support for SOURCE_DATE_EPOCH in quickbook

[mhekkel]

I'm a happy user of boostbook and quickbook to generate the documentation for my software. This software is also part of Debian and there I run into the problem that my packages are not reproducible, due to the fact that quickbook writes out the current date as a last-revised string.
The solution to this is really very simple, patch quickbook to pick up the value of the environment variable SOURCE_DATE_EPOCH and use that instead of time() as the last-revised date.

The patch might look like this:

diff tools/quickbook/src/quickbook.cpp tools/quickbook/src/quickbook-n.cpp
469c469,473
<             time_t t = std::time(0);
---
>             time_t t;
>                       if (getenv("SOURCE_DATE_EPOCH"))
>                               t = strtol(getenv("SOURCE_DATE_EPOCH"), nullptr, 10);
>                       else
>                               t = std::time(0);

More information on reproducible builds can be found at https://reproducible-builds.org/ and https://wiki.debian.org/ReproducibleBuilds/Howto

Hope this can be fixed.

-maarten

[mhekkel]

Sorry, wrong project. Should have been quickbook of course.
Submitted a pull request at boostorg/quickbook#12