Fix IdAttributeValue generation in interactive mode

src/Components/Web/src/Forms/InputBase.cs

@@ -207,13 +207,7 @@ protected string NameAttributeValue
 
             if (_shouldGenerateFieldNames)
             {
-                if (_formattedValueExpression is null && ValueExpression is not null)
-                {
-                    _formattedValueExpression = FieldPrefix != null ? FieldPrefix.GetFieldName(ValueExpression) :
-                        ExpressionFormatter.FormatLambda(ValueExpression);
-                }
-
-                return _formattedValueExpression ?? string.Empty;
+                return GetFieldName();
             }
 
             return string.Empty;
@@ -225,7 +219,7 @@ protected string NameAttributeValue
     /// </summary>
     /// <remarks>
     /// If an explicit "id" is provided via <see cref="AdditionalAttributes"/>, that value takes precedence.
-    /// Otherwise, the id is derived from <see cref="NameAttributeValue"/> with invalid characters sanitized.
+    /// Otherwise, the id is a sanitized version of <see cref="NameAttributeValue"/> in SSR mode; generated independently in interactive mode.
     /// </remarks>
     protected string IdAttributeValue
     {
@@ -236,10 +230,20 @@ protected string IdAttributeValue
                 return Convert.ToString(idAttributeValue, CultureInfo.InvariantCulture) ?? string.Empty;
             }
 
-            return FieldIdGenerator.SanitizeHtmlId(NameAttributeValue);
+            var fieldName = NameAttributeValue;
+            if (string.IsNullOrEmpty(fieldName))
+            {
+                fieldName = GetFieldName();
+            }
+
+            return FieldIdGenerator.SanitizeHtmlId(fieldName);
         }
     }
 
+    private string GetFieldName()
+        => _formattedValueExpression ??= FieldPrefix?.GetFieldName(ValueExpression!)
+            ?? ExpressionFormatter.FormatLambda(ValueExpression!);
+
     /// <inheritdoc />
     public override Task SetParametersAsync(ParameterView parameters)
     {

src/Components/Web/test/Forms/InputTextTest.cs

@@ -63,6 +63,26 @@ public async Task ExplicitIdOverridesGenerated()
         Assert.Equal("custom-id", idAttribute.AttributeValue);
     }
 
+    [Fact]
+    public async Task RendersIdAttribute_WhenShouldUseFieldIdentifiersIsFalse_InteractiveMode()
+    {
+        // simulate interactive mode where ShouldUseFieldIdentifiers is false
+        var model = new TestModel();
+        var editContext = new EditContext(model) { ShouldUseFieldIdentifiers = false };
+        var rootComponent = new TestInputHostComponent<string, InputText>
+        {
+            EditContext = editContext,
+            ValueExpression = () => model.StringProperty,
+        };
+
+        var componentId = await RenderAndGetInputTextComponentIdAsync(rootComponent);
+        var frames = _testRenderer.GetCurrentRenderTreeFrames(componentId);
+
+        // id should still be generated for Label/Input association to work in interactive mode
+        var idAttribute = frames.Array.Single(f => f.FrameType == RenderTreeFrameType.Attribute && f.AttributeName == "id");
+        Assert.Equal("model_StringProperty", idAttribute.AttributeValue);
+    }
+
     private async Task<int> RenderAndGetInputTextComponentIdAsync(TestInputHostComponent<string, InputText> hostComponent)
     {
         var hostComponentId = _testRenderer.AssignRootComponentId(hostComponent);