Marshaling string.Empty across the C#<->JS boundary may be broken

[kg]

It seems like at some point recently we may have broken the ability to properly marshal string.Empty across the language boundary. Blazor has some various bits that do things like str ?? string.Empty or str ?? "" and those used to work but no longer do, for some reason they're printing null. If you replace them with $"{str}" that doesn't work either, but $"'{str}'" will produce '' like you would expect. The problem seems to be specific to 0-character strings.

I dug through the related code and tried some various changes but I can't figure out what's broken. At this point I also don't see anything wrong with the C# responsible for it in their implementation, but I may be missing something because it's very weird.

cc @pavelsavara @maraf since we've all been touching some related stuff lately, maybe one of you has ideas?

I can reproduce this locally in a built aspnetcore checkout via: aspnetcore\src\Components\test\E2ETest> dotnet test -c Debug --filter Microsoft.AspNetCore.Components.E2ETest.Tests.RoutingTest.CanArriveAtPageWithOptionalParametersNotProvided

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Issue Details

---

It seems like at some point recently we may have broken the ability to properly marshal string.Empty across the language boundary. Blazor has some various bits that do things like ```str ?? string.Empty``` or ```str ?? ""``` and those used to work but no longer do, for some reason they're printing ```null```. If you replace them with ```$"{str}"``` that doesn't work either, but ```$"'{str}'"``` will produce ```''``` like you would expect. The problem seems to be specific to 0-character strings. I dug through the related code and tried some various changes but I can't figure out what's broken. At this point I also don't see anything wrong with the C# responsible for it in their implementation, but I may be missing something because it's very weird. cc @pavelsavara @maraf since we've all been touching some related stuff lately, maybe one of you has ideas? I can reproduce this locally in a built aspnetcore checkout via: ```aspnetcore\src\Components\test\E2ETest> dotnet test -c Debug --filter Microsoft.AspNetCore.Components.E2ETest.Tests.RoutingTest.CanArriveAtPageWithOptionalParametersNotProvided```

Author:	kg
Assignees:	-
Labels:	`bug`, `arch-wasm`, `blazor-wasm`
Milestone:	-

[kg]

I'll note that copy_root erroneously does

        if (pLengthBytes && pChars) {

instead of

        if (lengthBytes && pChars) {

but that doesn't actually fix it.

[pavelsavara]

@kg could you please describe expected vs actual behavior you observe ?

[kg]

The test fails because a "" becomes "null" instead of "", producing "your age is null." In the test output

On May 8, 2022 12:22:42 AM PDT, Pavel Savara @.> wrote: @. could you please describe expected vs actual behavior you observe ?

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• kg (mobile)

[pavelsavara]

I run into similar issue recently. My root cause was that JavaScript

var a=""
if (!a){
  throw new Error("this could be null, undefined or empty")
}

the proper test is

var a=""
if (a===undefined || a===null){
  throw new Error("this could be null or undefined but not empty")
}

[pavelsavara]

Probably https://github.com/dotnet/runtime/blob/24714ef76bad58d04e014f9a7496035a407ed800/src/mono/wasm/runtime/strings.ts#L62 And https://github.com/dotnet/runtime/blob/24714ef76bad58d04e014f9a7496035a407ed800/src/mono/wasm/runtime/strings.ts#L126

[kg]

Part of the problem was how I was using the string decoder in blazor. Going to open a PR to address our side