nixpkgs/pkgs/top-level/release-lib.nix
Emily 8725e466ef release: forbid use of lib.fileset in Nixpkgs
Due to Nix bug <https://github.com/NixOS/nix/issues/11503>,
`builtins.filterSource` and chroot stores interact in a confusing
and broken way that breaks `lib.fileset`. This means that uses of
the API inside Nixpkgs keep breaking the NixOS installer, blocking
the channel. The resulting error messages are inscrutable (they look
like “the installer test is trying to download `curl`…?” and
eventually bottom out in a derivation that has the wrong `outPath`
because of the chroot store causing an incorrect `lib.fileset` result).

Whenever this happens, someone (well, in practice K900 or I)
has to bisect the change that introduced it and remove the use of
`lib.fileset`. This has happened at least three times in the past
four months (I believe I might actually be missing one here, but
these are the ones I remember and could easily dig up):

* <https://github.com/NixOS/nixpkgs/pull/340046>
* <https://github.com/NixOS/nixpkgs/pull/352491>
* <https://github.com/NixOS/nixpkgs/pull/369459>

The options I see here are:

1. Forbid use of `lib.fileset` within Nixpkgs until the Nix bug is
   fixed. This is the approach taken here. External users of Nixpkgs
   can continue to use the API as normal, but using it from within
   something that affects any release jobset `outPath`s will cause an
   evaluation failure with a hopefully‐helpful error message.

2. Forbid `lib.fileset` and also all of the other library APIs that use
   `builtins.filterSource`. I’m happy to do this, but so far none of
   those have broken the installer, so I decided to start small and
   worry about the others if they end up causing a problem in practice.

3. Forbid `builtins.filterSource` directly. This is hard and would
   require more invasive `builtins.scopedImport` crimes to do at
   evaluation time. I think this would realistically have to be done in
   something like nixpkgs-vet instead and I didn’t have much luck
   shoehorning a check like this into that codebase when I tried.

4. Fix the Nix bug. This would be great! But also it doesn’t seem to be
   happening any time soon, it seems difficult to fix in a way that
   doesn’t subtly break compatibility with the previous semantics, and
   arguably the fix would need backporting all the way back to 2.3
   given our minimum version policy.

5. Do nothing; have people continue to innocuously use `lib.fileset`
   throughout Nixpkgs, breaking the installer whenever one of them
   sneaks in to that closure, causing the channel to be blocked and
   requiring expensive bisections to narrow down the inscrutable test
   failure to the package using `lib.fileset`, which then needs moving
   back off it. This sucks for the people who keep having to track it
   down, holds back important channel bumps, and the criteria for when
   it’s okay to use `lib.fileset` are not realistically possible to
   teach to all contributors.

I'd be happy to work on (2) as an alternative; (3) would be difficult
and seems like overkill, (4) is not really something I trust myself
to do and wouldn’t address the immediate problem, and (5) isn’t
sustainable. I think that the current approach here is the best
trade‐off for now, as `lib.fileset` seems to be the only prominent
user of the `builtins.filterSource` API that works with full store
paths, exposing it to the Nix bug. It’s unfortunate to lose the
nice API, but since we can’t rely on it to produce correct results
and the channels keep getting blocked as a result, I don’t think
we really have an alternative right now.
2024-12-31 15:01:04 +00:00

