Make the flake options work when using the daemon

When setting flake-local options (with the `nixConfig` field), forward
these options to the daemon in case we’re using one.

This is necessary in particular for options like `binary-caches` or
`post-build-hook` to make sense.

Fix <343239fc8a (r44356843)>

tests/flake-local-settings.sh

@@ -0,0 +1,35 @@
+source common.sh
+
+clearStore
+rm -rf $TEST_HOME/.cache $TEST_HOME/.config $TEST_HOME/.local
+
+cp ./simple.nix ./simple.builder.sh ./config.nix $TEST_HOME
+
+cd $TEST_HOME
+
+rm -f post-hook-ran
+cat <<EOF > echoing-post-hook.sh
+#!/bin/sh
+
+echo "ThePostHookRan" > $PWD/post-hook-ran
+EOF
+chmod +x echoing-post-hook.sh
+
+cat <<EOF > flake.nix
+{
+    nixConfig.post-build-hook = "$PWD/echoing-post-hook.sh";
+
+    outputs = a: {
+       defaultPackage.$system = import ./simple.nix;
+    };
+}
+EOF
+
+# Ugly hack for testing
+mkdir -p .local/share/nix
+cat <<EOF > .local/share/nix/trusted-settings.json
+{"post-build-hook":{"$PWD/echoing-post-hook.sh":true}}
+EOF
+
+nix build
+test -f post-hook-ran || fail "The post hook should have ran"

tests/local.mk

@@ -46,6 +46,7 @@ nix_tests = \
   recursive.sh \
   describe-stores.sh \
   flakes.sh \
+  flake-local-settings.sh \
   build.sh \
   compute-levels.sh \
   repl.sh \