Fix prefixItems / minItems / maxItems tuple generation

[duncanbeevers]

Changes

Closes #2048

• Extract types generation for Array-type schemas to transformArraySchemaObject method
• Throw error when OpenAPI items is array
• Generate correct number of union members for minItems * maxItems unions
• Generate readonly tuple members for minItems & maxItems unions
• Generate readonly spread member for prefixItems tuple
• Preserve prefixItems type members in minItems & maxItems tuples
• Generate spread member for prefixItems tuple with no minItems / maxItems constraints
• Add test case for error thrown when OpenAPI items is array
• Add test case for heterogeneous item members: items: oneOf: [{ type: 'string' }, { type: 'number' }]
• Add test cases for minItems + maxItems schema generating empty tuple, as outlined in --array-length with minItems: 1 generates empty array #2048
• Add test cases for many combinations of arrayLength and immutable options, and prefixItems, minItems, maxItems schemas

The previous union+tuples generation implementation was a little hair-ball, and difficult for me to parse, so I replaced it with a stepped implementation, returning early with results whenever possible.

• first returning the full min + max union-of-tuples if possible; each union member may be readonly, but not the union as a whole
• next, returning the min tuple if possible; the tuple as a whole may be readonly, as well as its spread members.
• finally, returning the simple array type, which may be readonly

Examples

Here's a simple schema, and the before+after generated types.

☕ minItems empty tuple

components:
  schemas:
    TwoNumbers:
      type: array
      items:
        type: number
      minItems: 1
      maxItems: 2

// Before
export interface components {
    schemas: {
        TwoNumbers: [
        ] | [
            number
        ];
    };
    …

// After
export interface components {
    schemas: {
        TwoNumbers: [
            number
        ] | [
            number,
            number
        ];
    };
    …

📖 readonly spread type

components:
  schemas:
    OneNumber:
      type: array
      items:
        type: number
      minItems: 1

// Before
export interface components {
    schemas: {
        readonly OneNumber: [
            number,
            ...number[]
        ];
    };
    …

// After
export interface components {
    schemas: {
        readonly OneNumber: readonly [
            number,
            ...readonly number[]
        ];
    };
    …

🙉 preserve prefixItems

components:
  schemas:
    WithPrefixItems:
      type: array
      items:
        type: string
      prefixItems:
        - type: string
          enum:
            - professor
        - type: string
          enum:
            - student
      minItems: 2
      maxItems: 4

// Before
export interface components {
    schemas: {
        WithPrefixItems: [
            "doctor",
            "intern"
        ];
    };
    …

// After
export interface components {
    schemas: {
        WithPrefixItems: [
            "doctor",
            "intern",
            ...string[]
        ];
    };
    …

The same schema with the arrayLength: true option set generates quite different types.

// Before
export interface components {
    schemas: {
        WithPrefixItems: [
        ] | [
            [
                "doctor",
                "intern"
            ]
        ] | [
            [
                "doctor",
                "intern"
            ],
            [
                "doctor",
                "intern"
            ]
        ];
    };
    …

// After
export interface components {
    schemas: {
        WithPrefixItems: [
            "doctor",
            "intern"
        ] | [
            "doctor",
            "intern",
            string
        ] | [
            "doctor",
            "intern",
            string,
            string
        ];
    };
    …

How to Review

• Ensure generated schemas are all still acceptable
• Ensure code-style is appropriate
• Ensure newly-readonly spread member is acceptable (this may qualify as a breaking change)
• Ensure new error behavior on OpenAPI items is array is acceptable
• Ensure new spread behavior on prefixItems schemas is acceptable
• Look closely at the new tests cases, and changes to old test cases, including options and schemas passed to the schema transformer
• This PR undoes some of the work done in fix(openapi-typescript):transformSchemaObject support two-dimensional… #1489, updating its test case to use prefixItems and arrayLength in combination to generate the desired array-of-tuples

Checklist

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

[changeset-bot]

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Latest commit: 68d9191

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

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