Allow @bind-value to be specified on its own (#11401)

Author: ajaybhargavb

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -20,6 +20,7 @@ protected void NotifyAuthenticationStateChanged(System.Threading.Tasks.Task<Micr
     [Microsoft.AspNetCore.Components.BindElementAttribute("textarea", null, "value", "onchange")]
     [Microsoft.AspNetCore.Components.BindInputElementAttribute("checkbox", null, "checked", "onchange")]
     [Microsoft.AspNetCore.Components.BindInputElementAttribute("text", null, "value", "onchange")]
+    [Microsoft.AspNetCore.Components.BindInputElementAttribute(null, "value", "value", "onchange")]
     [Microsoft.AspNetCore.Components.BindInputElementAttribute(null, null, "value", "onchange")]
     public static partial class BindAttributes
     {

src/Components/Components/src/BindAttributes.cs

@@ -15,6 +15,10 @@ namespace Microsoft.AspNetCore.Components
     // when a specific type attribute is applied.
     [BindInputElement(null, null, "value", "onchange")]
 
+    // Handles cases like <input @bind-value="..." /> - this is a fallback and will be ignored
+    // when a specific type attribute is applied.
+    [BindInputElement(null, "value", "value", "onchange")]
+
     [BindInputElement("checkbox", null, "checked", "onchange")]
     [BindInputElement("text", null, "value", "onchange")]
 

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

@@ -81,6 +81,30 @@ public void CanBindTextbox_InitiallyPopulated()
             Assert.Equal(string.Empty, mirrorValue.GetAttribute("value"));
         }
 
+        [Fact]
+        public void CanBindTextbox_WithBindSuffixInitiallyPopulated()
+        {
+            var target = Browser.FindElement(By.Id("bind-with-suffix-textbox-initially-populated"));
+            var boundValue = Browser.FindElement(By.Id("bind-with-suffix-textbox-initially-populated-value"));
+            var mirrorValue = Browser.FindElement(By.Id("bind-with-suffix-textbox-initially-populated-mirror"));
+            var setNullButton = Browser.FindElement(By.Id("bind-with-suffix-textbox-initially-populated-setnull"));
+            Assert.Equal("Hello", target.GetAttribute("value"));
+            Assert.Equal("Hello", boundValue.Text);
+            Assert.Equal("Hello", mirrorValue.GetAttribute("value"));
+
+            // Modify target; verify value is updated and that textboxes linked to the same data are updated
+            target.Clear();
+            target.SendKeys("Changed value\t");
+            Browser.Equal("Changed value", () => boundValue.Text);
+            Assert.Equal("Changed value", mirrorValue.GetAttribute("value"));
+
+            // Remove the value altogether
+            setNullButton.Click();
+            Browser.Equal(string.Empty, () => target.GetAttribute("value"));
+            Assert.Equal(string.Empty, boundValue.Text);
+            Assert.Equal(string.Empty, mirrorValue.GetAttribute("value"));
+        }
+
         [Fact]
         public void CanBindTextArea_InitiallyBlank()
         {

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

@@ -15,6 +15,13 @@
     <input id="textbox-initially-populated-mirror" @bind="textboxInitiallyPopulatedValue" readonly />
     <button id="textbox-initially-populated-setnull" @onclick="@(() => { textboxInitiallyPopulatedValue = null; })">Set null</button>
 </p>
+<p>
+    Bind with value-suffix, Initially populated:
+    <input id="bind-with-suffix-textbox-initially-populated" @bind-value="textboxInitiallyPopulatedValue" />
+    <span id="bind-with-suffix-textbox-initially-populated-value">@textboxInitiallyPopulatedValue</span>
+    <input type="text" id="bind-with-suffix-textbox-initially-populated-mirror" @bind-value="textboxInitiallyPopulatedValue" readonly />
+    <button id="bind-with-suffix-textbox-initially-populated-setnull" @onclick="@(() => { textboxInitiallyPopulatedValue = null; })">Set null</button>
+</p>
 
 <h2>Numeric Textboxes</h2>
 <p>