Schniz/fnm · error · anyhow::Error

Can't convert path to string

Error message

Can't convert path to string

What it means

fnm's Fish shell integration builds a `set -gx PATH ...` statement from a `&Path` in `Shell::path`. `Path::to_str()` returns None when the path is not valid UTF-8, and that None becomes this anyhow error. It fires while generating shell setup output such as `fnm env --shell fish`.

Source

Thrown at src/shell/fish.rs:18

use crate::version_file_strategy::VersionFileStrategy;

use super::shell::Shell;
use indoc::formatdoc;
use std::path::Path;

#[derive(Debug)]
pub struct Fish;

impl Shell for Fish {
    fn to_clap_shell(&self) -> clap_complete::Shell {
        clap_complete::Shell::Fish
    }

    fn path(&self, path: &Path) -> anyhow::Result<String> {
        let path = path
            .to_str()
            .ok_or_else(|| anyhow::anyhow!("Can't convert path to string"))?;
        let path =
            super::windows_compat::maybe_fix_windows_path(path).unwrap_or_else(|| path.to_string());
        Ok(format!("set -gx PATH {path:?} $PATH;"))
    }

    fn set_env_var(&self, name: &str, value: &str) -> String {
        format!("set -gx {name} {value:?};")
    }

    fn use_on_cd(&self, config: &crate::config::FnmConfig) -> anyhow::Result<String> {
        let version_file_exists_condition = if config.resolve_engines() {
            "test -f .node-version -o -f .nvmrc -o -f package.json"
        } else {
            "test -f .node-version -o -f .nvmrc"
        };
        let autoload_hook = match config.version_file_strategy() {
            VersionFileStrategy::Local => formatdoc!(
                r"

View on GitHub (pinned to 86adc9676c)

Solutions

1. Check each candidate var: `for v in FNM_DIR FNM_MULTISHELL_PATH XDG_RUNTIME_DIR; printf '%s' "$$v" | iconv -f UTF-8 -t UTF-8 >/dev/null || echo "$v invalid"; end`.
2. Reset to safe values: `set -Ux FNM_DIR ~/.local/share/fnm` and `set -e FNM_MULTISHELL_PATH`, then restart the shell.
3. Ensure LANG/LC_ALL are UTF-8 locales so system tools emit UTF-8 paths.
4. Clear stale multishell entries under the fnm multishells storage dir and let fnm recreate them.

Example fix

# before
set -Ux FNM_DIR /mnt/data/bad\xffpath
fnm env --shell fish   # error: Can't convert path to string

# after
set -e FNM_DIR
set -Ux FNM_DIR ~/.local/share/fnm
fnm env --shell fish   # set -gx PATH ... emitted

fn fnm_paths_are_utf8() -> bool {
    ["FNM_DIR", "FNM_MULTISHELL_PATH", "XDG_RUNTIME_DIR", "XDG_CACHE_HOME"]
        .iter()
        .filter_map(std::env::var_os)
        .all(|v| v.to_str().is_some())
}

fn is_utf8_path(p: &std::path::Path) -> bool {
    p.to_str().is_some()
}

match fish_shell.path(&multishell_dir) {
    Ok(line) => println!("{line}"),
    Err(_) => eprintln!("fnm env failed; reset FNM_DIR/FNM_MULTISHELL_PATH to UTF-8 paths"),
}

When it happens

Trigger: Running `fnm env --shell fish` (or any command that renders the Fish PATH line) when the multishell path / fnm base dir contains non-UTF-8 bytes — typically via a polluted FNM_MULTISHELL_PATH, FNM_DIR, or the XDG runtime/temp dir they derive from.

Common situations: Fish config files (`config.fish`) saved in a non-UTF-8 encoding setting FNM_DIR; legacy-encoded home or temp directories; XDG_RUNTIME_DIR/XDG_CACHE_HOME containing invalid bytes; multishell dirs left over from a crashed session with mangled names.

Related errors

• Can't convert path to string
• Path is not valid UTF-8
• Can't read PATH
• Can't convert path to string
• Can't read PATH env var

AI-assisted analysis of Schniz/fnm@86adc9676c (2026-08-16). Data as JSON: /api/errors/a7c18b23a21d2e74. Report an issue: GitHub.