nixpkgs/pkgs/stdenv/generic/make-derivation.nix
2023-07-06 10:33:24 +02:00

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{ lib, config }:
stdenv:
let
checkMeta = import ./check-meta.nix {
inherit lib config;
# Nix itself uses the `system` field of a derivation to decide where
# to build it. This is a bit confusing for cross compilation.
inherit (stdenv) hostPlatform;
};
# Based off lib.makeExtensible, with modifications:
makeDerivationExtensible = rattrs:
let
# NOTE: The following is a hint that will be printed by the Nix cli when
# encountering an infinite recursion. It must not be formatted into
# separate lines, because Nix would only show the last line of the comment.
# An infinite recursion here can be caused by having the attribute names of expression `e` in `.overrideAttrs(finalAttrs: previousAttrs: e)` depend on `finalAttrs`. Only the attribute values of `e` can depend on `finalAttrs`.
args = rattrs (args // { inherit finalPackage overrideAttrs; });
# ^^^^
overrideAttrs = f0:
let
f = self: super:
# Convert f0 to an overlay. Legacy is:
# overrideAttrs (super: {})
# We want to introduce self. We follow the convention of overlays:
# overrideAttrs (self: super: {})
# Which means the first parameter can be either self or super.
# This is surprising, but far better than the confusion that would
# arise from flipping an overlay's parameters in some cases.
let x = f0 super;
in
if builtins.isFunction x
then
# Can't reuse `x`, because `self` comes first.
# Looks inefficient, but `f0 super` was a cheap thunk.
f0 self super
else x;
in
makeDerivationExtensible
(self: let super = rattrs self; in super // (if builtins.isFunction f0 || f0?__functor then f self super else f0));
finalPackage =
mkDerivationSimple overrideAttrs args;
in finalPackage;
# makeDerivationExtensibleConst == makeDerivationExtensible (_: attrs),
# but pre-evaluated for a slight improvement in performance.
makeDerivationExtensibleConst = attrs:
mkDerivationSimple
(f0:
let
f = self: super:
let x = f0 super;
in
if builtins.isFunction x
then
f0 self super
else x;
in
makeDerivationExtensible (self: attrs // (if builtins.isFunction f0 || f0?__functor then f self attrs else f0)))
attrs;
mkDerivationSimple = overrideAttrs:
# `mkDerivation` wraps the builtin `derivation` function to
# produce derivations that use this stdenv and its shell.
#
# See also:
#
# * https://nixos.org/nixpkgs/manual/#sec-using-stdenv
# Details on how to use this mkDerivation function
#
# * https://nixos.org/manual/nix/stable/expressions/derivations.html#derivations
# Explanation about derivations in general
{
# These types of dependencies are all exhaustively documented in
# the "Specifying Dependencies" section of the "Standard
# Environment" chapter of the Nixpkgs manual.
# TODO(@Ericson2314): Stop using legacy dep attribute names
# host offset -> target offset
depsBuildBuild ? [] # -1 -> -1
, depsBuildBuildPropagated ? [] # -1 -> -1
, nativeBuildInputs ? [] # -1 -> 0 N.B. Legacy name
, propagatedNativeBuildInputs ? [] # -1 -> 0 N.B. Legacy name
, depsBuildTarget ? [] # -1 -> 1
, depsBuildTargetPropagated ? [] # -1 -> 1
, depsHostHost ? [] # 0 -> 0
, depsHostHostPropagated ? [] # 0 -> 0
, buildInputs ? [] # 0 -> 1 N.B. Legacy name
, propagatedBuildInputs ? [] # 0 -> 1 N.B. Legacy name
, depsTargetTarget ? [] # 1 -> 1
, depsTargetTargetPropagated ? [] # 1 -> 1
, checkInputs ? []
, installCheckInputs ? []
, nativeCheckInputs ? []
, nativeInstallCheckInputs ? []
# Configure Phase
, configureFlags ? []
, cmakeFlags ? []
, mesonFlags ? []
, # Target is not included by default because most programs don't care.
