Implemented the exec builtin

Fixed readline and terminal interactions using stdin instead of /dev/tty

src/builtin/exec.rs

@@ -0,0 +1,50 @@
+use nix::{errno::Errno, unistd::execvpe};
+
+use crate::{
+  builtin::setup_builtin,
+  jobs::JobBldr,
+  libsh::error::{ShErr, ShErrKind, ShResult},
+  parse::{NdRule, Node, execute::ExecArgs},
+  procio::IoStack,
+  state,
+};
+
+pub fn exec_builtin(node: Node, io_stack: &mut IoStack, job: &mut JobBldr) -> ShResult<()> {
+  let NdRule::Command {
+    assignments: _,
+    argv,
+  } = node.class
+  else {
+    unreachable!()
+  };
+
+  let (expanded_argv, guard) = setup_builtin(argv, job, Some((io_stack, node.redirs)))?;
+  if let Some(g) = guard {
+    // Persist redirections so they affect the entire shell,
+    // not just this command call
+    g.persist()
+  }
+
+  if expanded_argv.is_empty() {
+    state::set_status(0);
+    return Ok(());
+  }
+
+  let args = ExecArgs::from_expanded(expanded_argv)?;
+
+  let cmd = &args.cmd.0;
+  let span = args.cmd.1;
+
+  let Err(e) = execvpe(cmd, &args.argv, &args.envp);
+
+  // execvpe only returns on error
+  let cmd_str = cmd.to_str().unwrap().to_string();
+  match e {
+    Errno::ENOENT => {
+      Err(ShErr::full(ShErrKind::CmdNotFound(cmd_str), "", span))
+    }
+    _ => {
+      Err(ShErr::full(ShErrKind::Errno(e), format!("{e}"), span))
+    }
+  }
+}