Improved typing for union types (#2151)

* Have unions not devolve into `IAnyType` with 10+ members.

* Improve typings for enums

* Remove no longer used scripts/generate-union-types.js

* Add an additional literal to union typechecking test

* spike: issue 1525 still broken

* test: add test for issue 1664

* spike: failing test for 1833

* test: remove failing tests

* test: add describe/test blocks

* test: remove failing tests (again)

* test: add test for issue 1525

---------

Co-authored-by: Tyler Williams <[email protected]>

Author: thegedge

__tests__/core/1525.test.ts

@@ -0,0 +1,33 @@
+import { types, Instance } from "../../src/index"
+
+describe("1525. Model instance maybe fields becoming TypeScript optional fields when included in a types.union", () => {
+  it("does not throw a typescript error", () => {
+    const Model = types.model("myModel", {
+      foo: types.string,
+      bar: types.maybe(types.integer)
+    })
+
+    const Store = types.model("store", {
+      itemWithoutIssue: Model,
+      itemWithIssue: types.union(types.literal("anotherValue"), Model)
+    })
+
+    interface IModel extends Instance<typeof Model> {}
+
+    interface FunctionArgs {
+      model1: IModel
+      model2: IModel
+    }
+
+    const store = Store.create({
+      itemWithoutIssue: { foo: "works" },
+      itemWithIssue: { foo: "has ts error in a regression" }
+    })
+
+    const f = (props: FunctionArgs) => {}
+
+    const itemWithoutIssueModel = store.itemWithoutIssue
+    const itemWithIssueModel = store.itemWithIssue === "anotherValue" ? null : store.itemWithIssue
+    itemWithIssueModel && f({ model1: itemWithoutIssueModel, model2: itemWithIssueModel })
+  })
+})

__tests__/core/1664.test.ts

@@ -0,0 +1,33 @@
+import { types as t } from "../../src/index"
+
+describe("1664. Array and model types are not inferred correctly when broken down into their components", () => {
+  test("should not throw a typescript error", () => {
+    // Simple concrete type with a creation type different than its instance type
+    const date = t.custom<string, Date>({
+      name: "Date",
+      fromSnapshot: (snapshot) => new Date(snapshot),
+      toSnapshot: (dt) => dt.toISOString(),
+      isTargetType: (val: unknown) => val instanceof Date,
+      getValidationMessage: (snapshot: unknown) =>
+        typeof snapshot !== "string" || isNaN(Date.parse(snapshot))
+          ? `${snapshot} is not a valid Date string`
+          : ""
+    })
+
+    //Wrap the date type in an array type. IArrayType is a sub-interface of IType.
+    const DateArray = t.array(date)
+
+    //Pass the array type to t.union, which infers the component types as <C, S, T>
+    const LoadableDateArray = t.union(t.literal("loading"), DateArray)
+
+    //Instantiate the type
+    const lda = LoadableDateArray.create([])
+
+    //Try to use the array type as an instance
+    if (lda !== "loading") {
+      //Error: type of lda is essentially `(string | Date)[] | undefined`
+      //The creation type has been mixed together with the instance type
+      const dateArray: Date[] = lda
+    }
+  })
+})

__tests__/core/type-system.test.ts

@@ -32,14 +32,21 @@ type DifferingKeys<ActualT, ExpectedT> = {
 }[keyof ActualT | keyof ExpectedT] &
   string
 
-type InexactErrorMessage<ActualT, ExpectedT> = `Mismatched property: ${DifferingKeys<
-  ActualT,
-  ExpectedT
->}`
+type NotExactErrorMessage<ActualT, ExpectedT> = ActualT extends Record<string, unknown>
+  ? ExpectedT extends Record<string, unknown>
+    ? `Mismatched property: ${DifferingKeys<ActualT, ExpectedT>}`
+    : "Expected a non-object type, but received an object"
+  : ExpectedT extends Record<string, unknown>
+  ? "Expected an object type, but received a non-object type"
+  : "Types are not exactly equal"
+
+type IsExact<T1, T2> = [T1] extends [T2] ? ([T2] extends [T1] ? Exact<T1, T2> : never) : never
 
 const assertTypesEqual = <ActualT, ExpectedT>(
   t: ActualT,
-  u: Exact<ActualT, ExpectedT> extends never ? InexactErrorMessage<ActualT, ExpectedT> : ExpectedT
+  u: IsExact<ActualT, ExpectedT> extends never
+    ? NotExactErrorMessage<ActualT, ExpectedT>
+    : ExpectedT
 ): [ActualT, ExpectedT] => [t, u] as [ActualT, ExpectedT]
 const _: unknown = undefined
 
@@ -1225,3 +1232,34 @@ test("object creation when composing with a model with no props", () => {
   // @ts-expect-error -- unknown prop
   true || Composed.create({ another: 5 })
 })
+
+test("union type inference verification for small number of types", () => {
+  const T = types.union(types.boolean, types.literal("test"), types.maybe(types.number))
+
+  type ITC = SnapshotIn<typeof T>
+  type ITS = SnapshotOut<typeof T>
+
+  assertTypesEqual(_ as ITC, _ as boolean | "test" | number | undefined)
+  assertTypesEqual(_ as ITS, _ as boolean | "test" | number | undefined)
+})
+
+test("union type inference verification for a large number of types", () => {
+  const T = types.union(
+    types.literal("a"),
+    types.literal("b"),
+    types.literal("c"),
+    types.literal("d"),
+    types.literal("e"),
+    types.literal("f"),
+    types.literal("g"),
+    types.literal("h"),
+    types.literal("i"),
+    types.literal("j")
+  )
+
+  type ITC = SnapshotIn<typeof T>
+  type ITS = SnapshotOut<typeof T>
+
+  assertTypesEqual(_ as ITC, _ as "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j")
+  assertTypesEqual(_ as ITS, _ as "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j")
+})

scripts/generate-union-types.js

@@ -8,14 +8,13 @@ export type UnionStringArray<T extends readonly string[]> = T[number]
 // these overloads also allow both mutable and immutable arrays, making types.enumeration<Enum>(Object.values(Enum)) possible.
 // the only case where this doesn't work is when passing to the function an array variable with a mutable type constraint;
 // for these cases, it will just fallback and assume the type is a generic string.
-export function enumeration<T extends readonly string[]>(
-  options: T
-): ISimpleType<UnionStringArray<T>>
+export function enumeration<T extends string>(
+  options: readonly T[]
+): ISimpleType<UnionStringArray<T[]>>
 export function enumeration<T extends string>(
   name: string,
-  options: T[]
+  options: readonly T[]
 ): ISimpleType<UnionStringArray<T[]>>
-
 /**
  * `types.enumeration` - Can be used to create an string based enumeration.
  * (note: this methods is just sugar for a union of string literals)
@@ -31,8 +30,11 @@ export function enumeration<T extends string>(
  * @param options possible values this enumeration can have
  * @returns
  */
-export function enumeration(name: string | string[], options?: any): ISimpleType<string> {
-  const realOptions: string[] = typeof name === "string" ? options! : name
+export function enumeration<T extends string>(
+  name: string | readonly T[],
+  options?: readonly T[]
+): ISimpleType<T[number]> {
+  const realOptions: readonly T[] = typeof name === "string" ? options! : name
   // check all options
   if (devMode()) {
     realOptions.forEach((option, i) => {
@@ -41,5 +43,5 @@ export function enumeration(name: string | string[], options?: any): ISimpleType
   }
   const type = union(...realOptions.map((option) => literal("" + option)))
   if (typeof name === "string") type.name = name
-  return type
+  return type as ISimpleType<T[number]>
 }