fix(prefix): Handle node_modules without package.json (#128)

This fixes running `npx` inside temporary projects (ones that have a
`node_modules` but don't have a `package.json`).

`getPrefix()` has useful cases:

1. Finds a path with a `package.json`, returns it.
2. Finds a path with a `node_modules`, returns it.
3. Finds nothing, returns the original path.

Cases 1 and 2 return a path that's useful to `npx`, but case 3 doesn't.
But, `localBinPath()` confused case 2 and 3 (by stating for a
`package.json`), making `npx` only work with case 1. That's no good.

This makes cases 1 and 2 distinct from case 3 (it just returns `false`
now). And `localBinPath()` no longer has to do any stating to
differentiate between paths and `false`, so it's happy. And now `npx`
can run without a local `package.json`. Yay!

Fixes: #104
Fixes: babel/babel#4066 (comment)

get-prefix.js

@@ -6,20 +6,21 @@ const path = require('path')
 const statAsync = promisify(require('fs').stat)
 
 module.exports = getPrefix
-function getPrefix (current, root) {
-  if (!root) {
-    const original = root = path.resolve(current)
-    while (path.basename(root) === 'node_modules') {
-      root = path.dirname(root)
-    }
-    if (original !== root) {
-      return Promise.resolve(root)
-    } else {
-      return getPrefix(root, root)
-    }
+function getPrefix (root) {
+  const original = root = path.resolve(root)
+  while (path.basename(root) === 'node_modules') {
+    root = path.dirname(root)
   }
-  if (isRootPath(current, process.platform)) {
+  if (original !== root) {
     return Promise.resolve(root)
+  } else {
+    return Promise.resolve(getPrefixFromTree(root))
+  }
+}
+
+function getPrefixFromTree (current) {
+  if (isRootPath(current, process.platform)) {
+    return false
   } else {
     return Promise.all([
       fileExists(path.join(current, 'package.json')),
@@ -30,8 +31,7 @@ function getPrefix (current, root) {
       if (hasPkg || hasModules) {
         return current
       } else {
-        const parent = path.dirname(current)
-        return getPrefix(parent, root)
+        return getPrefixFromTree(path.dirname(current))
       }
     })
   }

index.js

@@ -116,11 +116,7 @@ function npx (argv) {
 module.exports._localBinPath = localBinPath
 function localBinPath (cwd) {
   return require('./get-prefix.js')(cwd).then(prefix => {
-    const pkgjson = path.join(prefix, 'package.json')
-    return promisify(fs.stat)(pkgjson).then(
-      () => path.join(prefix, 'node_modules', '.bin'),
-      err => { if (err.code !== 'ENOENT') throw err }
-    )
+    return prefix && path.join(prefix, 'node_modules', '.bin')
   })
 }
 

test/get-prefix.js

@@ -40,11 +40,11 @@ test('detects if currently in an npm package using node_modules', t => {
   })
 })
 
-test('returns the same path if no package was found in parent dirs', t => {
+test('returns false if no package was found in parent dirs', t => {
   // Hopefully folks' tmpdir isn't inside an npm package ;)
   const tmp = os.tmpdir()
   return getPrefix(tmp).then(prefix => {
-    t.equal(prefix, tmp, 'returned the same path')
+    t.equal(prefix, false, 'returned the false')
   })
 })
 
@@ -70,17 +70,6 @@ test('doesn\'t go too far while navigating up', t => {
   })
 })
 
-test('returns root if we get there', t => {
-  let root = '/'
-  if (process.platform === 'win32') {
-    const currentDrive = process.cwd().match(/^([a-z]+):/i)[1]
-    root = `${currentDrive}:\\`
-  }
-  return getPrefix(root).then(prefix => {
-    t.equal(prefix, root, 'used the same root')
-  })
-})
-
 test('fileExists unit', t => {
   const fileExists = requireInject('../get-prefix.js', {
     fs: {