fix(po-format): remove duplicated references when lineNumbers is false

[itsyoboieltr]

Description

When lineNumbers: false is used, extracted PO catalogs currently keep duplicate #: reference lines if the same message appears multiple times in the same file. That creates unnecessary diff noise in source control even though the line numbers have already been intentionally removed.

This PR reduces that churn by deduplicating file-only references while preserving their original order.

Changes:

• deduplicate references in @lingui/format-po when lineNumbers: false
• deduplicate references in @lingui/format-po-gettext for the mergePlurals: true path, where merged plural entries could reintroduce duplicate file-only references
• add regression tests for both cases

This keeps the existing behavior unchanged when line numbers are enabled, and only removes repeated file references once multiple locations have collapsed to the same path.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Examples update

Fixes #2405

Checklist

• I have read the CONTRIBUTING and CODE_OF_CONDUCT docs
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)

[vercel]

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[timofei-iatsenko]

@itsyoboieltr hey, all current development happened in the next branch, could you change the basse of your PR to that?

[timofei-iatsenko]

Let's avoid the branching here and just leave the [...new Set(duplicateItems.flatMap((item) => item.references))] the same way as in the po formatter.

[itsyoboieltr]

fixed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.01%. Comparing base (dd43fb0) to head (b4e5bc2).
⚠️ Report is 334 commits behind head on next.

Additional details and impacted files

@@             Coverage Diff             @@
##             next    #2509       +/-   ##
===========================================
+ Coverage   76.66%   89.01%   +12.35%     
===========================================
  Files          81      118       +37     
  Lines        2083     3315     +1232     
  Branches      532      977      +445     
===========================================
+ Hits         1597     2951     +1354     
+ Misses        375      329       -46     
+ Partials      111       35       -76     

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[itsyoboieltr]

@timofei-iatsenko I reset the branch onto next, reapplied the fix there, and force-pushed. The PR should now be clean against next.

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Project	Deployment	Actions	Updated (UTC)
js-lingui	Ready	Preview	Apr 14, 2026 8:06am