# Including it then would cause needless mass rebuilds.
#
# TODO(@Ericson2314): Make [ "build" "host" ] always the default / resolve #87909
configurePlatforms ? lib.optionals
(stdenv.hostPlatform != stdenv.buildPlatform || config.configurePlatformsByDefault)
[ "build" "host" ]
# TODO(@Ericson2314): Make unconditional / resolve #33599
# Check phase
, doCheck ? config.doCheckByDefault or false
# TODO(@Ericson2314): Make unconditional / resolve #33599
# InstallCheck phase
, doInstallCheck ? config.doCheckByDefault or false
, # TODO(@Ericson2314): Make always true and remove / resolve #178468
strictDeps ? if config.strictDepsByDefault then true else stdenv.hostPlatform != stdenv.buildPlatform
, enableParallelBuilding ? config.enableParallelBuildingByDefault
, meta ? {}
, passthru ? {}
, pos ? # position used in error messages and for meta.position
(if attrs.meta.description or null != null
then builtins.unsafeGetAttrPos "description" attrs.meta
else if attrs.version or null != null
then builtins.unsafeGetAttrPos "version" attrs
else builtins.unsafeGetAttrPos "name" attrs)
, separateDebugInfo ? false
, outputs ? [ "out" ]
, __darwinAllowLocalNetworking ? false
, __impureHostDeps ? []
, __propagatedImpureHostDeps ? []
, sandboxProfile ? ""
, propagatedSandboxProfile ? ""
, hardeningEnable ? []
, hardeningDisable ? []
, patches ? []
, __contentAddressed ?
(! attrs ? outputHash) # Fixed-output drvs can't be content addressed too
&& config.contentAddressedByDefault
# Experimental. For simple packages mostly just works,
# but for anything complex, be prepared to debug if enabling.
, __structuredAttrs ? config.structuredAttrsByDefault or false
, env ? { }
, ... } @ attrs:
let
# TODO(@oxij, @Ericson2314): This is here to keep the old semantics, remove when
# no package has `doCheck = true`.
doCheck' = doCheck && stdenv.buildPlatform.canExecute stdenv.hostPlatform;
doInstallCheck' = doInstallCheck && stdenv.buildPlatform.canExecute stdenv.hostPlatform;
separateDebugInfo' = separateDebugInfo && stdenv.hostPlatform.isLinux;
outputs' = outputs ++ lib.optional separateDebugInfo' "debug";
# Turn a derivation into its outPath without a string context attached.
# See the comment at the usage site.
unsafeDerivationToUntrackedOutpath = drv:
if lib.isDerivation drv
then builtins.unsafeDiscardStringContext drv.outPath
else drv;
noNonNativeDeps = builtins.length (depsBuildTarget ++ depsBuildTargetPropagated
++ depsHostHost ++ depsHostHostPropagated
++ buildInputs ++ propagatedBuildInputs
++ depsTargetTarget ++ depsTargetTargetPropagated) == 0;
dontAddHostSuffix = attrs ? outputHash && !noNonNativeDeps || !stdenv.hasCC;
hardeningDisable' = if lib.any (x: x == "fortify") hardeningDisable
# disabling fortify implies fortify3 should also be disabled
then lib.unique (hardeningDisable ++ [ "fortify3" ])
else hardeningDisable;
supportedHardeningFlags = [ "fortify" "fortify3" "stackprotector" "pie" "pic" "strictoverflow" "format" "relro" "bindnow" ];
# Musl-based platforms will keep "pie", other platforms will not.
# If you change this, make sure to update section `{#sec-hardening-in-nixpkgs}`
# in the nixpkgs manual to inform users about the defaults.
defaultHardeningFlags = if stdenv.hostPlatform.isMusl &&
# Except when:
# - static aarch64, where compilation works, but produces segfaulting dynamically linked binaries.
# - static armv7l, where compilation fails.
!(stdenv.hostPlatform.isAarch && stdenv.hostPlatform.isStatic)
then supportedHardeningFlags
else lib.remove "pie" supportedHardeningFlags;
enabledHardeningOptions =
if builtins.elem "all" hardeningDisable'
then []
else lib.subtractLists hardeningDisable' (defaultHardeningFlags ++ hardeningEnable);
