make rebuilds dynamic targets even when some subtargets get built before an interrupt

[kendonB]

library(drake)
my_plan <- drake_plan(
  i = 1:10,
  mytarget = target({
    Sys.sleep(10)
    i
  }, dynamic = map(i))
)
make(my_plan,
     verbose = 1)
##> dynamic mytarget
##> subtarget mytarget_0b3474bd
##> subtarget mytarget_b2a5c9b8
##> subtarget mytarget_71f311ad
##> ### INTERRUPT HERE ###
make(my_plan,
     verbose = 1)
##> dynamic mytarget
##> subtarget mytarget_0b3474bd
##> subtarget mytarget_b2a5c9b8
##> subtarget mytarget_71f311ad

^{Created on 2020-03-11 but not by the reprex package (v0.3.0)}
I presume that as a dynamic target builds itself it is storing files - seems like make should record the subtargets as up-to-date in this case. Is that possible?

[kendonB]

duplicate of #1209?