Assemblyscript: The Imports type in index.d.ts of @assemblyscript/loader is broken.

[canyala-mf]

The problem; the type of env is not Record.

/** WebAssembly imports with an optional env object and two levels of nesting. */
export type Imports = {
   [key: string]: Record<string,unknown>;
   env?: {
      memory?: WebAssembly.Memory;
      table?: WebAssembly.Table;
      seed?(): number;
      abort?(msg: number, file: number, line: number, column: number): void;
      trace?(msg: number, numArgs?: number, ...args: number[]): void;
   };
};

A suggestion; make [key:string] type any as well as Record like the code below.

/** WebAssembly imports with an optional env object and two levels of nesting. */
export type Imports = {
   [key: string]: Record<string,unknown> | any;
   env?: {
      memory?: WebAssembly.Memory;
      table?: WebAssembly.Table;
      seed?(): number;
      abort?(msg: number, file: number, line: number, column: number): void;
      trace?(msg: number, numArgs?: number, ...args: number[]): void;
   };
};

[MaxGraey]

I don't see any reason for [key: string]: Record<string,unknown> | any. It means basically [key: string]: any and do it completely unsound. Could you provide some example which not working with existing solution?

[canyala-mf]

I hope the following explains the issue in more detail. :-)

You are right, it would be exactly the same as [key: string]: any, but it would possibly express intention only.
Below is a typescript file of mine that fails in loader/index.d.ts when compiling it with the latest tsc:

import * as fs from "fs";
import * as loader from "@assemblyscript/loader";
import ASModule from "../build/optimized";
const imports = { /* imports go here */ };
const asModule = loader.instantiateSync<typeof ASModule>(fs.readFileSync(__dirname + "/build/optimized.wasm"), imports);
// TypeScript API wrappers for AssemblyScript interop logic, also a good place to manage breaking changes etc.
const asm = asModule.exports;
export function add(a:number, b:number): number {
return asm.add(a, b);
}

tsc fails in loader/index.d.ts when compiling the above, reporting that env is not of type Record<string,unknown>, like the indexer [key: string]: Record<string,unknown> is. The types must be the same.

If I change [key: string]: Record<string,unknown> to [key: string]: Record<string,unknown>|any;, or to key: string]: any; it works.

The reason for this is that the two lines with env below are identical at _runtime_:

const x = an_object.env;
const x = an_object["env"];

And the type must match the line below as well ( also at _runtime_ ):

const y = an_object["someRandomText"];

The type can not be differentiated by the runtime value of the key: string.

It only works if the types are the same, i.e. if the type is any; which would avoid the typescript benefits regarding typing as you point out.

In an untyped javascript context the structure of Imports is ok but from a typescript context the structure should perhaps be something like the following instead (_it would break the current contract_):

Imports {
   imports: { [key:string]: Record<string,unknown> }; // A typescript friendly envelope for the imports
   env?: {... left out to shrink this...};
}

Perhaps a proper fix would be something like my experiment above but with som javascript magic to determine which contract is used by the caller? So that we do not break any code?

All the best, great work BTW!

I forked assemblyscript this morning and I have also published a package (@canyala/[email protected]) that contains the typescript friendly fix |any.

_It would be great to see a proper fix in the next release! :-)_

[MaxGraey]

So you want use own wrapper file?

Because asc could generate definitions for module via asc .... -d ./main.d.ts

And it should works as expected

[dcodeIO]

Fwiw, I had to change

export type Imports = {
   [key: string]: Record<string,unknown> | undefined; // <- undefined
   env?: {
      memory?: WebAssembly.Memory;
      table?: WebAssembly.Table;
      seed?(): number;
      abort?(msg: number, file: number, line: number, column: number): void;
      trace?(msg: number, numArgs?: number, ...args: number[]): void;
   };
};

to make the error in the TS playground go away.

[canyala-mf]

@dcodeIO Same as my problem then.

@MaxGraey Yes, I already know about the -d flag and I asc ...> optimized.d.ts which gives me working intellisense when implementing my wrapper. Without any or undefined like @dcodeIO mentioned it doesn't work. Thank you for the tip anyway. :-)

The reason for the wrapper is that I want to hide wasm interop details (strings, arrays, refcounting etc.) inside my api implementation. This way I will have an isolation layer that can handle future improvements and possible breaking changes.

The wrapper layer also has access to the dom which the wasm implementation do not have (yet). My intention is to use AssemblyScript/webassembly as an optimization for specific parts of my implementation in TypeScript.

[MaxGraey]

Yes, it seems, after some version of TypeScript, it became more strict about empty records. Previously, this was not a problem. @Canyala Thank you for finding this! Could you use undefined as suggested by @dcodeIO instead any in your PR #1508?

[canyala-mf]

Thanks! Great! That is a reasonable explanation @MaxGraey . Yes, I'll modify my PR to use undefined. A better choice, I agree. :-)

[dcodeIO]

Iiuc this issue should have been solved by https://github.com/AssemblyScript/assemblyscript/pull/1508, but feel free to reopen if I'm mistaken :)