# hardeningDisable additionally supports "all".
erroneousHardeningFlags = lib.subtractLists supportedHardeningFlags (hardeningEnable ++ lib.remove "all" hardeningDisable);
checkDependencyList = checkDependencyList' [];
checkDependencyList' = positions: name: deps: lib.flip lib.imap1 deps (index: dep:
if lib.isDerivation dep || dep == null || builtins.isString dep || builtins.isPath dep then dep
else if lib.isList dep then checkDependencyList' ([index] ++ positions) name dep
else throw "Dependency is not of a valid type: ${lib.concatMapStrings (ix: "element ${toString ix} of ") ([index] ++ positions)}${name} for ${attrs.name or attrs.pname}");
in if builtins.length erroneousHardeningFlags != 0
then abort ("mkDerivation was called with unsupported hardening flags: " + lib.generators.toPretty {} {
inherit erroneousHardeningFlags hardeningDisable hardeningEnable supportedHardeningFlags;
})
else let
doCheck = doCheck';
doInstallCheck = doInstallCheck';
buildInputs' = buildInputs
++ lib.optionals doCheck checkInputs
++ lib.optionals doInstallCheck installCheckInputs;
nativeBuildInputs' = nativeBuildInputs
++ lib.optional separateDebugInfo' ../../build-support/setup-hooks/separate-debug-info.sh
++ lib.optional stdenv.hostPlatform.isWindows ../../build-support/setup-hooks/win-dll-link.sh
++ lib.optionals doCheck nativeCheckInputs
++ lib.optionals doInstallCheck nativeInstallCheckInputs;
outputs = outputs';
references = nativeBuildInputs ++ buildInputs
++ propagatedNativeBuildInputs ++ propagatedBuildInputs;
dependencies = map (map lib.chooseDevOutputs) [
[
(map (drv: drv.__spliced.buildBuild or drv) (checkDependencyList "depsBuildBuild" depsBuildBuild))
(map (drv: drv.__spliced.buildHost or drv) (checkDependencyList "nativeBuildInputs" nativeBuildInputs'))
(map (drv: drv.__spliced.buildTarget or drv) (checkDependencyList "depsBuildTarget" depsBuildTarget))
]
[
(map (drv: drv.__spliced.hostHost or drv) (checkDependencyList "depsHostHost" depsHostHost))
(map (drv: drv.__spliced.hostTarget or drv) (checkDependencyList "buildInputs" buildInputs'))
]
[
(map (drv: drv.__spliced.targetTarget or drv) (checkDependencyList "depsTargetTarget" depsTargetTarget))
]
];
propagatedDependencies = map (map lib.chooseDevOutputs) [
[
(map (drv: drv.__spliced.buildBuild or drv) (checkDependencyList "depsBuildBuildPropagated" depsBuildBuildPropagated))
(map (drv: drv.__spliced.buildHost or drv) (checkDependencyList "propagatedNativeBuildInputs" propagatedNativeBuildInputs))
(map (drv: drv.__spliced.buildTarget or drv) (checkDependencyList "depsBuildTargetPropagated" depsBuildTargetPropagated))
]
[
(map (drv: drv.__spliced.hostHost or drv) (checkDependencyList "depsHostHostPropagated" depsHostHostPropagated))
(map (drv: drv.__spliced.hostTarget or drv) (checkDependencyList "propagatedBuildInputs" propagatedBuildInputs))
]
[
(map (drv: drv.__spliced.targetTarget or drv) (checkDependencyList "depsTargetTargetPropagated" depsTargetTargetPropagated))
]
];
computedSandboxProfile =
lib.concatMap (input: input.__propagatedSandboxProfile or [])
(stdenv.extraNativeBuildInputs
++ stdenv.extraBuildInputs
++ lib.concatLists dependencies);
computedPropagatedSandboxProfile =
lib.concatMap (input: input.__propagatedSandboxProfile or [])
(lib.concatLists propagatedDependencies);
computedImpureHostDeps =
lib.unique (lib.concatMap (input: input.__propagatedImpureHostDeps or [])
(stdenv.extraNativeBuildInputs
++ stdenv.extraBuildInputs
++ lib.concatLists dependencies));
computedPropagatedImpureHostDeps =
lib.unique (lib.concatMap (input: input.__propagatedImpureHostDeps or [])
(lib.concatLists propagatedDependencies));
envIsExportable = lib.isAttrs env && !lib.isDerivation env;
derivationArg =
(removeAttrs attrs
(["meta" "passthru" "pos"
"checkInputs" "installCheckInputs"
"nativeCheckInputs" "nativeInstallCheckInputs"
"__contentAddressed"
"__darwinAllowLocalNetworking"
"__impureHostDeps" "__propagatedImpureHostDeps"
"sandboxProfile" "propagatedSandboxProfile"]
++ lib.optional (__structuredAttrs || envIsExportable) "env"))
