What happened to TraceFileObserver.DEF_FILE_NAME ?

[odoublewen]

Hi,

Sometime between v25.04.8 and v25.10.0, the class field TraceFileObserver.DEF_FILE_NAME went away. This is how it looked in v24.05.8:

class TraceFileObserver implements TraceObserver {

    public static final String DEF_FILE_NAME = "trace-${TraceHelper.launchTimestampFmt()}.txt"
    ...

I haven't been able to figure our exactly the PR or commit when this happened. It's here in v24.05.8 and gone in v25.10.0. I can see in the release notes for 25.07.0-edge, it says:

• Update trace observers to V2 (Update trace observers to v2 #6257) [544b8c4]

I thought that might have something to do with it, but this merge commit didn't actually remove DEF_FILE_NAME.

Anyway, this removal broke a custom workflow.onComplete config that we use. One of the lines in the script tries to copy the trace file from its location (in the working dir where nf was run) to the output dir. How can we access the trace filename, now that DEF_FILE_NAME is gone?

[bentsherman]

The default file name was moved to TraceConfig in #6271 , which was some tech debt cleanup that we did for the config system.

So you can likely access it via TraceConfig.defaultFileName(). Just keep in mind that this isn't really part of the Nextflow language, so it's not guaranteed to work. If you create a plugin with a TraceObserver, you can do the same kind of thing but with access to the entire Nextflow runtime.

[odoublewen]

Thank you!

[odoublewen]

@bentsherman After some tinkering, I found that nextflow.Nextflow.session.config.trace?.file almost works for both nextflow versions before and after the 25.10 release.

For nextflow <25.10:

• It works when -with-trace is used with a specified trace file
• It works when -with-trace is used without any arguments

For nextflow >=25.10:

• It works when -with-trace is used with a specified trace file
• It doesn't work when -with-trace is used without any arguments (it returns null)

It would be nice if there was a way to access the trace filename that worked with newer or older nextflow versions. The problem I'm having with TraceFileObserver or TraceConfig is that these clases need to be imported, and that makes it impossible to write a try-catch block, since imports are done at compile time (in my limited groovy experience tells me).

[odoublewen]

I came up with a hacky solution, using a wildcard import, that works for newer and older nextflow versions:

import nextflow.trace.config.*

workflow.onComplete = {
    traceFile = nextflow.Nextflow.session.config.trace?.file
    if (!traceFile) {
        try {
            // This is necessary for nextflow >=25.10, when trace has the default filename
            // See https://github.com/nextflow-io/nextflow/discussions/6726
            traceFile = TraceConfig.defaultFileName()
        } catch (Exception) {
            // pass
        }
    }
    // do stuff with the traceFile
}