rule gen
    command = echo $out > $out

rule run
    command = (echo $out : $out.gen > $out.d) && (echo $out > $out)
    depfile = $out.d

build good: phony good1 good2

build good1: run || good1.gen
build good1.gen: gen

build good2: run || good2_phony
build good2_phony: phony good2.gen
build good2.gen: gen

build bad: run | input
build bad.gen: gen