[ideas] Propagate the condition of tar_skip in the downstream dependencies

[jospueyo]

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Description

I'm interested in using tar_skip() to run conditionally two parts of the pipeline based on a setup value. I can use tar_skip in all targets of both branches, but it would nice if the condition was propagated downstream.

library(targets)
tar_script({
    library(tarchetypes)
    mode <- "b"
    list(
        tar_skip(mode_a, paste("mode", mode), skip = mode != "a"), 
        tar_skip(mode_b, paste("mode", mode), skip = mode != "b"), 
        tar_target(mode_a2, paste(mode_a, 2)), 
        tar_target(mode_b2, paste(mode_b, 2))
    )
})
tar_make()
#> ▶ dispatched target mode_b
#> ● completed target mode_b [0 seconds]
#> ▶ dispatched target mode_a
#> ■ canceled target mode_a
#> ▶ dispatched target mode_b2
#> ● completed target mode_b2 [0 seconds]
#> ▶ dispatched target mode_a2
#> ● completed target mode_a2 [0 seconds]
#> ▶ completed pipeline [0.16 seconds]

^{Created on 2024-02-21 with reprex v2.0.2}

The result of target mode_a2 is " 2". IMHO, this target should also be skipped because its upstream dependency was skipped.

[wlandau]

I have no plans to make skips propagate, but you can apply tar_skip() or tar_cue_skip() to downstream targets.