Bazel benchmark for sandboxing performance

BUILD

# Benchmarks for sandbox performance
#
# Run with 'bazel build :gen_main' and measure the time it takes.

# Creates 15000 input files.
inputs = ["input_%s" % i for i in range(15000)]
genrule(
    name = "gen_inputs",
    outs = inputs,
    cmd = "date | tee $(OUTS) > /dev/null",
)

# Create 100 rules that depend on the input files.
genrules = ["genrule_%s" % i for i in range(100)]
[genrule(
    name = "gen_%s" % name,
    srcs = inputs,
    outs = [name],
    cmd = "cat $(SRCS) > \"$@\"",
) for name in genrules]

# One rule to rule them all in a final step.
genrule(
    name = "gen_main",
    srcs = genrules,
    outs = ["main"],
    cmd = "cat $(SRCS) > \"$@\"",
)