dagger/dagger · error

parse module registry: %w

Error message

parse module registry: %w

What it means

This error wraps any failure to parse the embedded JSON module registry into a list of registryModule entries. It is thrown by parseModuleRegistry when json.Unmarshal of the compiled-in registry data fails. Because the registry data is embedded at build time, this almost always indicates a corrupted or malformed registry blob rather than a user-actionable problem.

Source

Thrown at internal/cmd/dagger/mod.go:102

	// The module is recommended when any pattern matches at least one file.
	// An empty list means never recommended.
	Recommend []string `json:"recommend,omitempty"`
}

// embeddedModuleRegistry is the registry baked in at build time.
//
//go:embed modules.json
var embeddedModuleRegistry []byte

// loadModuleRegistry returns the embedded module registry.
func loadModuleRegistry() ([]registryModule, error) {
	return parseModuleRegistry(embeddedModuleRegistry)
}

func parseModuleRegistry(data []byte) ([]registryModule, error) {
	var mods []registryModule
	if err := json.Unmarshal(data, &mods); err != nil {
		return nil, fmt.Errorf("parse module registry: %w", err)
	}
	return mods, nil
}

// searchModuleRegistry returns modules whose name or description match query
// (case-insensitive substring), sorted by name. An empty query returns all.
func searchModuleRegistry(mods []registryModule, query string) []registryModule {
	out := make([]registryModule, 0, len(mods))
	q := strings.ToLower(query)
	for _, m := range mods {
		if q == "" ||
			strings.Contains(strings.ToLower(m.Name), q) ||
			strings.Contains(strings.ToLower(m.Description), q) {
			out = append(out, m)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out

View on GitHub (pinned to 82ba2681db)

Solutions

1. Regenerate or restore the embedded registry JSON so it is valid JSON matching []registryModule
2. Run 'dagger mod registry' style tests (TestParseModuleRegistry) to confirm the embedded data parses
3. Rebuild the binary so the embedded registry matches the current registryModule struct

Example fix

// before
var mods []registryModule
if err := json.Unmarshal(data, &mods); err != nil {
	return nil, fmt.Errorf("parse module registry: %w", err)
}
// after
// fix the source data instead of code:
// regenerate embeddedModuleRegistry so that `json.Unmarshal(data, &[]registryModule{})` succeeds

var probe []registryModule
if err := json.Unmarshal(embeddedModuleRegistry, &probe); err != nil {
	// surface build-time registry corruption early
	log.Fatalf("embedded module registry invalid: %v", err)
}

func isValidRegistry(data []byte) bool {
	var mods []registryModule
	return json.Unmarshal(data, &mods) == nil
}

mods, err := parseModuleRegistry(embeddedModuleRegistry)
if err != nil {
	var ue *json.UnmarshalTypeError
	if errors.As(err, &ue) { /* schema mismatch handling */ }
	return fmt.Errorf("registry unavailable: %w", err)
}

When it happens

Trigger: Calling parseModuleRegistry (directly or via loadModuleRegistry) when the embedded module registry JSON is malformed, has an unexpected schema (e.g. fields not matching registryModule), or fails to unmarshal into []registryModule.

Common situations: Corrupted build artifact or stale embedded registry after a schema change; a registry regeneration script emitted invalid JSON; running tests (TestParseModuleRegistry/TestEmbeddedModuleRegistryParses) against a hand-edited registry file.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• unmarshal index: %w
• parsing legacy config: %w
• failed to decode module config: %w
• decode %q: %w
• decode tag list from %q: %w

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/5d0163a41baf179b. Report an issue: GitHub.