absolute paths in `moduleDirectories` are invalid in Windows OS

[warren-bank]

https://github.com/facebook/jest
https://github.com/facebook/jest/tree/master/packages/jest-resolve
https://github.com/facebook/jest/blob/master/packages/jest-resolve/src/node_modules_paths.js

---

error:

• absolute paths in moduleDirectories are invalid in Windows OS
• results in CommonJS modules not being found
• import statements throw an Error
• all tests fail

---

evidence:

file:
packages/jest-resolve/src/node_modules_paths.js

line: 54

insert code:
console.log('dirs:', JSON.stringify(dirs, null, 2))

---

patch v1:

file:
packages/jest-resolve/src/node_modules_paths.js

line: 50

original code:
return path.join(prefix, aPath, moduleDir);

modified code:
return path.isAbsolute(moduleDir) ? moduleDir : path.join(prefix, aPath, moduleDir);

effects:

• dirs.length will not change
• dirs will contain paths.length duplicates of each absolute path in modules
• absolute paths will be valid
• absolute paths for Windows OS will no-longer be broken

---

patch v2:

file:
packages/jest-resolve/src/node_modules_paths.js

lines: 47 - 53

original code:

  const dirs = paths.reduce((dirs, aPath) => {
    return dirs.concat(
      modules.map(moduleDir => {
        return path.join(prefix, aPath, moduleDir);
      }),
    );
  }, []);

modified code:

  const dirs = paths
    .reduce((dirs, aPath) => {
      return dirs.concat(
        modules.map(moduleDir => {
          return path.isAbsolute(moduleDir) ? ((aPath === basedirAbs) ? moduleDir : null) : path.join(prefix, aPath, moduleDir);
        }),
      );
    }, [])
    .filter(dir => (dir !== null))
  ;

effects:

• each absolute path in modules is only returned for a particular iteration of paths.reduce()
• other iterations inject a null value
• dirs is then filtered to remove these null values
• dirs.length will be reduced, which could slightly boost performance
• absolute paths will be valid
• absolute paths for Windows OS will no-longer be broken

---

[warren-bank]

For a concrete example that's fairly minimal:

git clone "https://github.com/warren-bank/react-redux-bindings.git"
cd "react-redux-bindings"
npm install
cd "tests"
npm install
npm run test

Background:

• I wrote and tested this project in Linux.. not so long ago.. no problem
• I was laying on the sofa this evening
  • watching tv
  • browsing the web from Windows (ie: my hanging-around OS of choice)
  • re-reading some of the code in this project
  • felt the need to push a super minor update
  • ran the unit tests.. and all failed
  • "wtf?".. I ask
  • "did jest make a recent update that conflicts with my configuration?".. I ask
  • knowing that Windows generally sucks for development..
    • rebooted to Linux
    • ran the above set of commands
    • all tests pass
  • rebooted back to Windows
  • traced the problem (in jest)
  • figured out what's breaking and how to fix it
  • forked jest and submitted a pull request
  • made an issue in the tracker to be more verbose about the problem
  • and.. here we are :)

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