Ratchet React Compiler `panicThreshold` in non-prod builds: `critical_errors`, then `all_errors`

[MajorLift]

Performance audit finding · Severity: Medium (tooling/ratchet) · Effort: Medium, then ongoing · Fix risk: Simple (non-prod builds only) · Test safety net: N/A (build gate)
Owner: @MetaMask/mobile-platform (suggested)
File: babel.config.js:67
Depends on: #31500 (logger triage — provides the actionable-error list this ratchet burns down)

What is this about?

panicThreshold controls when a React Compiler diagnostic fails the build instead of silently skipping the file. Mobile currently runs the implicit default ('none'): every diagnostic is a silent skip, so compiler coverage can regress without anyone noticing. The ratchet makes a non-production build progressively intolerant:

Setting	Build fails on	Use
'none' (current/default)	never — failed files silently skipped	production, permanently
'critical_errors'	compiler-internal invariant violations	CI/debug gate, first target
'all_errors'	every diagnostic incl. unsupported syntax	CI/debug gate, end state

The extension tracks the same ladder as MetaMask-planning#6552 (enable critical_errors, fix violations) and #6553 (all_errors); its enablement-run split (metamask-extension#38007: 31 actionable errors vs 7,024 unsupported of 7,308 files) shows the actionable set a ratchet has to clear is small once the Todo category is excluded.

Scenario

N/A — build tooling.

Design

N/A.

Technical Details

1. Add an env-gated Babel config path (or CI job) that sets panicThreshold: 'critical_errors' in the 'react-compiler' plugin options for non-production builds. Production stays 'none' permanently — one un-compilable file must never block a release for an optional optimization.
2. Fix the actionable (non-Todo) errors surfaced by the Collect React Compiler coverage stats and triage actionable vs unsupported-syntax errors #31500 logger until the critical_errors gate passes; promote the gate to required CI.
3. Repeat toward 'all_errors'. What remains after that is the unsupported (Todo) set, re-diffed on compiler upgrades — Todos that newly compile are free wins, new errors are regressions the gate now catches.

Threat Modeling Framework

N/A — non-production build gate; no runtime change.

Acceptance Criteria

• Non-prod build passes at panicThreshold: 'critical_errors' and the gate runs in CI.
• Follow-up ratchet to 'all_errors' tracked, with the remaining actionable-error count trending to zero.
• Production builds verified unaffected ('none').

References

• Files: babel.config.js:67
• Depends on: Collect React Compiler coverage stats and triage actionable vs unsupported-syntax errors #31500; coverage-debt sibling: Migrate the ~53 class components skipped by React Compiler (coverage debt) #31501
• Extension counterparts: MetaMask-planning#6552, chore: fix for swaps button displaying on unsupported networks (#6473) #6553; reference implementation metamask-extension#38007 (--reactCompilerDebug={all|critical|none})
• Source: mms-performance skill, mm-react-compiler-error-triage (perf: Augment mms-performance with frontend learnings from the Extension performance audit skills#49)
• Status: tooling proposal

[metamask-ci]

Triage Agent

This issue appears to be a feature request, not a bug report.

Automated bug classification has been skipped. If this is actually a bug, please update the issue with reproduction steps and error details, then re-apply the triage label.