refactor(experimental): improve getTupleCodec type inferences (#2344)

This PR follows the footsteps of #2181 which improved the type inferences of `getStructCodec` and `getDataEnumCodec` by inferring the types from the provided codecs instead of inferring the other way around.

This PR does the same with the `getTupleCodec` and also makes use of the `DrainOuterGeneric` helper from the previous PR to reduce the amount of instantiations TypeScript does when resolving the codec types.

.changeset/green-experts-hang.md

@@ -0,0 +1,7 @@
+---
+'@solana/codecs-data-structures': patch
+---
+
+Improve `getTupleCodec` type inferences and performance
+
+The tuple codec now infers its encoded/decoded type from the provided codec array and uses the new `DrainOuterGeneric` helper to reduce the number of TypeScript instantiations.

packages/codecs-data-structures/README.md

@@ -137,16 +137,16 @@ const map = getMapDecoder(keyDecoder, valueDecoder).decode(bytes);
 The `getTupleCodec` function accepts any number of codecs — `T`, `U`, `V`, etc. — and returns a tuple codec of type `[T, U, V, …]` such that each item is in the order of the provided codecs.
 
 ```ts
-const itemCodecs = [getStringCodec(), getU8Codec(), getU64Codec()];
-const bytes = getTupleCodec(itemCodecs).encode(['alice', 42, 123]);
-const tuple = getTupleCodec(itemCodecs).decode(bytes);
+const codec = getTupleCodec([getStringCodec(), getU8Codec(), getU64Codec()]);
+const bytes = codec.encode(['alice', 42, 123]);
+const tuple = codec.decode(bytes);
 ```
 
 Separate `getTupleEncoder` and `getTupleDecoder` functions are also available.
 
 ```ts
-const bytes = getTupleEncoder(itemEncoders).encode(['alice', 42, 123]);
-const tuple = getTupleDecoder(itemDecoders).decode(bytes);
+const bytes = getTupleEncoder([getStringCodec(), getU8Codec()]).encode(['alice', 42]);
+const tuple = getTupleDecoder([getStringCodec(), getU8Codec()]).decode(bytes);
 ```
 
 ## Struct codec

packages/codecs-data-structures/src/__tests__/tuple-test.ts

@@ -27,7 +27,7 @@ describe('getTupleCodec', () => {
         expect(tuple([string(), u8()]).decode(b('0500000048656c6c6f2a'))).toStrictEqual(['Hello', 42]);
 
         // Different From and To types.
-        const tupleU8U64 = tuple<[number, bigint | number], [number, bigint]>([u8(), u64()]);
+        const tupleU8U64 = tuple([u8(), u64()]);
         expect(tupleU8U64.encode([1, 2])).toStrictEqual(b('010200000000000000'));
         expect(tupleU8U64.encode([1, 2n])).toStrictEqual(b('010200000000000000'));
         expect(tupleU8U64.decode(b('010200000000000000'))).toStrictEqual([1, 2n]);

packages/codecs-data-structures/src/__typetests__/tuple-typetest.ts

@@ -1,4 +1,7 @@
 import {
+    Codec,
+    Decoder,
+    Encoder,
     FixedSizeCodec,
     FixedSizeDecoder,
     FixedSizeEncoder,
@@ -13,21 +16,44 @@ import { getTupleCodec, getTupleDecoder, getTupleEncoder } from '../tuple';
 
 {
     // [getTupleEncoder]: It knows if the encoder is fixed size or variable size.
-    getTupleEncoder([]) satisfies FixedSizeEncoder<[]>;
-    getTupleEncoder([getU8Encoder()]) satisfies FixedSizeEncoder<[number]>;
-    getTupleEncoder([getU8Encoder(), getUtf8Encoder()]) satisfies VariableSizeEncoder<[number, string]>;
+    getTupleEncoder([]) satisfies FixedSizeEncoder<readonly []>;
+    getTupleEncoder([getU8Encoder()]) satisfies FixedSizeEncoder<readonly [number]>;
+    getTupleEncoder([getU8Encoder(), getUtf8Encoder()]) satisfies VariableSizeEncoder<readonly [number, string]>;
+}
+
+{
+    // [getTupleEncoder]: It infers the correct tuple type from the encoders.
+    getTupleEncoder([getU8Encoder(), getUtf8Encoder()]) satisfies Encoder<readonly [number, string]>;
+    // @ts-expect-error It does not combine all items into a single union type.
+    getTupleEncoder([getU8Encoder(), getUtf8Encoder()]) satisfies Encoder<readonly (number | string)[]>;
 }
 
