openldap: load client config from /etc, not the nix store

We want Openldap clients to load /etc/ldap.conf at runtime, not
${pkgs.openldap}/etc/ldap.conf which is always a sample config.

Pass sysconfdir=/etc at compile time, so that /etc/krb5.conf is embedded
in the library as the path of its config file.

Pass sysconfdir=${out}/etc at install time, so that the sample configs
and schema files are correctly included in the build output.

This hack works because the Makefiles are not smart enough to notice
that the sysconfdir variable has changed across invocations -- because
nobody ever writes their Makefiles to be that smart. :-)

Fixes #181937.

nixos/tests/openldap.nix

···
     olcRootDN: cn=root,dc=example
     olcRootPW: notapassword
   '';
+
+  ldapClientConfig = {
+    enable = true;
+    loginPam = false;
+    nsswitch = false;
+    server = "ldap://";
+    base = "dc=example";
+  };
+
 in {
   name = "openldap";
 
   nodes.machine = { pkgs, ... }: {
     environment.etc."openldap/root_password".text = "notapassword";
+
+    users.ldap = ldapClientConfig;
+
     services.openldap = {
       enable = true;
       urlList = [ "ldapi:///" "ldap://" ];
···
       manualConfigDir = {
         inheritParentConfig = false;
         configuration = { ... }: {
+          users.ldap = ldapClientConfig;
           services.openldap = {
             enable = true;
             configDir = "/var/db/slapd.d";
···
     with subtest("declarative contents"):
       machine.succeed('${specializations}/declarativeContents/bin/switch-to-configuration test')
       machine.wait_for_unit("openldap.service")
-      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword -b "dc=example"')
+      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword')
       machine.fail('ldapmodify -D cn=root,cn=config -w configpassword -f ${pkgs.writeText "rootpw.ldif" changeRootPw}')
 
     with subtest("mutable config"):
       machine.succeed('${specializations}/mutableConfig/bin/switch-to-configuration test')
-      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword -b "dc=example"')
+      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword')
       machine.succeed('ldapmodify -D cn=root,cn=config -w configpassword -f ${pkgs.writeText "rootpw.ldif" changeRootPw}')
-      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w foobar -b "dc=example"')
+      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w foobar')
 
     with subtest("manual config dir"):
       machine.succeed(
···
         'chown -R openldap:openldap /var/db/slapd.d /var/db/openldap',
         '${specializations}/manualConfigDir/bin/switch-to-configuration test',
       )
-      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword -b "dc=example"')
+      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w notapassword')
       machine.succeed('ldapmodify -D cn=root,cn=config -w configpassword -f ${pkgs.writeText "rootpw.ldif" changeRootPw}')
-      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w foobar -b "dc=example"')
+      machine.succeed('ldapsearch -LLL -D "cn=root,dc=example" -w foobar')
   '';
 })

pkgs/development/libraries/openldap/default.nix

···
     "STRIP="  # Disable install stripping as it breaks cross-compiling. We strip binaries anyway in fixupPhase.
     "STRIP_OPTS="
     "prefix=${placeholder "out"}"
-    "sysconfdir=${placeholder "out"}/etc"
+    "sysconfdir=/etc"
     "systemdsystemunitdir=${placeholder "out"}/lib/systemd/system"
     # contrib modules require these
     "moduledir=${placeholder "out"}/lib/modules"
···
 
   installFlags = [
     "prefix=${placeholder "out"}"
+    "sysconfdir=${placeholder "out"}/etc"
     "moduledir=${placeholder "out"}/lib/modules"
     "INSTALL=install"
   ];