Fix prefixItems / minItems / maxItems tuple generation (#2053)

[duncanbeevers]

🗣️ Discussion

This PR is an extraction of some work that has already landed in the 8.x branch. This is my first step in porting those changes to the 7.x branch.

Closes #2048

Changes

• Simplify minItems / maxItems tuple generation
• Introduces @total-typescript to accommodate Array.prototype.filter(Boolean) pattern
• Extract subroutine for transforming array schema objects
• Support items: false; prefixItems: … schemas; treat prefixItems as explicit tuple value.
• Support items: […schemas], treating items as explicit tuple value.

How to Review

• Ensure changes to newly-generated types are valid bug-fixes
• Ensure old behaviors are preserved where appropriate, to break fewer things when we release
• Ensure new behavior is gated behind --experimental-array-spread-members flag
• Ensure ts-reset types don't affect published openapi-ts types
  • ts-reset behaviors should not be active in plain repo with openapi-ts dependency
  • Importing openapi-ts for programmatic use shouldn't start allowing ts-reset behaviors.
• Ensure ts-reset types don't affect generated types
  • Importing openapi-typescript-generated types shouldn't start allowing ts-reset behavior.

🔧 Backwards-compatibility

In order to get a sense for the backwards-compatibility of this PR I pulled the full suite of tests from array.test.ts and ran them in main. Test output

Many test cases in this corpus cover behavior not-yet-tested in main, so this gives us a better sense of what will actually change.

Many of the new tests (expectedly) failed in this older context, and the errors fell into four categories.

1. New behavior gated behind the new --experimental-array-spread-members flag.
2. Mutable spread members for array schemas when immutable: true is set
3. Mutable tuples for array schemas with prefixItems when immutable: true is set
4. Broken tuples (original --array-length with minItems: 1 generates empty array #2048 problem)

Checklist

• Unit tests updated
• docs/ updated (if necessary)
• pnpm run update:examples run (only applicable for openapi-typescript)

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[changeset-bot]

🦋 Changeset detected

Latest commit: 8a09dea

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

This PR includes changesets to release 1 package

Name	Type
openapi-typescript	Minor

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[gzm0]

@drwpow you have looked at the 8.x equivalent of this. Do you also want to take this one, or shall I give it a stab to review?

[drwpow]

This PR looks good to me! Sorry, minor conflict in the PR, but with that resolved + changeset this is good to merge! No notes 🙂

[drwpow]

Going to close this PR to clean things up. It was approved in May 2025 but was never merged, and now has too many conflicts to resolve cleanly. The more recent PR #2546 seems to accomplish the same things for the most part, but doesn’t have conflicts and is passing.

Is there a way we can merge approved PRs quicker in the future? I know many PRs suffer from non-reviews, but we should work to merge & release approved PRs better if we can.