[NO-JIRA] Update Constitution Principle V to align with React 19 by xiaogliu · Pull Request #4508 · Skyscanner/backpack

Vincent Liu (xiaogliu) · 2026-05-20T08:45:31Z

Summary

Replace the "maintain both TypeScript types and prop-types during migration" bullet in Constitution Principle V (TypeScript Migration & Type Safety) with explicit guidance to drop prop-types and function-component defaultProps during migration.

Why

1. React 19 has removed both APIs. Per the React 19 upgrade guide:

In React 19, we're removing the propType checks from the React package, and using them will be silently ignored. […] We're also removing defaultProps from function components in place of ES6 default parameters.

So keeping them during migration is either no-op runtime code (propTypes) or actively broken (defaultProps on function components).

2. Recent migration practice already drops both APIs. Five consecutive TS migration PRs followed this pattern:

[CLOV-119] Migrate bpk-component-progress JS to TypeScript #4486 BpkProgress
[BpkRadio] Migrate JS to TypeScript #4475 BpkRadio
[CLOV-73][BpkFormValidation] Migrate JS to TypeScript #4473 BpkFormValidation
[CLOV-1589][BpkAutosuggest] Migrate JS to TypeScript #4303 BpkAutosuggest
[CLOV-106][BpkPagination] Migrate JS to TypeScript #4500 BpkPagination

The Constitution wording was generating reviewer friction (see #4500 review thread) because policy and practice had drifted apart.

Changes

Principle V: replaced the "maintain both" bullet with explicit migration guidance
Rationale: added React 19 upgrade guide link explaining why the change is required
Version bumped 1.0.2 → 1.1.0 (MINOR — principle guidance change)
Added v1.1.0 changelog entry and updated Last Amended date

Test plan

Constitution renders cleanly (markdown lint not run; this file isn't covered by the project linters)
No template files reference the old "maintain both" wording (verified with grep)

🤖 Generated with Claude Code

Replace the "maintain both TypeScript types and prop-types during migration" guidance with explicit instruction to remove prop-types and function-component defaultProps in favour of TypeScript types and ES6 destructuring defaults. Why: - React 19 removes propTypes and function-component defaultProps from the React package (https://react.dev/blog/2024/04/25/react-19-upgrade-guide#removed-proptypes-and-defaultprops), so retaining them is either no-op or actively broken - Recent migrations (BpkProgress #4486, BpkRadio #4475, BpkFormValidation #4473, BpkAutosuggest #4303, BpkPagination #4500) have all dropped both APIs in a single step; the Constitution should reflect that established practice Bump version 1.0.2 -> 1.1.0 (MINOR: principle guidance change). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

skyscanner-backpack-bot · 2026-05-20T08:46:57Z

Visit https://backpack.github.io/storybook-prs/4508 to see this build running in a browser.

Copilot

Pull request overview

Updates the Backpack Design System Constitution (Principle V) to align TypeScript migration guidance with React 19’s removal of function-component defaultProps support and React’s deprecation of built-in propTypes checking.

Changes:

Updates Principle V to instruct removing prop-types and function-component defaultProps during TS migrations.
Expands the Principle V rationale with a link to the React 19 upgrade guide.
Bumps the constitution version to 1.1.0 and updates version history/changelog metadata.

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skyscanner-backpack-bot · 2026-05-21T03:01:07Z

Visit https://backpack.github.io/storybook-prs/4508 to see this build running in a browser.

skyscanner-backpack-bot · 2026-05-21T03:42:21Z

Visit https://backpack.github.io/storybook-prs/4508 to see this build running in a browser.

- Drop the "no ES6 equivalent exists" phrasing for class-component defaultProps (class components can use destructuring defaults inside render); clarify that React 19 only stopped applying defaultProps for function components - Soften "React 19 removes propTypes" to "silently ignores propTypes checks" to match the upgrade guide language (the propTypes API is not removed, only the runtime checks are) Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

skyscanner-backpack-bot · 2026-05-21T03:44:16Z

Visit https://backpack.github.io/storybook-prs/4508 to see this build running in a browser.

