Humanizr/Humanizer · error · InvalidOperationException

Duration case phrases use unsupported plural rule '{pluralRu

Error message

Duration case phrases use unsupported plural rule '{pluralRule}'.

What it means

Thrown by GetRequiredMultipleForms when the plural rule string passed to DurationCaseNormalization.Parse does not match any of the known plural-rule identifiers. The switch expression has a default arm that throws for any unrecognized value, because the generator needs the plural rule to compute which multiple forms each phrase must define.

Source

Thrown at src/Humanizer.SourceGenerators/Common/DurationCaseModels.cs:842

                null,
                null,
                RequireReason(mapping.GetScalar("unsupported")!, $"{path}.unsupported"),
                ParseProvenance(mapping, path, required: false));
        }

        static ImmutableArray<string> GetRequiredMultipleForms(string? pluralRule) =>
            pluralRule switch
            {
                null or "none" => [],
                "singular-plural" => ["default", "plural"],
                "arabic-like" => ["default", "dual", "plural"],
                "arabic-cardinal" => ["default", "zero", "dual", "plural", "many"],
                "between2-and4-paucal" or "polish" => ["default", "paucal"],
                "south-slavic" or "russian" =>
                    ["default", "singular", "paucal"],
                "slovenian" => ["default", "dual", "paucal"],
                "lithuanian" => ["default", "singular", "plural"],
                _ => throw new InvalidOperationException(
                    $"Duration case phrases use unsupported plural rule '{pluralRule}'.")
            };

        static void ValidateReachableMultipleForms(
            SimpleYamlValue phraseValue,
            string path,
            ImmutableArray<string> requiredMultipleForms)
        {
            var phrase = ExpectMapping(phraseValue, path);
            if (!phrase.TryGetValue("multiple", out var multipleValue))
            {
                throw new InvalidOperationException(
                    $"Case overlay '{path}' must explicitly define numeric multiple forms.");
            }

            if (requiredMultipleForms.IsEmpty)
            {
                return;

View on GitHub (pinned to ffc2b77c0f)

Solutions

Check the locale's declared plural rule and compare it against the accepted values in GetRequiredMultipleForms: none, singular-plural, arabic-like, arabic-cardinal, between2-and4-paucal, polish, south-slavic, russian, slovenian, lithuanian.
Correct the plural rule to match one of the supported identifiers (or pass null/omit it for languages with no plural distinction).
If a genuinely new plural rule is needed, add a case to the switch in GetRequiredMultipleForms and specify the required forms array.

Example fix

# before
pluralRule: one-many
# after
pluralRule: singular-plural

Defensive patterns

Strategy: validation

Validate before calling

# Check plural rule against the supported set before building
$supported = @('none','singular-plural','arabic-like','arabic-cardinal','between2-and4-paucal','polish','south-slavic','russian','slovenian','lithuanian')
# Read the locale's declared pluralRule and verify membership

Prevention

Cross-reference the locale's pluralRule with the switch in GetRequiredMultipleForms before adding durationCases.
If the locale has no plural distinction, omit pluralRule or set it to 'none'.
When adding a new plural-rule family, update the generator switch and the locale schema simultaneously.

When it happens

Trigger: The locale YAML (or caller) supplies a pluralRule value that is not one of: null, 'none', 'singular-plural', 'arabic-like', 'arabic-cardinal', 'between2-and4-paucal', 'polish', 'south-slavic', 'russian', 'slovenian', or 'lithuanian'.

Common situations: A contributor introduces a new plural-rule family or renames an existing one in the locale metadata without updating the generator's switch table. Also occurs if a locale's plural rule is misspelled or uses a different casing/convention than expected.

Related errors

AI-assisted analysis of Humanizr/Humanizer@ffc2b77c0f (2026-08-13). Data as JSON: /api/errors/8aae1d06c92c1bef. Report an issue: GitHub.