add JTDDataType type

lib/jtd.ts

@@ -28,8 +28,8 @@ export {KeywordCxt}
 export {_, str, stringify, nil, Name, Code, CodeGen, CodeGenOptions} from "./compile/codegen"
 
 import type {AnySchemaObject, SchemaObject, JTDParser} from "./types"
-import type {JTDSchemaType} from "./types/jtd-schema"
-export {JTDSchemaType}
+import type {JTDSchemaType, JTDDataType} from "./types/jtd-schema"
+export {JTDSchemaType, JTDDataType}
 import AjvCore, {CurrentOptions} from "./core"
 import jtdVocabulary from "./vocabularies/jtd"
 import jtdMetaSchema from "./refs/jtd-schema"

lib/types/jtd-schema.ts

@@ -149,3 +149,67 @@ export type JTDSchemaType<T, D extends Record<string, unknown> = Record<string,
   // TODO these should only be allowed at the top level
   definitions?: {[K in keyof D]: JTDSchemaType<D[K], D>}
 }
+
+type JTDDataDef<S, D extends Record<string, unknown>> =
+  | (// ref
+    S extends {ref: string}
+      ? JTDDataDef<D[S["ref"]], D>
+      : // type
+      S extends {type: NumberType}
+      ? number
+      : S extends {type: "string"}
+      ? string
+      : S extends {type: "timestamp"}
+      ? string | Date
+      : // enum
+      S extends {enum: readonly (infer E)[]}
+      ? string extends E
+        ? never
+        : [E] extends [string]
+        ? E
+        : never
+      : // elements
+      S extends {elements: infer E}
+      ? JTDDataDef<E, D>[]
+      : // properties
+      S extends {
+          properties: Record<string, unknown>
+          optionalProperties?: Record<string, unknown>
+          additionalProperties?: boolean
+        }
+      ? {-readonly [K in keyof S["properties"]]-?: JTDDataDef<S["properties"][K], D>} &
+          {
+            -readonly [K in keyof S["optionalProperties"]]+?: JTDDataDef<
+              S["optionalProperties"][K],
+              D
+            >
+          }
+      : S extends {
+          properties?: Record<string, unknown>
+          optionalProperties: Record<string, unknown>
+          additionalProperties?: boolean
+        }
+      ? {-readonly [K in keyof S["properties"]]-?: JTDDataDef<S["properties"][K], D>} &
+          {
+            -readonly [K in keyof S["optionalProperties"]]+?: JTDDataDef<
+              S["optionalProperties"][K],
+              D
+            >
+          }
+      : // values
+      S extends {values: infer V}
+      ? Record<string, JTDDataDef<V, D>>
+      : // discriminator
+      S extends {discriminator: infer M; mapping: Record<string, unknown>}
+      ? [M] extends [string]
+        ? {
+            [K in keyof S["mapping"]]: JTDDataDef<S["mapping"][K], D> & {[KM in M]: K}
+          }[keyof S["mapping"]]
+        : never
+      : // empty
+        unknown)
+  | (S extends {nullable: true} ? null : never)
+
+export type JTDDataType<S> = S extends {definitions: Record<string, unknown>}
+  ? JTDDataDef<S, S["definitions"]>
+  : JTDDataDef<S, Record<string, never>>

spec/types/jtd-schema.spec.ts

@@ -1,6 +1,6 @@
 /* eslint-disable @typescript-eslint/no-empty-interface,no-void */
 import _Ajv from "../ajv_jtd"
-import type {JTDSchemaType} from "../../dist/jtd"
+import type {JTDSchemaType, JTDDataType} from "../../dist/jtd"
 import chai from "../chai"
 const should = chai.should()
 
@@ -19,6 +19,11 @@ interface B {
 
 type MyData = A | B
 
+interface LinkedList {
+  val: number
+  next?: LinkedList
+}
+
 const mySchema: JTDSchemaType<MyData> = {
   discriminator: "type",
   mapping: {
@@ -325,3 +330,106 @@ describe("JTDSchemaType", () => {
     void [isNull, numNotNull]
   })
 })
+
+describe("JTDDataType typechecks", () => {
+  it("should typecheck number schemas", () => {
+    const numSchema = {type: "float64"} as const
+    const num: TypeEquality<JTDDataType<typeof numSchema>, number> = true
+
+    void [num]
+  })
+
+  it("should typecheck string schemas", () => {
+    const strSchema = {type: "string"} as const
+    const str: TypeEquality<JTDDataType<typeof strSchema>, string> = true
+
+    void [str]
+  })
+
+  it("should typecheck timestamp schemas", () => {
+    const timeSchema = {type: "timestamp"} as const
+    const time: TypeEquality<JTDDataType<typeof timeSchema>, string | Date> = true
+
+    void [time]
+  })
+
+  it("should typecheck enum schemas", () => {
+    const enumSchema = {enum: ["a", "b"]} as const
+    const enumerated: TypeEquality<JTDDataType<typeof enumSchema>, "a" | "b"> = true
+
+    void [enumerated]
+  })
+
+  it("should typecheck elements schemas", () => {
+    const elementsSchema = {elements: {type: "float64"}} as const
+    const elem: TypeEquality<JTDDataType<typeof elementsSchema>, number[]> = true
+
+    void [elem]
+  })
+
+  it("should typecheck properties schemas", () => {
+    const bothPropsSchema = {
+      properties: {a: {type: "float64"}},
+      optionalProperties: {b: {type: "string"}},
+    } as const
+    const both: TypeEquality<JTDDataType<typeof bothPropsSchema>, {a: number; b?: string}> = true
+
+    const reqPropsSchema = {properties: {a: {type: "float64"}}} as const
+    const req: TypeEquality<JTDDataType<typeof reqPropsSchema>, {a: number}> = true
+
+    const optPropsSchema = {optionalProperties: {b: {type: "string"}}} as const
+    const opt: TypeEquality<JTDDataType<typeof optPropsSchema>, {b?: string}> = true
+
+    void [both, req, opt]
+  })
+
+  it("should typecheck values schemas", () => {
+    const valuesSchema = {values: {type: "float64"}} as const
+    const values: TypeEquality<JTDDataType<typeof valuesSchema>, Record<string, number>> = true
+
+    void [values]
+  })
+
+  it("should typecheck discriminator schemas", () => {
+    const discriminatorSchema = {
+      discriminator: "type",
+      mapping: {
+        a: {properties: {a: {type: "float64"}}},
+        b: {optionalProperties: {b: {type: "string"}}},
+      },
+    } as const
+    const disc: TypeEquality<JTDDataType<typeof discriminatorSchema>, A | B> = true
+
+    void [disc]
+  })
+
+  it("should typecheck ref schemas", () => {
+    const refSchema = {
+      definitions: {num: {type: "float64", nullable: true}},
+      ref: "num",
+      nullable: true,
+    } as const
+    const ref: TypeEquality<JTDDataType<typeof refSchema>, number | null> = true
+
+    // works for recursive schemas
+    const llSchema = {
+      definitions: {
+        node: {
+          properties: {val: {type: "float64"}},
+          optionalProperties: {next: {ref: "node"}},
+        },
+      },
+      ref: "node",
+    } as const
+    const list: TypeEquality<JTDDataType<typeof llSchema>, LinkedList> = true
+
+    void [ref, list]
+  })
+
+  it("should typecheck empty schemas", () => {
+    const emptySchema = {metadata: {}} as const
+    const empty: TypeEquality<JTDDataType<typeof emptySchema>, unknown> = true
+
+    void [empty]
+  })
+})