gohugoio/hugo · error

npm pack: failed to open package file

Error message

npm pack: failed to open package file: %w

What it means

In npm.Pack (modules/npm/package_builder.go:168). While walking the _jsconfig virtual filesystem for module package files, for each collected entry it calls m.Open(); if the underlying file cannot be opened the error is wrapped. This operates on the Hugo virtual fs that merges all module mounts, so the failure is at the file-open layer.

Solutions

1. Run 'hugo mod clean' then 'hugo mod tidy' to refresh the module cache.
2. Check the mount source path in the offending module/theme actually exists and is readable.
3. Remove or fix mounts that point at deleted package files.

Example fix

// before
[[module.mounts]]
source = "node_modules/pkg/package.json"
target = "_jsconfig/package.json"
// file missing on disk -> error

// after: ensure the source exists, or drop the mount
// (run `npm install` first, or remove the stale mount)

// verify each mounted package file is openable before building
for _, m := range cfg.Module.Mounts {
    if base := filepath.Base(m.Source); base == "package.json" || base == "package.hugo.json" {
        full := filepath.Join(workDir, m.Source)
        if f, err := os.Open(full); err != nil {
            return fmt.Errorf("mount source %s not openable: %w", full, err)
        } else { f.Close() }
    }
}

When it happens

Trigger: A module's mounted package.json/package.hugo.json entry exists in the virtual filesystem metadata but the backing file cannot be opened (permissions, broken symlink, race with file deletion, or a mount pointing to a removed path).

Common situations: A theme module mount referencing a package file that was deleted upstream; file permission issues in the module cache; symlinks in the module cache pointing nowhere; concurrent file changes during 'hugo server'.

Related errors

• abort: jekyll root contains neither posts nor drafts
• build filesystems
• could not determine content directory for
• create main fs
• already exists

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/e2921287b6b422ba. Report an issue: GitHub.

Appendix: source

Thrown at modules/npm/package_builder.go:168

			return nil
		},
	})
	if err := w.Walk(); err != nil {
		return err
	}

	// Process collected entries: for each module, prefer package.hugo.json
	// over package.json at the root level. Workspace package.json files are always processed.
	for _, e := range entries {
		m := e.info.Meta()
		// Skip root-level package.json if this module has package.hugo.json.
		if !e.isHugoJSON && e.isRootLevel && modulesWithHugoJSON[m.ModulePath()] {
			continue
		}

		f, err := m.Open()
		if err != nil {
			return fmt.Errorf("npm pack: failed to open package file: %w", err)
		}
		b.Add(m.ModulePath(), f)
		f.Close()
	}

	if b.Err() != nil {
		return fmt.Errorf("npm pack: failed to build: %w", b.Err())
	}

	// 4. Build the autogenerated workspace package.json.
	// Exclude deps already defined by the project itself — they don't
	// need to be duplicated in the workspace and it simplifies maintenance.
	moduleDeps := make(map[string]any)
	moduleDepsComments := make(map[string]any)
	for k, v := range b.dependencies {
		if b.dependenciesComments[k] != "project" {
			moduleDeps[k] = v
			moduleDepsComments[k] = b.dependenciesComments[k]

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