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Nested Editor<T> crashing because of bug in HtmlFieldPrefix.Combine method #53956

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sal-versij opened this issue Feb 12, 2024 · 3 comments · May be fixed by #58888
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Nested Editor<T> crashing because of bug in HtmlFieldPrefix.Combine method #53956

sal-versij opened this issue Feb 12, 2024 · 3 comments · May be fixed by #58888
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@MackinnonBuck
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area-blazor Includes: Blazor, Razor Components bug This issue describes a behavior which is not expected - a bug.
Milestone
8.0.x

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@sal-versij
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Is there an existing issue for this?

  • I have searched the existing issues

Describe the bug

Nesting more than 2 Editor leads to an exception

Expected Behavior

It should work properly and not throw any exception

Steps To Reproduce

https://github.com/sal-versij/NestedEditorTCrash

Just visit the home

Exceptions (if any)

Unhandled exception rendering component: Object reference not set to an instance of an object.
    System.NullReferenceException: Object reference not set to an instance of an object.
       at Microsoft.AspNetCore.Components.Forms.ExpressionFormatter.FormatLambda(LambdaExpression expression, String prefix)
       at Microsoft.AspNetCore.Components.Forms.HtmlFieldPrefix.GetFieldName(LambdaExpression expression)
       at Microsoft.AspNetCore.Components.Forms.InputBase`1.get_NameAttributeValue()
       at Microsoft.AspNetCore.Components.Forms.InputNumber`1.BuildRenderTree(RenderTreeBuilder builder)
       at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)

.NET Version

8.0.100

Anything else?

After searching why this happens, I've found that in HtmlFieldPrefix.cs:23 the loop is not actually looping through the whole _rest because it uses restLength - 1 instead of length - 1 or restLength itself, thus it's ignoring the last element of _rest that is left as the default value in expressions: null, this is propagated to the inputs inside the innermost editor that, when executing GetFieldName(...) throws because _rest of the input contains a null value passed to ExpressionFormatter.FormatLambda that throws NullReferenceException at ExpressionFormatter.cs:41
@dotnet-issue-labeler dotnet-issue-labeler bot added the area-blazor Includes: Blazor, Razor Components label Feb 12, 2024
@javiercn javiercn added this to the 8.0.x milestone Feb 12, 2024
@mkArtakMSFT mkArtakMSFT added the bug This issue describes a behavior which is not expected - a bug. label Mar 25, 2024
@sal-versij
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Is there any update on the state for a fix of this issue?

@github-project-automation github-project-automation bot moved this to 8.0.x in Servicing Aug 28, 2024
@sgarnovsky
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Got stuck with the same issue.
Feel like it is like a feature (to limit using Editor w/o nesting), but there is no other way to handle it as all related to HtmlFieldPrefix code is internal.

See, a misprint is still here: https://github.com/dotnet/aspnetcore/blame/de68d4212113859604d9e57cf7d674b167a8a317/src/Components/Web/src/Forms/HtmlFieldPrefix.cs#L23

public HtmlFieldPrefix Combine(LambdaExpression other)
    {
        var restLength = _rest?.Length ?? 0;
        var length = restLength + 1;
        var expressions = new LambdaExpression[length];
        //for (var i = 0; i < restLength - 1; i++)
        for (var i = 0; i < **length** - 1; i++)
        {
            expressions[i] = _rest![i];
        }

        expressions[length - 1] = other;

        return new HtmlFieldPrefix(initial, expressions);
    }

A fix should be pretty easy, just use a "length - 1" in a for loop above.

How we can make to speed up applying a fix for this issue?

@sgarnovsky
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sgarnovsky commented Oct 25, 2024 •
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.Net 9 RC still has this bug...
https://github.com/dotnet/aspnetcore/blob/v9.0.0-rc.2.24474.3/src/Components/Web/src/Forms/HtmlFieldPrefix.cs

This is frustrating... So a powerful feature but can't be used fully due to this simple issue.

@sgarnovsky sgarnovsky mentioned this issue Oct 29, 2024
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sgarnovsky added a commit to sgarnovsky/aspnetcore that referenced this issue Nov 12, 2024
@sgarnovsky
Update HtmlFieldPrefix.cs
fe80d94 
This a fix for nested Editor<T> described in this issue: dotnet#53956
@sgarnovsky sgarnovsky linked a pull request Nov 12, 2024 that will close this issue
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@MackinnonBuck MackinnonBuck

Labels
area-blazor Includes: Blazor, Razor Components bug This issue describes a behavior which is not expected - a bug.
Projects
Servicing
Status: 8.0.x
Milestone
8.0.x
5 participants
@javiercn @MackinnonBuck @sgarnovsky @sal-versij @mkArtakMSFT