draft: core(exec): Add attribute to check for idempotency attributes

lib/puppet/type/exec.rb

@@ -21,6 +21,10 @@ module Puppet
         command only when some other resource is changed. (See the notes on refreshing
         below.)
 
+      The `enable_idempotency_check` attribute is used to check if one of the above mentioned
+      attributes has been set. The parameter defaults to `false` and raises an error if
+      enabled and no idempotency attributes has been set.
+
       The state managed by an `exec` resource represents whether the specified command
       _needs to be_ executed during the catalog run. The target state is always that
       the command does not need to be executed. If the initial state is that the
@@ -582,6 +586,39 @@ def check(value)
       end
     end
 
+    newcheck(:enable_idempotency_check) do
+      desc <<-'EOT'
+        Warning: disabling idempotency validation might result in changes
+        in EVERY Puppet run!
+
+        Idempotency is ensured by setting either one of the following
+        attributes:
+
+        - `creates`
+        - `onlyif`
+        - `unless`
+        - `refreshonly`
+      EOT
+
+      defaultto :false
+      newvalues(:true, :false)
+
+      def check(value)
+        if value == :true
+          result = true
+          param = [:onlyif, :unless, :refreshonly, :creates]
+          result = false unless (resource.to_hash.keys & param).any?
+          unless result
+            raise ArgumentError, _("Missing idempotency. Set at least one of 'onlyif', 'unless', 'refreshonly', 'creates' or disable check by adding 'enable_idempotency_check => false' ")
+          end
+
+          result
+        else
+          true
+        end
+      end
+    end
+
     # Exec names are not isomorphic with the objects.
     @isomorphic = false
 

spec/unit/type/exec_spec.rb

@@ -648,6 +648,39 @@ def instance(path)
       @test = Puppet::Type.type(:exec).new(:name => @executable)
     end
 
+    describe "enable_idempotency_check" do
+
+      [:true, :false].each do |value|
+        it "should accept '#{value}'" do
+          @test[:enable_idempotency_check] = value
+          expect(@test[:enable_idempotency_check]).to eq(value)
+        end
+      end
+
+      [1, 0, "1", "0", "yes", "y", "no", "n"].each do |value|
+        it "should reject '#{value}'" do
+          expect { @test[:enable_idempotency_check] = value }.
+            to raise_error(Puppet::Error,
+              /Invalid value #{value.inspect}\. Valid values are true, false/
+            )
+        end
+      end
+
+      context "without an idempotency check" do
+        it "should raise error" do
+          type = Puppet::Type.type(:exec).new(:name => @command, :enable_idempotency_check => true)
+          expect(type[:enable_idempotency_check]).to eq(:true)
+        end
+      end
+
+      context "with an idempotency check" do
+        it "should not fail" do
+          type = Puppet::Type.type(:exec).new(:name => @command, :enable_idempotency_check => true, :refreshonly => true)
+          expect(type).to be
+        end
+      end
+    end
+
     describe ":refreshonly" do
       { :true => false, :false => true }.each do |input, result|
         it "should return '#{result}' when given '#{input}'" do