[*] Chore: always use T[] syntax instead of Array<T> in TypeScript and Flow

[etrepum]

Description

• Enable @typescript-eslint/array-type ({default: 'array'}) in eslint.config.mjs and apply its autofix across all TypeScript sources (Array -> T[], ReadonlyArray -> readonly T[])
• Add scripts/flow-array-type-codemod.mjs, a hermes-parser based codemod that rewrites Array to T[] in the hand-maintained packages//flow/.js.flow files and the Flow libdefs in libdefs/*.js (--check reports offenders without writing), and run it

Test plan

Type-only change

[vercel]

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview, Comment	Jun 11, 2026 5:39am
lexical-playground	Ready	Preview, Comment	Jun 11, 2026 5:39am

[potatowagon]

Reviewed by Navi (Tater Thoughts Bobblehead) on behalf of @potatowagon.

LGTM ✅

Summary: Pure mechanical style enforcement — converts all Array<T> syntax to T[] across 133 files (TypeScript source, Flow type defs, and test files). Adds @typescript-eslint/array-type ESLint rule to enforce going forward, and includes a new scripts/flow-array-type-codemod.mjs to maintain the same convention in Flow files.

What I checked:

• Semantic equivalence: Array<T> and T[] are semantically identical in both TypeScript and Flow. The transformations are purely syntactic — no runtime behavior changes.
• Complex type handling: Verified that union/intersection types in array positions are correctly parenthesized (e.g. Array<string | Token> → (string | Token)[], Array<typeof undefined | boolean | null | string> → (typeof undefined | boolean | null | string)[]). The codemod script has a POSTFIX_SAFE_TYPES set to distinguish cases needing parens.
• ReadonlyArray handling: ReadonlyArray<T> correctly becomes readonly T[] (verified in useLexicalCommandsLog.ts and vitest.setup.mts).
• Flow files: Flow libdefs and .js.flow files are also updated consistently. The codemod script uses hermes-parser for Flow parsing, which is the correct tool.
• No API surface changes: Only type syntax is changing — no renamed exports, no changed function signatures, no behavioral changes. Safe for www consumers.
• CI: ALL checks pass — unit tests (Node 22.x + 24.x), browser tests (all platforms), e2e tests (full matrix including collab), integrity checks, CLA, and Vercel deployments.
• Edge cases in codemod: The script uses innermost-first fixed-point approach for nested Array<Array<T>> cases, and re-parses after each pass to ensure offset correctness. Robust implementation.

www compat: ✅ No impact. No removed/renamed exports, no changed public API types at runtime. The Flow type defs maintain the same semantic meaning.

Ready to approve.