fix(types): specify ArrayBuffer as a backing buffer type for TextEncoder.encode()

[magurotuna]

This patch updates the TextEncoder interface type declarations to correctly specify ArrayBuffer as the backing buffer type for the encode() method, aligning with the spec and addressing the change introduced in TypeScript 5.7 about making ArrayVBufferLike a default buffer type behind Uint8Array.

Problem

TypeScript 5.7 changed the default backing buffer type for Uint8Array from ArrayBuffer to ArrayBufferLike (which is a union of ArrayBuffer and SharedArrayBuffer). However, TextEncoder.encode() per specification always returns a Uint8Array backed by a standard ArrayBuffer, never a SharedArrayBuffer. This mismatch causes type errors when passing the buffer to functions expecting ArrayBuffer:

const data = new TextEncoder().encode("hello");

function processData(d: ArrayBuffer) { /* ... */ }

processData(data.buffer);

Type check result with Deno v2.4.4:

Check file:///tmp/arraybuffer.ts
TS2345 [ERROR]: Argument of type 'ArrayBufferLike' is not assignable to parameter of type 'ArrayBuffer'.
  Type 'SharedArrayBuffer' is missing the following properties from type 'ArrayBuffer': resizable, resize, detached, transfer, transferToFixedLength
processData(data.buffer) // Type error: ArrayBufferLike is not assignable to ArrayBuffer
            ~~~~~~~~~~~
    at file:///tmp/arraybuffer.ts:7:13

error: Type checking failed.

Solution

This issue is resolved in this patch by explicitly specifying Uint8Array<ArrayBuffer> as the return type for encode().

Also, the second parameter type of encodeInto() is updated to Uint8Array<ArrayBufferLike> to make it less confusing and more explicit.

Refs

• Incorrect type returned by TextEncoder.encode microsoft/TypeScript#60846
• fix: make TextEncoder.prototype.encode return Uint8Array<ArrayBuffer> microsoft/TypeScript-DOM-lib-generator#1893
• Support generic Uint8Array<ArrayBuffer> microsoft/TypeScript-DOM-lib-generator#1944

[magurotuna]

Removed this interface because it simply appears to be a duplicate with less document

[dsherret]

I think this specific issue was fixed in TypeScript 5.9. We should wait for that before landing probably and wait for the minor release because this is breaking.

https://devblogs.microsoft.com/typescript/announcing-typescript-5-9/#lib.d.ts-changes

[petamoriken]

Since TypeScript 4.7, ArrayBuffer and SharedArrayBuffer have been distinguished when using types from ES2024. As of TypeScript 4.9, this distinction is also made for types from ES2023 and earlier (by microsoft/TypeScript#60150).

Personally, I don't feel the need to wait for TypeScript 4.9, but I don't have a strong opinion.

[dsherret]

This specific issue was only fixed recently in microsoft/TypeScript-DOM-lib-generator#1944 for TS 5.9, so I think we should wait in order to align (plus it's a breaking change)

[petamoriken]

That's true. That makes sense 👍

[magurotuna]

oh ok thanks for the detail. let's wait for that

[dsherret]

LGTM now