Add numeric constraint to type parameter of mapped types with name type and array constraints

src/compiler/checker.ts

@@ -13767,6 +13767,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function forEachMappedTypePropertyKeyTypeAndIndexSignatureKeyType(type: Type, include: TypeFlags, stringsOnly: boolean, cb: (keyType: Type) => void) {
+        if (isTupleType(type)) {
+            forEachType(getUnionType(getElementTypes(type).map((_, i) => getStringLiteralType("" + i))), cb);
+            return;
+        }
+        if (isArrayType(type)) {
+            cb(numberType);
+            return;
+        }
         for (const prop of getPropertiesOfType(type)) {
             cb(getLiteralTypeFromProperty(prop, include));
         }
@@ -16116,8 +16124,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 }
             }
             // Given a homomorphic mapped type { [K in keyof T]: XXX }, where T is constrained to an array or tuple type, in the
-            // template type XXX, K has an added constraint of number | `${number}`.
-            else if (type.flags & TypeFlags.TypeParameter && parent.kind === SyntaxKind.MappedType && node === (parent as MappedTypeNode).type) {
+            // template type XXX, K has an added constraint of number | `${number}`. The same is added in the optional name type.
+            else if (type.flags & TypeFlags.TypeParameter && parent.kind === SyntaxKind.MappedType && (node === (parent as MappedTypeNode).type || node === (parent as MappedTypeNode).nameType)) {
                 const mappedType = getTypeFromTypeNode(parent as TypeNode) as MappedType;
                 if (getTypeParameterFromMappedType(mappedType) === getActualTypeVariable(type)) {
                     const typeParameter = getHomomorphicTypeVariable(mappedType);

tests/baselines/reference/mappedTypeHomomorphicTupleInstantiationNameTypeKeys.symbols

@@ -0,0 +1,36 @@
+//// [tests/cases/compiler/mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts] ////
+
+=== mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts ===
+// https://github.com/microsoft/TypeScript/pull/55774#issuecomment-1813484949
+
+type Mapper<T> = {
+>Mapper : Symbol(Mapper, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 2, 12))
+
+  [K in keyof T as K]: T[K] extends NonNullable<T[K]> ? T[K] : never;
+>K : Symbol(K, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 3, 3))
+>T : Symbol(T, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 2, 12))
+>K : Symbol(K, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 3, 3))
+>T : Symbol(T, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 2, 12))
+>K : Symbol(K, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 3, 3))
+>NonNullable : Symbol(NonNullable, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 2, 12))
+>K : Symbol(K, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 3, 3))
+>T : Symbol(T, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 2, 12))
+>K : Symbol(K, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 3, 3))
+
+};
+
+type Mapped = Mapper<[1, 2]>;
+>Mapped : Symbol(Mapped, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 4, 2))
+>Mapper : Symbol(Mapper, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 0, 0))
+
+type Keys = keyof Mapper<[1, 2]>;
+>Keys : Symbol(Keys, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 6, 29))
+>Mapper : Symbol(Mapper, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 0, 0))
+
+type SomeType = Mapped[Keys]; // ok
+>SomeType : Symbol(SomeType, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 7, 33))
+>Mapped : Symbol(Mapped, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 4, 2))
+>Keys : Symbol(Keys, Decl(mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts, 6, 29))
+

tests/baselines/reference/mappedTypeHomomorphicTupleInstantiationNameTypeKeys.types

@@ -0,0 +1,20 @@
+//// [tests/cases/compiler/mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts] ////
+
+=== mappedTypeHomomorphicTupleInstantiationNameTypeKeys.ts ===
+// https://github.com/microsoft/TypeScript/pull/55774#issuecomment-1813484949
+
+type Mapper<T> = {
+>Mapper : Mapper<T>
+
+  [K in keyof T as K]: T[K] extends NonNullable<T[K]> ? T[K] : never;
+};
+
+type Mapped = Mapper<[1, 2]>;
+>Mapped : Mapper<[1, 2]>
+
+type Keys = keyof Mapper<[1, 2]>;
+>Keys : "0" | "1"
+
+type SomeType = Mapped[Keys]; // ok
+>SomeType : 2 | 1
+

tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.symbols

@@ -0,0 +1,149 @@
+//// [tests/cases/compiler/mappedTypeTupleConstraintTypeParameterInNameType.ts] ////
+
+=== mappedTypeTupleConstraintTypeParameterInNameType.ts ===
+// based on https://github.com/microsoft/TypeScript/issues/55762
+
+declare class Decoder<T> {
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 22))
+
+  decode(arrayBuffer: ArrayBuffer): T;
+>decode : Symbol(Decoder.decode, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 26))
+>arrayBuffer : Symbol(arrayBuffer, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 3, 9))
+>ArrayBuffer : Symbol(ArrayBuffer, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 22))
+}
+
+type ValueTypeOf<T extends Decoder<any>> = T extends Decoder<infer R>
+>ValueTypeOf : Symbol(ValueTypeOf, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 4, 1))
+>T : Symbol(T, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 6, 17))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+>T : Symbol(T, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 6, 17))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+>R : Symbol(R, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 6, 66))
+
+  ? R
+>R : Symbol(R, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 6, 66))
+
+  : never;
+
+type StructDescriptor = ReadonlyArray<
+>StructDescriptor : Symbol(StructDescriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 8, 10))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --))
+
+  readonly [key: string, type: Decoder<any>]
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+
+>;
+
+type StructTypeFor<Descriptor extends StructDescriptor> = {
+>StructTypeFor : Symbol(StructTypeFor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 12, 2))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 14, 19))
+>StructDescriptor : Symbol(StructDescriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 8, 10))
+
+  [K in keyof Descriptor as Descriptor[K][0]]: ValueTypeOf<Descriptor[K][1]>;
+>K : Symbol(K, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 15, 3))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 14, 19))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 14, 19))
+>K : Symbol(K, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 15, 3))
+>ValueTypeOf : Symbol(ValueTypeOf, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 4, 1))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 14, 19))
+>K : Symbol(K, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 15, 3))
+
+};
+
+class StructDecoder<const Descriptor extends StructDescriptor> extends Decoder<
+>StructDecoder : Symbol(StructDecoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 16, 2))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 18, 20))
+>StructDescriptor : Symbol(StructDescriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 8, 10))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+
+  StructTypeFor<Descriptor>
+>StructTypeFor : Symbol(StructTypeFor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 12, 2))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 18, 20))
+
+> {
+  constructor(descriptor: Descriptor) {
+>descriptor : Symbol(descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 21, 14))
+>Descriptor : Symbol(Descriptor, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 18, 20))
+
+    super();
+>super : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+  }
+}
+
+declare const i32Decoder: Decoder<number>;
+>i32Decoder : Symbol(i32Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 26, 13))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+
+declare const i64Decoder: Decoder<bigint>;
+>i64Decoder : Symbol(i64Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 27, 13))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+
+const structDecoder1 = new StructDecoder([
+>structDecoder1 : Symbol(structDecoder1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 29, 5))
+>StructDecoder : Symbol(StructDecoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 16, 2))
+
+  ["a", i32Decoder],
+>i32Decoder : Symbol(i32Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 26, 13))
+
+  ["b", i64Decoder],
+>i64Decoder : Symbol(i64Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 27, 13))
+
+]);
+
+const struct1 = structDecoder1.decode(new ArrayBuffer(100));
+>struct1 : Symbol(struct1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 34, 5))
+>structDecoder1.decode : Symbol(Decoder.decode, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 26))
+>structDecoder1 : Symbol(structDecoder1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 29, 5))
+>decode : Symbol(Decoder.decode, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 26))
+>ArrayBuffer : Symbol(ArrayBuffer, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+const v1_1: number = struct1.a;
+>v1_1 : Symbol(v1_1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 36, 5))
+>struct1.a : Symbol(a)
+>struct1 : Symbol(struct1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 34, 5))
+>a : Symbol(a)
+
+const v1_2: bigint = struct1.b;
+>v1_2 : Symbol(v1_2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 37, 5))
+>struct1.b : Symbol(b)
+>struct1 : Symbol(struct1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 34, 5))
+>b : Symbol(b)
+
+declare const descriptor2: [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]
+>descriptor2 : Symbol(descriptor2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 39, 13))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+>Decoder : Symbol(Decoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 0, 0))
+
+const structDecoder2 = new StructDecoder(descriptor2);
+>structDecoder2 : Symbol(structDecoder2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 40, 5))
+>StructDecoder : Symbol(StructDecoder, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 16, 2))
+>descriptor2 : Symbol(descriptor2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 39, 13))
+
+const struct2 = structDecoder2.decode(new ArrayBuffer(100));
+>struct2 : Symbol(struct2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 42, 5))
+>structDecoder2.decode : Symbol(Decoder.decode, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 26))
+>structDecoder2 : Symbol(structDecoder2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 40, 5))
+>decode : Symbol(Decoder.decode, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 2, 26))
+>ArrayBuffer : Symbol(ArrayBuffer, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+const v2_1: number = struct2.a;
+>v2_1 : Symbol(v2_1, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 44, 5))
+>struct2.a : Symbol(a)
+>struct2 : Symbol(struct2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 42, 5))
+>a : Symbol(a)
+
+const v2_2: string = struct2.b;
+>v2_2 : Symbol(v2_2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 45, 5))
+>struct2.b : Symbol(b)
+>struct2 : Symbol(struct2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 42, 5))
+>b : Symbol(b)
+
+const v2_3: bigint = struct2.c;
+>v2_3 : Symbol(v2_3, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 46, 5))
+>struct2.c : Symbol(c)
+>struct2 : Symbol(struct2, Decl(mappedTypeTupleConstraintTypeParameterInNameType.ts, 42, 5))
+>c : Symbol(c)
+

