So that it can be printed by `nix describe-stores`

Allow `-` and `.` in the RFC schemes as stated by
[RFC3986](https://tools.ietf.org/html/rfc3986#section-3.1).

Practically, this is needed so that `ssh-ng` is a valid URI scheme

When opening a store, only try the stores whose `uriSchemes()` include
the current one

Using virtual inheritance means that only the default constructors of
the parent classes will be called, which isn't what we want

Using the `*Config` class hierarchy

Rework the `Store` hierarchy so that there's now one hierarchy for the
store configs and one for the implementations (where each implementation
extends the corresponding config). So a class hierarchy like

```
StoreConfig-------->Store
    |                 |
    v                 v
SubStoreConfig----->SubStore
    |                 |
    v                 v
SubSubStoreConfig-->SubSubStore
```

(with virtual inheritance to prevent DDD).

The advantage of this architecture is that we can now introspect the configuration of a store without having to instantiate the store itself

The default value is initialized when creating the setting and unchanged
after that

Don't let it just contain the value, but also the other fields of the
setting (description, aliases, etc..)

Add a new `init()` method to the `Store` class that is supposed to
handle all the effectful initialisation needed to set-up the store.
The constructor should remain side-effect free and just initialize the
c++ data structure.

The goal behind that is that we can create “dummy” instances of each
store to query static properties about it (the parameters it accepts for
example)

Directly register the store classes rather than a function to build an
instance of them.
This gives the possibility to introspect static members of the class or
choose different ways of instantiating them.

We no longer need the `*Opt` to disambiguate.

Otherwise, we will associate fixed-output derivations with outputs that
they did indeed produce, but which had the wrong hash. That's no good.

gracefully handle old daemon versions

Add a fallback path in `queryPartialDerivationOutputMap` for daemons
that don't support it.

Also upstreams a couple methods from `SSHStore` to `RemoteStore` as this
is needed to handle the fallback path.

Escape `${` in strings when printing Nix expressions

Otherwise the result of the printing can't be parsed back correctly by
Nix (because the unescaped `${` will be parsed as the begining of an
anti-quotation).

Fix #3989

Fixes #3992.

Fix auto argument passing for more auto arguments than formals

Add ccls files to .gitignore

Fix unspecified behaviour in readStorePathCAMap

When deploying a Hydra instance with current Nix master, most builds
would not run because of errors like this:

  queue monitor: error: --- Error --- hydra-queue-runner
  error: --- UsageError --- nix-daemon
  not a content address because it is not in the form '<prefix>:<rest>': /nix/store/...-somedrv

The last error message is from parseContentAddress, which expects a
colon-separated string, however what we got here is a store path.

Looking at the worker protocol, the following message sent to the Nix
daemon caused the error above:

  0x1E -> wopQuerySubstitutablePathInfos
  0x01 -> Number of paths
  0x16 -> Length of string
  "/nix/store/...-somedrv"
  0x00 -> Length of string
  ""

Looking at writeStorePathCAMap, the store path is indeed the first field
that's transmitted. However, readStorePathCAMap expects it to be the
*second* field *on my machine*, since expression evaluation order is a
classic form of unspecified behaviour[1] in C++.

This has been introduced in https://github.com/NixOS/nix/pull/3689,
specifically in commit 66a62b31.

[1]: https://en.wikipedia.org/wiki/Unspecified_behavior#Order_of_evaluation_of_subexpressions



Signed-off-by: aszlig <aszlig@nix.build>

Co-authored-by: lf- <lf-@users.noreply.github.com>

The change in 62620071 didn't account
for when the number of auto arguments is bigger than the number of
formal arguments. This causes the following:

  $ nix-instantiate --eval -E '{ ... }@args: args.foo' --argstr foo foo
  nix-instantiate: src/libexpr/attr-set.hh:55: void nix::Bindings::push_back(const nix::Attr&): Assertion `size_ < capacity_' failed.
  Aborted (core dumped)

Add `nix-shell` support for preserving PS1

Fixes https://github.com/NixOS/nix/issues/1268

`nix-shell` will now preserve `PS1` if the `NIX_SHELL_PRESERVE_PROMPT`
environment variable is set.

 - More and better comments

 - The easier renames