Move some code out of Et2Select into parent mixin for better re-use

Any child that has selectbox type functionality (extends Et2WidgetWithSelectMixin) needs to implement:
- _optionTargetNode() : HTMLElement
- _optionTemplate(option : SelectOption) : TemplateResult

api/js/etemplate/Et2Select/Et2Select.ts

@@ -9,7 +9,7 @@
 
 
 import {LionSelect} from "@lion/select";
-import {css, html, PropertyValues, render, repeat, TemplateResult} from "@lion/core";
+import {css, html, PropertyValues, TemplateResult} from "@lion/core";
 import {cssImage} from "../Et2Widget/Et2Widget";
 import {StaticOptions} from "./StaticOptions";
 import {Et2widgetWithSelectMixin} from "./Et2WidgetWithSelectMixin";
@@ -73,37 +73,35 @@ export class Et2Select extends Et2WidgetWithSelect
 		this.querySelector('select').append(...this.querySelectorAll('option'));
 
 		// if _inputNode was not available by the time set_value() got called
-		if (this.getValue() !== this.modelValue)
+		if(this.getValue() !== this.modelValue)
 		{
 			this.set_value(this.modelValue);
 		}
 	}
 
+	/**
+	 * Get the node where we're putting the selection options
+	 *
+	 * @returns {HTMLElement}
+	 */
+	get _optionTargetNode() : HTMLElement
+	{
+		return this._inputNode;
+	}
+
 	/** @param {import('@lion/core').PropertyValues } changedProperties */
 	updated(changedProperties : PropertyValues)
 	{
 		super.updated(changedProperties);
-		if(changedProperties.has('select_options'))
+
-		{
+		if(changedProperties.has('select_options') || changedProperties.has("value") || changedProperties.has('empty_label'))
-			// Add in actual options as children to select
-			if(this._inputNode)
-			{
-				// We use this.get_select_options() instead of this.select_options so children can override
-				// This is how sub-types get their options in
-				render(html`${this._emptyLabelTemplate()}
-                        ${repeat(this.get_select_options(), (option : SelectOption) => option.value, this._optionTemplate.bind(this))}`,
-					this._inputNode
-				);
-			}
-		}
-		if (changedProperties.has('select_options') || changedProperties.has("value") || changedProperties.has('empty_label'))
 		{
 			// value not in options AND NOT (having an empty label and value)
-			if (this.get_select_options().length > 0 && this.get_select_options().filter((option) => option.value == this.modelValue).length === 0 &&
+			if(this.get_select_options().length > 0 && this.get_select_options().filter((option) => option.value == this.modelValue).length === 0 &&
-				!(typeof this.empty_label !== 'undefined' && (this.modelValue||"") === ""))
+				!(typeof this.empty_label !== 'undefined' && (this.modelValue || "") === ""))
 			{
 				// --> use first option
-				this.modelValue = ""+this.get_select_options()[0]?.value;	// ""+ to cast value of 0 to "0", to not replace with ""
+				this.modelValue = "" + this.get_select_options()[0]?.value;	// ""+ to cast value of 0 to "0", to not replace with ""
 			}
 			// Re-set value, the option for it may have just shown up
 			this._inputNode.value = this.modelValue || "";

api/js/etemplate/Et2Select/Et2WidgetWithSelectMixin.ts

@@ -9,7 +9,7 @@
 
 import {Et2InputWidget} from "../Et2InputWidget/Et2InputWidget";
 import {StaticOptions} from "./StaticOptions";
-import {dedupeMixin, html, PropertyValues, TemplateResult} from "@lion/core";
+import {dedupeMixin, html, PropertyValues, render, repeat, TemplateResult} from "@lion/core";
 import {et2_readAttrWithDefault} from "../et2_core_xml";
 import {find_select_options, SelectOption} from "./FindSelectOptions";
 