// (lib.optionalAttrs (attrs ? name || (attrs ? pname && attrs ? version)) {
name =
let
# Indicate the host platform of the derivation if cross compiling.
# Fixed-output derivations like source tarballs shouldn't get a host
# suffix. But we have some weird ones with run-time deps that are
# just used for their side-affects. Those might as well since the
# hash can't be the same. See #32986.
hostSuffix = lib.optionalString
(stdenv.hostPlatform != stdenv.buildPlatform && !dontAddHostSuffix)
"-${stdenv.hostPlatform.config}";
# Disambiguate statically built packages. This was originally
# introduce as a means to prevent nix-env to get confused between
# nix and nixStatic. This should be also achieved by moving the
# hostSuffix before the version, so we could contemplate removing
# it again.
staticMarker = lib.optionalString stdenv.hostPlatform.isStatic "-static";
in
lib.strings.sanitizeDerivationName (
if attrs ? name
then attrs.name + hostSuffix
else
# we cannot coerce null to a string below
assert lib.assertMsg (attrs ? version && attrs.version != null) "The version attribute cannot be null.";
"${attrs.pname}${staticMarker}${hostSuffix}-${attrs.version}"
);
}) // lib.optionalAttrs __structuredAttrs { env = checkedEnv; } // {
builder = attrs.realBuilder or stdenv.shell;
args = attrs.args or ["-e" (attrs.builder or ./default-builder.sh)];
inherit stdenv;
# The `system` attribute of a derivation has special meaning to Nix.
# Derivations set it to choose what sort of machine could be used to
# execute the build, The build platform entirely determines this,
# indeed more finely than Nix knows or cares about. The `system`
# attribute of `buildPlatfom` matches Nix's degree of specificity.
# exactly.
inherit (stdenv.buildPlatform) system;
userHook = config.stdenv.userHook or null;
__ignoreNulls = true;
inherit __structuredAttrs strictDeps;
depsBuildBuild = lib.elemAt (lib.elemAt dependencies 0) 0;
nativeBuildInputs = lib.elemAt (lib.elemAt dependencies 0) 1;
depsBuildTarget = lib.elemAt (lib.elemAt dependencies 0) 2;
depsHostHost = lib.elemAt (lib.elemAt dependencies 1) 0;
buildInputs = lib.elemAt (lib.elemAt dependencies 1) 1;
depsTargetTarget = lib.elemAt (lib.elemAt dependencies 2) 0;
depsBuildBuildPropagated = lib.elemAt (lib.elemAt propagatedDependencies 0) 0;
propagatedNativeBuildInputs = lib.elemAt (lib.elemAt propagatedDependencies 0) 1;
depsBuildTargetPropagated = lib.elemAt (lib.elemAt propagatedDependencies 0) 2;
depsHostHostPropagated = lib.elemAt (lib.elemAt propagatedDependencies 1) 0;
propagatedBuildInputs = lib.elemAt (lib.elemAt propagatedDependencies 1) 1;
depsTargetTargetPropagated = lib.elemAt (lib.elemAt propagatedDependencies 2) 0;
# This parameter is sometimes a string, sometimes null, and sometimes a list, yuck
configureFlags = let inherit (lib) optional elem; in
configureFlags
++ optional (elem "build" configurePlatforms) "--build=${stdenv.buildPlatform.config}"
++ optional (elem "host" configurePlatforms) "--host=${stdenv.hostPlatform.config}"
++ optional (elem "target" configurePlatforms) "--target=${stdenv.targetPlatform.config}";
cmakeFlags =
cmakeFlags
++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) ([
"-DCMAKE_SYSTEM_NAME=${lib.findFirst lib.isString "Generic" (lib.optional (!stdenv.hostPlatform.isRedox) stdenv.hostPlatform.uname.system)}"
