how to add timestamp info by genrule?

[furyNerd]

hi

my BUILD file is:

genrule(
    name = "gen_dyna_ts",
    outs = ["gen_dyna_ts.h"],
    cmd = """
        echo "uint64_t dyna_ts = $$(date '+%s');" > $@       
    """,
)

cc_library(
    name = "dyna_ts",
    hdrs = [":gen_dyna_ts"],
    copts = ["-std=c++17"],
    # data = [":gen_dyna_ts"], # also tried this
)

and my build cmd is

bazel build //path/to/BUILD_dir:dyna_ts

and by

cat path/to/gen_dyna_ts.h

show that the gen_dyna_ts.h was successfully generated, but only once.
when i bazel build //path/to/BUILD_dir:dyna_ts twice or more times, the dynamic-timestamp info in gen_dyna_ts.h keeps the same as the first time. i know it is the cache works but this is not what i want, i wish every time i bazel build //path/to/BUILD_dir:dyna_ts the timestamp info could be updated.

could that be possible? (though i understand this is not conform to the best practices of bazel).

btw: i'm not allow to change the build cmd by using something like bazel build --nocache_test_results //path/to/BUILD_dir:dyna_ts, the BUILD file is my only trick point.

thanks

[ahumesky]

I replied to your stackoverflow comment: https://stackoverflow.com/questions/79016161/how-can-i-generate-a-file-with-the-time-of-bazel-build-and-include-it-in-build-o/79019453?noredirect=1#comment140539857_79019453

The first thing that comes to mind is if you can delete the file that the genrule outputs (gen_dyna_ts.h), then bazel will rerun the genrule with the updated time.

[furyNerd]

thanks for the confirmation. if this is what designed, it's a bit sad for my case.
i also tried deleting gen_dyna_ts.h, it works only when i delete it outside bazel (genrule) manually (which is out of my permission).
but the following method still keeps the timestamp as last cached genrule edited/saved/called time, not expected timestamp of calling bazel build //path/to/BUILD_dir:dyna_ts:

genrule(
    name = "gen_dyna_ts",
    outs = ["gen_dyna_ts.h"],
    cmd = """
        rm -rf $@
        echo "uint64_t dyna_ts = $$(date '+%s');" > $@       
    """,
)

i also tried a quite dirty method, it looks like could works most of the time by keep updating BUILD_TS:

genrule(
    name = "gen_dyna_ts",
    outs = ["gen_dyna_ts.h"],
    cmd = """
        BUILD_TS=1750747394923923631
        dir_repo=$$(realpath $$(pwd))
        sed -i "0,/BUILD_TS=[0-9]\\+/ s//BUILD_TS=$$(date '+%s%N')/" $${dir_repo}/path/to/this/BUILD
        echo "uint64_t dyna_ts = $$(date '+%s');" > $@       
    """,
    tags = ["local"],  # this is the most tricky part
)

it will dirty the git repo by updating this BUILD file, but i think it could be reverted automaticly by a new genrule depend on the srcs by dyna_ts, to clean the dirty. but this is too ugly to make a further try