`nextflow lint --format` breaks map merge expression (+) when piped to process via |

[kubrian]

Bug report

Expected behavior and actual behavior

nextflow lint --format should preserve the semantics of multiline method chains. Instead, it reformats closures containing map merge expressions (+) across multiple lines in a way that breaks subsequent parsing, producing an Unexpected input: '+' error on the next lint run. The bug only occurs when the method chain is piped to another process via |.

Steps to reproduce the problem

Save the following as test.nf:

workflow {
    channel_A = channel.fromList([[[var_a: 1], 2], [[var_a: 3], 4]])
    some_previous_chaining = channel.value(1)

    // This line:
    channel_A
        .combine(some_previous_chaining)
        .map { meta, b, _c -> [meta + [var_b: b]] }
        | some_process

    // Gets reformatted to:
    // channel_A.combine(some_previous_chaining).map { meta, b, _c -> [meta
    //     + [var_b: b]] }
    //     | some_process
    // ...which causes "Unexpected input: '+'" on the next lint run.

    // No bug when NOT piping to another process:
    channel_A
        .combine(some_previous_chaining)
        .map { meta, b, _c -> [meta + [var_b: b]] }
        .set { some_channel }
    some_process(some_channel)
}

process some_process {
    input:
    val(meta)

    script:
    """
    echo ${meta}
    """
}

Run twice:

nextflow lint -format test.nf

Program output

> nextflow lint -format test.nf
Nextflow linting complete!
 ✅ 1 file had no errors (1 formatted)
> nextflow lint -format test.nf
Error test.nf:7:9: Unexpected input: '+'
│   7 |         + [var_b: b]] }
╰     |         ^

Error test.nf:7:9: Unexpected input: '+'
│   7 |         + [var_b: b]] }
╰     |         ^

Nextflow linting complete!
 ❌ 1 file had 2 errors

Environment

• Nextflow version: 25.10.4.11173
• Java version: openjdk version "11.0.30" 2026-01-20
• Operating system: Windows (WSL2)
• Zsh version: 5.8.1 (x86_64-ubuntu-linux-gnu)