feat: Improve variant not found error message (#7)

lib/phlex/variants.rb

@@ -39,9 +39,19 @@ def build_variants_style(variants)
             next value if value
           end
 
-          raise VariantNotFoundError, "Variant `#{variant}: #{option.inspect}` doesn't exist"
+          raise_variant_not_found_error(options, variant, option)
         end
       end
+
+      def raise_variant_not_found_error(options, variant, option)
+        message = if options
+          "Option #{option.inspect} for #{variant.inspect} variant doesn't exist. Valid options are: #{options.keys}"
+        else
+          "Variant #{variant.inspect} doesn't exist. Available variants are: #{self::STYLE_VARIANTS.keys}"
+        end
+
+        raise VariantNotFoundError, message
+      end
     end
 
     private

spec/phlex/variants_spec.rb

@@ -142,25 +142,33 @@ def view_template
     expect(actual_html).to eq expected_html
   end
 
-  it "raises error with non existent variants" do
+  it "raises error with non existent options" do
     example = phlex_class do
       style do
         variants do
           color do
             primary "btn-primary"
             danger "btn-danger"
           end
+
+          size do
+            sm "btn-sm"
+            md "btn-md"
+          end
         end
       end
     end
 
+    missing_option = "Option :warning for :color variant doesn't exist. Valid options are: [:primary, :danger]"
+    missing_variant = "Variant :disabled doesn't exist. Available variants are: [:color, :size]"
+
     expect do
       example.build_style(color: :warning)
-    end.to raise_error(Phlex::Variants::VariantNotFoundError, "Variant `color: :warning` doesn't exist")
+    end.to raise_error(Phlex::Variants::VariantNotFoundError, missing_option)
 
     expect do
       example.build_style(disabled: true)
-    end.to raise_error(Phlex::Variants::VariantNotFoundError, "Variant `disabled: true` doesn't exist")
+    end.to raise_error(Phlex::Variants::VariantNotFoundError, missing_variant)
   end
 
   it "allows defining boolean variants" do