Add property computed: proc { ... } for non-sticky value

2 files changed, 170 insertions, 14 deletions

diff --git a/lib/chef/mixin/params_validate.rb b/lib/chef/mixin/params_validate.rb
index 3edc761ffc..c5836122a2 100644
--- a/lib/chef/mixin/params_validate.rb
+++ b/lib/chef/mixin/params_validate.rb
@@ -97,6 +97,8 @@ class Chef
         else
           default = NOT_PASSED
         end
+        computed = validation.delete(:computed)
+        computed ||= validation.delete('computed')
         coerce    = validation.delete(:coerce)
         coerce  ||= validation.delete('coerce')
         name_property   = validation.delete(:name_property)
@@ -131,8 +133,12 @@ class Chef
           # Get the default value
           else
             _pv_required(opts, symbol, required, explicitly_allows_nil?(symbol, validation)) if required
-            _pv_default(opts, symbol, default) unless default == NOT_PASSED
-            _pv_name_property(opts, symbol, name_property)
+            if !opts.has_key?(symbol)
+              got_default = true
+              _pv_computed(opts, symbol, computed)
+              _pv_default(opts, symbol, default) unless default == NOT_PASSED
+              _pv_name_property(opts, symbol, name_property)
+            end
 
             if opts.has_key?(symbol)
               # Handle lazy defaults.
@@ -150,7 +156,7 @@ class Chef
               validate(opts, { symbol => validation })
 
               # Defaults are presently "stickily" set on the instance
-              self.instance_variable_set(iv_symbol, opts[symbol])
+              self.instance_variable_set(iv_symbol, opts[symbol]) unless got_default && computed
             end
           end
 
@@ -321,6 +327,33 @@ class Chef
       end
 
       #
+      # A computed default value (non-sticky).
+      #
+      # When the property is not assigned, this will be used.
+      #
+      # @example
+      #   ```ruby
+      #   property :x
+      #   property :y, computed: proc { x+2 }
+      #   ```
+      #
+      # @example
+      #   ```ruby
+      #   property :x
+      #   property :y, computed: proc { |r| r.x+2 }
+      #   ```
+      #
+      def _pv_computed(opts, key, computed_value)
+        if !opts.has_key?(key) && computed_value
+          if computed_value.arity >= 1
+            opts[key] = computed_value.call(self)
+          else
+            opts[key] = instance_eval(&computed_value)
+          end
+        end
+      end
+
+      #
       # List of regexes values that must match.
       #
       # Uses regex.match() to evaluate. At least one must match for the value to
diff --git a/spec/unit/property_spec.rb b/spec/unit/property_spec.rb
index 8c01bf7b49..f048355269 100644
--- a/spec/unit/property_spec.rb
+++ b/spec/unit/property_spec.rb
@@ -281,9 +281,9 @@ describe "Chef::Resource.property" do
         resource.x lazy { 10 }
         expect(resource.property_is_set?(:x)).to be_truthy
       end
-      it "when x is retrieved, property_is_set?(:x) is false" do
+      it "when x is retrieved, property_is_set?(:x) is true" do
         resource.x
-        expect(resource.property_is_set?(:x)).to be_falsey
+        expect(resource.property_is_set?(:x)).to be_truthy
       end
     end
 
@@ -367,8 +367,7 @@ describe "Chef::Resource.property" do
           expect(resource.x.object_id).to eq(value.object_id)
         end
         it "Multiple instances of x receive the exact same value" do
-          # TODO this isn't really great behavior, but it's noted here so we find out
-          # if it changed.
+          # Bleagh.  But it's what we do.
           expect(resource.x.object_id).to eq(resource_class.new('blah2').x.object_id)
         end
       end
@@ -377,11 +376,11 @@ describe "Chef::Resource.property" do
         it "when x is not set, it returns {}" do
           expect(resource.x).to eq({})
         end
-        # it "The value is different each time it is called" do
-        #   value = resource.x
-        #   expect(value).to eq({})
-        #   expect(resource.x.object_id).not_to eq(value.object_id)
-        # end
+        it "The value is the same each time it is called" do
+          value = resource.x
+          expect(value).to eq({})
+          expect(resource.x.object_id).to eq(value.object_id)
+        end
         it "Multiple instances of x receive different values" do
           expect(resource.x.object_id).not_to eq(resource_class.new('blah2').x.object_id)
         end
@@ -407,7 +406,7 @@ describe "Chef::Resource.property" do
         it "x is run in the context of each instance it is run in" do
           expect(resource.x).to eq "blah1"
           expect(resource_class.new('another').x).to eq "another2"
-          # expect(resource.x).to eq "blah3"
+          expect(resource.x).to eq "blah1"
         end
       end
 
@@ -418,7 +417,7 @@ describe "Chef::Resource.property" do
         it "x is passed the value of each instance it is run in" do
           expect(resource.x).to eq "classblah1"
           expect(resource_class.new('another').x).to eq "classanother2"
-          # expect(resource.x).to eq "classblah3"
+          expect(resource.x).to eq "classblah1"
         end
       end
     end
@@ -535,6 +534,130 @@ describe "Chef::Resource.property" do
     end
   end
 
