RFR: 8275745: Reproducible copyright headers

[Magnus Ihse Bursie]

On Sun, 24 Oct 2021 12:11:57 GMT, Emmanuel Bourg <duke at openjdk.java.net> wrote:

>> The copyright headers are generated at build time, and the year inserted in the template depends on the current date. This means the headers are not reproducible if the project is built a year later. The year in the headers could be derived from the SOURCE_DATE_EPOCH environment variable to make the build reproducible (this variable is already used in other parts of the build).
>
> Yes that's fine. I guess this involves setting the `COPYRIGHT_YEAR` variable in `make/autoconf/jdk-options.m4` to a value derived from `SOURCE_DATE_EPOCH` (with `SOURCE_DATE_EPOCH` having the priority over `--with-copyright-year` or the opposite?), and then pick the value of `COPYRIGHT_YEAR` in `CopyrightHeaders.java` and `EquivMapsGenerator.java`, right?

@ebourg I have now modified this patch so it uses COPYRIGHT_YEAR, and sets COPYRIGHT_YEAR based on SOURCE_DATE_EPOCH, if it exists. The patch is in a branch in my personal fork, https://github.com/magicus/jdk/tree/reproducible-copyright-year.

If you think it looks good, we have two possible ways forward. Either you close this PR, and I open a new targeting the same JBS issue, and credit you as co-author. Or you integrate my branch into this PR, and credit me as co-author. Any of them is OK for me, but I think the former is simpler.

-------------

PR: https://git.openjdk.java.net/jdk/pull/1498