facebook/flow · error

Realpath failed for existent path {}

Error message

Realpath failed for existent path {}

What it means

Flow resolves realpaths by walking to the deepest existing prefix (find_real_prefix), canonicalizing that prefix, then re-attaching the non-existent suffix. The prefix is guaranteed to exist, so cached_canonicalize failing means the OS refused realpath on an existing path: symlink loop (ELOOP), permission denied traversing a symlinked component (EACCES), I/O error, or a race where the path vanished between the exists() check and canonicalize.

Source

Thrown at rust_port/crates/flow_common/src/files.rs:1432

        rev_suffix.insert(0, basename);
        let prefix = Path::new(path)
            .parent()
            .map(|p| p.to_string_lossy().into_owned())
            .unwrap_or_else(|| ".".to_string());
        // Sys.file_exists should always return true for / and for . so we should never get into
        // infinite recursion. Let's assert that
        assert!(prefix != path);
        if Path::new(&prefix).exists() {
            prefix
        } else {
            find_real_prefix(&prefix, rev_suffix)
        }
    }

    let mut rev_suffix = Vec::new();
    let real_prefix = find_real_prefix(path, &mut rev_suffix);
    let abs = cached_canonicalize(Path::new(&real_prefix))
        .unwrap_or_else(|_| panic!("Realpath failed for existent path {}", real_prefix));
    let abs_str = abs.to_string_lossy().into_owned();
    rev_suffix.iter().fold(abs_str, |acc, part| {
        Path::new(&acc).join(part).to_string_lossy().into_owned()
    })
}

pub fn module_file_exts(options: &FileOptions) -> Vec<&str> {
    options
        .module_file_exts
        .iter()
        .map(|s| s.as_str())
        .collect()
}

pub fn node_resolver_dirnames(options: &FileOptions) -> &[String] {
    &options.node_resolver_dirnames
}

View on GitHub (pinned to 5c86586199)

Solutions

1. Reproduce with readlink -f <path from the panic> to see where resolution breaks
2. Remove or fix looping/broken symlinks in the reported path (find -type l and inspect)
3. Fix traversal permissions on symlink targets along the path
4. Retry after stopping processes that were deleting/moving files, if it was a race

Example fix

# before
ln -s b a; ln -s a b   # cycle inside the repo
flow check              # panics: Realpath failed for existent path <prefix>

# after
rm a b
flow check

# before running flow over a tree with symlinks
find . -type l -exec readlink -f {} + 2>&1 | grep -i 'loop\|too many levels\|denied' && echo "fix these symlinks first"

When it happens

Trigger: A symlink cycle (a -> b -> a) inside the project or an ancestor; a symlink chain whose resolution needs permissions the user lacks; NFS/automount returning EIO; concurrent deletion making the prefix disappear mid-resolution.

Common situations: Monorepos with circular symlinks generated by tooling (pnpm-style links, yarn workspaces hacks); shared machines where a parent dir is traversable but a link target is not; editor/file-watcher activity deleting files while flow resolves paths.

Related errors

• failed to get current directory
• failed to read input file
• flow.js wasm is still loading; await flow.ready first.
• fd_of_path: mkdir_no_fail({:?}): {}
• fd_of_path: open({:?}): {}

AI-assisted analysis of facebook/flow@5c86586199 (2026-08-20). Data as JSON: /api/errors/0e89df37baed8706. Report an issue: GitHub.