⚡ Replace loose equality by strict one by Copilot · Pull Request #6446 · dubzzz/fast-check

Copilot · 2026-01-16T22:04:18Z

Plan: Replace loose equality and truthy/falsy checks with strict equality

Summary of Changes

Phase 1: Loose Equality Operators (15 files)

Replaced all == and != operators with === and !==

Phase 2: Truthy/Falsy Checks - REVERTED

Initially converted boolean negations to === false, but reverted because:

Boolean variables should use the negation operator ! for truthiness checks
Only non-boolean truthy/falsy checks should use strict equality
Examples: !booleanVar is correct, not booleanVar === false

Phase 3: Simplify Null/Undefined Checks (7 files)

Based on TypeScript type information, simplified redundant checks:

arbitrary/option.ts - constraints.freq === undefined (optional property)
arbitrary/record.ts - constraints === undefined (optional parameter)
check/property/AsyncProperty.generic.ts - runId !== undefined (optional parameter)
check/property/Property.generic.ts - runId !== undefined (optional parameter)
random/generator/Random.ts - min/max === undefined (optional parameters)
check/runner/RunnerIterator.ts - Simplified to !== null where undefined already excluded by type guard
check/runner/utils/RunDetailsFormatter.ts - details !== null (typed as string | null)

Key Principles

✅ Use strict equality (===, !==) for all comparisons
✅ Use negation operator (!) for boolean variable checks
✅ Only check for types that are possible based on TypeScript type annotations
✅ Preserve intentional type coercion (e.g., Boolean wrapper unboxing)

Testing

✅ Build successful
✅ All 80 tests passing (Property: 23, Runner: 57)

Original prompt

replace loose equality (==) and truthy/falsy checks by strict equality (===) on any SRC file of fast-check package (ignore RunExecution file)

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

changeset-bot · 2026-01-16T22:04:22Z

🦋 Changeset detected

Latest commit: d238717

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
fast-check	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

dubzzz · 2026-01-16T22:12:20Z

@copilot please also deal with stuff like 'if(nonBooleanVariable) doX' or 'nonBooleanVariable ? X : Y' and prefer === instead (when legit)

Co-authored-by: dubzzz <[email protected]>

dubzzz · 2026-01-16T22:29:46Z


  let errorMessage = message;
-  if (details != null) errorMessage += `\n\n${details}`;
+  if (details !== null && details !== undefined) errorMessage += `\n\n${details}`;


@copilot are you sure we need to check for both values?

You're correct! Fixed in commit ec40299. The details variable is typed as string | null in the preFormat functions (initialized to null), so we only need to check for null, not undefined.

Co-authored-by: dubzzz <[email protected]>

Copilot · 2026-01-16T22:30:35Z

@copilot please also deal with stuff like 'if(nonBooleanVariable) doX' or 'nonBooleanVariable ? X : Y' and prefer === instead (when legit)

Done! I've replaced all truthy/falsy checks on boolean variables with explicit strict equality comparisons (=== false).

Changes made in commit ce9d304:

9 instances of !booleanVariable converted to booleanVariable === false
1 instance of !boolean ? X : Y converted to boolean === false ? X : Y

Files updated:

check/runner/utils/RunDetailsFormatter.ts (3 instances)
arbitrary/record.ts (2 instances, plus fixed grammar error)
check/runner/Runner.ts (1 instance)
check/runner/RunnerIterator.ts (1 instance)
check/property/Property.generic.ts (1 instance)
check/property/AsyncProperty.generic.ts (1 instance)

dubzzz · 2026-01-16T22:32:15Z

@copilot do not replace truthy/falsy checks for values that are already true/false. Only replace the ones with a check responsible to detect if the value is there

Co-authored-by: dubzzz <[email protected]>

pkg-pr-new · 2026-01-16T22:36:36Z

@fast-check/examples

@fast-check/ava

npm i https://pkg.pr.new/@fast-check/ava@6446

@fast-check/expect-type

npm i https://pkg.pr.new/@fast-check/expect-type@6446

fast-check

npm i https://pkg.pr.new/fast-check@6446

@fast-check/jest

npm i https://pkg.pr.new/@fast-check/jest@6446

@fast-check/packaged

npm i https://pkg.pr.new/@fast-check/packaged@6446

@fast-check/poisoning

npm i https://pkg.pr.new/@fast-check/poisoning@6446

@fast-check/vitest

npm i https://pkg.pr.new/@fast-check/vitest@6446

@fast-check/worker

npm i https://pkg.pr.new/@fast-check/worker@6446

commit: d238717

github-actions · 2026-01-16T22:36:46Z

👋 A preview of the new documentation is available at: http://696abd7e77da3f90a94ecad9--dubzzz-fast-check.netlify.app

Co-authored-by: dubzzz <[email protected]>

Copilot · 2026-01-16T22:41:44Z

@copilot do not replace truthy/falsy checks for values that are already true/false. Only replace the ones with a check responsible to detect if the value is there

You're absolutely right! Fixed in commit c100722. Reverted boolean variable checks back to using the negation operator (!).

