Respect SOURCE_DATE_EPOCH

[andersk]

If the SOURCE_DATE_EPOCH environment variable is set, then (1) use UTC for all timestamps and (2) replace all timestamps with min(timestamp, SOURCE_DATE_EPOCH). This allows projects using AsciiDoc to build reproducibly without being patched to pass extra flags.

(We don’t expose UTC timestamps as a separate command line option as in #70, but that shouldn’t be necessary because a user who knows they want UTC can run env TZ=UTC asciidoc. The goal here is to enable reproducibility without requiring special consideration by all AsciiDoc users.)

[elextr]

Please document in the user guide the change in semantics of the four attributes and add an environment variables section to the man page.

[andersk]

Documented.

[lamby]

Any update on this? :)

[elextr]

@lamby thanks for pinging.

Has anybody (other than the OP) tested it? Also I noticed something on reviewing that I have questioned.

[lamby]

@elextr Thanks for the update on this.

has anybody (other than the OP) tested it?

I've just tested it this PR on a few packages and it appears to work great.

[elextr]

Appears to match what Asciidoctor does so committed.

[lamby]

Many thanks :)