this logs unpackTarfile calls as an `actUnknown` activity, which
unfortunately doesn't report any progress for now. for the reasoning
behind this choice, see the previous iterations of this CL (cl/5590)
as well as the attached comments (the crux of the conversion is in DMs,
unfortunately). in short:
- i could't make a new ActivityType because that would be a breaking
change to the daemon protocol, including with previous lix versions
- i can't use actFileTransfer because that would show up as a download,
which would be confusing for both users and tools
- i can't use actCopyPath /or/ actCopyPaths because that would break
NAR/substitution accounting when doing remote builds
also, ArchiveDecompressionSource, which is apparently used for
decompressing logs etc, does its own custom decompression without using
unpackTarfile, so it is not affected by this. from what i can tell,
unpackTarfile is only used for:
- fetchtarball fetcher
- git fetcher
- channel unpacking
- nix-prefetch-url
Fixes#1213
Change-Id: I68f3be520681d8889292353dd41ab19a60c5eeea