[Blazor] DisplayName/Label: ExpressionMemberAccessor caches every accessor expression instance (memory leak on Blazor Server) #70031

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

ExpressionMemberAccessor._memberInfoCache is a static ConcurrentDictionary<Expression, MemberInfo>. Expression uses reference equality, and a lambda such as () => Model.Code builds a new expression tree on every evaluation, so every parent render of <DisplayName For="..."> or <Label For="..."> adds a new entry. Each entry keeps the expression alive, and with it the captured closure / component instance and everything it references. On Blazor Server this grows for the lifetime of the process. InputNumber / InputDate hit the same path on every parsing error (#68667).

The _displayNameCache keyed by (MemberInfo, culture) is fine; only the expression-keyed cache is the problem.

Expected Behavior

The cache size is bounded by the number of distinct members, e.g. resolve the MemberInfo from the expression without caching by expression instance.

Steps To Reproduce

net11.0 console app with <FrameworkReference Include="Microsoft.AspNetCore.App" /> (reflection only reads the internal cache size):

using System.Collections;
using System.ComponentModel;
using System.Linq.Expressions;
using System.Reflection;

var type = typeof(Microsoft.AspNetCore.Components.Forms.DisplayName<>).Assembly
    .GetType("Microsoft.AspNetCore.Components.Forms.ExpressionMemberAccessor", true)!;
var get = type.GetMethods(BindingFlags.Public | BindingFlags.Static)
    .First(m => m.Name == "GetDisplayName" && m.IsGenericMethod).MakeGenericMethod(typeof(string));
var cache = (ICollection)type.GetField("_memberInfoCache", BindingFlags.NonPublic | BindingFlags.Static)!.GetValue(null)!;
var page = new Page();
for (var i = 0; i < 1000; i++)
{
    Expression<Func<string>> accessor = () => page.Model.Code; // new instance, like every render
    get.Invoke(null, [accessor]);
}
Console.WriteLine(cache.Count); // prints 1000

class Page { public Model Model { get; } = new(); }
class Model { [DisplayName("Code")] public string Code { get; set; } = ""; }

The same happens with <DisplayName For="@(() => Model.Code)" /> inside a form that re-renders on every field change.

Exceptions (if any)

None.

.NET Version

11.0.100-rc.2.26504.105 (Microsoft.AspNetCore.App 11.0.0-rc.2.26504.105)

Anything else?

src/Components/Web/src/Forms/ExpressionMemberAccessor.cs, same on main.