Instead, `Hash` uses `std::optional<HashType>`. In the future, we may
also make `Hash` itself require a known hash type, encoraging people to
use `std::optional<Hash>` instead.
See documentattion in header and comments in implementation for details.
This is actually done in preparation for floating ca derivations, not
multi-output fixed ca derivations, but the distinction doesn't yet
mattter.
Thanks @cole-h for finding and fixing a bunch of typos.
Today's fixed output derivations and regular derivations differ in a few
ways which are largely orthogonal. This replaces `isFixedOutput` with a
`type` that returns an enum of possible combinations.
This allows overriding the priority of substituters, e.g.
$ nix-store --store ~/my-nix/ -r /nix/store/df3m4da96d84ljzxx4mygfshm1p0r2n3-geeqie-1.4 \
--substituters 'http://cache.nixos.org?priority=100 daemon?priority=10'
Fixes#3264.
Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.
Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.
Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).
A corrupt entry in .links prevents adding a fixed version of that file
to the store in any path. The user experience is that corruption
present in the store 'spreads' to new paths added to the store:
(With store optimisation enabled)
1. A file in the store gets corrupted somehow (eg: filesystem bug).
2. The user tries to add a thing to the store which contains a good copy
of the corrupted file.
3. The file being added to the store is hashed, found to match the bad
.links entry, and is replaced by a link to the bad .links entry.
(The .links entry's hash is not verified during add -- this would
impose a substantial performance burden.)
4. The user observes that the thing in the store that is supposed to be
a copy of what they were trying to add is not a correct copy -- some
files have different contents! Running "nix-store --verify
--check-contents --repair" does not fix the problem.
This change makes "nix-store --verify --check-contents --repair" fix
this problem. Bad .links entries are simply removed, allowing future
attempts to insert a good copy of the file to succeed.
