InputSchemes now only have a getAccessor(). They could be implemented
internally by fetching the input to the store, but in that case they
will just return a FSInputAccessor.
`--override-input` id snarky because it takes two arguments, so it
doesn't play well when completed in the middle of the CLI (since the
argument just after gets interpreted as its second argument). So use
`--update-input` instead
I recently got fairly confused why the following expression didn't have
any effect
{
description = "Foobar";
inputs.sops-nix = {
url = github:mic92/sops-nix;
inputs.nixpkgs_22_05.follows = "nixpkgs";
};
}
until I found out that the input was called `nixpkgs-22_05` (please note
the dash vs. underscore).
IMHO it's not a good idea to not throw an error in that case and
probably leave end-users rather confused, so I implemented a small check
for that which basically checks whether `follows`-declaration from
overrides actually have corresponding inputs in the transitive flake.
In fact this was done by accident already in our own test-suite where
the removal of a `follows` was apparently forgotten[1].
Since the key of the `std::map` that holds the `overrides` is a vector
and we have to find the last element of each vector (i.e. the override)
this has to be done with a for loop in O(n) complexity with `n` being
the total amount of overrides (which shouldn't be that large though).
Please note that this doesn't work with nested expressions, i.e.
inputs.fenix.inputs.nixpkgs.follows = "...";
which is a known problem[2].
For the expression demonstrated above, an error like this will be
thrown:
error: sops-nix has a `follows'-declaration for a non-existant input nixpkgs_22_05!
[1] 2664a216e5
[2] https://github.com/NixOS/nix/issues/5790
- Don't use `printf` for the expected result, but just use bash's `$' '`
litteral strings
- Quote the `nix` call result
- Invert the order in the comparisons (just because it feels more
natural)
Basically an attempt to resume fixing #5543 for a breakage introduced
earlier[1]. Basically, when evaluating an older `nixpkgs` with
`nix-shell` the following error occurs:
λ ma27 [~] → nix-shell -I nixpkgs=channel:nixos-18.03 -p nix
error: anonymous function at /nix/store/zakqwc529rb6xcj8pwixjsxscvlx9fbi-source/pkgs/top-level/default.nix:20:1 called with unexpected argument 'inNixShell'
at /nix/store/zakqwc529rb6xcj8pwixjsxscvlx9fbi-source/pkgs/top-level/impure.nix:82:1:
81|
82| import ./. (builtins.removeAttrs args [ "system" "platform" ] // {
| ^
83| inherit config overlays crossSystem;
This is a problem because one of the main selling points of Nix is that
you can evaluate any old Nix expression and still get the same result
(which also means that it *still evaluates*). In fact we're deprecating,
but not removing a lot of stuff for that reason such as unquoted URLs[2]
or `builtins.toPath`. However this property was essentially thrown away
here.
The change is rather simple: check if `inNixShell` is specified in the
formals of an auto-called function. This means that
{ inNixShell ? false }:
builtins.trace inNixShell
(with import <nixpkgs> { }; makeShell { name = "foo"; })
will show `trace: true` while
args@{ ... }:
builtins.trace args.inNixShell
(with import <nixpkgs> { }; makeShell { name = "foo"; })
will throw the following error:
error: attribute 'inNixShell' missing
This is explicitly needed because the function in
`pkgs/top-level/impure.nix` of e.g. NixOS 18.03 has an ellipsis[3], but
passes the attribute-set on to another lambda with formals that doesn't
have an ellipsis anymore (hence the error from above). This was perhaps
a mistake, but we can't fix it anymore. This also means that there's
AFAICS no proper way to check if the attr-set that's passed to the Nix
code via `EvalState::autoCallFunction` is eventually passed to a lambda
with formals where `inNixShell` is missing.
However, this fix comes with a certain price. Essentially every
`shell.nix` that assumes `inNixShell` to be passed to the formals even
without explicitly specifying it would break with this[4]. However I think
that this is ugly, but preferable:
* Nix 2.3 was declared stable by NixOS up until recently (well, it still
is as long as 21.11 is alive), so most people might not have even
noticed that feature.
* We're talking about a way shorter time-span with this change being
in the wild, so the fallout should be smaller IMHO.
[1] 9d612c393a
[2] https://github.com/NixOS/rfcs/pull/45#issuecomment-488232537
[3] https://github.com/NixOS/nixpkgs/blob/release-18.03/pkgs/top-level/impure.nix#L75
[4] See e.g. the second expression in this commit-message or the changes
for `tests/ca/nix-shell.sh`.
