Follow-up: RSC Rspack doctor lazyCompilation check false-warns on equivalent configs

[ihabadham]

Summary

Follow-up to #4227 and #4234.

Related longer-term RSC/Rspack architecture tracking: #3488 and #3553.

react_on_rails:doctor:rsc currently recognizes only the generated literal Rspack dev config pattern:

clientWebpackConfig.lazyCompilation = false;

Equivalent custom configs can produce an effective lazyCompilation: false final Rspack config, but doctor still warns:

Rspack lazyCompilation can leave the RSC client manifest empty in normal bin/dev mode.
config/rspack/development.js does not appear to disable lazyCompilation while the dev server is running.

Why this matters

Generated RSC + Rspack apps are OK after the dev-server lazy-compilation fix. This is narrower: apps that customize their Rspack config can get misleading doctor output even when lazy compilation is actually disabled or intentionally excluded for RSC-critical modules.

This is not urgent runtime breakage, but it can confuse advanced users and future RSC/Rspack work.

Empirical check

Fresh RORP + RSC + Rspack app generated from current main after #4234.

For each variant, I reset generated Rspack config files, applied one config shape, evaluated the real final Rspack config under WEBPACK_SERVE=true, then ran:

bundle exec rails react_on_rails:doctor:rsc

Result matrix:

Variant	Effective Rspack lazyCompilation	Doctor lazy check
Generated literal assignment	false	✅ success
clientWebpackConfig.lazyCompilation = { entries: false, imports: false }	object disables both	⚠️ warns
Object.assign(clientWebpackConfig, { lazyCompilation: false })	false	⚠️ warns
helper function in separate file	false	⚠️ warns
ternary rscWebpackConfig ? false : ...	false	⚠️ warns
object with custom test() excluding RSC refs	object/function	⚠️ warns
disabled in clientWebpackConfig.js	false	⚠️ warns
disabled in rspack.config.js after env config loads	false	⚠️ warns
no disable control	unset	⚠️ warns

Expected

Doctor should either:

1. detect the final effective Rspack dev-server config more accurately, or
2. make the warning wording explicit that it only failed to find the generated literal config pattern.

Actual

Doctor warning implies lazy compilation is not disabled even when the final evaluated config has lazyCompilation: false.

Notes

The test(module) row only proves the detector cannot recognize that category. It does not claim every custom test() predicate is safe for every app.

This should probably be P3/fix-later unless maintainers want doctor polish now.

[justin808]

Shakapacker offers tools and leverages https://github.com/shakacode/pack-config-diff and others to find the content in a normalized manner. This can help.