] ++ lib.optionals (stdenv.hostPlatform.uname.processor != null) [
"-DCMAKE_SYSTEM_PROCESSOR=${stdenv.hostPlatform.uname.processor}"
] ++ lib.optionals (stdenv.hostPlatform.uname.release != null) [
"-DCMAKE_SYSTEM_VERSION=${stdenv.hostPlatform.uname.release}"
] ++ lib.optionals (stdenv.hostPlatform.isDarwin) [
"-DCMAKE_OSX_ARCHITECTURES=${stdenv.hostPlatform.darwinArch}"
] ++ lib.optionals (stdenv.buildPlatform.uname.system != null) [
"-DCMAKE_HOST_SYSTEM_NAME=${stdenv.buildPlatform.uname.system}"
] ++ lib.optionals (stdenv.buildPlatform.uname.processor != null) [
"-DCMAKE_HOST_SYSTEM_PROCESSOR=${stdenv.buildPlatform.uname.processor}"
] ++ lib.optionals (stdenv.buildPlatform.uname.release != null) [
"-DCMAKE_HOST_SYSTEM_VERSION=${stdenv.buildPlatform.uname.release}"
]);
mesonFlags =
let
# See https://mesonbuild.com/Reference-tables.html#cpu-families
cpuFamily = platform: with platform;
/**/ if isAarch32 then "arm"
else if isx86_32 then "x86"
else platform.uname.processor;
crossFile = builtins.toFile "cross-file.conf" ''
[properties]
needs_exe_wrapper = ${lib.boolToString (!stdenv.buildPlatform.canExecute stdenv.hostPlatform)}
[host_machine]
system = '${stdenv.targetPlatform.parsed.kernel.name}'
cpu_family = '${cpuFamily stdenv.targetPlatform}'
cpu = '${stdenv.targetPlatform.parsed.cpu.name}'
endian = ${if stdenv.targetPlatform.isLittleEndian then "'little'" else "'big'"}
[binaries]
llvm-config = 'llvm-config-native'
'';
crossFlags = lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [ "--cross-file=${crossFile}" ];
in crossFlags ++ mesonFlags;
inherit patches;
inherit doCheck doInstallCheck;
inherit outputs;
} // lib.optionalAttrs (__contentAddressed) {
inherit __contentAddressed;
# Provide default values for outputHashMode and outputHashAlgo because
# most people won't care about these anyways
outputHashAlgo = attrs.outputHashAlgo or "sha256";
outputHashMode = attrs.outputHashMode or "recursive";
} // lib.optionalAttrs (enableParallelBuilding) {
inherit enableParallelBuilding;
enableParallelChecking = attrs.enableParallelChecking or true;
enableParallelInstalling = attrs.enableParallelInstalling or true;
} // lib.optionalAttrs (hardeningDisable != [] || hardeningEnable != [] || stdenv.hostPlatform.isMusl) {
NIX_HARDENING_ENABLE = enabledHardeningOptions;
} // lib.optionalAttrs (stdenv.hostPlatform.isx86_64 && stdenv.hostPlatform ? gcc.arch) {
requiredSystemFeatures = attrs.requiredSystemFeatures or [] ++ [ "gccarch-${stdenv.hostPlatform.gcc.arch}" ];
} // lib.optionalAttrs (stdenv.buildPlatform.isDarwin) {
inherit __darwinAllowLocalNetworking;
# TODO: remove lib.unique once nix has a list canonicalization primitive
__sandboxProfile =
let profiles = [ stdenv.extraSandboxProfile ] ++ computedSandboxProfile ++ computedPropagatedSandboxProfile ++ [ propagatedSandboxProfile sandboxProfile ];
final = lib.concatStringsSep "\n" (lib.filter (x: x != "") (lib.unique profiles));
in final;
__propagatedSandboxProfile = lib.unique (computedPropagatedSandboxProfile ++ [ propagatedSandboxProfile ]);
__impureHostDeps = computedImpureHostDeps ++ computedPropagatedImpureHostDeps ++ __propagatedImpureHostDeps ++ __impureHostDeps ++ stdenv.__extraImpureHostDeps ++ [
"/dev/zero"
"/dev/random"
"/dev/urandom"
"/bin/sh"
];