 {
     // [getTupleDecoder]: It knows if the decoder is fixed size or variable size.
-    getTupleDecoder([]) satisfies FixedSizeDecoder<[]>;
-    getTupleDecoder([getU8Decoder()]) satisfies FixedSizeDecoder<[number]>;
-    getTupleDecoder([getU8Decoder(), getUtf8Decoder()]) satisfies VariableSizeDecoder<[number, string]>;
+    getTupleDecoder([]) satisfies FixedSizeDecoder<readonly []>;
+    getTupleDecoder([getU8Decoder()]) satisfies FixedSizeDecoder<readonly [number]>;
+    getTupleDecoder([getU8Decoder(), getUtf8Decoder()]) satisfies VariableSizeDecoder<readonly [number, string]>;
+}
+
+{
+    // [getTupleDecoder]: It infers the correct tuple type from the decoders.
+    getTupleDecoder([getU8Decoder(), getUtf8Decoder()]) satisfies Decoder<readonly [number, string]>;
+    // Because decoder types are returned (and not requested), Decoder<[number, string]> does satisfy Decoder<(number | string)[]>.
+    getTupleDecoder([getU8Decoder(), getUtf8Decoder()]) satisfies Decoder<readonly (number | string)[]>;
+    // @ts-expect-error However, we cannot do things like swapping the order of the types.
+    getTupleDecoder([getU8Decoder(), getUtf8Decoder()]) satisfies Decoder<readonly [string, number]>;
 }
 
 {
     // [getTupleCodec]: It knows if the codec is fixed size or variable size.
-    getTupleCodec([]) satisfies FixedSizeCodec<[]>;
-    getTupleCodec([getU8Codec()]) satisfies FixedSizeCodec<[number]>;
-    getTupleCodec([getU8Codec(), getUtf8Codec()]) satisfies VariableSizeCodec<[number, string]>;
+    getTupleCodec([]) satisfies FixedSizeCodec<readonly []>;
+    getTupleCodec([getU8Codec()]) satisfies FixedSizeCodec<readonly [number]>;
+    getTupleCodec([getU8Codec(), getUtf8Codec()]) satisfies VariableSizeCodec<readonly [number, string]>;
+}
+
+{
+    // [getTupleCodec]: It infers the correct tuple type from the codecs.
+    getTupleCodec([getU8Codec(), getUtf8Codec()]) satisfies Codec<readonly [number, string]>;
+    // @ts-expect-error It does not combine all items into a single union type.
+    getTupleCodec([getU8Codec(), getUtf8Codec()]) satisfies Codec<readonly (number | string)[]>;
 }

packages/codecs-data-structures/src/map.ts

@@ -87,7 +87,7 @@ export function getMapDecoder<TToKey, TToValue>(
     config: MapCodecConfig<NumberDecoder> = {},
 ): Decoder<Map<TToKey, TToValue>> {
     return mapDecoder(
-        getArrayDecoder(getTupleDecoder([key, value]), config as object),
+        getArrayDecoder(getTupleDecoder([key, value]), config as object) as Decoder<[TToKey, TToValue][]>,
         (entries: [TToKey, TToValue][]): Map<TToKey, TToValue> => new Map(entries),
     );
 }

packages/codecs-data-structures/src/tuple.ts

@@ -1,3 +1,4 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
 import {
     Codec,
     combineCodec,
@@ -15,40 +16,31 @@ import {
 } from '@solana/codecs-core';
 
 import { assertValidNumberOfItemsForCodec } from './assertions';
-import { getFixedSize, getMaxSize, sumCodecSizes } from './utils';
+import { DrainOuterGeneric, getFixedSize, getMaxSize, sumCodecSizes } from './utils';
 
-type WrapInFixedSizeEncoder<TFrom> = {
-    [P in keyof TFrom]: FixedSizeEncoder<TFrom[P]>;
-};
-type WrapInEncoder<TFrom> = {
-    [P in keyof TFrom]: Encoder<TFrom[P]>;
-};
-type WrapInFixedSizeDecoder<TTo> = {
-    [P in keyof TTo]: FixedSizeDecoder<TTo[P]>;
-};
-type WrapInDecoder<TTo> = {
-    [P in keyof TTo]: Decoder<TTo[P]>;
-};
-type WrapInCodec<TFrom, TTo extends TFrom> = {
-    [P in keyof TFrom]: Codec<TFrom[P], TTo[P]>;
-};
-type WrapInFixedSizeCodec<TFrom, TTo extends TFrom> = {
-    [P in keyof TFrom]: FixedSizeCodec<TFrom[P], TTo[P]>;
-};
+type GetEncoderTypeFromItems<TItems extends readonly Encoder<any>[]> = DrainOuterGeneric<{
+    [I in keyof TItems]: TItems[I] extends Encoder<infer TFrom> ? TFrom : never;
+}>;
 
-// eslint-disable-next-line @typescript-eslint/no-explicit-any
-type AnyArray = any[];
+type GetDecoderTypeFromItems<TItems extends readonly Decoder<any>[]> = DrainOuterGeneric<{
+    [I in keyof TItems]: TItems[I] extends Decoder<infer TTo> ? TTo : never;
+}>;
 
