add button action "setExtraData"

Author: jrief

assets/tag-attributes.pegjs

@@ -112,6 +112,9 @@ Function
   = 'setFieldValue' _ '(' _ target:PATH _ ',' _ source:SOURCEARG _ ')' {
     return {_funcName: 'setFieldValue', _funcArgs: [target.split('.'), source]};
   }
+  / 'setExtraData' _ '(' _ target:PATH _ ',' _ source:SOURCEARG _ ')' {
+    return {_funcName: 'setExtraData', _funcArgs: [target.split('.'), source]};
+  }
   / 'deletePartial' _ '(' _ target:PATH _ ',' _ source:SOURCEARG _ ')' {
     return {_funcName: 'deletePartial', _funcArgs: [target.split('.'), source]};
   }

client/django-formset/DjangoFormset.ts

@@ -946,6 +946,17 @@ class DjangoButton {
 		}
 	}
 
+	/**
+	 * Transfer value from one element to another one.
+ 	 */
+	//@allowedAction
+	private setExtraData(target: Path, source: FieldValue) {
+		return (response: Response) => {
+			this.formset.setExtraData(target, source);
+			return Promise.resolve(response);
+		}
+	}
+
 	//@allowedAction
 	private deletePartial(target: Path, source: FieldValue) {
 		return (response: Response) => {
@@ -2327,6 +2338,10 @@ export class DjangoFormset implements DjangoFormset {
 		}
 	}
 
+	public setExtraData(path: Path, value: any) {
+		setDataValue(this.extraData, path, value);
+	}
+
 	public findFirstErrorReport() : Element|null {
 		for (const form of this.forms) {
 			const errorReportElement = form.findFirstErrorReport();

docs/source/buttons.rst

@@ -100,6 +100,10 @@ as queued actions for buttons in **django-formset**:
   the latter case that value is transferred to the target field.
   By prefixing the source value with a ``^`` caret, the value is taken from a response object
   fetched by a previous request.
+* ``setExtraData(path.to.target, source_value)`` sets a value to be submitted as extra data along
+  with the form data. The target path specifies where to store that value inside the extra data
+  object. The source value can be a string, number or a boolean.  By prefixing the source value with
+  a ``^`` caret, the value is taken from a response object fetched by a previous request.
 * ``emit("event name")`` emit a named event to the DOM.
 * ``clearErrors`` clears all error annotations from a previously failed form validation.
 * ``activate`` activates the button to be intercepted by another component, for instance in