OTA translations show literal placeholders instead of substituted values

[LeventeAsztalosAlpian]

OTA translations show literal placeholders instead of substituted values

Describe the bug

When fetching translations via OTA (Over-The-Air updates), placeholder substitution fails and literal placeholder syntax (e.g., {currentStep}, {userName}) appears in the UI instead of the actual values passed to the localization method.

To Reproduce

Steps to reproduce the behavior:

1. SDK configuration:

// main.dart
await Crowdin.init(
  distributionHash: 'your_distribution_hash',
  updatesInterval: Duration(minutes: 15),
);

await Crowdin.loadTranslations(Locale('fr'));

2. Create an ARB file without @metadata (as downloaded from Crowdin CLI):

{
  "@@locale": "fr",
  "step_x_of_x": "Étape {currentStep} sur {totalSteps}"
}

3. Upload to Crowdin and configure OTA distribution

4. Use the translation with parameters in your app:

final text = AppLocalizations.of(context).stepXOfX(1, 5);
print(text); // Expected: "Étape 1 sur 5"

5. Observe the output showing literal placeholders: "Étape {currentStep} sur {totalSteps}"

Expected behavior

The placeholder values should be substituted with the provided arguments:

• Input: stepXOfX(1, 5)
• Expected output: "Étape 1 sur 5"

The SDK's automatic placeholder inference (via Message._inferPlaceholders()) should detect {currentStep} and {totalSteps} from the translation string and make them available for substitution, even without explicit @metadata entries.

Environment

• Crowdin Flutter SDK: 0.8.0
• Flutter version: [e.g. 3.24.0]
• Dart version: [e.g. 3.5.0]

Screenshots

Example showing the issue:

UI Display: "Étape {currentStep} sur {totalSteps}"
Expected:   "Étape 1 sur 5"

Root Cause

In lib/src/common/gen_l10n_types.dart, the Message._inferPlaceholders() method (lines ~508-534) correctly parses the translation string and creates Placeholder objects for detected placeholders. However, these inferred placeholders are stored in a local undeclaredPlaceholders map that is never merged into the instance's placeholders map.

void _inferPlaceholders(Map<LocaleInfo, String> filenames) {
  final Map<String, Placeholder> undeclaredPlaceholders = <String, Placeholder>{};
  
  // ... placeholder detection logic ...
  
  if (placeholder == null) {
    placeholder = Placeholder(resourceId, identifier, <String, Object?>{});
    undeclaredPlaceholders[identifier] = placeholder;  // ← Stored but never merged
  }
  
  // ← MISSING: placeholders.addAll(undeclaredPlaceholders);
}

When Extractor.findPlaceholders() runs, it iterates over message.placeholders, which is empty, so no substitution occurs.

Proposed Fix

Add one line at the end of _inferPlaceholders() in lib/src/common/gen_l10n_types.dart:

void _inferPlaceholders(Map<LocaleInfo, String> filenames) {
  final Map<String, Placeholder> undeclaredPlaceholders = <String, Placeholder>{};
  
  // ... existing code ...
  
  // Merge inferred placeholders into the instance's placeholders map
  placeholders.addAll(undeclaredPlaceholders);
}

[andrii-bodnar]

Hi @LeventeAsztalosAlpian, thanks for reporting this!

At first glance, it seems to be the same issue as that described in #61, doesn't it?

[LeventeAsztalosAlpian]

Hi @andrii-bodnar, thanks for the quick response! I think #61 is a different issue. The problem there, is that Flutter's standard gen-l10n tool requires metadata for all placeholders. But the Crowdin CLI download doesn't include @metadata entries. So if we add new keys with placeholder at the crowdin website, than the fetched arb file won't be compatible with flutter gen-l10n. This issue is about the Over-The-Air update. But #61 is also affecting our workflow. We had to implement a custom script to solve that problem in our project.

[andrii-bodnar]

@LeventeAsztalosAlpian, thanks a lot for the additional details! So, the problem is probably how Crowdin exports these strings. Could you please confirm whether I have understood you correctly: does the bug only occur for strings that are manually added to the resource file via the UI and then released to the distribution?

[LeventeAsztalosAlpian]

@andrii-bodnar no, this affect every string which have a placeholder. All of those strings will appear with literal placeholders when OTA update happens. I described where is the problem and what is the solution in the issue. I tested it, and with the proposed one line fix it works as expected.

[andrii-bodnar]

Thank you, @LeventeAsztalosAlpian! Would you be interested in submitting a pull request with the suggested fix?

[LeventeAsztalosAlpian]

@andrii-bodnar yes I can.

[andrii-bodnar]

Available in 0.8.1.