Move schema utilities into core (#26565)

packages/core/src/schema.ts

@@ -0,0 +1,108 @@
+import { Option, Schema, SchemaGetter } from "effect"
+import { zod, ZodOverride } from "./effect-zod"
+
+/**
+ * Integer greater than zero.
+ */
+export const PositiveInt = Schema.Int.check(Schema.isGreaterThan(0))
+
+/**
+ * Integer greater than or equal to zero.
+ */
+export const NonNegativeInt = Schema.Int.check(Schema.isGreaterThanOrEqualTo(0))
+
+/**
+ * Optional public JSON field that can hold explicit `undefined` on the type
+ * side but encodes it as an omitted key, matching legacy `JSON.stringify`.
+ */
+export const optionalOmitUndefined = <S extends Schema.Top>(schema: S) =>
+  Schema.optionalKey(schema).pipe(
+    Schema.decodeTo(Schema.optional(schema), {
+      decode: SchemaGetter.passthrough({ strict: false }),
+      encode: SchemaGetter.transformOptional(Option.filter((value) => value !== undefined)),
+    }),
+    Schema.annotate({ [ZodOverride]: zod(schema).optional() }),
+  )
+
+/**
+ * Strip `readonly` from a nested type. Stand-in for `effect`'s `Types.DeepMutable`
+ * until `effect:core/x228my` ("Types.DeepMutable widens unknown to `{}`") lands.
+ *
+ * The upstream version falls through `unknown` into `{ -readonly [K in keyof T]: ... }`
+ * where `keyof unknown = never`, so `unknown` collapses to `{}`. This local
+ * version gates the object branch on `extends object` (which `unknown` does
+ * not) so `unknown` passes through untouched.
+ *
+ * Primitive bailout matches upstream — without it, branded strings like
+ * `string & Brand<"SessionID">` fall into the object branch and get their
+ * prototype methods walked.
+ *
+ * Tuple branch preserves readonly tuples (e.g. `ConfigPlugin.Spec`'s
+ * `readonly [string, Options]`); the general array branch would otherwise
+ * widen them to unbounded arrays.
+ */
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type DeepMutable<T> = T extends string | number | boolean | bigint | symbol | Function
+  ? T
+  : T extends readonly [unknown, ...unknown[]]
+    ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+    : T extends readonly (infer U)[]
+      ? DeepMutable<U>[]
+      : T extends object
+        ? { -readonly [K in keyof T]: DeepMutable<T[K]> }
+        : T
+
+/**
+ * Attach static methods to a schema object. Designed to be used with `.pipe()`:
+ *
+ * @example
+ *   export const Foo = fooSchema.pipe(
+ *     withStatics((schema) => ({
+ *       zero: schema.make(0),
+ *       from: Schema.decodeUnknownOption(schema),
+ *     }))
+ *   )
+ */
+export const withStatics =
+  <S extends object, M extends Record<string, unknown>>(methods: (schema: S) => M) =>
+  (schema: S): S & M =>
+    Object.assign(schema, methods(schema))
+
+/**
+ * Nominal wrapper for scalar types. The class itself is a valid schema —
+ * pass it directly to `Schema.decode`, `Schema.decodeEffect`, etc.
+ *
+ * Overrides `~type.make` on the derived `Schema.Opaque` so `Schema.Schema.Type`
+ * of a field using this newtype resolves to `Self` rather than the underlying
+ * branded phantom. Without that override, passing a class instance to code
+ * typed against `Schema.Schema.Type<FieldSchema>` would require a cast even
+ * though the values are structurally equivalent at runtime.
+ *
+ * @example
+ *   class QuestionID extends Newtype<QuestionID>()("QuestionID", Schema.String) {
+ *     static make(id: string): QuestionID {
+ *       return this.make(id)
+ *     }
+ *   }
+ *
+ *   Schema.decodeEffect(QuestionID)(input)
+ */
+export function Newtype<Self>() {
+  return <const Tag extends string, S extends Schema.Top>(tag: Tag, schema: S) => {
+    abstract class Base {
+      declare readonly _newtype: Tag
+
+      static make(value: Schema.Schema.Type<S>): Self {
+        return value as unknown as Self
+      }
+    }
+
+    Object.setPrototypeOf(Base, schema)
+
+    return Base as unknown as (abstract new (_: never) => { readonly _newtype: Tag }) & {
+      readonly make: (value: Schema.Schema.Type<S>) => Self
+    } & Omit<Schema.Opaque<Self, S, {}>, "make" | "~type.make"> & {
+        readonly "~type.make": Self
+      }
+  }
+}