fix(api): merge fallback export translations by term

[samuelmbabhazi]

Fixes #420

Root cause

The fallback export path merges the fallback locale list and the requested locale list with lodash merge, which merges arrays by index. At that point the requested locale list has been filtered down to translated terms only, so the two arrays are not aligned: the positional merge pairs unrelated terms, drops entries and duplicates others in the resulting file. A quick illustration with three fallback terms and one translated term:

merge(
  [{ term: 'a', translation: 'fa' }, { term: 'b', translation: 'fb' }, { term: 'c', translation: 'fc' }],
  [{ term: 'c', translation: 'tc' }],
);
// [{ term: 'c', translation: 'tc' }, { term: 'b', translation: 'fb' }, { term: 'c', translation: 'fc' }]
// term 'a' is gone and term 'c' appears twice

Fix

Merge by term instead: build a map of the translations the requested locale actually has, then walk the full fallback list and override where a translation exists. Every term from the fallback list is kept, lexical order is preserved, and the lodash import is no longer needed.

Tests

A new e2e test creates a locale that translates only one of the two terms and exports it with the fully translated locale as fallback. On develop the export contains a single key with the fallback value instead of two keys, which reproduces the report. With the fix the export contains both terms, the translated one with its own value and the untranslated one with the fallback value. The full e2e suite passes on SQLite (116 tests) and on Postgres 16 (116 tests), and the unit suite passes (41 tests).

---

Summary by cubic

Fix fallback export by merging translations by term instead of by array position, preserving all keys and lexical order across flat and nested formats. Prevents missing and duplicated entries when exporting a partially translated locale. Fixes #420.

• Bug Fixes
  • Replaced lodash positional merge with a term-indexed overlay of the requested locale onto the fallback list.
  • Added e2e tests for jsonflat and jsonnested, covering nested terms and confirming untranslated keys use the fallback while translated keys remain.

^{Written for commit b48805d. Summary will update on new commits.}

[coderabbitai]

Summary by CodeRabbit

• Bug Fixes

  • Improved translation exports when using a fallback locale.
  • Untranslated terms now receive fallback translations, while existing requested-locale translations remain unchanged.

• Tests

  • Added end-to-end coverage for fallback translation behavior in flat and nested JSON exports.

Walkthrough

The export controller now merges fallback and requested translations by term key. An end-to-end test verifies flat and nested exports with partial Dutch translations and German fallback values.

Changes

Fallback export correction

Layer / File(s)	Summary
Term-keyed fallback merge api/src/controllers/exports.controller.ts, api/test/export.e2e-spec.ts	The export merge matches translations by term key and retains fallback values for missing requested-locale translations. The integration test verifies flat and nested JSON exports with Dutch translations and de_DE fallback values.

Estimated code review effort: 2 (Simple) | ~10 minutes

Poem

Poem

I’m a rabbit with terms in my track,
Each key finds the right value back.
Dutch fills what it knows,
German supplies missing rows,
Flat and nested exports stay on track.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes address issue #420 by preserving all fallback terms and overriding matching terms for flat and nested exports.
Out of Scope Changes check	✅ Passed	The controller fix and export tests are directly related to the fallback translation export objective.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly states that fallback export translations are merged by term.
Description check	✅ Passed	The description explains the fallback export bug, the term-based fix, and the related tests.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@api/test/export.e2e-spec.ts`:
- Around line 114-143: The fallback export test should also validate the full
response contract for nested output and lexical key ordering. Extend the
existing test after the jsonflat request with a jsonnested request using the
same locale and fallback parameters, assert both translated values in the nested
structure, and verify the response keys appear in lexical order.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 4865e862-db95-4bc0-a89d-c856a3832ece

📥 Commits

Reviewing files that changed from the base of the PR and between 9b04d47 and 942da3f.

📒 Files selected for processing (2)

• api/src/controllers/exports.controller.ts
• api/test/export.e2e-spec.ts

[cubic-dev-ai]

All reported issues were addressed across 2 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.1% Duplication on New Code

See analysis details on SonarQube Cloud

[greptile-apps]

Greptile Summary

This change fixes fallback exports so requested-locale translations replace fallback values by term name instead of array position. It also adds coverage for a locale with one translated term and a complete fallback locale.

T-Rex validation blocked

• Missing package/runtime binding: The focused NestJS and Supertest export test could not start because the environment lacks a loadable better-sqlite3 native binding for Node v24.18.1. Rebuilding the dependency failed because the installed version is incompatible with that runtime, so the endpoint did not produce an HTTP response.

Confidence Score: 5/5

T-Rex Logs

What T-Rex did

• T-Rex prepared a focused NestJS and Supertest reproduction to exercise the endpoint GET /api/v1/projects/:projectId/exports with locale=nl and fallbackLocale=de_DE.
• The PR test compiled but failed during SQLite initialization due to Could not locate the bindings file, so no HTTP status or export body could be observed.
• A native SQLite binding rebuild was attempted but failed under Node v24.18.1, indicating that a compatible better-sqlite3 binary or supported Node runtime is required.
• Validation of the expected runnable endpoint defined an HTTP 200 OK status with a body containing {"term.one":"eins","term.two":"twee"}, but this could not be observed due to the initialization failure.
• The test analysis identified the exact missing item as a compatible better-sqlite3 binary for Node v24.18.1 and noted the rebuild failed due to an incompatible toolchain.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: 942da3f | Re-trigger Greptile}