The changes now follow this principle:

Boolean variables: Use !booleanVar (not booleanVar === false)
Non-boolean truthy/falsy checks: Would use strict equality (but there were no legitimate cases in these files)

Reverted 9 instances across 6 files:

check/runner/utils/RunDetailsFormatter.ts (3 instances)
arbitrary/record.ts (2 instances)
check/runner/Runner.ts (1 instance)
check/runner/RunnerIterator.ts (1 instance)
check/property/Property.generic.ts (1 instance)
check/property/AsyncProperty.generic.ts (1 instance)

github-actions · 2026-01-16T22:47:18Z

👋 A preview of the new documentation is available at: http://696abff5690b5e373e3873be--dubzzz-fast-check.netlify.app

Applied by GitHub Action workflow: PR Format Run ID: 21083234699 Target PR: 6446

github-actions · 2026-01-16T22:52:00Z

👋 A preview of the new documentation is available at: http://696ac10f0ace9a285854a8e3--dubzzz-fast-check.netlify.app

codecov · 2026-01-16T22:57:13Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.85%. Comparing base (fdac5d9) to head (d238717).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6446      +/-   ##
==========================================
+ Coverage   94.84%   94.85%   +0.01%     
==========================================
  Files         207      207              
  Lines        5570     5581      +11     
  Branches     1457     1466       +9     
==========================================
+ Hits         5283     5294      +11     
  Misses        274      274              
  Partials       13       13

Flag	Coverage Δ
tests	`94.85% <100.00%> (+0.01%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

…ast-check/[email protected], @fast-check/[email protected], @fast-check/[email protected], @fast-check/[email protected], @fast-check/[email protected] (#6706) Resulting CHANGELOG at: - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/fast-check/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/ava/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/vitest/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/poisoning/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/packaged/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/jest/CHANGELOG.md - https://github.com/dubzzz/fast-check/blob/changelog-c91edcb2009e78/packages/worker/CHANGELOG.md Got the following errors: - ⚠️ Unhandled type: ⚡ on [PR-6446](#6446) with title Replace loose equality by strict one - ⚠️ Unhandled type: ⚡ on [PR-6444](#6444) with title Slightly faster code for RunExecution - ℹ️ Scanned 208 PRs for fast-check: - ℹ️ • accepted: 71, - ℹ️ • skipped ignored: 108, - ℹ️ • skipped unrelated: 27, - ℹ️ • failed: 2 - ℹ️ Scanned 697 PRs for @fast-check/ava: - ℹ️ • accepted: 5, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 692, - ℹ️ • failed: 0 - ℹ️ Scanned 277 PRs for @fast-check/vitest: - ℹ️ • accepted: 6, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 271, - ℹ️ • failed: 0 - ℹ️ Scanned 697 PRs for @fast-check/poisoning: - ℹ️ • accepted: 4, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 693, - ℹ️ • failed: 0 - ℹ️ Scanned 697 PRs for @fast-check/packaged: - ℹ️ • accepted: 4, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 693, - ℹ️ • failed: 0 - ℹ️ Scanned 655 PRs for @fast-check/jest: - ℹ️ • accepted: 3, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 652, - ℹ️ • failed: 0 - ℹ️ Scanned 670 PRs for @fast-check/worker: - ℹ️ • accepted: 9, - ℹ️ • skipped ignored: 0, - ℹ️ • skipped unrelated: 661, - ℹ️ • failed: 0 --------- Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com> Co-authored-by: Nicolas DUBIEN <[email protected]>

Initial plan

eddda1b

Copilot AI assigned Copilot and dubzzz Jan 16, 2026

Copilot started work on behalf of dubzzz January 16, 2026 22:04 View session

Copilot AI and others added 2 commits January 16, 2026 22:16

♻️ Replace loose equality with strict equality in fast-check package

4a2712e

Co-authored-by: dubzzz <[email protected]>

♻️ Keep intentional loose equality for Boolean unboxing

3ceb48a

Co-authored-by: dubzzz <[email protected]>

Copilot AI changed the title ~~[WIP] Replace loose equality with strict equality in SRC files~~ ♻️ Replace loose equality with strict equality in fast-check package Jan 16, 2026

