Since c4c3c15c19 (#4251) building Nix for
macOS with sandboxing fails:
```
getting status of /nix/var/nix/profiles/per-user/root/channels/nixpkgs: Operation not permitted
```
This happens, because `EvalSettings::getDefaultNixPath` tries to access
paths outside the sandbox. Since the state-dir is not required for
doc generation, it is set to the dummy folder. This needs to be done
for all nix invocations during doc generation, as
`EvalSettings::getDefaultNixPath` is called unconditionally.
Without setting HGPLAIN, the user's environment leaks into
hg invocations, which means that the output may not be in the
expected format.
HGPLAIN is the Mercurial-recommended solution for this in that
it's intended for uses by scripts and programs which are looking
to parse Mercurial's output in a consistent manner.
This fixes a bug I encountered where `nix-store -qR` will deadlock when
the `--include-outputs` flag is passed and `max-connections=1`.
The deadlock occurs because `RemoteStore::queryDerivationOutputs` takes
the only connection from the connection pool and uses it to check the
daemon version. If the version is new enough, it calls
`Store::queryDerivationOutputs`, which eventually calls
`RemoteStore::queryPartialDerivationOutputMap`, where we take another
connection from the connection pool to check the version again. Because
we still haven't released the connection from the caller, this waits for
a connection to be available, causing a deadlock.
This diff solves the issue by using `getProtocol` to check the protocol
version in the caller `RemoteStore::queryDerivationOutputs`, which
immediately frees the connection back to the pool before returning the
protocol version. That way we've already freed the connection by the
time we call `RemoteStore::queryPartialDerivationOutputMap`.
Fixes:
$ nix build --store /tmp/nix /home/eelco/Dev/patchelf#hydraJobs.build.x86_64-linux
warning: Git tree '/home/eelco/Dev/patchelf' is dirty
error: --- RestrictedPathError ------------------------------------------------------------------------------------------- nix
access to path '/tmp/nix/nix/store/xmkvfmffk7xfnazykb5kx999aika8an4-source/flake.nix' is forbidden in restricted mode
(use '--show-trace' to show detailed location information)
Until now, it was not possible to substitute missing paths from e.g.
`https://cache.nixos.org` on a remote server when building on it using
the new `ssh-ng` protocol.
This is because every store implementation except legacy `ssh://`
ignores the substitution flag passed to `Store::queryValidPaths` while
the `legacy-ssh-store` substitutes the remote store using
`cmdQueryValidPaths` when the remote store is opened with `nix-store
--serve`.
This patch slightly modifies the daemon protocol to allow passing an
integer value suggesting whether to substitute missing paths during
`wopQueryValidPaths`. To implement this on the daemon-side, the
substitution logic from `nix-store --serve` has been moved into a
protected method named `Store::substitutePaths` which gets currently
called from `LocalStore::queryValidPaths` and `Store::queryValidPaths`
if `maybeSubstitute` is `true`.
Fixes#2770
