feat: store msgctxt from Gettext (.po) files

[Anty0]

Summary

• Parse and store msgctxt from PO files instead of ignoring it with a warning
• Combine msgctxt + \u0004 (EOT) separator + msgid as the key name, following the GNU gettext standard
• Store raw msgctxt in key custom metadata (_poFileMsgCtxt)
• Export msgctxt line before msgid when the custom value is present
• Display msgctxt visually in the translations UI with a dimmed prefix and | separator

Closes #3053

Summary by CodeRabbit

New Features

• Added full support for PO file message contexts (msgctxt). Translations with context information can now be properly imported, stored, and exported while maintaining all context metadata
• Translation keys with message context are now visually distinguished in the interface, making it easier to identify and manage contextual translations

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR implements support for storing and handling the msgctxt (message context) field from Gettext (.po) files. Changes span the entire PO format lifecycle: parser now captures msgctxt instead of treating it as unsupported, the processor combines it with msgid as the key and stores context as metadata, the exporter reconstructs msgctxt on output, and the frontend displays context distinctly.

Changes

Cohort / File(s)	Summary
PO Format Constants backend/data/src/main/kotlin/io/tolgee/formats/po/contsants.kt	Added two constants: PO_FILE_MSG_CTXT_CUSTOM_KEY to identify msgctxt metadata and PO_MSGCTXT_SEPARATOR (Unicode U+0004) to delimit msgctxt from msgid in combined keys.
PO Parsing backend/data/src/main/kotlin/io/tolgee/formats/po/in/PoParser.kt	Replaced error emission for msgctxt with flag-based handling; now collects msgctxt content via expectMsgCtxt state flag instead of rejecting it as unsupported.
Translation Data Model backend/data/src/main/kotlin/io/tolgee/formats/po/in/data/PoParsedTranslation.kt	Added msgctxt StringBuilder property to store message context during parsing.
PO Processing backend/data/src/main/kotlin/io/tolgee/formats/po/in/PoFileProcessor.kt	Introduced buildKeyName() helper to combine msgctxt and msgid with separator, and storeMsgCtxt() to persist context as custom metadata; applied to both singular and plural translation paths.
PO Exporting backend/data/src/main/kotlin/io/tolgee/formats/po/out/PoFileExporter.kt	Added logic to extract msgctxt from combined key, write msgctxt field to file, and use actual msgid (with separator stripped) for msgid and plural forms; introduced writeMsgCtxt() helper and updated writeMsgIdPlural() signature.
Frontend Display webapp/src/views/projects/translations/CellKey.tsx	Replaced direct keyName rendering with KeyNameWithContext component that splits on separator and displays msgctxt and msgid as separate styled elements.
Parser Tests backend/data/src/test/kotlin/io/tolgee/unit/formats/po/in/PoParserTest.kt	Added test verifying correct parsing of msgctxt, msgid, msgstr, and plural forms across contextual and non-contextual entries.
Processor Tests backend/data/src/test/kotlin/io/tolgee/unit/formats/po/in/PoFileProcessorTest.kt	Added tests validating msgctxt handling: distinct key generation per context, correct metadata storage, and preservation of non-contexted keys.
Exporter Tests backend/data/src/test/kotlin/io/tolgee/unit/formats/po/out/PoFileExporterTest.kt	Added tests for msgctxt export with simple and plural forms, using helper exporters and constants to validate output structure.
Test Resource backend/data/src/test/resources/import/po/example_msgctxt.po	Added German PO translation file with msgctxt examples: menu (Open/Close), dialog (Open), stats (plural), and uncontexted Hello entry.

Sequence Diagram(s)

sequenceDiagram
    participant PO as PO File
    participant Parser as PoParser
    participant Model as PoParsedTranslation
    participant Processor as PoFileProcessor
    participant Storage as Translation<br/>Storage
    
    PO->>Parser: Read msgctxt field
    Parser->>Parser: Set expectMsgCtxt flag
    Parser->>Model: Append to msgctxt StringBuilder
    PO->>Parser: Read msgid field
    Parser->>Model: Store msgid
    PO->>Parser: Read msgstr field
    Parser->>Model: Store msgstr
    Processor->>Model: Retrieve msgctxt & msgid
    Processor->>Processor: buildKeyName()<br/>Result: msgctxt\u0004msgid
    Processor->>Storage: Store key with<br/>msgctxt metadata
    Storage->>Storage: msgctxt field =<br/>PO_FILE_MSG_CTXT_CUSTOM_KEY

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• fix: fallback to key if PO_FILE_MSG_ID_PLURAL_CUSTOM_KEY unavailable #3224 — Modifies PO plural export logic in PoFileExporter (writeMsgIdPlural and plural msgid handling), overlapping code paths with msgctxt exporting changes.

Suggested reviewers

• JanCizmar

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🐰 Hopping through gettext fields so spry,
msgctxt now captured, no more goodbye,
Context and messages in harmony blend,
With separator magic, confusion will end! ✨🌿

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: store msgctxt from Gettext (.po) files' accurately describes the main change: adding support for parsing and storing msgctxt from PO files.
Linked Issues check	✅ Passed	All coding objectives from issue #3053 are met: msgctxt is imported using key scheme, custom metadata stores raw msgctxt for round-trip export, UI displays msgctxt with context separator, and comprehensive tests validate the implementation.
Out of Scope Changes check	✅ Passed	All changes are directly related to msgctxt support: parser/exporter modifications, constant definitions, test resources, and minimal UI display logic for the context separator.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch jirikuchynka/po-msgctxt

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[JanCizmar]

Q: Why do you store it also in the meta field?