Use SOURCE_DATE_EPOCH with GNU install

[Ludovic Courtès]

Hi David,

David Kleuker <post at davidak.de> skribis:

> [davidak at nixos:~]$ diffoscope /nix/store/cwmpm1kk3pfw1d5x5wfv691fw378gsjl-agave-16 /nix/store/8p0bn5y6nlcrkclz4vz4rxjycs2imiwl-agave-16
> --- /nix/store/cwmpm1kk3pfw1d5x5wfv691fw378gsjl-agave-16
> +++ /nix/store/8p0bn5y6nlcrkclz4vz4rxjycs2imiwl-agave-16
> ├── stat {}
> │ @@ -1,7 +1,7 @@
> │
> │ Size: 4096 Blocks: 8 IO Block: 4096 directory
> │ Access: (0555/dr-xr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
> │
> │ Modify: 1970-01-01 00:00:01.000000000 +0000
> │
> │ - Birth: 2020-07-20 09:02:11.688603176 +0000
> │ + Birth: 2020-07-20 08:47:51.046971751 +0000

As you can see above, Nix resets the modification time (“mtime”) of
installed files to the Epoch plus one second.

The creation time reported as “Birth” is an extension, not reported by
stat(2), but fortunately it’s a piece of information that’s generally
not used.

Perhaps diffoscope should omit the creation time by default?

Thanks,
Ludo’.