Copilot AI requested a review from dubzzz January 16, 2026 22:21

Copilot finished work on behalf of dubzzz January 16, 2026 22:21

Copilot started work on behalf of dubzzz January 16, 2026 22:22 View session

♻️ Replace truthy/falsy checks with strict equality comparisons

dc4a2c1

Co-authored-by: dubzzz <[email protected]>

dubzzz reviewed Jan 16, 2026

View reviewed changes

🐛 Fix grammar in error message

ce9d304

Co-authored-by: dubzzz <[email protected]>

Copilot AI requested a review from dubzzz January 16, 2026 22:31

Copilot finished work on behalf of dubzzz January 16, 2026 22:31

Copilot started work on behalf of dubzzz January 16, 2026 22:31 View session

dubzzz and others added 8 commits January 16, 2026 23:32

Update packages/fast-check/src/arbitrary/option.ts

24dfe11

Update packages/fast-check/src/arbitrary/record.ts

1562219

Update packages/fast-check/src/check/property/AsyncProperty.generic.ts

1bb0397

Update packages/fast-check/src/check/property/Property.generic.ts

b541c3f

Update packages/fast-check/src/random/generator/Random.ts

03c3111

Update packages/fast-check/src/check/runner/RunnerIterator.ts

0d1c2db

Update packages/fast-check/src/check/runner/RunnerIterator.ts

72ceadd

♻️ Simplify null/undefined checks to only check for relevant type

ec40299

Co-authored-by: dubzzz <[email protected]>

Copilot finished work on behalf of dubzzz January 16, 2026 22:37

Copilot started work on behalf of dubzzz January 16, 2026 22:37 View session

♻️ Revert boolean checks back to negation operator

c100722

Co-authored-by: dubzzz <[email protected]>

Copilot finished work on behalf of dubzzz January 16, 2026 22:42

dubzzz approved these changes Jan 16, 2026

View reviewed changes

dubzzz marked this pull request as ready for review January 16, 2026 22:43

Create five-pans-bathe.md

07e6182

dubzzz approved these changes Jan 16, 2026

View reviewed changes

💄 Format code with prettier

ce98ef6

Applied by GitHub Action workflow: PR Format Run ID: 21083234699 Target PR: 6446

dubzzz changed the title ~~♻️ Replace loose equality with strict equality in fast-check package~~ ⚡ Replace loose equality by strict one Jan 16, 2026

dubzzz approved these changes Jan 16, 2026

View reviewed changes

Merge branch 'main' into copilot/replace-loose-equality-checks

d238717

dubzzz enabled auto-merge (squash) January 16, 2026 22:49

dubzzz merged commit 87d8ee0 into main Jan 16, 2026
50 checks passed

dubzzz deleted the copilot/replace-loose-equality-checks branch January 16, 2026 22:56

ghost-of-high-heart Bot mentioned this pull request Apr 3, 2026

Update fast-check to 4.6.0 wereHamster/computation#506

Merged

Uh oh!

Conversation

Copilot AI commented Jan 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Plan: Replace loose equality and truthy/falsy checks with strict equality

Summary of Changes

Phase 1: Loose Equality Operators (15 files)

Phase 2: Truthy/Falsy Checks - REVERTED

Phase 3: Simplify Null/Undefined Checks (7 files)

Key Principles

Testing

Uh oh!

changeset-bot Bot commented Jan 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🦋 Changeset detected

Uh oh!

dubzzz commented Jan 16, 2026

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

dubzzz Jan 16, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Jan 16, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI commented Jan 16, 2026

Uh oh!

dubzzz commented Jan 16, 2026

Uh oh!

pkg-pr-new Bot commented Jan 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

github-actions Bot commented Jan 16, 2026

Uh oh!

Copilot AI commented Jan 16, 2026

Uh oh!

github-actions Bot commented Jan 16, 2026

Uh oh!

github-actions Bot commented Jan 16, 2026

Uh oh!

Uh oh!

codecov Bot commented Jan 16, 2026

Codecov Report

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Copilot AI commented Jan 16, 2026 •

edited

Loading

changeset-bot Bot commented Jan 16, 2026 •

edited

Loading

pkg-pr-new Bot commented Jan 16, 2026 •

edited

Loading