@@ -17,6 +17,37 @@ import {find_select_options, SelectOption} from "./FindSelectOptions";
  * Base class for things that do selectbox type behaviour, to avoid putting too much or copying into read-only
  * selectboxes, also for common handling of properties for more special selectboxes.
  *
+ * As with most other widgets that extend Lion components, do not override render().
+ * To extend this mixin, override:
+ * - _optionTargetNode(): Return the HTMLElement where the "options" go.
+ * - _optionTemplate(option:SelectOption): Renders the option.  To use a special widget, use its tag in render.
+ * Select option:
+ * ```js
+ * 		return html`
+ *             <option value="${option.value}" title="${option.title}" ?selected=${option.value == this.modelValue}>
+ *                 ${option.label}
+ *             </option>`;
+ * ```
+ *
+ *
+ * or pass it off to a different WebComponent:
+ *
+ * ```js
+ * _optionTemplate(option:SelectOption) : TemplateResult
+ * {
+ *     return html`
+ *           <special-option-tag .value=${option}></special-option-tag>`;
+ * }
+ * ```
+ *
+ * Optionally, you can override:
+ * - _emptyLabelTemplate(): How to render the empty label
+ * - slots(): Most Lion components have an input slot where the <input> tag is created.
+ * You can specify something else, or return {} to do your own thing.  This is a little more complicated.  You should
+ * also override _inputGroupInputTemplate() to do what you normally would in render().
+ *
+ *
+ * Technical note:
  * LionSelect (and any other LionField) use slots to wrap a real DOM node.  ET2 doesn't expect this,
  * so we have to create the input node (via slots()) and respect that it is _external_ to the Web Component.
  * This complicates things like adding the options, since we can't just override _inputGroupInputTemplate()
@@ -65,6 +96,21 @@ export const Et2widgetWithSelectMixin = dedupeMixin((superclass) =>
 			{
 				this.set_select_options(find_select_options(this));
 			}
+
+			// Add in actual option tags to the DOM based on the new select_options
+			if(changedProperties.has('select_options'))
+			{
+				// Add in options as children to the target node
+				if(this._optionTargetNode)
+				{
+					// We use this.get_select_options() instead of this.select_options so children can override
+					// This is how the sub-types with static options (day of week, month, etc.) get their options in
+					render(html`${this._emptyLabelTemplate()}
+                            ${repeat(this.get_select_options(), (option : SelectOption) => option.value, this._optionTemplate.bind(this))}`,
+						this._optionTargetNode
+					);
+				}
+			}
 		}
 
 		/**
@@ -121,19 +167,55 @@ export const Et2widgetWithSelectMixin = dedupeMixin((superclass) =>
 			return this.select_options;
 		}
 
+		/**
+		 * Get the node where we're putting the options
+		 *
+		 * If this were a normal selectbox, this would be just the <select> tag (this._inputNode) but in a more
+		 * complicated widget, this could be anything.
+		 *
+		 * @overridable
+		 * @returns {HTMLElement}
+		 */
+		get _optionTargetNode() : HTMLElement
+		{
+			return <HTMLElement><unknown>this;
+		}
+
 		/**
 		 * Render the "empty label", used when the selectbox does not currently have a value
 		 *
-		 * @returns {}
+		 * @overridable
+		 * @returns {TemplateResult}
 		 */
 		_emptyLabelTemplate() : TemplateResult
 		{
 			return html`${this.empty_label}`;
 		}
 
+		/**
+		 * Render a single option
+		 *
+		 * Override this method to specify how to render each option.
+		 * In a normal selectbox, this would be something like:
+		 *```
+		 * <option value="${option.value}" title="${option.title}" ?selected=${option.value == this.modelValue}>
+		 *     ${option.label}
+		 * </option>`;
+		 * ```
+		 * but you can do whatever you need.  To use a different WebComponent, just use its tag instead of "option".
+		 * We should even be able to pass the whole SelectOption across
+		 * ```
+		 * <special-option .value=${option}></special-option>
+		 * ```
+		 *
+		 * @overridable
+		 * @param {SelectOption} option
+		 * @returns {TemplateResult}
+		 */
 		_optionTemplate(option : SelectOption) : TemplateResult
 		{
-			return html``;
+			return html`
+                <span>Override _optionTemplate(). ${option.value} => ${option.label}</span>`;
 		}
 
 		/**