language/node: adjustments for npm 5.0.x

Goes with: https://github.com/Homebrew/homebrew-core/pull/14085

Library/Homebrew/language/node.rb

@@ -4,6 +4,17 @@ module Language
       "cache=#{HOMEBREW_CACHE}/npm_cache\n"
     end
 
+    def self.pack_for_installation
+      # Homebrew assumes the buildpath/testpath will always be disposable
+      # and from npm 5.0.0 the logic changed so that when a directory is
+      # fed to `npm install` only symlinks are created linking back to that
+      # directory, consequently breaking that assumption. We require a tarball
+      # because npm install creates a "real" installation when fed a tarball.
+      output = Utils.popen_read("npm pack").chomp
+      raise "npm failed to pack #{Dir.pwd}" unless $?.exitstatus.zero?
+      output
+    end
+
     def self.setup_npm_environment
       npmrc = Pathname.new("#{ENV["HOME"]}/.npmrc")
       # only run setup_npm_environment once per formula
@@ -14,7 +25,7 @@ module Language
       npmrc.write npm_cache_config
       # explicitly use our npm and node-gyp executables instead of the user
       # managed ones in HOMEBREW_PREFIX/lib/node_modules which might be broken
-      ENV.prepend_path "PATH", Formula["node"].opt_libexec/"npm/bin"
+      ENV.prepend_path "PATH", Formula["node"].opt_libexec/"bin"
     end
 
     def self.std_npm_install_args(libexec)
@@ -22,8 +33,16 @@ module Language
       # tell npm to not install .brew_home by adding it to the .npmignore file
       # (or creating a new one if no .npmignore file already exists)
       open(".npmignore", "a") { |f| f.write("\n.brew_home\n") }
+
+      pack = pack_for_installation
+
       # npm install args for global style module format installed into libexec
-      ["--verbose", "--global", "--prefix=#{libexec}", "."]
+      %W[
+        --verbose
+        --global
+        --prefix=#{libexec}
+        #{Dir.pwd}/#{pack}
+      ]
     end
 
     def self.local_npm_install_args