Remove activation at startup, add helper

This removes the gem activation from the startup and adds a
helper for properly activating gems based on the defined
runtime constraints of the vagrant specification at loading
time.

bin/vagrant

@@ -10,16 +10,6 @@ if Thread.respond_to?(:report_on_exception=)
   Thread.report_on_exception = false
 end
 
-# Activate all the runtime dependencies before
-# moving on.
-begin
-  Gem::Specification.find_by_name("vagrant").runtime_dependencies.each do |dep|
-    gem(dep.name, dep.requirement.as_list)
-  end
-rescue Gem::MissingSpecError
-  $stderr.puts "WARN: Failed to locate vagrant specification for dependency loading"
-end
-
 # Split arguments by "--" if its there, we'll recombine them later
 argv = ARGV.dup
 argv_extra = []
@@ -117,7 +107,6 @@ end
 
 env = nil
 begin
-  require 'log4r'
   require 'vagrant'
   require 'vagrant/bundler'
   require 'vagrant/cli'

lib/vagrant/shared_helpers.rb

@@ -168,7 +168,7 @@ def self.enable_resolv_replace
     if ENV["VAGRANT_ENABLE_RESOLV_REPLACE"]
       if !ENV["VAGRANT_DISABLE_RESOLV_REPLACE"]
         begin
-          require "resolv-replace"
+          Vagrant.require "resolv-replace"
           true
         rescue
           false
@@ -192,7 +192,7 @@ def self.global_logger=(log)
   # @return [Logger]
   def self.global_logger
     if @_global_logger.nil?
-      require "log4r"
+      Vagrant.require "log4r"
       @_global_logger = Log4r::Logger.new("vagrant::global")
     end
     @_global_logger
@@ -226,6 +226,68 @@ def self.default_cli_options
     @_default_cli_options.dup
   end
 
+  # Loads the provided path. If the base of the path
+  # is a Vagrant runtime dependency, the gem will be
+  # activated with the proper constraint first.
+  #
+  # NOTE: This is currently disabled by default and
+  # will transition to enabled by default as more
+  # non-installer based environments are tested.
+  #
+  # @return [nil]
+  def self.require(path)
+    catch(:activation_complete) do
+      # If activation is not enabled, don't attempt activation
+      throw :activation_complete if ENV["VAGRANT_ENABLE_GEM_ACTIVATION"].nil?
+
+      # If it's a vagrant path, don't do anything.
+      throw :activation_complete if path.to_s.start_with?("vagrant/")
+
+      # Attempt to fetch the vagrant specification
+      if @_vagrant_spec.nil?
+        @_vagrant_activated_dependencies = {}
+        begin
+          @_vagrant_spec = Gem::Specification.find_by_name("vagrant")
+        rescue Gem::MissingSpecError
+          # If it couldn't be found, print a warning to stderr and bail
+          if !@_spec_load_failure_warning
+            $stderr.puts "WARN: Failed to locate vagrant specification for dependency loading"
+            @_spec_load_failure_warning = true
+          end
+
+          throw :activation_complete
+        end
+      end
+
+      # Attempt to get the name of the gem by the given path
+      dep_name = Gem::Specification.find_by_path(path)&.name
+
+      # Bail if a dependency name cannot be determined
+      throw :activation_complete if dep_name.nil?
+
+      # Bail if already activated
+      throw :activation_complete if @_vagrant_activated_dependencies[dep_name]
+
+      # Extract the dependency from the runtime dependency list
+      dependency = @_vagrant_spec.runtime_dependencies.detect do |d|
+        d.name == dep_name
+      end
+
+      # If the dependency isn't found, bail
+      throw :activation_complete if dependency.nil?
+
+      # Activate the gem
+      gem(dependency.name, dependency.requirement.as_list)
+puts "Activated: #{dependency.name}"
+      @_vagrant_activated_dependencies[dependency.name] = true
+    end
+
+    # Finally, require the provided path.
+    ::Kernel.require(path)
+
+    nil
+  end
+
   # Check if Vagrant is running in server mode
   #
   # @return [Boolean]

test/unit/plugins/guests/linux/cap/mount_smb_shared_folder_test.rb

@@ -59,6 +59,7 @@
       allow(comm).to receive(:execute).with(any_args)
       allow(machine).to receive(:guest).and_return(guest)
       allow(guest).to receive(:capability).with(:shell_expand_guest_path, mount_guest_path).and_return(mount_guest_path)
+      allow(ENV).to receive(:[]).and_call_original
       allow(ENV).to receive(:[]).with("VAGRANT_DISABLE_SMBMFSYMLINKS").and_return(false)
       allow(ENV).to receive(:[]).with("GEM_SKIP").and_return(false)
       allow(cap).to receive(:display_mfsymlinks_warning)