Set multiple fields/variables/params using filters (#6130)

* Add action-setmultiplefields and setmultiplevariables, and extend action-sendmessage

* Add getfield operator

* Remove getfield operator

See discussion at https://github.com/Jermolene/TiddlyWiki5/pull/6130#issuecomment-949911439

* Add docs

* Adjust whitespace

* Add support for assigning multiple indexes to action-setmultiplefields

core/modules/widgets/setmultiplevariables.js

@@ -0,0 +1,81 @@
+/*\
+title: $:/core/modules/widgets/setmultiplevariables.js
+type: application/javascript
+module-type: widget
+
+Widget to set multiple variables at once from a list of names and a list of values
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var Widget = require("$:/core/modules/widgets/widget.js").widget;
+
+var SetMultipleVariablesWidget = function(parseTreeNode,options) {
+    this.initialise(parseTreeNode,options);
+};
+
+/*
+Inherit from the base widget class
+*/
+SetMultipleVariablesWidget.prototype = new Widget();
+
+/*
+Render this widget into the DOM
+*/
+SetMultipleVariablesWidget.prototype.render = function(parent,nextSibling) {
+    this.parentDomNode = parent;
+    this.computeAttributes();
+    this.execute();
+    this.renderChildren(parent,nextSibling);
+};
+
+/*
+Compute the internal state of the widget
+*/
+SetMultipleVariablesWidget.prototype.execute = function() {
+    // Setup our variables
+    this.setVariables();
+    // Construct the child widgets
+    this.makeChildWidgets();
+};
+
+
+SetMultipleVariablesWidget.prototype.setVariables = function() {
+    // Set the variables
+    var self = this,
+        filterNames = this.getAttribute("$names",""),
+        filterValues = this.getAttribute("$values","");
+    this.variableNames = [];
+    this.variableValues = [];
+    if(filterNames && filterValues) {
+        this.variableNames = this.wiki.filterTiddlers(filterNames,this);
+        this.variableValues = this.wiki.filterTiddlers(filterValues,this);
+        $tw.utils.each(this.variableNames,function(varname,index) {
+            self.setVariable(varname,self.variableValues[index]);
+        });
+    }
+};
+
+/*
+Refresh the widget by ensuring our attributes are up to date
+*/
+SetMultipleVariablesWidget.prototype.refresh = function(changedTiddlers) {
+    var filterNames = this.getAttribute("$names",""),
+        filterValues = this.getAttribute("$values",""),
+        variableNames = this.wiki.filterTiddlers(filterNames,this),
+        variableValues = this.wiki.filterTiddlers(filterValues,this);
+    if(!$tw.utils.isArrayEqual(this.variableNames,variableNames) || !$tw.utils.isArrayEqual(this.variableValues,variableValues)) {
+        this.refreshSelf();
+        return true;
+    }
+    return this.refreshChildren(changedTiddlers);
+};
+
+exports["setmultiplevariables"] = SetMultipleVariablesWidget;
+
+})();
+