fix(typescript): emit named type alias for root-level array types

[schani]

Bug

TypeScript did not generate correct types when a JSON Schema's root type is an array of objects.

For this schema:

{
    "$ref": "#/definitions/GetResp",
    "definitions": {
        "GetResp": { "title": "GetResp", "type": "array", "items": { "$ref": "#/definitions/SomeObject" } },
        "SomeObject": {
            "title": "SomeObject",
            "type": "object",
            "additionalProperties": false,
            "properties": { "name": { "type": "string" } },
            "required": ["name"]
        }
    }
}

TypeScript generated:

export interface PR {
    name: string;
}

— the array wrapper was silently dropped and the object interface was named after the array (PR, from the root array's title/filename) instead of after the object (SomeObject), and there was no named array type at all.

Go, by contrast, correctly generates type PR []SomeObject plus a separate type SomeObject struct {...}.

Root cause

TypeScriptRenderer inherited JavaScriptRenderer#namedTypeToNameForTopLevel, which uses directlyReachableSingleNamedType to collapse a root type onto the single named type reachable through it — including through an ArrayType. For a root array of objects, this assigns the top-level name to the item object type instead of the array itself, and TypeScript (unlike some other languages) never separately emits a named alias for array top levels, so the array wrapper disappears entirely.

Fix

In packages/quicktype-core/src/language/TypeScriptFlow/TypeScriptRenderer.ts:

• Override namedTypeToNameForTopLevel to return undefined for ArrayType, so root-level arrays keep their own top-level name instead of collapsing onto their item type (this mirrors the same pattern already used by other renderers, e.g. DartRenderer, GolangRenderer, CSharpRenderer).
• Emit export type <Name> = <Item>[]; for root-level array types in emitTypes.
• Use the array alias (rather than an inline array-of-item-type expression) in the Convert class's method signatures and in the "how to use" usage comment.

Flow and other renderers are unaffected.

Test coverage

• test/inputs/schema/root-array-ref.schema (+ .1.json sample) — new end-to-end JSON Schema fixture exercising a root-level array of a named object type, run via the existing schema-* fixture machinery for every language (compiles/round-trips for all languages, including TypeScript).
• test/unit/typescript-root-array-schema.test.ts — unit test asserting the exact generated structure (export interface SomeObject, export type PR = SomeObject[];, and that export interface PR is not generated), since the fixture round-trip test alone can't express "these exact type names/structure must be produced."

Verification (local)

• npm run build passes.
• Repro re-run after the fix now produces the expected output:

  export interface SomeObject {
      name: string;
  }
  
  export type PR = SomeObject[];

• QUICKTEST=true FIXTURE=schema-typescript script/test — full suite passes for all schema fixtures including the new root-array-ref.schema; the only failure (vega-lite.schema TS2411 errors from tsc) was confirmed to be pre-existing on unmodified master (verified by stashing this fix and re-running), unrelated to this change.
• npx vitest run test/unit — all 164 unit tests across 26 files pass, including the new test.
• CI will additionally validate the full fixture matrix across all languages.

Fixes #1309

🤖 Generated with Claude Code

[github-actions]

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70 files differ — 45 modified, 25 new, 0 deleted
2439 changed lines — +2111 / −328

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