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{ supportedSystems
, system ? builtins.currentSystem
, packageSet ? (import ../..)
, scrubJobs ? true
, # Attributes passed to nixpkgs. Don't build packages marked as unfree.
nixpkgsArgs ? {
config = { allowUnfree = false; inHydra = true; };
__allowFileset = false;
}
}:
let
lib = import ../../lib;
inherit (lib)
addMetaAttrs
any
derivations
filter
flip
genAttrs
getAttrFromPath
hydraJob
id
isDerivation
lists
maintainers
mapAttrs
mapAttrs'
mapAttrsRecursive
matchAttrs
meta
nameValuePair
platforms
recursiveUpdate
subtractLists
systems
;
pkgs = packageSet (recursiveUpdate { inherit system; config.allowUnsupportedSystem = true; } nixpkgsArgs);
hydraJob' = if scrubJobs then hydraJob else id;
/* !!! Hack: poor man's memoisation function. Necessary to prevent
Nixpkgs from being evaluated again and again for every
job/platform pair. */
mkPkgsFor = crossSystem: let
packageSet' = args: packageSet (args // { inherit crossSystem; } // nixpkgsArgs);
pkgs_x86_64_linux = packageSet' { system = "x86_64-linux"; };
pkgs_i686_linux = packageSet' { system = "i686-linux"; };
pkgs_aarch64_linux = packageSet' { system = "aarch64-linux"; };
pkgs_riscv64_linux = packageSet' { system = "riscv64-linux"; };
pkgs_aarch64_darwin = packageSet' { system = "aarch64-darwin"; };
pkgs_armv6l_linux = packageSet' { system = "armv6l-linux"; };
pkgs_armv7l_linux = packageSet' { system = "armv7l-linux"; };
pkgs_x86_64_darwin = packageSet' { system = "x86_64-darwin"; };
pkgs_x86_64_freebsd = packageSet' { system = "x86_64-freebsd"; };
pkgs_i686_freebsd = packageSet' { system = "i686-freebsd"; };
pkgs_i686_cygwin = packageSet' { system = "i686-cygwin"; };
pkgs_x86_64_cygwin = packageSet' { system = "x86_64-cygwin"; };
in system:
if system == "x86_64-linux" then pkgs_x86_64_linux
else if system == "i686-linux" then pkgs_i686_linux
else if system == "aarch64-linux" then pkgs_aarch64_linux
else if system == "riscv64-linux" then pkgs_riscv64_linux
else if system == "aarch64-darwin" then pkgs_aarch64_darwin
else if system == "armv6l-linux" then pkgs_armv6l_linux
else if system == "armv7l-linux" then pkgs_armv7l_linux
else if system == "x86_64-darwin" then pkgs_x86_64_darwin
else if system == "x86_64-freebsd" then pkgs_x86_64_freebsd
else if system == "i686-freebsd" then pkgs_i686_freebsd
else if system == "i686-cygwin" then pkgs_i686_cygwin
else if system == "x86_64-cygwin" then pkgs_x86_64_cygwin
else abort "unsupported system type: ${system}";
pkgsFor = pkgsForCross null;
# More poor man's memoisation
pkgsForCross = let
examplesByConfig = flip mapAttrs'
systems.examples
(_: crossSystem: nameValuePair crossSystem.config {
inherit crossSystem;
pkgsFor = mkPkgsFor crossSystem;
});
native = mkPkgsFor null;
in crossSystem: let
candidate = examplesByConfig.${crossSystem.config} or null;
in if crossSystem == null
then native
else if candidate != null && matchAttrs crossSystem candidate.crossSystem
then candidate.pkgsFor
else mkPkgsFor crossSystem; # uncached fallback
# Given a list of 'meta.platforms'-style patterns, return the sublist of
# `supportedSystems` containing systems that matches at least one of the given
# patterns.
#
# This is written in a funny way so that we only elaborate the systems once.
supportedMatches = let
supportedPlatforms = map
(system: systems.elaborate { inherit system; })
supportedSystems;
in metaPatterns: let
anyMatch = platform:
any (meta.platformMatch platform) metaPatterns;
matchingPlatforms = filter anyMatch supportedPlatforms;
in map ({ system, ...}: system) matchingPlatforms;
assertTrue = bool:
if bool
then pkgs.runCommand "evaluated-to-true" {} "touch $out"
else pkgs.runCommand "evaluated-to-false" {} "false";
/* The working or failing mails for cross builds will be sent only to
the following maintainers, as most package maintainers will not be
interested in the result of cross building a package. */
crossMaintainers = [ ];
# Generate attributes for all supported systems.
forAllSystems = genAttrs supportedSystems;
# Generate attributes for all systems matching at least one of the given
# patterns
forMatchingSystems = metaPatterns: genAttrs (supportedMatches metaPatterns);
/* Build a package on the given set of platforms. The function `f'
is called for each supported platform with Nixpkgs for that
platform as an argument . We return an attribute set containing
a derivation for each supported platform, i.e. { x86_64-linux =
f pkgs_x86_64_linux; i686-linux = f pkgs_i686_linux; ... }. */
testOn = testOnCross null;
/* Similar to the testOn function, but with an additional
'crossSystem' parameter for packageSet', defining the target
platform for cross builds. */
testOnCross = crossSystem: metaPatterns: f: forMatchingSystems metaPatterns
(system: hydraJob' (f (pkgsForCross crossSystem system)));
/* Given a nested set where the leaf nodes are lists of platforms,
map each leaf node to `testOn [platforms...] (pkgs:
pkgs.<attrPath>)'. */
mapTestOn = _mapTestOnHelper id null;
_mapTestOnHelper = f: crossSystem: mapAttrsRecursive
(path: metaPatterns: testOnCross crossSystem metaPatterns
(pkgs: f (getAttrFromPath path pkgs)));
/* Similar to the testOn function, but with an additional 'crossSystem'
* parameter for packageSet', defining the target platform for cross builds,
* and triggering the build of the host derivation. */
mapTestOnCross = _mapTestOnHelper
(addMetaAttrs { maintainers = crossMaintainers; });
/* Recursive for packages and apply a function to them */
recursiveMapPackages = f: mapAttrs (name: value:
if isDerivation value then
f value
else if value.recurseForDerivations or false || value.recurseForRelease or false then
recursiveMapPackages f value
else
[]
);
/* Gets the list of Hydra platforms for a derivation */
getPlatforms = drv:
drv.meta.hydraPlatforms
or (subtractLists (drv.meta.badPlatforms or [])
(drv.meta.platforms or supportedSystems));
/* Recursively map a (nested) set of derivations to an isomorphic
set of meta.platforms values. */
packagePlatforms = recursiveMapPackages getPlatforms;
in {
/* Common platform groups on which to test packages. */
inherit (platforms) unix linux darwin cygwin all;
inherit
assertTrue
forAllSystems
forMatchingSystems
hydraJob'
lib
mapTestOn
mapTestOnCross
recursiveMapPackages
getPlatforms
packagePlatforms
pkgs
pkgsFor
pkgsForCross
supportedMatches
testOn
testOnCross
;
}