Use `std::string_view` in a few more places

Allow empty hash in derivations

This replaces the copy&paste with a helper function in hash.hh.

This function was used in only one place, where it could easily be
replaced by readDerivation() since it's not
performance-critical. (This function appears to have been modelled
after queryDerivationOutputs(), which exists only to make the garbage
collector faster.)

Add tests for pool.hh

Add an option to print the logs in a machine-readable format

libutils/hash: remove default encoding

Actually test nix-env with a remote store

Prelink static libraries into an object file

This combines the *.o into a big .o producing one translation unit.
This preserve our unused static initializers, as specified in the C++
standard:

  If no variable or function is odr-used from a given translation
  unit, the non-local variables defined in that translation unit may
  never be initialized (this models the behavior of an on-demand
  dynamic library).

Note that this is very similar to how the --whole-archive flag works.
One advantage of this is that users of the final .a library don’t have
to worry about specifying --whole-archive, or that we have unused
static initializers at all!

WSL1 doesn’t support i686-linux emulation, see https://github.com/microsoft/wsl/issues/2468

fetchTarball, fetchTree, and fetchGit all have *optional* hash attrs.
This means that we need to be careful with what we allow to avoid
accidentally making these defaults. When ‘hash = ""’ we assume the
empty hash is wanted.

follow up of https://github.com/NixOS/nix/pull/3544

This allows hash="" so that it can be used for debugging purposes. For
instance, this gives you an error message like:

  warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000'
  hash mismatch in fixed-output derivation '/nix/store/asx6qw1r1xk6iak6y6jph4n58h4hdmbm-nix':
    wanted: sha256:0000000000000000000000000000000000000000000000000000
    got:    sha256:0fpfhipl9v1mfzw2ffmxiyyzqwlkvww22bh9wcy4qrfslb4jm429

Needed so that we can include it as a logger in loggers.cc without
adding a dependency on nix

This also requires moving names.hh to libutil to prevent a circular
dependency between libmain and libexpr

The `remote-store` test loads the `user-env` one to test nix-env when
using the daemon, but actually does it incorrectly because every test
starts (in `common.sh`) by resetting the value of `NIX_REMOTE`, meaning
that the `user-env` test will never use the daemon.

Fix this by setting `NIX_REMOTE_` before sourcing `user-env.sh` in the
`remote-store` test, so that `NIX_REMOTE` is correctly set inside the
test

Make the printing of the build logs systematically go through the
logger, and replicate the behavior of `no-build-output` by having two
different loggers (one that prints the build logs and one that doesn't)

Add a new `--log-format` cli argument to change the format of the logs.
The possible values are
- raw (the default one for old-style commands)
- bar (the default one for new-style commands)
- bar-with-logs (equivalent to `--print-build-logs`)
- internal-json (the internal machine-readable json format)

Add error message when FileIngestionMethod is out of bounds

Alternative fix to #3661. The cause was that 'name' is a
std::string_view into a temporary which could get overwritten.

Add `src/libutil/tests/libutil-tests` to `.gitignore`

I gather this comes from the new unit tests.

bool coerces anything >0 to true, but in the future we may have other
file ingestion methods. This shows a better error message when the
“recursive” byte isn’t 1.

Fixes #3648.

This will make it easier to reason about the hash encoding and switch to
SRI everywhere where possible.

This was a latent bug that just appeared because of the tests that were
added. Remember to wait for CI! :)

Remove `addToStore` variant as requested by `FIXME`

Co-authored-by: James Lee <jbit@jbit.net>