Richard-Shen (RichardSyq)

Left two inline suggestions for the constitution/template consistency points.

Richard-Shen (RichardSyq) · 2026-05-21T08:03:26Z

- ✅ .specify/templates/plan-template.md - Updated structure and removed package.json reference
- ✅ .specify/templates/tasks-template.md - Updated with correct task sequence and examples
-Follow-up TODOs: None - all templates aligned and corrected
+- ✅ No template changes required


Suggestion: could we update the task template in the same PR?

Principle V now says migrated components should replace prop-types with TypeScript types and use ES6 defaults instead of function-component defaultProps, but .specify/templates/tasks-template.md still generates a task to “Add prop-types for runtime validation” and a Constitution Check for “TypeScript types + prop-types during migration”.

That leaves newly generated tasks contradicting the updated constitution. I think T015 should be reworded to match the new guidance, and this Sync Impact Report should no longer say “No template changes required”.

Good catch — fixed in 8a1e7af. Updated .specify/templates/tasks-template.md T015 to drop the "Add prop-types for runtime validation" sub-step and reworded its Constitution Check to match the new Principle V (TypeScript types REQUIRED; prop-types and function-component defaultProps MUST NOT be used). Also corrected the Sync Impact Report to list this template change instead of "No template changes required".

Richard-Shen (RichardSyq) · 2026-05-21T08:03:26Z

+- V. TypeScript Migration & Type Safety: replaced "maintain both TypeScript types
+  and prop-types during migration" with explicit guidance to remove prop-types
+  and function-component defaultProps in favour of TypeScript types and ES6
+  destructuring defaults, aligning with React 19 (which removed both APIs).


Small wording suggestion: could we tighten this summary to match the more precise wording in the principle body?

“React 19 (which removed both APIs)” still sounds like both propTypes and defaultProps APIs were removed wholesale. The React 19 upgrade guide is narrower: React now ignores propTypes checks, and defaultProps no longer applies to function components, while class components still support defaultProps.

Maybe:

aligning with React 19, which ignores propTypes checks and no longer applies defaultProps for function components.

Agreed — the summary was still too strong. Updated in 8a1e7af to mirror the body wording: "aligning with React 19, which ignores propTypes checks and no longer applies defaultProps for function components."

- Tighten Sync Impact Report summary to mirror the precise body wording: React 19 ignores propTypes checks and no longer applies defaultProps for function components — it does not "remove both APIs" wholesale - Update tasks-template.md T015 to align with the new Principle V: drop "Add prop-types for runtime validation" sub-step, switch the default-values sub-step to ES6 destructuring defaults, and rewrite the Constitution Check to forbid prop-types and function-component defaultProps (matches the React 19 upgrade guide) - Sync Impact Report Templates status now lists the template change Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

skyscanner-backpack-bot · 2026-05-25T09:22:54Z

Visit https://backpack.github.io/storybook-prs/4508 to see this build running in a browser.

Richard-Shen (RichardSyq)

LGTM

Copilot AI review requested due to automatic review settings May 20, 2026 08:45

Vincent Liu (xiaogliu) added the skip-changelog label May 20, 2026

Copilot started reviewing on behalf of Vincent Liu (xiaogliu) May 20, 2026 08:46 View session

Copilot AI reviewed May 20, 2026

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Comment thread .specify/memory/constitution.md Outdated

Vincent Liu (xiaogliu) added the patch Patch production bug label May 21, 2026

Merge branch 'main' into xiaogliu/constitution-v-update

4a57294

Vincent Liu (xiaogliu) removed the patch Patch production bug label May 21, 2026

Merge branch 'main' into xiaogliu/constitution-v-update

8aad215

Richard-Shen (RichardSyq) reviewed May 21, 2026

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Richard-Shen (RichardSyq) approved these changes May 25, 2026

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Vincent Liu (xiaogliu) merged commit 7471c24 into main May 25, 2026
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Vincent Liu (xiaogliu) deleted the xiaogliu/constitution-v-update branch May 25, 2026 10:27

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Vincent Liu (xiaogliu) commented May 20, 2026

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