[Drizzle ORM]: feat: Add getTableMetadata for JSON-serializable table introspection

[nbouvrette]

Summary

Adds a new dialect-agnostic public export to drizzle-orm:

import { getTableMetadata, type TableMetadata, type ColumnMetadata } from 'drizzle-orm'

const meta = getTableMetadata(usersTable)
// {
//   name: 'users',
//   schema: null,
//   baseName: 'users',
//   columns: {
//     id:   { name: 'id',   dataType: 'number', columnType: 'PgSerial', sqlType: 'serial', notNull: true, hasDefault: true,  primary: true,  isUnique: false, generated: null, generatedIdentity: null, enumValues: null },
//     name: { name: 'name', dataType: 'string', columnType: 'PgText',   sqlType: 'text',   notNull: true, hasDefault: false, primary: false, isUnique: false, generated: null, generatedIdentity: null, enumValues: null },
//   },
// }

getTableMetadata walks a Drizzle Table and produces a plain, JSON-serializable object containing the column properties that downstream tools care about: name, dataType, columnType, sqlType, notNull, hasDefault, primary, isUnique, generated, generatedIdentity, enumValues, plus dialect-specific extras when present (length, dimensions, size, textType, baseColumn for arrays — recursive).

Key properties:

• One generic export, all four dialects (pg, mysql, sqlite, singlestore) — no per-dialect imports
• Pure data: no functions, no SQL fragments, no Symbol-keyed properties — JSON.parse(JSON.stringify(meta)) deep-equals meta
• Backward compatible: existing getTableConfig is untouched

Why

Today, validation extensions like drizzle-zod (and drizzle-valibot, drizzle-typebox, drizzle-arktype) require users to import the runtime Table object to derive a Zod schema. That import transitively pulls in pgTable, every column constructor, and the rest of drizzle-orm/pg-core into shared client bundles where Zod schemas are used (tRPC + React forms, etc.). Measured cost in a real Vite-built app: ~56 KB gzipped on first load.

Exposing the metadata as a plain object lets downstream packages (and any third-party codegen tool) operate on data alone — no need to import Table at runtime on the client. This is the foundation issue #941 has been waiting on: with this in place, a thin drizzle-zod companion entry that consumes TableMetadata directly becomes possible, and the runtime cost drops to a few KB. (Follow-up PRs in drizzle-kit and drizzle-zod can land independently; this PR stands on its own.)

The shape was chosen by reading what drizzle-zod, drizzle-valibot, drizzle-typebox, and drizzle-arktype all currently consume from Column instances — a strict superset of what each needs, and a strict subset of what getTableConfig returns. FK references, indexes, composite primary keys, checks, RLS, and policies are intentionally not included: none of the validation extensions consume them, and including dialect-specific extras would force the function to import per-dialect packages.

What this PR is NOT

• Not a change to createInsertSchema / createSelectSchema in drizzle-zod
• Not a CLI / codegen change in drizzle-kit
• Not a deprecation of getTableConfig

It's a pure additive primitive that other packages can build on.

Test plan

• 32 new unit tests across tests/get-table-metadata-{pg,mysql,sqlite,singlestore,serializable}.test.ts
• Covers: basic shapes, schema-qualified tables, every primitive column dataType, notNull / hasDefault / primary / isUnique flags, dialect-specific extras (length, dimensions, size, textType), recursive array baseColumn, enumValues, generated / generatedIdentity
• One cross-dialect serialization contract test: JSON.parse(JSON.stringify(getTableMetadata(t))) deep-equals the original (guarantees no functions, SQL, or Symbols leak through)
• pnpm test in drizzle-orm/ is green: 599/599 tests pass, including exports.test.ts (no export-name conflicts)

Run locally with:

cd drizzle-orm
pnpm test -- get-table-metadata

[nbouvrette]

@AndriiSherman @Sukairo-02 any chance you could consider this PR? its an highly voted issue and I'm happy to get it to the finish line with whatever feedback you can provide.