+  context "Chef::Resource::PropertyType#computed" do
+    context "hash computed default" do
+      with_property ':x, computed: proc { {} }' do
+        it "when x is not set, it returns {}" do
+          expect(resource.x).to eq({})
+        end
+        it "The value is different each time it is called" do
+          value = resource.x
+          expect(value).to eq({})
+          expect(resource.x.object_id).not_to eq(value.object_id)
+        end
+        it "Multiple instances of x receive different values" do
+          expect(resource.x.object_id).not_to eq(resource_class.new('blah2').x.object_id)
+        end
+      end
+    end
+
+    context "with a class with 'blah' as both class and instance methods" do
+      before do
+        resource_class.class_eval do
+          def self.blah
+            'class'
+          end
+          def blah
+            "#{name}#{next_index}"
+          end
+        end
+      end
+
+      with_property ':x, computed: proc { blah }' do
+        it "x is run in context of the instance" do
+          expect(resource.x).to eq "blah1"
+        end
+        it "x is run in the context of each instance it is run in" do
+          expect(resource.x).to eq "blah1"
+          expect(resource_class.new('another').x).to eq "another2"
+          expect(resource.x).to eq "blah3"
+        end
+      end
+
+      with_property ':x, computed: proc { |x| "#{blah}#{x.blah}" }' do
+        it "x is run in context of the class (where it was defined) and passed the instance" do
+          expect(resource.x).to eq "classblah1"
+        end
+        it "x is passed the value of each instance it is run in" do
+          expect(resource.x).to eq "classblah1"
+          expect(resource_class.new('another').x).to eq "classanother2"
+          expect(resource.x).to eq "classblah3"
+        end
+      end
+    end
+
+    context "validation of computed defaults" do
+      with_property ":x, String, computed: proc { Namer.next_index }" do
+        it "when the resource is created, no error is raised" do
+          resource
+        end
+        it "when x is set, no error is raised" do
+          expect(resource.x 'hi').to eq 'hi'
+          expect(resource.x).to eq 'hi'
+        end
+        it "when x is retrieved, a validation error is raised" do
+          expect { resource.x }.to raise_error Chef::Exceptions::ValidationFailed
+          expect(Namer.current_index).to eq 1
+        end
+      end
+
+      with_property ":x, computed: proc { Namer.next_index }, is: proc { |v| Namer.next_index; true }" do
+        it "validation is run each time" do
+          expect(resource.x).to eq 1
+          expect(Namer.current_index).to eq 2
+          expect(resource.x).to eq 3
+          expect(Namer.current_index).to eq 4
+        end
+      end
+    end
+
+    context "coercion of computed defaults" do
+      with_property ':x, coerce: proc { |v| "#{v}#{next_index}" }, computed: proc { 10 }' do
+        it "when the resource is created, the proc is not yet run" do
+          resource
+          expect(Namer.current_index).to eq 0
+        end
+        it "when x is set, coercion is run" do
+          expect(resource.x 'hi').to eq 'hi1'
+          expect(resource.x).to eq 'hi1'
+          expect(Namer.current_index).to eq 1
+        end
+      end
+
+      with_property ':x, proc { |v| Namer.next_index; true }, coerce: proc { |v| "#{v}#{next_index}" }, computed: proc { 10 }' do
+        it "coercion is run each time x is retrieved" do
+          expect(Namer.current_index).to eq 0
+          expect(resource.x).to eq '101'
+          expect(Namer.current_index).to eq 2
+          expect(resource.x).to eq '103'
+          expect(Namer.current_index).to eq 4
+        end
+      end
+
+      context "validation and coercion of computed defaults" do
+        with_property ':x, String, coerce: proc { |v| "#{v}#{next_index}" }, computed: proc { 10 }' do
+          it "when x is retrieved, it is coerced before validating and passes" do
+            expect(resource.x).to eq '101'
+          end
+        end
+        with_property ':x, Integer, coerce: proc { |v| "#{v}#{next_index}" }, computed: proc { 10 }' do
+          it "when x is retrieved, it is coerced before validating and fails" do
+            expect { resource.x }.to raise_error Chef::Exceptions::ValidationFailed
+          end
+        end
+        with_property ':x, proc { |v| Namer.next_index; true }, coerce: proc { |v| "#{v}#{next_index}" }, computed: proc { 10 }' do
+          it "coercion and validation is only run the first time x is retrieved" do
+            expect(Namer.current_index).to eq 0
+            expect(resource.x).to eq '101'
+            expect(Namer.current_index).to eq 2
+            expect(resource.x).to eq '103'
+            expect(Namer.current_index).to eq 4
+          end
+        end
+      end
+    end
+  end
+
   context "Chef::Resource#lazy" do
     with_property ':x' do
       it "setting x to a lazy value does not run it immediately" do