Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Stencil Version

4.43.0

Current Behavior

When running stencil build --dev --watch --serve, the initial build completes normally. On any subsequent file change, the rebuild hangs indefinitely at:

generate lazy + source maps started ...

Root Cause

Stencil 4.43.0 bundles Rollup 4.34.9, which contains a known deadlock bug (rollup/rollup#5848):

1. On rebuild, Rollup passes all cached modules (3687 in our case) through addModuleSource, which uses a fileOperationQueue limited to maxParallelFileOps (default: 20)
2. The @rollup/plugin-commonjs load hook calls this.load() internally
3. With enough concurrent modules, the outer load calls saturate the 20-slot queue, and the nested this.load() calls queue behind them — creating a deadlock where no task can complete

This was fixed in Rollup 4.44.0 (rollup/rollup#5986) by setting the default maxParallelFileOps to Infinity.

Related Issues

• #6253 — same symptom, attributed to maxParallelFileOps but the fix (PR feat(compiler): support maxParallelFileOps in RollupInputOptions #6255) only exposed the config option without changing the default
• rollup/rollup#5848 — upstream bug report and fix

Suggested Fix

Update the bundled Rollup from 4.34.9 to ≥4.44.0.

As a temporary workaround, disabling the Rollup cache (setting cache: false in the rollup input options within bundleOutput) also resolves the issue, at the cost of slightly slower rebuilds (~7s full re-bundle vs near-instant from cache).

Expected Behavior

Watch mode rebuilds should complete without hanging.

Steps to Reproduce

1. Use a Stencil project with a large number of components (100+ components, 3000+ modules in the Rollup graph)
2. Run stencil build --dev --watch --serve
3. Wait for initial build to complete
4. Modify any component file
5. Rebuild hangs at "generate lazy + source maps started"

System Info

macOS (Apple Silicon)
Stencil: 4.43.0 (bundles Rollup 4.34.9)
Node: 22.x

Debug Data

Instrumentation of Stencil's compiler confirms the hang:

[invalidateRollupCaches] changedFiles=1 invalidated=0 totalModules=3687
[bundleOutput] id=lazy cacheModules=3687 maxParallelFileOps=undefined

rollup() is called with 3687 cached modules and maxParallelFileOps defaulting to 20, and never returns.