__propagatedImpureHostDeps = computedPropagatedImpureHostDeps ++ __propagatedImpureHostDeps;
} //
# If we use derivations directly here, they end up as build-time dependencies.
# This is especially problematic in the case of disallowed*, since the disallowed
# derivations will be built by nix as build-time dependencies, while those
# derivations might take a very long time to build, or might not even build
# successfully on the platform used.
# We can improve on this situation by instead passing only the outPath,
# without an attached string context, to nix. The out path will be a placeholder
# which will be replaced by the actual out path if the derivation in question
# is part of the final closure (and thus needs to be built). If it is not
# part of the final closure, then the placeholder will be passed along,
# but in that case we know for a fact that the derivation is not part of the closure.
# This means that passing the out path to nix does the right thing in either
# case, both for disallowed and allowed references/requisites, and we won't
# build the derivation if it wouldn't be part of the closure, saving time and resources.
# While the problem is less severe for allowed*, since we want the derivation
# to be built eventually, we would still like to get the error early and without
# having to wait while nix builds a derivation that might not be used.
# See also https://github.com/NixOS/nix/issues/4629
lib.optionalAttrs (attrs ? disallowedReferences) {
disallowedReferences =
map unsafeDerivationToUntrackedOutpath attrs.disallowedReferences;
} //
lib.optionalAttrs (attrs ? disallowedRequisites) {
disallowedRequisites =
map unsafeDerivationToUntrackedOutpath attrs.disallowedRequisites;
} //
lib.optionalAttrs (attrs ? allowedReferences) {
allowedReferences =
lib.mapNullable unsafeDerivationToUntrackedOutpath attrs.allowedReferences;
} //
lib.optionalAttrs (attrs ? allowedRequisites) {
allowedRequisites =
lib.mapNullable unsafeDerivationToUntrackedOutpath attrs.allowedRequisites;
};
meta = checkMeta.commonMeta { inherit validity attrs pos references; };
validity = checkMeta.assertValidity { inherit meta attrs; };
checkedEnv =
let
overlappingNames = lib.attrNames (builtins.intersectAttrs env derivationArg);
in
assert lib.assertMsg envIsExportable
"When using structured attributes, `env` must be an attribute set of environment variables.";
assert lib.assertMsg (overlappingNames == [ ])
"The env attribute set cannot contain any attributes passed to derivation. The following attributes are overlapping: ${lib.concatStringsSep ", " overlappingNames}";
lib.mapAttrs
(n: v: assert lib.assertMsg (lib.isString v || lib.isBool v || lib.isInt v || lib.isDerivation v)
"The env attribute set can only contain derivation, string, boolean or integer attributes. The ${n} attribute is of type ${builtins.typeOf v}."; v)
env;
in
lib.extendDerivation
validity.handled
({
# A derivation that always builds successfully and whose runtime
# dependencies are the original derivations build time dependencies
# This allows easy building and distributing of all derivations
# needed to enter a nix-shell with
# nix-build shell.nix -A inputDerivation
inputDerivation = derivation (derivationArg // {
# Add a name in case the original drv didn't have one
name = derivationArg.name or "inputDerivation";
# This always only has one output
outputs = [ "out" ];
# Propagate the original builder and arguments, since we override
# them and they might contain references to build inputs
_derivation_original_builder = derivationArg.builder;
_derivation_original_args = derivationArg.args;
builder = stdenv.shell;
# The bash builtin `export` dumps all current environment variables,
# which is where all build input references end up (e.g. $PATH for
# binaries). By writing this to $out, Nix can find and register
# them as runtime dependencies (since Nix greps for store paths
# through $out to find them)
args = [ "-c" ''
export > $out
for var in $passAsFile; do
pathVar="''${var}Path"
printf "%s" "$(< "''${!pathVar}")" >> $out
done
'' ];
# inputDerivation produces the inputs; not the outputs, so any
# restrictions on what used to be the outputs don't serve a purpose
# anymore.
allowedReferences = null;
allowedRequisites = null;
disallowedReferences = [ ];
disallowedRequisites = [ ];
});
inherit passthru overrideAttrs;
inherit meta;
} //
# Pass through extra attributes that are not inputs, but
# should be made available to Nix expressions using the
# derivation (e.g., in assertions).
passthru)
(derivation (derivationArg // lib.optionalAttrs envIsExportable checkedEnv));
in
fnOrAttrs:
if builtins.isFunction fnOrAttrs
then makeDerivationExtensible fnOrAttrs
else makeDerivationExtensibleConst fnOrAttrs