Make resolv-replace loading optional not automatic

lib/vagrant/shared_helpers.rb

@@ -134,15 +134,17 @@ module Vagrant
   #
   # @return [boolean] enabled or not
   def self.enable_resolv_replace
-    if !ENV["VAGRANT_DISABLE_RESOLV_REPLACE"]
-      begin
-        require "resolv-replace"
-        true
-      rescue
+    if ENV["VAGRANT_ENABLE_RESOLV_REPLACE"]
+      if !ENV["VAGRANT_DISABLE_RESOLV_REPLACE"]
+        begin
+          require "resolv-replace"
+          true
+        rescue
+          false
+        end
+      else
         false
       end
-    else
-      false
     end
   end
 end

test/unit/vagrant/shared_helpers_test.rb

@@ -143,4 +143,23 @@ describe Vagrant do
       expect(subject.prerelease?).to be(false)
     end
   end
+
+  describe "#enable_resolv_replace" do
+    it "should not attempt to require resolv-replace by default" do
+      expect(subject).not_to receive(:require).with("resolv-replace")
+      subject.enable_resolv_replace
+    end
+
+    it "should require resolv-replace when VAGRANT_ENABLE_RESOLV_REPLACE is set" do
+      expect(subject).to receive(:require).with("resolv-replace")
+      with_temp_env("VAGRANT_ENABLE_RESOLV_REPLACE" => "1"){ subject.enable_resolv_replace }
+    end
+
+    it "should not require resolv-replace when VAGRANT_DISABLE_RESOLV_REPLACE is set" do
+      expect(subject).not_to receive(:require).with("resolv-replace")
+      with_temp_env("VAGRANT_ENABLE_RESOLV_REPLACE" => "1", "VAGRANT_DISABLE_RESOLV_REPLACE" => "1") do
+        subject.enable_resolv_replace
+      end
+    end
+  end
 end

website/source/docs/other/environmental-variables.html.md

@@ -219,8 +219,11 @@ shared folders. Defaults to true if the option is not set. This can be overridde
 on a per-folder basis within your Vagrantfile config by settings the
 `SharedFoldersEnableSymlinksCreate` option to true.
 
+## `VAGRANT_ENABLE_RESOLV_REPLACE`
+
+Use the Ruby Resolv library in place of the libc resolver.
+
 ## `VAGRANT_DISABLE_RESOLV_REPLACE`
 
-Vagrant will automatically load `resolv-replace` to use Ruby's Resolv library
-in place of the libc resolver. This behavior can be disabled by setting this
-environment variable.
+Vagrant can optionally use the Ruby Resolv library in place of the libc resolver.
+This can be disabled setting this environment variable.