This environment variable, if defined during the build process,
indicates a fixed time that should be used in place of "now" when
such a time is explicitely referenced.
This allows for reproducible builds of micropython.
See https://reproducible-builds.org/specs/source-date-epoch/
Signed-off-by: iTitou <moiandme@gmail.com>
Some downstream projects may use tags in their repositories for more than
just designating MicroPython releases. In those cases, the
makeversionhdr.py script would end up using a different tag than intended.
So tell `git describe` to only match tags that look like a MicroPython
version tag, such as `v1.12` or `v2.0`.
It's more robust to have the version defined statically in a header file,
rather than dynamically generating it via git using a git tag. In case
git doesn't exist, or a different source control tool is used, it's
important to still have the uPy version number available.
iTitou
Mike Wadsten
Damien George
omtinez