feat(users/Profpatsch): set up stow for nix-home r/3577

nix-home is (hopefully) gonna be a home-manager alternative for my
home directory.

Files are symlinked into the home directory via GNU stow (since that
is a tried and tested tool), so first step is to set up the base code
for that.

Implements a small tool that reads a single environment variable and
prints it to stdout.

Change-Id: Ifa3fd9f9e1cedc52c3002196d3971b02cb840e80
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4832
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
Autosubmit: Profpatsch <mail@profpatsch.de>

1 files changed, 21 insertions, 0 deletions

diff --git a/users/Profpatsch/execline/default.nix b/users/Profpatsch/execline/default.nix
index 1f75b97591..c6a8d284a6 100644
--- a/users/Profpatsch/execline/default.nix
+++ b/users/Profpatsch/execline/default.nix
@@ -5,8 +5,29 @@ let
     name = "exec-helpers";
   } (builtins.readFile ./exec_helpers.rs);
 
+  print-one-env = depot.nix.writers.rustSimple {
+    name = "print-one-env";
+    dependencies = [
+      depot.users.Profpatsch.execline.exec-helpers
+    ];
+  } ''
+    extern crate exec_helpers;
+    use std::os::unix::ffi::OsStrExt;
+    use std::io::Write;
+
+    fn main() {
+      let args = exec_helpers::args("print-one-env", 1);
+      let valname = std::ffi::OsStr::from_bytes(&args[0]);
+      match std::env::var_os(&valname) {
+        None => exec_helpers::die_user_error("print-one-env", format!("Env variable `{:?}` is not set", valname)),
+        Some(val) => std::io::stdout().write_all(&val.as_bytes()).unwrap()
+      }
+    }
+  '';
+
 in depot.nix.readTree.drvTargets {
   inherit
     exec-helpers
+    print-one-env
     ;
 }