node_modules/npm/lib/link.js

// link with no args: symlink the folder to the global location
// link with package arg: symlink the global to the local

var npm = require("./npm.js")
  , symlink = require("./utils/link.js")
  , fs = require("graceful-fs")
  , log = require("npmlog")
  , asyncMap = require("slide").asyncMap
  , chain = require("slide").chain
  , path = require("path")
  , build = require("./build.js")
  , npa = require("npm-package-arg")

module.exports = link

link.usage = "npm link (in package dir)"
           + "\nnpm link <pkg> (link global into local)"

link.completion = function (opts, cb) {
  var dir = npm.globalDir
  fs.readdir(dir, function (er, files) {
    cb(er, files.filter(function (f) {
      return !f.match(/^[\._-]/)
    }))
  })
}

function link (args, cb) {
  if (process.platform === 'win32') {
    var semver = require('semver')
    if (!semver.gte(process.version, '0.7.9')) {
      var msg = 'npm link not supported on windows prior to node 0.7.9'
      var e = new Error(msg)
      e.code = 'ENOTSUP'
      e.errno = require('constants').ENOTSUP
      return cb(e)
    }
  }

  if (npm.config.get("global")) {
    return cb(new Error("link should never be --global.\n"
                       +"Please re-run this command with --local"))
  }

  if (args.length === 1 && args[0] === ".") args = []
  if (args.length) return linkInstall(args, cb)
  linkPkg(npm.prefix, cb)
}

function linkInstall (pkgs, cb) {
  asyncMap(pkgs, function (pkg, cb) {
    var t = path.resolve(npm.globalDir, "..")
      , pp = path.resolve(npm.globalDir, pkg)
      , rp = null
      , target = path.resolve(npm.dir, pkg)

    function n (er, data) {
      if (er) return cb(er, data)
      // install returns [ [folder, pkgId], ... ]
      // but we definitely installed just one thing.
      var d = data.filter(function (d) { return !d[3] })
      var what = npa(d[0][0])
      pp = d[0][1]
      pkg = what.name
      target = path.resolve(npm.dir, pkg)
      next()
    }

    // if it's a folder, a random not-installed thing, or not a scoped package,
    // then link or install it first
    if (pkg[0] !== "@" && (pkg.indexOf("/") !== -1 || pkg.indexOf("\\") !== -1)) {
      return fs.lstat(path.resolve(pkg), function (er, st) {
        if (er || !st.isDirectory()) {
          npm.commands.install(t, pkg, n)
        } else {
          rp = path.resolve(pkg)
          linkPkg(rp, n)
        }
      })
    }

    fs.lstat(pp, function (er, st) {
      if (er) {
        rp = pp
        return npm.commands.install(t, pkg, n)
      } else if (!st.isSymbolicLink()) {
        rp = pp
        next()
      } else {
        return fs.realpath(pp, function (er, real) {
          if (er) log.warn("invalid symbolic link", pkg)
          else rp = real
          next()
        })
      }
    })

    function next () {
      chain
        ( [ [function (cb) {
              log.verbose("link", "symlinking %s to %s",  pp, target)
              cb()
            }]
          , [symlink, pp, target]
          // do not run any scripts
          , rp && [build, [target], npm.config.get("global"), build._noLC, true]
          , [ resultPrinter, pkg, pp, target, rp ] ]
        , cb )
    }
  }, cb)
}

function linkPkg (folder, cb_) {
  var me = folder || npm.prefix
    , readJson = require("read-package-json")

  log.verbose("linkPkg", folder)

  readJson(path.resolve(me, "package.json"), function (er, d) {
    function cb (er) {
      return cb_(er, [[d && d._id, target, null, null]])
    }
    if (er) return cb(er)
    if (!d.name) {
      er = new Error("Package must have a name field to be linked")
      return cb(er)
    }
    var target = path.resolve(npm.globalDir, d.name)
    symlink(me, target, false, true, function (er) {
      if (er) return cb(er)
      log.verbose("link", "build target", target)
      // also install missing dependencies.
      npm.commands.install(me, [], function (er) {
        if (er) return cb(er)
        // build the global stuff.  Don't run *any* scripts, because
        // install command already will have done that.
        build([target], true, build._noLC, true, function (er) {
          if (er) return cb(er)
          resultPrinter(path.basename(me), me, target, cb)
        })
      })
    })
  })
}

function resultPrinter (pkg, src, dest, rp, cb) {
  if (typeof cb !== "function") cb = rp, rp = null
  var where = dest
  rp = (rp || "").trim()
  src = (src || "").trim()
  // XXX If --json is set, then look up the data from the package.json
  if (npm.config.get("parseable")) {
    return parseableOutput(dest, rp || src, cb)
  }
  if (rp === src) rp = null
  console.log(where + " -> " + src + (rp ? " -> " + rp: ""))
  cb()
}

function parseableOutput (dest, rp, cb) {
  // XXX this should match ls --parseable and install --parseable
  // look up the data from package.json, format it the same way.
  //
  // link is always effectively "long", since it doesn't help much to
  // *just* print the target folder.
  // However, we don't actually ever read the version number, so
  // the second field is always blank.
  console.log(dest + "::" + rp)
  cb()
}