c273c15cb1
‘scopedImport’ works like ‘import’, except that it takes a set of attributes to be added to the lexical scope of the expression, essentially extending or overriding the builtin variables. For instance, the expression scopedImport { x = 1; } ./foo.nix where foo.nix contains ‘x’, will evaluate to 1. This has a few applications: * It allows getting rid of function argument specifications in package expressions. For instance, a package expression like: { stdenv, fetchurl, libfoo }: stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } can now we written as just stdenv.mkDerivation { ... buildInputs = [ libfoo ]; } and imported in all-packages.nix as: bar = scopedImport pkgs ./bar.nix; So whereas we once had dependencies listed in three places (buildInputs, the function, and the call site), they now only need to appear in one place. * It allows overriding builtin functions. For instance, to trace all calls to ‘map’: let overrides = { map = f: xs: builtins.trace "map called!" (map f xs); # Ensure that our override gets propagated by calls to # import/scopedImport. import = fn: scopedImport overrides fn; scopedImport = attrs: fn: scopedImport (overrides // attrs) fn; # Also update ‘builtins’. builtins = builtins // overrides; }; in scopedImport overrides ./bla.nix * Similarly, it allows extending the set of builtin functions. For instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library functions could be added to the default scope. There is a downside: calls to scopedImport are not memoized, unlike import. So importing a file multiple times leads to multiple parsings / evaluations. It would be possible to construct the AST only once, but that would require careful handling of variables/environments. |
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.. | ||
lang | ||
add.sh | ||
binary-cache.sh | ||
binary-patching.nix | ||
binary-patching.sh | ||
build-hook.hook.sh | ||
build-hook.nix | ||
build-hook.sh | ||
check-refs.nix | ||
check-refs.sh | ||
common.sh.in | ||
config.nix | ||
dependencies.builder0.sh | ||
dependencies.builder1.sh | ||
dependencies.builder2.sh | ||
dependencies.nix | ||
dependencies.sh | ||
dump-db.sh | ||
export-graph.nix | ||
export-graph.sh | ||
export.sh | ||
fallback.sh | ||
fetchurl.nix | ||
fetchurl.sh | ||
filter-source.nix | ||
filter-source.sh | ||
fixed.builder1.sh | ||
fixed.builder2.sh | ||
fixed.nix | ||
fixed.sh | ||
gc-concurrent.builder.sh | ||
gc-concurrent.nix | ||
gc-concurrent.sh | ||
gc-concurrent2.builder.sh | ||
gc-runtime.nix | ||
gc-runtime.sh | ||
gc.sh | ||
hash-check.nix | ||
hash.sh | ||
import-derivation.nix | ||
import-derivation.sh | ||
init.sh | ||
install-package.sh | ||
lang.sh | ||
local.mk | ||
logging.sh | ||
misc.sh | ||
multiple-outputs.nix | ||
multiple-outputs.sh | ||
negative-caching.nix | ||
negative-caching.sh | ||
nix-build.sh | ||
nix-channel.sh | ||
nix-copy-closure.nix | ||
nix-profile.sh | ||
nix-pull.sh | ||
nix-push.sh | ||
optimise-store.sh | ||
parallel.builder.sh | ||
parallel.nix | ||
parallel.sh | ||
referrers.sh | ||
remote-builds.nix | ||
remote-store.sh | ||
repair.sh | ||
secure-drv-outputs.nix | ||
secure-drv-outputs.sh | ||
simple.builder.sh | ||
simple.nix | ||
simple.sh | ||
substituter.sh | ||
substituter2.sh | ||
substitutes.sh | ||
substitutes2.sh | ||
timeout.builder.sh | ||
timeout.nix | ||
timeout.sh | ||
user-envs.builder.sh | ||
user-envs.nix | ||
user-envs.sh |