meson: correctly differentiate $profiledir and $sysconfdir/profile.d

The configured sysconfdir is used to look for nix.conf, so it needs
to be /etc, and not $out/etc, so we separate out the place where shell
profile files are installed, which is the only other place sysconfdir is
at all used.

See https://git.lix.systems/lix-project/lix/issues/231#issuecomment-1989
for more info.

Change-Id: Idbed8ba82e711b8a9d6b6127904befa27d58e279

meson.build

@@ -45,7 +45,6 @@ prefix = get_option('prefix')
 path_opts = [
   # Meson built-ins.
   'datadir',
-  'sysconfdir',
   'bindir',
   'mandir',
   'libdir',
@@ -55,12 +54,14 @@ path_opts = [
   'store-dir',
   'state-dir',
   'log-dir',
+  'profile-dir',
 ]
 # For your grepping pleasure, this loop sets the following variables that aren't mentioned
 # literally above:
 # store_dir
 # state_dir
 # log_dir
+# profile_dir
 foreach optname : path_opts
   varname = optname.replace('-', '_')
   path = get_option(optname)
@@ -71,6 +72,13 @@ foreach optname : path_opts
   endif
 endforeach
 
+# sysconfdir doesn't get anything installed to directly, and is only used to
+# tell Lix where to look for nix.conf, so it doesn't get appended to prefix.
+sysconfdir = get_option('sysconfdir')
+if not fs.is_absolute(sysconfdir)
+  sysconfdir = '/' / sysconfdir
+endif
+
 enable_docs = get_option('enable-docs')
 
 enable_tests = get_option('enable-tests')

meson.options

@@ -50,3 +50,8 @@ option('log-dir', type : 'string', value : '/nix/var/log',
 option('enable-docs', type : 'boolean', value : true,
   description : 'whether to build documentation',
 )
+
+# A relative path means it gets appended to prefix.
+option('profile-dir', type : 'string', value : 'etc/profile.d',
+  description : 'the path to install shell profile files',
+)

scripts/meson.build

@@ -20,7 +20,7 @@ foreach rc : [ '.sh', '.fish', '-daemon.sh', '-daemon.fish' ]
     input : 'nix-profile' + rc  + '.in',
     output : 'nix' + rc,
     install : true,
-    install_dir : sysconfdir / 'profile.d',
+    install_dir : profile_dir,
     install_mode : 'rw-r--r--',
     configuration : {
       'localstatedir': state_dir,