Problem

I tried to use knip in Yarn PnP environments with this vite.config.ts

import react from "@vitejs/plugin-react";
import { defineConfig } from "vite";
import svgr from "vite-plugin-svgr";

export default defineConfig({
  plugins: [react(), svgr()],
});

and this error occured:

ERROR: Error loading vite.config.ts
Reason: (0, vitePluginSvgr.default) is not a function

This error only occurred in Yarn PnP, and did not appear in Yarn with node_modules or in other package managers that resolve module paths through node_modules.

I analyzed the root cause and found that the failure was due to the following reasons:

1. knip loads config files using jiti internally:

   // Inside knip's loader
   const config = await jiti.import("./vite.config.ts", { default: true });

2. Multiple scenarios cause CJS version selection:

   // Scenario 1: Yarn PnP - mlly fails, fallback to require.resolve
   resolved = ctx.nativeRequire.resolve("vite-plugin-svgr");
   // → selects dist/index.cjs instead of dist/index.js
   
   // Scenario 2: Forced require conditions
   const result = await jiti.import("vite-plugin-svgr", {
     default: true,
     conditions: ["require", "node"],
   });

3. CJS module structure:

   // dist/index.cjs contains:
   module.exports = {
     default: function vitePluginSvgr() {
       /* ... */
     },
     __esModule: true,
   };

4. jiti's interop logic fails:

   // When Node.js loads CJS via ESM import(), the result is:
   const loaded = { default: function, __esModule: true };
   
   // jiti receives this loaded module and should unwrap it
   // With { default: true }, jiti should return the function directly
   // But current interop logic returns the whole object instead

Solution

The problem lies in jiti's interopDefault Proxy logic. When { default: true } is used, jiti tries to unwrap the default export, but the current logic doesn't handle CJS interop objects properly.

Current logic (broken):

if (prop === "default") {
  return defIsNil ? mod : def; // Returns the whole CJS object
}

Fixed logic:

if (prop === "default") {
  // Detect CJS interop pattern: { default: function, __esModule: true }
  if (
    !defIsNil &&
    typeof def === "object" &&
    typeof def.default === "function"
  ) {
    return def.default; // Unwrap and return the actual function
  }
  return defIsNil ? mod : def; // Keep existing behavior for other cases
}

Result

AS-IS

const plugin = await jiti.import("vite-plugin-svgr", { default: true });
console.log(typeof plugin); // 'object'
console.log(typeof plugin.default); // 'function'
plugin(); // TypeError: plugin is not a function

TO-BE

const plugin = await jiti.import("vite-plugin-svgr", { default: true });
console.log(typeof plugin); // 'function'
plugin(); // Works correctly

Reproduce Bug

You can compare the AS-IS and TO-BE examples here: https://github.com/jungwoo3490/repro-jiti-396

1. Clone the repository

git clone https://github.com/jungwoo3490/repro-jiti-396.git && cd repro-jiti-396

2. Move to the as-is directory, install dependencies, and run knip.

cd as-is && yarn install && yarn knip

then you should see the following error log:

3. Move to the jiti directory, install dependencies, and build the project.

The jiti code here has already been modified as described above.

cd ../jiti && pnpm install && pnpn build

4. Move to the to-be directory, install dependencies, and run knip:

The to-be setup uses the modified jiti bundle.

cd ../to-be && yarn install && yarn knip

then you should see the following successful output: