Snakefile

shell.executable("bash")

rule all:
    input:
        "d.out",

rule A:
    output:
        "a.out",
    shell:
        "echo 'text' > {output}"

rule B:
    input:
        ancient("a.out"),
    output:
        "b_{i}.out",
    shell:
        "cat {input} > {output}"

# rule C is required for #946
#  use `range(20)` so test will pass in < 5% of cases where issue is present
rule C:
    input:
        expand("b_{i}.out", i=list(range(20))),
    output:
        "c.out",
    shell:
        "cat {input} > {output}"

# For #946, 'a.out' is required as input, but does not need to be `ancient()`
rule D:
    input:
        "a.out",
        "c.out",
    output:
        "d.out",
    shell:
        "cat {input} > {output}"