2 files changed, 125 insertions, 0 deletions
diff --git a/users/Profpatsch/execline/default.nix b/users/Profpatsch/execline/default.nix
new file mode 100644
index 000000000000..1f75b97591fc
--- /dev/null
+++ b/users/Profpatsch/execline/default.nix
@@ -0,0 +1,12 @@
+{ depot, pkgs, lib, ... }:
+
+let
+  exec-helpers = depot.nix.writers.rustSimpleLib {
+    name = "exec-helpers";
+  } (builtins.readFile ./exec_helpers.rs);
+
+in depot.nix.readTree.drvTargets {
+  inherit
+    exec-helpers
+    ;
+}
diff --git a/users/Profpatsch/execline/exec_helpers.rs b/users/Profpatsch/execline/exec_helpers.rs
new file mode 100644
index 000000000000..b9e1f5797386
--- /dev/null
+++ b/users/Profpatsch/execline/exec_helpers.rs
@@ -0,0 +1,113 @@
+use std::os::unix::process::CommandExt;
+use std::ffi::OsStr;
+use std::os::unix::ffi::{OsStringExt, OsStrExt};
+
+pub fn no_args(current_prog_name: &str) -> () {
+    let mut args = std::env::args_os();
+    // remove argv[0]
+    let _ = args.nth(0);
+    if args.len() > 0 {
+        die_user_error(current_prog_name, format!("Expected no arguments, got {:?}", args.collect::<Vec<_>>()))
+    }
+}
+
+pub fn args(current_prog_name: &str, no_of_positional_args: usize) -> Vec<Vec<u8>> {
+    let mut args = std::env::args_os();
+    // remove argv[0]
+    let _ = args.nth(0);
+    if args.len() != no_of_positional_args {
+        die_user_error(current_prog_name, format!("Expected {} arguments, got {}, namely {:?}", no_of_positional_args, args.len(), args.collect::<Vec<_>>()))
+    }
+    args.map(|arg| arg.into_vec()).collect()
+}
+
+pub fn args_for_exec(current_prog_name: &str, no_of_positional_args: usize) -> (Vec<Vec<u8>>, Vec<Vec<u8>>) {
+    let mut args = std::env::args_os();
+    // remove argv[0]
+    let _ = args.nth(0);
+    let mut args = args.map(|arg| arg.into_vec());
+    let mut pos_args = vec![];
+    // get positional args
+    for i in 1..no_of_positional_args+1 {
+            pos_args.push(
+                args.nth(0).expect(
+                    &format!("{}: expects {} positional args, only got {}", current_prog_name, no_of_positional_args, i))
+            );
+    }
+    // prog... is the rest of the iterator
+    let prog : Vec<Vec<u8>> = args.collect();
+    (pos_args, prog)
+}
+
+pub fn exec_into_args<'a, 'b, Args, Arg, Env, Key, Val>(current_prog_name: &str, args: Args, env_additions: Env) -> !
+    where
+    Args: IntoIterator<Item = Arg>,
+    Arg: AsRef<[u8]>,
+    Env: IntoIterator<Item = (Key, Val)>,
+    Key: AsRef<[u8]>,
+    Val: AsRef<[u8]>,
+{
+    // TODO: is this possible without collecting into a Vec first, just leaving it an IntoIterator?
+    let args = args.into_iter().collect::<Vec<Arg>>();
+    let mut args = args.iter().map(|v| OsStr::from_bytes(v.as_ref()));
+    let prog = args.nth(0).expect(&format!("{}: first argument must be an executable", current_prog_name));
+    // TODO: same here
+    let env = env_additions.into_iter().collect::<Vec<(Key, Val)>>();
+    let env = env.iter().map(|(k,v)| (OsStr::from_bytes(k.as_ref()), OsStr::from_bytes(v.as_ref())));
+    let err = std::process::Command::new(prog).args(args).envs(env).exec();
+    die_missing_executable(current_prog_name, format!("exec failed: {}, while trying to execing into {:?}", err, prog));
+}
+
+/// Exit 1 to signify a generic expected error
+/// (e.g. something that sometimes just goes wrong, like a nix build).
+pub fn die_expected_error<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+  die_with(1, current_prog_name, msg)
+}
+
+/// Exit 100 to signify a user error (“the user is holding it wrong”).
+/// This is a permanent error, if the program is executed the same way
+/// it should crash with 100 again.
+pub fn die_user_error<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+    die_with(100, current_prog_name, msg)
+}
+
+/// Exit 101 to signify an unexpected crash (failing assertion or panic).
+/// This is the same exit code that `panic!()` emits.
+pub fn die_panic<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+    die_with(101, current_prog_name, msg)
+}
+
+/// Exit 111 to signify a temporary error (such as resource exhaustion)
+pub fn die_temporary<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+    die_with(111, current_prog_name, msg)
+}
+
+/// Exit 126 to signify an environment problem
+/// (the user has set up stuff incorrectly so the program cannot work)
+pub fn die_environment_problem<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+    die_with(126, current_prog_name, msg)
+}
+
+/// Exit 127 to signify a missing executable.
+pub fn die_missing_executable<S>(current_prog_name: &str, msg: S) -> !
+where S: AsRef<str>
+{
+    die_with(127, current_prog_name, msg)
+}
+
+fn die_with<S>(status: i32, current_prog_name: &str, msg: S) -> !
+    where S: AsRef<str>
+{
+    eprintln!("{}: {}", current_prog_name, msg.as_ref());
+    std::process::exit(status)
+}