fix(users/Profpatsch/execline): fix exec_into_args off-by-1 r/2185

We expect the users to pass an actual prog, not an argv, so 0 is the
program to exec into.

Also improve the exec error, by including the program we tried to exec
into (the rust IO error doesn’t contain the name).

Change-Id: I664f9f717e4f82bfc1b1da3bd7114124b7582d5f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2489
Reviewed-by: Profpatsch <mail@profpatsch.de>
Tested-by: BuildkiteCI

1 files changed, 2 insertions, 2 deletions

diff --git a/users/Profpatsch/execline/exec_helpers.rs b/users/Profpatsch/execline/exec_helpers.rs
index 3e74ffc722..9a67ffe45d 100644
--- a/users/Profpatsch/execline/exec_helpers.rs
+++ b/users/Profpatsch/execline/exec_helpers.rs
@@ -31,12 +31,12 @@ pub fn exec_into_args<'a, 'b, Args, Arg, Env, Key, Val>(current_prog_name: &str,
     // 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(1).expect(&format!("{}: first argument must be an executable", current_prog_name));
+    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: {:?}", err));
+    die_missing_executable(current_prog_name, format!("exec failed: {}, while trying to execing into {:?}", err, prog));
 }
 
 /// Exit 1 to signify a generic expected error