What causes "%s:%s parse string: %w" in kataras/iris?

Read the wrapped cause: it names the locale ID, the key, and the template parse error — fix that string in the translation file

kataras/iris · error

%s:%s parse string: %w

Error message

%s:%s parse string: %w

What it means

When a translation value is a string, locale.setMap parses it with the message printer (template variables, plural forms, funcs). If parsing fails, the error is wrapped as "localeID:key parse string" so you can tell which locale and key contained the bad string.

Source

Thrown at i18n/internal/locale.go:67

	vars := getVars(loc, VarsKey, keyValues)
	if isRoot {
		loc.Vars = vars
	} else {
		vars = removeVarsDuplicates(append(vars, loc.Vars...))
	}

	for k, v := range keyValues {
		form, isPlural := loc.Options.PluralFormDecoder(loc, k)
		if isPlural {
			k = key
		} else if !isRoot {
			k = key + "." + k
		}

		switch value := v.(type) {
		case string:
			if err := loc.setString(c, k, value, vars, form); err != nil {
				return fmt.Errorf("%s:%s parse string: %w", loc.ID, key, err)
			}
		case Map:
			// fmt.Printf("%s is map\n", fullKey)
			if err := loc.setMap(c, k, value); err != nil {
				return fmt.Errorf("%s:%s parse map: %w", loc.ID, key, err)
			}

		default:
			return fmt.Errorf("%s:%s unexpected type of %T as value", loc.ID, key, value)
		}
	}

	return nil
}

func (loc *Locale) setString(c *Catalog, key string, value string, vars []Var, form PluralForm) (err error) {
	isPlural := form != nil

View on GitHub (pinned to 7bedaf55a0)

Solutions

Read the wrapped cause: it names the locale ID, the key, and the template parse error — fix that string in the translation file
Validate all {{...}} placeholders match declared variables and that braces are balanced
Check that any template functions used exist in the i18n options
Add a startup test that loads all locale files to surface parse errors at build/deploy time

Example fix

// before (en.yml)
greeting: "Hello {{name"   // unclosed variable
// after
greeting: "Hello {{name}}!"

Defensive patterns

Strategy: try-catch

Validate before calling

func validatePlaceholders(s string, vars []string) error {
    for _, m := range regexp.MustCompile(`\{\{([^}]+)\}\}`).FindAllStringSubmatch(s, -1) {
        if !slices.Contains(vars, strings.TrimSpace(m[1])) { return fmt.Errorf("unknown var %q", m[1]) }
    }
    return nil
}

Try / catch

if err := loc.Load(c, kv); err != nil {
    var perr *template.Error // or match "parse string"
    if strings.Contains(err.Error(), "parse string") {
        log.Printf("bad translation string: %v", err)
    }
    return err
}

Prevention

Add a startup/CI test that loads every locale file
Keep placeholders balanced and matching declared variables
Lint translations with a YAML/JSON schema plus template check
After editing template funcs, grep locale files for their usage

When it happens

Trigger: Storing translation maps (via i18n.New loader, catalog.Store or locale.Load) where a value's string uses invalid template syntax — unclosed {{variable}}, unknown function, bad plural form syntax, or a referenced variable not declared in vars.

Common situations: Translators editing .yml/.json/.toml locale files introduce a typo like {{naame}} or stray '{{'; a template func was removed but strings still call it; plural form markers malformed after an editor mangled the file.

Related errors

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/3cb5782d7f14dc8c. Report an issue: GitHub.