Report an error on duplicate workflow name definitions

[bentsherman]

Close #4086

Consider the following pipeline script:

// main.nf
include { WORK_ONE } from './w1'

workflow WORK_ONE {
    WORK_ONE ()
}

workflow {
    WORK_ONE ()
}

// w1.nf
workflow WORK_ONE {
    exit 0, "wf1"
}

Currently this causes a stack overflow error:

$ nextflow run gh-4086
N E X T F L O W  ~  version 23.06.0-edge
Launching `gh-4086/main.nf` [sick_williams] DSL2 - revision: c420b3da5f
ERROR ~ Unexpected error [StackOverflowError]

 -- Check script 'gh-4086/main.nf' at line: 4 or see '.nextflow.log' file for more details

With this PR, Nextflow will warn about the duplicate workflow name:

$ ../launch.sh run gh-4086
N E X T F L O W  ~  version 23.06.0-edge
Launching `gh-4086/main.nf` [jolly_avogadro] DSL2 - revision: db2d0fa85b
WARN: A process with name 'WORK_ONE' is defined more than once in module script: /home/bent/projects/nextflow-io_nextflow/sketches/gh-4086/main.nf -- Make sure to not define a function with the same name as a workflow or process
ERROR ~ Unexpected error [StackOverflowError]

 -- Check script 'gh-4086/main.nf' at line: 4 or see '.nextflow.log' file for more details

And if strict mode is enabled, this warning will become an error.

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[pditommaso]

It would be nice to add a unit test to validate this

[bentsherman]

If you define two functions with the same name with different signatures, can they both be used or only the last definition? That will affect whether we should return an error or only a warning if the duplicates are both functions.

[bentsherman]

Did some testing, found that function overloading works the same as in Groovy as far as I can tell. If you define two functions with the same signatures, the Groovy compiler catches it before Nextflow. So checkComponentName() pertains mainly to checking for any duplicates introduced by module imports.

Since we changed it to always be an error, I had to remove a test that allows duplicate module imports.

Also, I think ScriptMeta::validate() is dead code. It checks for duplicate functions, but that should always be caught by checkComponentName() when the function is imported. I couldn't find a test case that triggered an error from validate().

[pditommaso]

If I understand correctly, the exception is thrown irrespective of the strict flag, right?

[bentsherman]

Correct

[pditommaso]

Ok, update the PR title to reflect that