docker/cli · error

expected a map or a list, got %T: %#v

Error message

expected a map or a list, got %T: %#v

What it means

Error "expected a map or a list, got %T: %#v" thrown in docker/cli.

Source

Thrown at cli/compose/loader/loader.go:847

			for i, allowSep := range allowSeps {
				entry := fmt.Sprint(entry)
				k, v, ok := strings.Cut(entry, allowSep)
				if ok {
					// Entry uses this allowed separator. Add it to the result, using
					// sep as a separator.
					result = append(result, fmt.Sprintf("%s%s%s", k, sep, v))
					break
				} else if i == len(allowSeps)-1 {
					// No more separators to try, keep the entry if allowNil.
					if allowNil {
						result = append(result, k)
					}
				}
			}
		}
		return result
	}
	panic(fmt.Errorf("expected a map or a list, got %T: %#v", listOrMapping, listOrMapping))
}

func transformMappingOrListFunc(sep string, allowNil bool) TransformerFunc {
	return func(data any) (any, error) {
		return transformMappingOrList(data, sep, allowNil), nil
	}
}

func transformMappingOrList(mappingOrList any, sep string, allowNil bool) any {
	switch values := mappingOrList.(type) {
	case map[string]any:
		return toMapStringString(values, allowNil)
	case []any:
		result := make(map[string]any)
		for _, v := range values {
			key, val, hasValue := strings.Cut(v.(string), sep)
			switch {
			case !hasValue && allowNil:

View on GitHub (pinned to e9452d6e78)

When it happens

Trigger: Thrown at cli/compose/loader/loader.go:847 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/2f2f02f35d182ba3.json. Report an issue: GitHub.