kernel/v2: support the preserve_order option (documented)

plugins/kernel_v2/config/vm.rb

@@ -108,21 +108,26 @@ module VagrantPlugins
 
           # Merge provisioners. First we deal with overrides and making
           # sure the ordering is good there. Then we merge them.
-          new_provs = []
+          new_provs   = []
+          other_provs = other.provisioners.dup
           @provisioners.each do |p|
             if p.id
-              other_p = other.provisioners.find { |o| p.id == o.id }
+              other_p = other_provs.find { |o| p.id == o.id }
               if other_p
                 # There is an override. Take it.
                 other_p.config = p.config.merge(other_p.config)
-                next
+                next if !other_p.preserve_order
+
+                # We're preserving order, delete from other
+                p = other_p
+                other_provs.delete(other_p)
               end
             end
 
             # There is an override, merge it into the
             new_provs << p.dup
           end
-          other.provisioners.each do |p|
+          other_provs.each do |p|
             new_provs << p.dup
           end
           result.instance_variable_set(:@provisioners, new_provs)
@@ -254,6 +259,7 @@ module VagrantPlugins
           @provisioners << prov
         end
 
+        prov.preserve_order = !!options[:preserve_order]
         prov.add_config(options, &block)
         nil
       end

plugins/kernel_v2/config/vm_provisioner.rb

@@ -20,6 +20,12 @@ module VagrantPlugins
       # @return [Object]
       attr_accessor :config
 
+      # Whether or not to preserve the order when merging this with a
+      # parent scope.
+      #
+      # @return [Boolean]
+      attr_accessor :preserve_order
+
       def initialize(id, name)
         @logger = Log4r::Logger.new("vagrant::config::vm::provisioner")
         @logger.debug("Provisioner defined: #{name}")
@@ -28,6 +34,7 @@ module VagrantPlugins
         @id      = id
         @invalid = false
         @name    = name
+        @preserve_order = false
 
         # Attempt to find the provisioner...
         if !Vagrant.plugin("2").manager.provisioners[name]

test/unit/plugins/kernel_v2/config/vm_test.rb

@@ -74,6 +74,28 @@ describe VagrantPlugins::Kernel_V2::VMConfig do
         expect(merged_provs[2].config.inline).
           to eq("foo-overload")
       end
+
+      it "can preserve order for overrides" do
+        subject.provision("shell", inline: "foo", id: "original")
+        subject.provision("shell", inline: "other", id: "other")
+
+        other = described_class.new
+        other.provision("shell", inline: "bar")
+        other.provision(
+          "shell", inline: "foo-overload", id: "original",
+          preserve_order: true)
+
+        merged = subject.merge(other)
+        merged_provs = merged.provisioners
+
+        expect(merged_provs.length).to eql(3)
+        expect(merged_provs[0].config.inline).
+          to eq("foo-overload")
+        expect(merged_provs[1].config.inline).
+          to eq("other")
+        expect(merged_provs[2].config.inline).
+          to eq("bar")
+      end
     end
   end
 end