fix(compiler): silence INVALID_ANNOTATION and SOURCEMAP_BROKEN warnings from workerPlugin

[Scan0815]

What is the current behavior?

Every project that bundles a *.worker.ts (or *.worker.tsx) entry emits two bundling warnings on every build:

[ WARN  ]  Bundling Warning INVALID_ANNOTATION
           src/<name>.worker.ts?worker (4:19): A comment "/*@__PURE__*/" in "src/<name>.worker.ts?worker"
           contains an annotation that Rollup cannot interpret due to the position of the comment.
           The comment will be removed to avoid issues.

[ WARN  ]  Bundling Warning SOURCEMAP_BROKEN
           [plugin workerPlugin] Sourcemap is likely to be incorrect: a plugin (workerPlugin) was used
           to transform files, but didn't generate a sourcemap for the transformation. Consult the
           plugin documentation for help.

The SOURCEMAP_BROKEN variant has been tracked as a validated bug for over three years (#3476, opened against v2.17.1, labels Bug: Validated, Help Wanted). A minimal reproduction repo is linked from that issue: https://github.com/Scan0815/stencil-source-map-error. Both warnings originate from src/compiler/bundle/worker-plugin.ts. There is no user-facing way to suppress them: validateRollupConfig (src/compiler/config/validate-rollup-config.ts) whitelists only context, moduleContext, treeshake, external, maxParallelFileOps from rollupConfig.inputOptions, so an onwarn override on stencil.config.ts is dropped before reaching Rollup. The hardcoded ignoreWarnCodes set in src/utils/logger/logger-rollup.ts does not include either code.

Fixes #3476

What is the new behavior?

Two independent fixes in src/compiler/bundle/worker-plugin.ts:

1. INVALID_ANNOTATION — /*@__PURE__*/ is meaningful only in front of call or new expressions. In getWorkerMain and getInlineWorker the marker was placed in front of import.meta.ROLLUP_FILE_URL_*, a property access. Rollup cannot apply pure-side-effect analysis there and strips the comment with the warning above. The two stale markers on workerPath are removed. The remaining /*@__PURE__*/ markers on the actual createWorker(...) / createWorkerProxy(...) calls are unchanged and still effective.

2. SOURCEMAP_BROKEN (#3476) — the transform hook returned synthetic wrapper code without a sourcemap. The Rollup plugin convention for transforms that produce code with no useful source-position mapping is to return map: { mappings: '' }. All five transform return paths now do so: the mocked hydrate/worker-platform branch and the four real-bundle branches (?worker, ?worker-inline, proxy + inline-proxy).

Neither change alters runtime behavior. The two commits are kept separate so each fix is independently revertable.

Documentation

N/A — no public API surface change.

Does this introduce a breaking change?

• Yes
• No

Testing

• npx tsc --noEmit passes after each commit.
• ESLint reports no new errors on src/compiler/bundle/worker-plugin.ts (a pre-existing simple-import-sort/imports finding on main is left untouched to keep this PR focused).
• Full project build (npm run build) and end-to-end verification against the bug: Bundling Warning SOURCEMAP_BROKEN if web-worker is used #3476 reproduction repo have not been performed locally and are deferred to CI / reviewer verification. Steps to reproduce remain those in the original issue.
• No new unit tests added: the touched helpers are non-exported template-string builders and the bundling transforms return synthetic wrapper code; both fixes are warning-suppressing only and have no behavioral surface that a Jest spec could meaningfully assert beyond duplicating the snippet. Happy to add a targeted spec if reviewers prefer.

Other information

The two affected helpers (getWorkerMain, getInlineWorker) and the four transform return branches were unchanged in behavior across recent history, so this is purely a hygiene fix on long-standing output. Disclosure: I'm the original reporter of #3476.

[Copilot]

Pull request overview

This PR addresses persistent Rollup bundling warnings emitted whenever a project bundles *.worker.ts / *.worker.tsx entries, by fixing the warning sources inside the internal workerPlugin implementation.

Changes:

• Remove invalid /*@__PURE__*/ annotations that were placed on import.meta.ROLLUP_FILE_URL_* property access, which triggers Rollup’s INVALID_ANNOTATION warning.
• Return an explicit empty sourcemap (map: { mappings: '' }) from all transform paths that generate synthetic wrapper modules, silencing SOURCEMAP_BROKEN.

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[johnjenkins]

LGTM