Previously, meta.platforms would be checked for each package when
generating package attributes for a system, so that unsupported packages
would not have an output attribute. This commit removes that behavior.
Now `nix flake show` will succeed even if packages fail to evaluate on
other platforms. `nix flake show --all-systems` will still fail though.
A user whose flake only has a package would expect it to be used when
running `nix develop`. But since theres probably an automatically
created devShell, the package's deps will not be available in the shell.
If a default package exists, it makes sense for its deps to be available
by default in the default devShell.
`nullOr`'s merge function requires definitions to all be null or all be
non-null. It was being used where the intent was that null be used as a
value representing unset, and as such the merge should return null if
all definitions are null and ignore nulls otherwise. This adds a type
with that merge semantics.
If a package uses `pkgs` and tries to get a non-existing package, there
will be an uncachable error. As we cannot control this, this method
needs to be removed. Instead of using this method, the mocked pkgs
should be extended to support more cases.
If a package depends on a package with same name, this causes an
infinite recursion as it tries to depend on itself. This is not likely
what was intended, and breaks ability to re-export packages, so instead
if a package depends on the same name, that now refers to the previous
version.
Many attributes can take moduleArgs when auto-loaded in order to
facilitate access to them from other files. Those same attributes could
not take moduleArgs when included directly, which was inconsistent.
With this change, all attributes that could take moduleArgs when
auto-loaded can now always do so. Auto-loading no longer needs special
cases.
Previously, the packages outputs would be evalutated using callPackage
on the package set, but the package set already contains the package. If
another package depends on it, the dependency would be the version from
the package set. By grabbing the packages from the package set, each
package only needs to be evaluated once.
Since evaluating pkgs is expensive, this speeds up evaluation of flakes
with `packages.default` by attempting to get the name using a pkgs set
containing only mocked builders that just return the name.
In order to speed up evalutation of flakes setting `packages.default`,
this trys to compute the pname in multiple ways, ordered by speed. The
pname can be set manually, which is fastest. To avoid computing a new
nixpkgs and flakelight overlays, the second option just uses callPackage
from stock nixpkgs. If that fails, the prior, most accurate, method is
used which creates a new nixpkgs with all the overlays available.
Using `perSystem` to implement per-system attributes ties all the
per-system attributes together; all the `perSystem` functions must run
to determine output attrs. By generating them separately, the generation
can be done lazily.
