Apply selection to options even within markup block or optgroup. Fixes #5616 #10648

src/Components/Browser.JS/src/Rendering/BrowserRenderer.ts

@@ -238,6 +238,17 @@ export class BrowserRenderer {
         break;
       }
     }
+
+    // We handle setting 'value' on a <select> in two different ways:
+    // [1] When inserting a corresponding <option>, in case you're dynamically adding options
+    // [2] After we finish inserting the <select>, in case the descendant options are being
+    //     added as an opaque markup block rather than individually
+    // Right here we implement [2]
+    if (newDomElementRaw instanceof HTMLSelectElement && selectValuePropname in newDomElementRaw) {
+      const selectValue = newDomElementRaw[selectValuePropname];
+      newDomElementRaw.value = selectValue;
+      delete newDomElementRaw[selectValuePropname];
+    }
   }
 
   private insertComponent(batch: RenderBatch, parent: LogicalElement, childIndex: number, frame: RenderTreeFrame) {
@@ -317,7 +328,8 @@ export class BrowserRenderer {
           // <select> is special, in that anything we write to .value will be lost if there
           // isn't yet a matching <option>. To maintain the expected behavior no matter the
           // element insertion/update order, preserve the desired value separately so
-          // we can recover it when inserting any matching <option>.
+          // we can recover it when inserting any matching <option> or after inserting an
+          // entire markup block of descendants.
           element[selectValuePropname] = value;
         }
         return true;
@@ -330,10 +342,11 @@ export class BrowserRenderer {
           element.removeAttribute('value');
         }
         // See above for why we have this special handling for <select>/<option>
-        const parentElement = element.parentElement;
-        if (parentElement && (selectValuePropname in parentElement) && parentElement[selectValuePropname] === value) {
-          this.tryApplyValueProperty(batch, parentElement, attributeFrame);
-          delete parentElement[selectValuePropname];
+        // Note that this is only one of the two cases where we set the value on a <select>
+        const selectElem = this.findClosestAncestorSelectElement(element);
+        if (selectElem && (selectValuePropname in selectElem) && selectElem[selectValuePropname] === value) {
+          this.tryApplyValueProperty(batch, selectElem, attributeFrame);
+          delete selectElem[selectValuePropname];
         }
         return true;
       }
@@ -353,6 +366,18 @@ export class BrowserRenderer {
     }
   }
 
+  private findClosestAncestorSelectElement(element: Element | null) {
+    while (element) {
+      if (element instanceof HTMLSelectElement) {
+        return element;
+      } else {
+        element = element.parentElement;
+      }
+    }
+
+    return null;
+  }
+
   private insertFrameRange(batch: RenderBatch, componentId: number, parent: LogicalElement, childIndex: number, frames: ArrayValues<RenderTreeFrame>, startIndex: number, endIndexExcl: number): number {
     const origChildIndex = childIndex;
     for (let index = startIndex; index < endIndexExcl; index++) {

src/Components/test/E2ETest/Tests/BindTest.cs

@@ -214,6 +214,19 @@ namespace Microsoft.AspNetCore.Components.E2ETest.Tests
             Assert.Equal("Fourth choice", target.SelectedOption.Text);
         }
 
+        [Fact]
+        public void CanBindSelectToMarkup()
+        {
+            var target = new SelectElement(Browser.FindElement(By.Id("select-markup-box")));
+            var boundValue = Browser.FindElement(By.Id("select-markup-box-value"));
+            Assert.Equal("Second choice", target.SelectedOption.Text);
+            Assert.Equal("Second", boundValue.Text);
+
+            // Modify target; verify value is updated
+            target.SelectByText("Third choice");
+            Browser.Equal("Third", () => boundValue.Text);
+        }
+
         [Fact]
         public void CanBindTextboxInt()
         {

src/Components/test/testassets/BasicTestApp/BindCasesComponent.razor

@@ -145,18 +145,32 @@
 <h2>Select</h2>
 <p>
     <select id="select-box" @bind="selectValue">
-        <option value=@SelectableValue.First>First choice</option>
-        <option value=@SelectableValue.Second>Second choice</option>
-        <option value=@SelectableValue.Third>Third choice</option>
-        @if (includeFourthOption)
-        {
-            <option value=@SelectableValue.Fourth>Fourth choice</option>
-        }
+        <optgroup label="Some choices"> <!-- Show it also works with optgroup -->
+            <option value=@SelectableValue.First>First choice</option>
+            <option value=@SelectableValue.Second>Second choice</option>
+            <option value=@SelectableValue.Third>Third choice</option>
+            @if (includeFourthOption)
+            {
+                <option value=@SelectableValue.Fourth>Fourth choice</option>
+            }
+        </optgroup>
     </select>
     <span id="select-box-value">@selectValue</span>
     <button id="select-box-add-option" @onclick="AddAndSelectNewSelectOption">Add and select new item</button>
 </p>
 
+<h2>Select (markup block)</h2>
+<p>
+    <select id="select-markup-box" @bind="selectMarkupValue">
+        <optgroup label="Some choices">
+            <option value="First">First choice</option>
+            <option value="Second">Second choice</option>
+            <option value="Third">Third choice</option>
+        </optgroup>
+    </select>
+    <span id="select-markup-box-value">@selectMarkupValue</span>
+</p>
+
 @code {
 string textboxInitiallyBlankValue = null;
 string textboxInitiallyPopulatedValue = "Hello";
@@ -187,6 +201,7 @@ Guid textboxGenericGuidValue = Guid.Empty;
 bool includeFourthOption = false;
 enum SelectableValue { First, Second, Third, Fourth }
 SelectableValue selectValue = SelectableValue.Second;
+SelectableValue selectMarkupValue = SelectableValue.Second;
 
 void AddAndSelectNewSelectOption()
 {