K4m7v2pz's Blog

Summary: This article documents troubleshooting cargo not found in new WezTerm tabs running Nushell on macOS (Apple Silicon). Core issues include nushell not sourcing ~/.cargo/env, the default config directory not being ~/.config/nushell/, and string interpolation syntax differences.

1. Symptoms

Running cargo run in a new WezTerm tab with nushell:

~/Documents/Code.localized/ra2md> cargo run
Error: nu::shell::external_command
  × External command failed
   ╭─[repl_entry #3:1:1]
 1 │ cargo run
   · ──┬──
   ·   ╰── Command `cargo` not found
   ╰────
  help: `cargo` is neither a Nushell built-in or a known external command

Each time, manually sourcing ~/.config/nushell/env.nu would temporarily fix it, but a new tab would break again.

2. Root Causes (Three Issues Stacking)

2.1 Nushell Doesn’t Source ~/.cargo/env

When rustup is installed, it writes a shell script to ~/.cargo/env (a case ":${PATH}:"…esac block) that can only be sourced by bash/zsh and other POSIX shells. Nushell’s syntax is different — it cannot and will not source this file. So while source "$HOME/.cargo/env" in ~/.zshrc works for zsh, nushell does nothing on startup — cargo never makes it into PATH.

2.2 Nushell’s Default Config Directory Isn’t ~/.config/nushell/

This is the biggest trap. Following XDG conventions, many people (myself included) modify ~/.config/nushell/env.nu, only to find their changes have no effect. Nushell 0.113 on macOS uses:

~/Library/Application Support/nushell/

Not ~/.config/nushell/. Verify with:

echo $nu.default-config-dir
echo $nu.env-path          # ~/Library/Application Support/nushell/env.nu
echo $nu.config-path       # ~/Library/Application Support/nushell/config.nu

I had correctly added path add "~/.cargo/bin" in ~/.config/nushell/env.nu, and sourcing it worked — but when WezTerm launched nushell, it loaded the file from the default path instead. Editing the wrong file is the core of this pitfall.

2.3 Nushell String Interpolation Differs from Bash

While initially editing ~/.config/nushell/env.nu, I also hit a syntax issue. The original attempt:

$env.PATH = ($env.PATH | prepend "$env.HOME/.cargo/bin")

In nushell, double-quoted strings do NOT interpolate variables. "$env.HOME/.cargo/bin" is treated as a literal string $env.HOME/.cargo/bin, adding a nonexistent directory to PATH. The correct syntax uses $"..." string interpolation with (...) subexpressions:

$env.PATH = ($env.PATH | prepend $"($env.HOME)/.cargo/bin")

Or better yet — use nushell’s built-in path add utility (from std/util), which auto-expands ~:

use std/util "path add"
path add "~/.cargo/bin"

3. Fix

Edit the file that is actually loaded: ~/Library/Application Support/nushell/env.nu, and add path add "~/.cargo/bin". Full change:

# env.nu
# Always make ~/.local/bin visible (where atomcode lives), even when the
# terminal was started as a non-login shell and ~/.zshrc never ran.
use std/util "path add"
path add "~/.local/bin"
# cargo / rustup binaries — nushell doesn't auto-source ~/.cargo/env (it's an sh script)
path add "~/.cargo/bin"

Verification:

which cargo
# → /Users/<user>/.cargo/bin/cargo
cargo run

New WezTerm tabs work without manual sourcing.

4. Summary

5. References

• Nushell configuration docs: Configuration | Nushell
• Nushell string interpolation: https://www.nushell.sh/language/_strings.html
• rustup file ~/.cargo/env: POSIX shell only
• Nushell std/util module: use std/util "path add" provides the path add command