Support indexer use in InputBase

Is your feature request related to a problem? Please describe the problem.

I’m looking to create a group of InputCheckbox components, and have all of their values stored in Dictionary<object, bool> where the value indicates if the checkbox is checked or not. Logically I tried something like:

@foreach(var kvp in dict) {
  <InputCheckbox @bind-Value="dict[kvp.Key]"></InputCheckbox>
}

This doesn’t work though, as the indexer on Dictionary<> is actually an InstanceMethodCallExpression1, and thus runs afoul of FieldIdentifier’s “MemberExpressions only rule”, throwing The provided expression contains a InstanceMethodCallExpression1 which is not supported. FieldIdentifier only supports simple member accessors (fields, properties) of an object.

https://github.com/dotnet/aspnetcore/blob/dc98f4b9580fde664c6ae88f9712467ff8e96bc4/src/Components/Forms/src/FieldIdentifier.cs#L103-L106

Creating a wrapper around my dictionary boolean does solve the problem, however, as the expression is once more a member access:

class BooleanWrapper {
  public bool Value { get; set; }
}

//...

Dictionary<object, BooleanWrapper> dict = new();

@foreach(var kvp in dict) {
  <InputCheckbox @bind-Value="dict[kvp.Key].Value"></InputCheckbox>
}

Describe the solution you’d like

It doesn’t seem like it’d be too difficult to get FieldIdentifier to support simple index access by adding some additional logic to ParseAccessor that follows calls to get_Item on arrays or dictionaries. I’d be happy to write the PR for it myself if there was any interest in such a thing.

[oiBio]

you BoolWrapper class works, you just need to but the object in a inline variable first. Like this

    @foreach (var kvp in dict)
    {
        var obj = dict[kvp.Key];
        <InputCheckbox @bind-Value="obj.Value"></InputCheckbox>
    }

[javiercn]

Done as part of https://github.com/dotnet/aspnetcore/pull/48990