refactor: use a SpecialShape to describe union and intersection type

microsoft/TypeScript#35562

Author: NWYLZW

src/index.spec.ts

@@ -404,39 +404,65 @@ describe('intersect', () => {
 
     const case1 = t.intersect([1, Number])
     expectTypeOf(case1).toEqualTypeOf<t.Schema<
-      t.Schema<1, 1> & t.Schema<NumberConstructor, number>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<1, 1>,
+          t.Schema<NumberConstructor, number>
+        ]
+      >,
       1
     >>()
     expectTypeOf<t.Infer<typeof case1>>()
       .toEqualTypeOf<1>()
 
     const case2 = t.intersect([1, Number, String])
     expectTypeOf(case2).toEqualTypeOf<t.Schema<
-      t.Schema<1, 1> & t.Schema<NumberConstructor, number> & t.Schema<StringConstructor, string>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<1, 1>,
+          t.Schema<NumberConstructor, number>,
+          t.Schema<StringConstructor, string>
+        ]
+      >,
       never
     >>()
     expectTypeOf<t.Infer<typeof case2>>()
       .toEqualTypeOf<never>()
 
     const case3 = t.intersect([Number, t.unknown()])
     expectTypeOf(case3).toEqualTypeOf<t.Schema<
-      t.Schema<NumberConstructor, number> & t.Schema<typeof t.Symbols.unknown, unknown>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<NumberConstructor, number>,
+          t.Schema<typeof t.Symbols.unknown, unknown>
+        ]
+      >,
       number
     >>()
     expectTypeOf<t.Infer<typeof case3>>()
       .toEqualTypeOf<number>()
 
     const case4 = t.intersect([Number, t.never()])
     expectTypeOf(case4).toEqualTypeOf<t.Schema<
-      t.Schema<NumberConstructor, number> & t.Schema<typeof t.Symbols.never, never>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<NumberConstructor, number>,
+          t.Schema<typeof t.Symbols.never, never>
+        ]
+      >,
       never
     >>()
     expectTypeOf<t.Infer<typeof case4>>()
       .toEqualTypeOf<never>()
 
     const case5 = t.intersect([Number, t.any()])
     expectTypeOf(case5).toEqualTypeOf<t.Schema<
-      t.Schema<NumberConstructor, number> & t.Schema<any, any>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<NumberConstructor, number>,
+          t.Schema<any, any>
+        ]
+      >,
       any
     >>()
     expectTypeOf<t.Infer<typeof case5>>()
@@ -448,14 +474,24 @@ describe('intersect', () => {
     // because {} & null and {} & undefined just get tossed away.
     const case6 = t.intersect([Number, {}])
     expectTypeOf(case6).toEqualTypeOf<t.Schema<
-      t.Schema<NumberConstructor, number> & t.Schema<{}, {}>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<NumberConstructor, number>,
+          t.Schema<{}, {}>
+        ]
+      >,
       number
     >>()
     expectTypeOf<t.Infer<typeof case6>>()
       .toEqualTypeOf<number>()
     const case7 = t.intersect([Number, t({})])
     expectTypeOf(case7).toEqualTypeOf<t.Schema<
-      t.Schema<NumberConstructor, number> & t.Schema<{}, {}>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<NumberConstructor, number>,
+          t.Schema<{}, {}>
+        ]
+      >,
       number
     >>()
     expectTypeOf<t.Infer<typeof case7>>()
@@ -465,12 +501,12 @@ describe('intersect', () => {
     const case0 = t.union([1, 2, '3']).and(String)
     //    ^?
     expectTypeOf(case0).toEqualTypeOf<t.Schema<
-      & (
-        | t.Schema<1, 1>
-        | t.Schema<2, 2>
-        | t.Schema<'3', '3'>
-      )
-      & t.Schema<StringConstructor, string>,
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<1, 1> | t.Schema<2, 2> | t.Schema<'3', '3'>,
+          t.Schema<StringConstructor, string>
+        ]
+      >,
       '3'
     >>()
     expectTypeOf<t.Infer<typeof case0>>()
@@ -517,11 +553,13 @@ describe('intersect', () => {
       // `a${String}`
     ])
     expectTypeOf(case0).toEqualTypeOf<t.Schema<
-      t.Schema<
-        t.Schema<'a', 'a'> | t.Schema<'ab', 'ab'> | t.Schema<'b', 'b'>,
-        'a' | 'ab' | 'b'
-      > & t.Schema<`a${string}`, `a${string}`>,
-      ('a' | 'ab' | 'b') & `a${string}`
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<t.Schema<'a', 'a'> | t.Schema<'ab', 'ab'> | t.Schema<'b', 'b'>, 'a' | 'ab' | 'b'>,
+          t.Schema<`a${string}`, `a${string}`>
+        ]
+      >,
+      'a' | 'ab'
     >>()
     expectTypeOf<t.Infer<typeof case0>>().toEqualTypeOf<T0>()
 
@@ -532,11 +570,13 @@ describe('intersect', () => {
       `a${0 as number}`
     ])
     expectTypeOf(case1).toEqualTypeOf<t.Schema<
-      t.Schema<
-        t.Schema<'a', 'a'> | t.Schema<'ax', 'ax'> | t.Schema<'a12', 'a12'> | t.Schema<'b', 'b'>,
-        'a' | 'ax' | 'a12' | 'b'
-      > & t.Schema<`a${number}`, `a${number}`>,
-      ('a' | 'ax' | 'a12' | 'b') & `a${number}`
+      t.SpecialShape<
+        t.SpecialShapes['intersection'], [
+          t.Schema<t.Schema<'a', 'a'> | t.Schema<'ax', 'ax'> | t.Schema<'a12', 'a12'> | t.Schema<'b', 'b'>, 'a' | 'ax' | 'a12' | 'b'>,
+          t.Schema<`a${number}`, `a${number}`>
+        ]
+      >,
+      'a12'
     >>()
     expectTypeOf<t.Infer<typeof case1>>().toEqualTypeOf<T1>()
   })

src/index.ts

@@ -49,6 +49,21 @@ literal.Undefined = `__DO_NOT_USE_SAME_LITERAL_${
 }__IF_YOU_WANT_TO_USE_IT__` as const
 
 export namespace t {
+  export const specialShapes = {
+    union: Symbol('union'),
+    intersection: Symbol('intersection')
+  } as {
+    readonly union: unique symbol
+    readonly intersection: unique symbol
+  }
+  export type SpecialShapes = typeof specialShapes
+  export interface SpecialShape<
+    T extends SpecialShapes[keyof SpecialShapes],
+    S extends readonly Schema<any, any>[] = []
+  > {
+    type: T
+    schemas: S
+  }
   interface SchemaMeta<Shape, T> {
   }
   interface SchemaMethods<Shape, T> {
@@ -135,7 +150,7 @@ export namespace t {
       [Schemas] extends [never]
         ? Schema<typeof symbols.never, never>
         : Schema<
-          T2I<Schemas>,
+          SpecialShape<SpecialShapes['intersection'], Schemas>,
           T2I<InferT<Schemas>>
         >
     ) : never