Compilation error when declaring typed params in params {} block (you tried to assign a value to the class 'java.lang.Boolean')

[xies4]

Expected behavior and actual behavior

Expected:

Either:

• Nextflow accepts type annotations in the params {} block (e.g., save_intermeds: Boolean = false)

or

• The compiler surfaces a clearer, actionable error explaining that the params scope is an untyped map and does not support type annotations, with guidance to use save_intermeds = false.

Actual: Script fails to compile with:

you tried to assign a value to the class 'java.lang.Boolean'

which suggests a misuse of the Boolean class rather than explaining the constraint of the params block.

Steps to reproduce the problem

1. Create test.nf with the following contents:

params {
    // Path to input data.
    input: Path

    // Whether to save intermediate files.
    save_intermeds: Boolean = false
}

workflow {
    println "params.input = ${params.input}"
    println "params.save_intermeds = ${params.save_intermeds}"
}

2. Run:

nextflow run test.nf --input test.txt

Program output

N E X T F L O W   ~  version 25.10.0

Launching `test.nf` [gloomy_volhard] DSL2 - revision: 08815e7ae7

ERROR ~ Script compilation error
- file : /mnt/ccrsf-static/Analysis/xies4/RnD_projects/repro_DNAmeth/data/test.nf
- cause: you tried to assign a value to the class 'java.lang.Boolean'
 @ line 6, column 21.
       save_intermeds: Boolean = false
                       ^

1 error


 -- Check '.nextflow.log' file for details

Environment

Nextflow version: 25.10.0

Java version: openjdk 24.0.2 2025-07-15

Operating system: Linux fsitgl-head01p.ncifcrf.gov 4.18.0-553.77.1.0.1.el8_10.x86_64 #1 SMP Tue Sep 30 01:24:10 PDT 2025 x86_64 x86_64 x86_64 GNU/Linux

Bash version: GNU bash, version 4.4.20(1)-release (x86_64-redhat-linux-gnu)

Can you help on address the issue? Thanks.

[bentsherman]

Did you enable the strict syntax as noted in the documentation?

[xies4]

Please see the screenshot for the command lines I tried. I did enable the strict syntax: `NXF_SYNTAX_PARSER=v2`. Thank you for your help.

[bentsherman]

Environment variables typically need to be set using export, otherwise it won't remember the setting when you run subsequent commands

[xies4]

You're right — using export was the key. Once I did that, the environment variable persisted and the issue was resolved. Thanks for pointing that out!