Fails to mock module from lib if no `"main"` entry in `package.json`

Describe the bug

I'm developing a plugin for an Electron app. The app provides type definitions to plugin devs in a library with the following package.json: https://github.com/obsidianmd/obsidian-api/blob/master/package.json

So in my code I import stuff like this:

import { parseYaml } from "obsidian";

I bundle the plugin, and the application consumes that bundle, injecting "obsidian" as an external dependency (which is not present at plugin build-time).

Once I try to mock "obsidian" either with a factory method or with __mocks__, Vitest gives me grief:

Error: Failed to resolve entry for package "obsidian". The package may have incorrect main/module/exports specified in its package.json.
 ❯ packageEntryFailure node_modules/vite/dist/node/chunks/dep-df561101.js:28691:11
 ❯ resolvePackageEntry node_modules/vite/dist/node/chunks/dep-df561101.js:28688:5
 ❯ tryNodeResolve node_modules/vite/dist/node/chunks/dep-df561101.js:28419:20
 ❯ Context.resolveId node_modules/vite/dist/node/chunks/dep-df561101.js:28180:28
 ❯ Object.resolveId node_modules/vite/dist/node/chunks/dep-df561101.js:44207:32
 ❯ MessagePort.<anonymous> node_modules/vitest/dist/vendor-index.b271ebe4.js:59:20

And indeed, once I manually add a dummy main.js and update package.json in the library with "main": "./main.js", Vitest is happy.

Reproduction

1. Install the library: npm i obsidian
2. Create a test file
3. Add and run the following test:

import { parseYaml } from "obsidian";

vi.mock("obsidian", () => {
  return {
    parseYaml() {
      return "result"
    }
  };
});

test("mocked method works", () => {
  expect(parseYaml("")).toEqual("result");
});

System Info

System:
    OS: Windows 10 10.0.22621
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz
    Memory: 9.56 GB / 31.50 GB
  Binaries:
    Node: 18.16.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.19 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 9.5.1 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.22621.2134.0), Chromium (116.0.1938.54)
    Internet Explorer: 11.0.22621.1
  npmPackages:
    vite: ^4.4.9 => 4.4.9
    vitest: ^0.34.3 => 0.34.3

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

Start with the linked reproduction: install obsidian, run the TypeScript test containing vi.mock("obsidian"), and inspect how the package.json without a main entry is resolved. The fix is done when the mocked module works without adding a dummy main.js, while the existing reproduction still passes.