tests/baselines/reference/mappedTypeTupleConstraintTypeParameterInNameType.types

@@ -0,0 +1,129 @@
+//// [tests/cases/compiler/mappedTypeTupleConstraintTypeParameterInNameType.ts] ////
+
+=== mappedTypeTupleConstraintTypeParameterInNameType.ts ===
+// based on https://github.com/microsoft/TypeScript/issues/55762
+
+declare class Decoder<T> {
+>Decoder : Decoder<T>
+
+  decode(arrayBuffer: ArrayBuffer): T;
+>decode : (arrayBuffer: ArrayBuffer) => T
+>arrayBuffer : ArrayBuffer
+}
+
+type ValueTypeOf<T extends Decoder<any>> = T extends Decoder<infer R>
+>ValueTypeOf : ValueTypeOf<T>
+
+  ? R
+  : never;
+
+type StructDescriptor = ReadonlyArray<
+>StructDescriptor : readonly (readonly [key: string, type: Decoder<any>])[]
+
+  readonly [key: string, type: Decoder<any>]
+>;
+
+type StructTypeFor<Descriptor extends StructDescriptor> = {
+>StructTypeFor : StructTypeFor<Descriptor>
+
+  [K in keyof Descriptor as Descriptor[K][0]]: ValueTypeOf<Descriptor[K][1]>;
+};
+
+class StructDecoder<const Descriptor extends StructDescriptor> extends Decoder<
+>StructDecoder : StructDecoder<Descriptor>
+>Decoder : Decoder<StructTypeFor<Descriptor>>
+
+  StructTypeFor<Descriptor>
+> {
+  constructor(descriptor: Descriptor) {
+>descriptor : Descriptor
+
+    super();
+>super() : void
+>super : typeof Decoder
+  }
+}
+
+declare const i32Decoder: Decoder<number>;
+>i32Decoder : Decoder<number>
+
+declare const i64Decoder: Decoder<bigint>;
+>i64Decoder : Decoder<bigint>
+
+const structDecoder1 = new StructDecoder([
+>structDecoder1 : StructDecoder<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>new StructDecoder([  ["a", i32Decoder],  ["b", i64Decoder],]) : StructDecoder<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>StructDecoder : typeof StructDecoder
+>[  ["a", i32Decoder],  ["b", i64Decoder],] : [["a", Decoder<number>], ["b", Decoder<bigint>]]
+
+  ["a", i32Decoder],
+>["a", i32Decoder] : ["a", Decoder<number>]
+>"a" : "a"
+>i32Decoder : Decoder<number>
+
+  ["b", i64Decoder],
+>["b", i64Decoder] : ["b", Decoder<bigint>]
+>"b" : "b"
+>i64Decoder : Decoder<bigint>
+
+]);
+
+const struct1 = structDecoder1.decode(new ArrayBuffer(100));
+>struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>structDecoder1.decode(new ArrayBuffer(100)) : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>structDecoder1.decode : (arrayBuffer: ArrayBuffer) => StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>structDecoder1 : StructDecoder<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>decode : (arrayBuffer: ArrayBuffer) => StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>new ArrayBuffer(100) : ArrayBuffer
+>ArrayBuffer : ArrayBufferConstructor
+>100 : 100
+
+const v1_1: number = struct1.a;
+>v1_1 : number
+>struct1.a : number
+>struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>a : number
+
+const v1_2: bigint = struct1.b;
+>v1_2 : bigint
+>struct1.b : bigint
+>struct1 : StructTypeFor<readonly [readonly ["a", Decoder<number>], readonly ["b", Decoder<bigint>]]>
+>b : bigint
+
+declare const descriptor2: [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]
+>descriptor2 : [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]
+
+const structDecoder2 = new StructDecoder(descriptor2);
+>structDecoder2 : StructDecoder<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>new StructDecoder(descriptor2) : StructDecoder<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>StructDecoder : typeof StructDecoder
+>descriptor2 : [["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]
+
+const struct2 = structDecoder2.decode(new ArrayBuffer(100));
+>struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>structDecoder2.decode(new ArrayBuffer(100)) : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>structDecoder2.decode : (arrayBuffer: ArrayBuffer) => StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>structDecoder2 : StructDecoder<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>decode : (arrayBuffer: ArrayBuffer) => StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>new ArrayBuffer(100) : ArrayBuffer
+>ArrayBuffer : ArrayBufferConstructor
+>100 : 100
+
+const v2_1: number = struct2.a;
+>v2_1 : number
+>struct2.a : number
+>struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>a : number
+
+const v2_2: string = struct2.b;
+>v2_2 : string
+>struct2.b : string
+>struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>b : string
+
+const v2_3: bigint = struct2.c;
+>v2_3 : bigint
+>struct2.c : bigint
+>struct2 : StructTypeFor<[["a", Decoder<number>], ["b", Decoder<string>], ...["c", Decoder<bigint>][]]>
+>c : bigint
+