fix(i18n): keep production sourcemaps usable when the i18n plugin rewrites a chunk (#25691) (CP: 25.3)

[vaadin-bot]

This PR cherry-picks changes from the original PR #25691 to branch 25.3.

Original PR description

Summary

The Vaadin i18n build plugin replaced the sourcemap of every chunk with an empty one, so all .map files of an app built with build.sourcemap enabled were useless. The plugin now rewrites chunks at a point where the bundler keeps the original sourcemap, and leaves untouched chunks alone.

Fixes #16679

What changed

Behavior change: only apps that build with build.sourcemap enabled are affected, and only for the better — their .map files now contain the real sources instead of being empty. Chunk output itself is unchanged, so no API or runtime behavior changes for anyone else.

• rollup-plugin-vaadin-i18n.js moves the chunk rewriting from generateBundle to renderChunk. The bundler then composes the map returned by the plugin with the map it already has for that chunk. Chunks the plugin does not touch return null and keep their sourcemap as is. generateBundle still collects the translation keys.
• The registerChunk calls are now found with a regular expression instead of an exact string match. It tolerates a renamed i18n binding and rewritten string quotes, so duplicate calls are removed and the chunk name marker is replaced also when the bundler has reformatted the rendered chunk.
• The vite-production test app now uses Hilla translations in two frontend modules (via a small stub of @vaadin/hilla-react-i18n) and builds with sourcemaps on, so the tests actually run through the rewriting path.

Test summary

#	Status	What the test verifies	Why it matters
1	✅	Every .map file reachable from the entry bundle has non-empty sources, non-empty mappings, and the contents of each source	This is the bug: a rewritten chunk got a map with no sources, so the browser could not map the bundle back to the original files
2	✅	Chunks the plugin does not rewrite still have a usable sourcemap	The early return null must not drop maps the bundler produced
3	✅	The chunk that contains translations calls registerChunk with its own served file name, and the marker is gone	A wrong or unreplaced name means the runtime cannot load the translations of that chunk
4	✅	That chunk has exactly one registerChunk call	Duplicate calls from several modules must be removed; a missed match would also leave a stale marker behind
5	❗ gap	Matching when the bundler renames the i18n binding or rewrites the string quotes	The regex exists for this case, but no test forces that output shape; whether it happens depends on the minifier settings of the test app

Tests added on this branch:

• SourceMapsIT.bundleSourceMapsPointToOriginalSources — rows 1, 2
• I18nChunkIT.chunkRegistersItselfUnderItsOwnName — rows 3, 4

Left untested on purpose: BundleAccess is a test helper that only downloads bundle files, so it is covered indirectly by both ITs.

[github-actions]

The chunk rewrite moves from generateBundle to renderChunk, so the bundler composes the sourcemap instead of the plugin overwriting it

flowchart LR
    subgraph Before
        direction TB
        B1["bundler renders chunk (has original map)"] -->|passes chunk| B2["generateBundle() rewrites chunk, sets chunk.map"]
        B2 -->|overwrites with source-less generateMap| B3[".map has no sources (empty)"]
    end
    subgraph After
        direction TB
        A1["renderChunk() rewrites chunk, returns map or null (new)"]:::changed -->|returns code+map| A2["bundler composes returned map with original"]:::changed
        A2 -->|composed map| A3[".map has real sources"]
        A1 -.->|keys only, no map write| A4["generateBundle() collects translation keys"]
    end
    Before ~~~ After
    classDef changed stroke:#c9a227,stroke-width:3px

Loading

Before, rollup-plugin-vaadin-i18n.js rewrote each chunk in generateBundle and assigned chunk.map = magicString.generateMap(), overwriting the bundler's sourcemap with one that has no sources, so every .map file was empty. After, the rewrite runs in renderChunk, which returns {code, map} (or null for untouched chunks); the bundler then composes that map with the chunk's original, keeping real sources, while generateBundle only collects keys. Mechanism per the pull request description and the diff.

Diagram Bot draws the mechanism this pull request touches; it does not review the change. Verify it against the diff.

Generated by Diagram Bot for issue #25707 · ◷

[vaadin-bot]

This PR is eligible for auto-merging policy, so it has been approved automatically. If there are pending conditions, auto merge (with 'squash' method) has been enabled for this PR [Message is sent from bot]

[github-actions]

Test Results

 1 443 files  +2   1 527 suites  +2   1h 37m 53s ⏱️ + 1m 3s
12 078 tests +2  12 010 ✅ +2  68 💤 ±0  0 ❌ ±0 
12 396 runs  +2  12 328 ✅ +2  68 💤 ±0  0 ❌ ±0 

Results for commit 45018c2. ± Comparison against base commit 5112714.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud