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python3.pkgs: fix splice through unsupported hosts

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Previously, unless unsupported platforms were allowed, the following
would fail to evaluate (from an "x86_64-linux" system):

    pkgsCross.x86_64-freebsd.__splicedPackages.docutils.__spliced.buildHost

It shouldn't have, because the buildHost package ends up being for
Linux.  This broke evaluation of e.g. pkgsCross.x86_64-freebsd.libdrm,
because it has docutils in nativeBuildInputs.  mkDerivation would try
to go through __spliced.buildHost on docutils to get to the Linux
version, but the check in ensurePythonModules would kick in first,
triggering the meta check because of the equality check in the
implementation of hasPythonModule, which would fail because Python is
not marked as supported on FreeBSD in Nixpkgs at the moment.  Thus,
even though they're not supposed to be, the meta checks would be
triggered even though the only attribute being accessed on the
unsupported derivation was __spliced.

We can fix this by using the same mechanism used to implement the meta
checks themselves: lib.extendDerivation.  Now, attempting to access
drvPath or outPath on an attribute that fails the validity check will
produce the same error as before, but other accesses will be allowed
through, fixing splicing.

I've tested evaluation of packages that pass and fail the validity
check, and confirmed that the behaviour is still correct.
This commit is contained in:
Alyssa Ross 2023-01-26 20:12:52 +00:00
parent 02ee33a5c1
commit b682fef8e9
1 changed files with 6 additions and 2 deletions
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8
pkgs/development/interpreters/python/default.nix
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@ -36,8 +36,12 @@
stdenv
];
providesSetupHook = lib.attrByPath [ "provides" "setupHook"] false;
valid = value: !lib.isDerivation value || pythonPackages.hasPythonModule value || providesSetupHook value || lib.elem value exceptions;
func = name: value: if (valid value) then value else throw "${name} should use `buildPythonPackage` or `toPythonModule` if it is to be part of the Python packages set.";
valid = value: pythonPackages.hasPythonModule value || providesSetupHook value || lib.elem value exceptions;
func = name: value:
if lib.isDerivation value then
lib.extendDerivation (valid value || throw "${name} should use `buildPythonPackage` or `toPythonModule` if it is to be part of the Python packages set.") {} value
else
value;
in lib.mapAttrs func items;
in ensurePythonModules (callPackage
# Function that when called