Description

PO file flags (like #, fuzzy or custom flags like #, myTag) are lost when running lingui extract again. The extra.flags field from the existing catalog is not preserved during the merge process.

The bug is in packages/cli/src/api/catalog/mergeCatalog.ts. When merging catalogs, the code takes rest from nextCatalog (extracted messages) which doesn't contain flags, and only preserves translation from prevCatalog. The extra.flags field is silently discarded.

Verifications

• I've checked the docs and this isn't covered there.
• I've searched existing issues on GitHub.

Reproduction Steps

1. Create a PO file with a flag

cat > messages.po << 'EOF'
msgid "Hello"
msgstr "Hallo"
#, myTag
EOF

2. Run extract

lingui extract

3. Check the PO file - the flag "#, myTag" is gone

Or programmatically:

import { mergeCatalog } from "@lingui/cli/api"

const prevCatalog = {
  "Hello": {
    translation: "Hallo",
    extra: { flags: ["myTag"] }
  }
}

const nextCatalog = {
  "Hello": {
    message: "Hello",
    origin: [["src/app.ts", 1]]
  }
}


const result = mergeCatalog(prevCatalog, nextCatalog, false, {})
console.log(result["Hello"].extra?.flags) // undefined

Expected Behavior

The flags should be preserved from the existing catalog when running extract. Flags are translator/tooling metadata that should persist across extractions, similar to how translation is preserved.

Macro Support

Not using macro

Lingui Version

5.8.0

Babel Version

@babel/core@7.28.3

Framework

Affects CLI command