feat(proto): add rudimentary support for custom widgets

Enables the use of arbitrary custom widgets from proto annotations. No
assumptions made on the name of type of the widget.

Custom widget options can be provided either as YAML key/values or as
raw YAML strings.

cmd/protoc-gen-netlify-cms/main.go

@@ -271,6 +271,11 @@ func genField(g *generatedYAMLFile, field *cmsv1.Field) {
 			g.Down()
 		}
 		g.Y("multiple: ", strconv.FormatBool(widget.RelationWidget.Multiple))
+	case *cmsv1.Widget_CustomWidget:
+		g.Y("widget: ", strconv.Quote(widget.CustomWidget.GetWidget()))
+		for _, option := range widget.CustomWidget.GetOptions() {
+			g.Y(option)
+		}
 	}
 }
 

example/admin/config.yml

@@ -155,3 +155,14 @@ collections:
         hint: "An int64 value."
         widget: "number"
         value_type: "int"
+
+      - name: "custom_value"
+        label: "CUSTOM VALUE"
+        comment: "A value with a custom widget."
+        required: false
+        hint: "A value with a custom widget."
+        widget: "test"
+        bar: 'baz'
+        foo: 5
+        outer:
+          inner: 42

proto/einride/netlify/cms/example/v1/kitchen_sink.proto

@@ -56,6 +56,17 @@ message KitchenSink {
   // An int64 value.
   int64 int64_value = 9;
 
+  // A value with a custom widget.
+  string custom_value = 10 [(einride.netlify.cms.v1.field) = {
+    widget: {
+      custom_widget: {
+        widget: "test"
+        options: "outer:"
+        options: "  inner: 42"
+      }
+    }
+  }];
+
   // Example enum.
   enum ExampleEnum {
     // Default value. This value is unused.

proto/einride/netlify/cms/v1/annotations.proto

@@ -231,6 +231,8 @@ message Widget {
     StringWidget string_widget = 19;
     // Text widget.
     TextWidget text_widget = 20;
+    // Custom widget.
+    CustomWidget custom_widget = 21;
   }
   // Add field validation by specifying a list with a regex pattern and an error message.
   // More extensive validation can be achieved with custom widgets.
@@ -242,6 +244,14 @@ message Widget {
   }
 }
 
+// The boolean widget translates a toggle switch input to a true/false value.
+message CustomWidget {
+  // Type of the custom widget.
+  string widget = 1;
+  // Widget options, as raw YAML strings appended to the custom widget.
+  repeated string options = 2;
+}
+
 // The boolean widget translates a toggle switch input to a true/false value.
 message BooleanWidget {
   // Default value.

proto/gen/cms/einride/netlify/cms/example/v1/config.yml

@@ -155,3 +155,12 @@ collections:
         hint: "An int64 value."
         widget: "number"
         value_type: "int"
+
+      - name: "custom_value"
+        label: "CUSTOM VALUE"
+        comment: "A value with a custom widget."
+        required: false
+        hint: "A value with a custom widget."
+        widget: "test"
+        outer:
+          inner: 42