 /**
  * Creates a encoder for a tuple-like array.
  *
  * @param items - The encoders to use for each item in the tuple.
  */
-export function getTupleEncoder<TFrom extends AnyArray>(
-    items: WrapInFixedSizeEncoder<[...TFrom]>,
-): FixedSizeEncoder<TFrom>;
-export function getTupleEncoder<TFrom extends AnyArray>(items: WrapInEncoder<[...TFrom]>): VariableSizeEncoder<TFrom>;
-export function getTupleEncoder<TFrom extends AnyArray>(items: WrapInEncoder<[...TFrom]>): Encoder<TFrom> {
+export function getTupleEncoder<const TItems extends readonly FixedSizeEncoder<any>[]>(
+    items: TItems,
+): FixedSizeEncoder<GetEncoderTypeFromItems<TItems>>;
+export function getTupleEncoder<const TItems extends readonly Encoder<any>[]>(
+    items: TItems,
+): VariableSizeEncoder<GetEncoderTypeFromItems<TItems>>;
+export function getTupleEncoder<const TItems extends readonly Encoder<any>[]>(
+    items: TItems,
+): Encoder<GetEncoderTypeFromItems<TItems>> {
+    type TFrom = GetEncoderTypeFromItems<TItems>;
     const fixedSize = sumCodecSizes(items.map(getFixedSize));
     const maxSize = sumCodecSizes(items.map(getMaxSize)) ?? undefined;
 
@@ -75,16 +67,24 @@ export function getTupleEncoder<TFrom extends AnyArray>(items: WrapInEncoder<[..
  *
  * @param items - The decoders to use for each item in the tuple.
  */
-export function getTupleDecoder<TTo extends AnyArray>(items: WrapInFixedSizeDecoder<[...TTo]>): FixedSizeDecoder<TTo>;
-export function getTupleDecoder<TTo extends AnyArray>(items: WrapInDecoder<[...TTo]>): VariableSizeDecoder<TTo>;
-export function getTupleDecoder<TTo extends AnyArray>(items: WrapInDecoder<[...TTo]>): Decoder<TTo> {
+
+export function getTupleDecoder<const TItems extends readonly FixedSizeDecoder<any>[]>(
+    items: TItems,
+): FixedSizeDecoder<GetDecoderTypeFromItems<TItems>>;
+export function getTupleDecoder<const TItems extends readonly Decoder<any>[]>(
+    items: TItems,
+): VariableSizeDecoder<GetDecoderTypeFromItems<TItems>>;
+export function getTupleDecoder<const TItems extends readonly Decoder<any>[]>(
+    items: TItems,
+): Decoder<GetDecoderTypeFromItems<TItems>> {
+    type TTo = GetDecoderTypeFromItems<TItems>;
     const fixedSize = sumCodecSizes(items.map(getFixedSize));
     const maxSize = sumCodecSizes(items.map(getMaxSize)) ?? undefined;
 
     return createDecoder({
         ...(fixedSize === null ? { maxSize } : { fixedSize }),
         read: (bytes: Uint8Array, offset) => {
-            const values = [] as AnyArray as TTo;
+            const values = [] as Array<any> & TTo;
             items.forEach(item => {
                 const [newValue, newOffset] = item.read(bytes, offset);
                 values.push(newValue);
@@ -100,17 +100,20 @@ export function getTupleDecoder<TTo extends AnyArray>(items: WrapInDecoder<[...T
  *
  * @param items - The codecs to use for each item in the tuple.
  */
-export function getTupleCodec<TFrom extends AnyArray, TTo extends TFrom = TFrom>(
-    items: WrapInFixedSizeCodec<[...TFrom], [...TTo]>,
-): FixedSizeCodec<TFrom, TTo>;
-export function getTupleCodec<TFrom extends AnyArray, TTo extends TFrom = TFrom>(
-    items: WrapInCodec<[...TFrom], [...TTo]>,
-): VariableSizeCodec<TFrom, TTo>;
-export function getTupleCodec<TFrom extends AnyArray, TTo extends TFrom = TFrom>(
-    items: WrapInCodec<[...TFrom], [...TTo]>,
-): Codec<TFrom, TTo> {
+export function getTupleCodec<const TItems extends readonly FixedSizeCodec<any>[]>(
+    items: TItems,
+): FixedSizeCodec<GetEncoderTypeFromItems<TItems>, GetDecoderTypeFromItems<TItems> & GetEncoderTypeFromItems<TItems>>;
+export function getTupleCodec<const TItems extends readonly Codec<any>[]>(
+    items: TItems,
+): VariableSizeCodec<
+    GetEncoderTypeFromItems<TItems>,
+    GetDecoderTypeFromItems<TItems> & GetEncoderTypeFromItems<TItems>
+>;
+export function getTupleCodec<const TItems extends readonly Codec<any>[]>(
+    items: TItems,
+): Codec<GetEncoderTypeFromItems<TItems>, GetDecoderTypeFromItems<TItems> & GetEncoderTypeFromItems<TItems>> {
     return combineCodec(
-        getTupleEncoder(items as WrapInEncoder<[...TFrom]>),
-        getTupleDecoder(items as WrapInDecoder<[...TTo]>),
+        getTupleEncoder(items),
+        getTupleDecoder(items) as Decoder<GetDecoderTypeFromItems<TItems> & GetEncoderTypeFromItems<TItems>>,
     );
 }