Orphaned expression breaks the application

[YordanYanakiev]

Describe the bug

If inside a Blazor HTML expression there is orphaned symbol or expression it will break the application in result without any kind of error or warning in Visual Studio "Error list"

To Reproduce

for instance :
<img id="@((@context as TreeProxyDataModel).id)" class="eimage" src="/f.png" @onclick="@((e) =>MemberFunction((@context as TreeProxyDataModel).id, e))" />

add ")", "." or anything in a random position

<img id="@((@context as TreeProxyDataModel).id)" class="eimage" src="/f.png" ) @onclick="@((e) =>MemberFunction((@context as TreeProxyDataModel).id, e))" />

• No exception, error or warning will be resulted.

Further technical details

• ASP.NET Core version : 3.1
• Include the output of dotnet --info

.NET Core SDK (reflecting any global.json):
Version: 3.1.100
Commit: cd82f021f4

Runtime Environment:
OS Name: Windows
OS Version: 6.3.9600
OS Platform: Windows
RID: win81-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.100\

Host (useful for support):
Version: 3.1.0
Commit: 65f04fb6db

.NET Core SDKs installed:
2.0.2 [C:\Program Files\dotnet\sdk]
2.1.700 [C:\Program Files\dotnet\sdk]
2.1.801 [C:\Program Files\dotnet\sdk]
2.1.802 [C:\Program Files\dotnet\sdk]
3.0.100 [C:\Program Files\dotnet\sdk]
3.1.100-preview2-014569 [C:\Program Files\dotnet\sdk]
3.1.100 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0-preview2.19528.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0-preview2.19525.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.0-preview2.19525.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version
  Visual Studio 2019 Preview 16.5.0 preview 1.0

[javiercn]

@YordanYanakiev thanks for contacting us.

@NTaylorMullen is this a compiler issue? It's definitely invalid HTML, but other than that, I'm not sure if we should intervene here (other than making sure we don't produce incorrect code for this case).

[YordanYanakiev]

Hello @javiercn
The example You have posted is about pure HTML which is not the case.
Put any random symbol in Blazor HTML component expression, not clean HTML code.
<SurveyPrompt Title="How is Blazor working for you?" ) />
for instance in the basic template.
I've prepared such example for You to be easier to investigate.
OprhanedExpression.zip

• Inside index.razor is the issue inside the example above.

[mkArtakMSFT]

Thanks for the details, @YordanYanakiev.
Given this is a user-error scenario, we'll look into addressing this during 5.0 timeline, as we're currently focused on the upcoming Blazor WASM release, which is in May.

[SteveSandersonMS]

I checked, and the error message coming back on the JS side is pretty clear:

WASM: Microsoft.JSInterop.JSException: Failed to execute 'setAttribute' on 'Element': ')' is not a valid attribute name.

This is behaving as expected for this malformed HTML.

[SteveSandersonMS]

<SurveyPrompt Title="How is Blazor working for you?" ) />

That's also an error (a different one), because this is trying to supply a component parameter called (, and no such parameter is defined.