inflate-shrinkwrap: Allow shrinkwraps to elide dev dependencies

If your shrinkwrap contains NO dev dependencies then we'll still try to
install them from your package.json instead of assuming you NEVER want dev
dependencies.

Credit: @iarna
Reviewed-By: @zkat
PR-URL: npm/npm#14327

lib/install/deps.js

@@ -404,6 +404,11 @@ function loadDeps (tree, log, next) {
 exports.loadDevDeps = function (tree, log, next) {
   validate('OOF', arguments)
   if (!tree.package.devDependencies) return andFinishTracker.now(log, next)
+  // if any of our prexisting children are from a shrinkwrap then we skip
+  // loading dev deps as the shrinkwrap will already have provided them for us.
+  if (tree.children.some(function (child) { return child.shrinkwrapDev })) {
+    return andFinishTracker.now(log, next)
+  }
   asyncMap(Object.keys(tree.package.devDependencies), function (dep, done) {
     // things defined as both dev dependencies and regular dependencies are treated
     // as the former

lib/install/inflate-shrinkwrap.js

@@ -24,9 +24,17 @@ function inflateShrinkwrap (topPath, tree, swdeps, finishInflating) {
   validate('SOOF', arguments)
   var onDisk = {}
   tree.children.forEach(function (child) { onDisk[moduleName(child)] = child })
-  tree.children = []
   var dev = npm.config.get('dev') || (!/^prod(uction)?$/.test(npm.config.get('only')) && !npm.config.get('production')) || /^dev(elopment)?$/.test(npm.config.get('only'))
   var prod = !/^dev(elopment)?$/.test(npm.config.get('only'))
+
+  // If the shrinkwrap has no dev dependencies in it then we'll leave the one's
+  // already on disk. If it DOES have dev dependencies then ONLY those in the
+  // shrinkwrap will be included.
+  var swHasDev = Object.keys(swdeps).some(function (name) { return swdeps[name].dev })
+  tree.children = swHasDev ? [] : tree.children.filter(function (child) {
+    return tree.package.devDependencies[moduleName(child)]
+  })
+
   return asyncMap(Object.keys(swdeps), doRealizeAndInflate, finishInflating)
 
   function doRealizeAndInflate (name, next) {
@@ -41,6 +49,7 @@ function inflateShrinkwrap (topPath, tree, swdeps, finishInflating) {
       var child = onDisk[name]
       if (childIsEquivalent(sw, requested, child)) {
         if (!child.fromShrinkwrap) child.fromShrinkwrap = requested.raw
+        if (sw.dev) child.shrinkwrapDev = true
         tree.children.push(child)
         annotateMetadata(child.package, requested, requested.raw, topPath)
         return inflateShrinkwrap(topPath, child, dependencies || {}, next)