error, and so no error gets reported 😅

But you said it later reports an Unexpected character: '"' error right? So where does that come from?

[awgymer]

That report (for unexpected ") is a different compilation error that actually causes failure to compile and it doesn't happen when you have \ (slash space).

The slash-space case is weird because it prints that error but ultimately compiles and runs