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nixpkgs/lib/composable-derivation.nix

114 lines
4.2 KiB

{lib, pkgs}:
let inherit (lib) nv nvs; in
{
# composableDerivation basically mixes these features:
# - fix function
# - mergeAttrBy
# - provides shortcuts for "options" such as "--enable-foo" and adding
# buildInputs, see php example
#
# It predates styles which are common today, such as
# * the config attr
# * mkDerivation.override feature
# * overrideDerivation (lib/customization.nix)
#
# Some of the most more important usage examples (which could be rewritten if it was important):
# * php
# * postgis
# * vim_configurable
#
# A minimal example illustrating most features would look like this:
# let base = composableDerivation { (fixed: let inherit (fixed.fixed) name in {
# src = fetchurl {
# }
# buildInputs = [A];
# preConfigre = "echo ${name}";
# # attention, "name" attr is missing, thus you cannot instantiate "base".
# }
# in {
# # These all add name attribute, thus you can instantiate those:
# v1 = base.merge ({ name = "foo-add-B"; buildInputs = [B]; }); // B gets merged into buildInputs
# v2 = base.merge ({ name = "mix-in-pre-configure-lines" preConfigre = ""; });
# v3 = base.replace ({ name = "foo-no-A-only-B;" buildInputs = [B]; });
# }
#
# So yes, you can think about it being something like nixos modules, and
# you'd be merging "features" in one at a time using .merge or .replace
# Thanks Shea for telling me that I rethink the documentation ..
#
# issues:
# * its complicated to understand
# * some "features" such as exact merge behaviour are burried in mergeAttrBy
# and defaultOverridableDelayableArgs assuming the default behaviour does
# the right thing in the common case
# * Eelco once said using such fix style functions are slow to evaluate
# * Too quick & dirty. Hard to understand for others. The benefit was that
# you were able to create a kernel builder like base derivation and replace
# / add patches the way you want without having to declare function arguments
#
# nice features:
# declaring "optional featuers" is modular. For instance:
# flags.curl = {
# configureFlags = ["--with-curl=${curl.dev}" "--with-curlwrappers"];
# buildInputs = [curl openssl];
# };
# flags.other = { .. }
# (Example taken from PHP)
#
# alternative styles / related features:
# * Eg see function supporting building the kernel
# * versionedDerivation (discussion about this is still going on - or ended)
# * composedArgsAndFun
# * mkDerivation.override
# * overrideDerivation
# * using { .., *Support ? false }: like configurable options.
# To find those examples use grep
#
# To sum up: It exists for historical reasons - and for most commonly used
# tasks the alternatives should be used
#
# If you have questions about this code ping Marc Weber.
composableDerivation = {
mkDerivation ? pkgs.stdenv.mkDerivation,
# list of functions to be applied before defaultOverridableDelayableArgs removes removeAttrs names
# prepareDerivationArgs handles derivation configurations
applyPreTidy ? [ lib.prepareDerivationArgs ],
# consider adding addtional elements by derivation.merge { removeAttrs = ["elem"]; };
removeAttrs ? ["cfg" "flags"]
}: (lib.defaultOverridableDelayableArgs ( a: mkDerivation a)
{
inherit applyPreTidy removeAttrs;
}).merge;
# some utility functions
# use this function to generate flag attrs for prepareDerivationArgs
# E nable D isable F eature
edf = {name, feat ? name, enable ? {}, disable ? {} , value ? ""}:
nvs name {
set = {
configureFlags = ["--enable-${feat}${if value == "" then "" else "="}${value}"];
} // enable;
unset = {
configureFlags = ["--disable-${feat}"];
} // disable;
};
# same for --with and --without-
# W ith or W ithout F eature
wwf = {name, feat ? name, enable ? {}, disable ? {}, value ? ""}:
nvs name {
set = enable // {
configureFlags = ["--with-${feat}${if value == "" then "" else "="}${value}"]
++ lib.maybeAttr "configureFlags" [] enable;
};
unset = disable // {
configureFlags = ["--without-${feat}"]
++ lib.maybeAttr "configureFlags" [] disable;
};
};
}