microsoft / microsoft/TypeScript

Ability for checker to resolve modules by node similar to program when providing custom host

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Description

### 🔍 Search Terms

module resolution location

### ✅ Viability Checklist

- [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
- [x] This wouldn't change the runtime behavior of existing JavaScript code
- [x] This could be implemented without emitting different JS based on the types of the expressions
- [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
- [x] This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
- [x] This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

### ⭐ Suggestion

The program provides the ability to resolve modules based on the specific string literal node, but the checker only resolves based on specifier text and node resolution mode. This means that if module specifiers with the same text and resolution mode resolve to different modules, the checker will always resolve to the same module based on whatever was last inserted into the program's `ModeAwareCache`.

https://github.com/microsoft/TypeScript/blob/47ca599979c418ade9b0a2f4107c305822472e44/src/compiler/program.ts#L1973-L1975

### 📃 Motivating Example

```ts
import text from "./data.txt" with { type: "text" };
import bytes from "./data.txt" with { type: "bytes" };
const { default: textDynamic } = await import("./data.txt", { with: { type: "text" }});
const { default: bytesDynamic } = await import("./data.txt", { with: { type: "bytes" }});

let invalid: number;
invalid = text;
invalid = textDynamic;
invalid = bytes;
invalid = bytesDynamic;

let validText: string;
validText = text;
validText = textDynamic;

let validBytes: Uint8Array;
validBytes = bytes;
validBytes = bytesDynamic;
```

Currently outputs:

```
[ERROR]: Type 'Uint8Array' is not assignable to type 'number'.
invalid = text;
~~~~~~~
at file:///V:/scratch/main.ts:7:1

TS2322 [ERROR]: Type 'Uint8Array' is not assignable to type 'number'.
invalid = textDynamic;
~~~~~~~
at file:///V:/scratch/main.ts:8:1

TS2322 [ERROR]: Type 'Uint8Array' is not assignable to type 'number'.
invalid = bytes;
~~~~~~~
at file:///V:/scratch/main.ts:9:1

TS2322 [ERROR]: Type 'Uint8Array' is not assignable to type 'number'.
invalid = bytesDynamic;
~~~~~~~
at file:///V:/scratch/main.ts:10:1

TS2322 [ERROR]: Type 'Uint8Array' is not assignable to type 'string'.
validText = text;
~~~~~~~~~
at file:///V:/scratch/main.ts:13:1

TS2322 [ERROR]: Type 'Uint8Array' is not assignable to type 'string'.
validText = textDynamic;
~~~~~~~~~
at file:///V:/scratch/main.ts:14:1

Found 6 errors.
```

If I swap the last two dynamic imports then it will error on `validBytes` instead of `validText`.

### 💻 Use Cases

1. Implementing `bytes` and `text` imports in Deno (which will be unstable and is currently non-standard: https://github.com/whatwg/html/issues/9444)

Contributor guide

Open the contributing guide

Research direction

Start by reading the cited module-resolution logic in src/compiler/program.ts around lines 1973-1975, then trace how the checker resolves the imports in the motivating example. Done means checker resolution can use the specific module-specifier node so identical text and resolution mode can resolve to different modules.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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