Completing C# await keyword in non-async methods results in the wrong cursor location being used due to formatting.

[NTaylorMullen]

Describe the bug:
Completing the await keyword in non-async methods results in Razor generating an incompatible edit that moves the cursor location.

Version used:
17.2-Preview1+

To reproduce:

1. Open a Razor file with the following text and cursor at the pipe (|):

@code {
    private void Foo()
    {
        aw|
    }
}

2. Manually invoke completion (ctrl + space) and select await

Expected Behavior:
Cursor is after await

Actual Behavior:

Additional Notes:

I dug into why this was happening and C# is depending on completionItem/resolve to fill out the text edit for that completion item. Only problem is the TextEdit C# returns is valid but Razor transforms it into something invalid.

Original C# completion item text edit (from C# server):

"textEdit": {
    "range": {
        "start": {
        "line": 97,
        "character": 12
        },
        "end": {
        "line": 99,
        "character": 10
        }
    },
    "newText": "async void Foo()\r\n    {\r\n        await"
},

After Razor formats the edit (from our HTMLC# server):

"textEdit": {
    "range": {
        "start": {
        "line": 0,
        "character": 7
        },
        "end": {
        "line": 4,
        "character": 4
        }
    },
    "newText": "\r\n    private async void Foo()\r\n    {\r\n        await\r\n    "
},

Note the extra newline and spaces after await.

One extra piece I found interesting is that C#'s completion item says it's a snippet but doesn't actually provide any tab-stops. Technically this is valid in the LSP specification but felt weird (fyi @dibarbet).

[DoctorKrolic]

Just interesting: how did you get what LSP sends to the client (and vice versa if it is possible)? I've tried once, but it was buried somewhere too deeply, so I didn't find out how to get the raw text of requests and responses in the end...

[NTaylorMullen]

Just interesting: how did you get what LSP sends to the client (and vice versa if it is possible)? I've tried once, but it was buried somewhere too deeply, so I didn't find out how to get the raw text of requests and responses in the end...

If you boot devenv.exe with the /log parameter you can see all of the requests / responses & their content in %localappdata%\Temp\VisualStudio\LSP

[davidwengier]

Are we using GetMinimalChanges in this formatting path? If so, are we setting lineDiffOnly to false? Could try that?

[allisonchou]

@dibarbet would you mind validating whether this is fixed by your recent changes?

[dibarbet]

it is not - it needs this fix - dotnet/roslyn#60499 (+ razor side fix for formatting which I have locally) as well as a fix for dotnet/roslyn#60598

[NTaylorMullen]

Fixed via: #6626

[DoctorKrolic]

Will this fix work in 17.4 p1 by default, or some settings will be requred to be changed? I've seen some tweaks around new single-server completion (whatever this means) and as far as I know it won't be enabled for all clients by default. If I'll need to change this setting, can you please tell where to find it, thanks!

[NTaylorMullen]

Will work by default. I pushed single server completion on-by-default in 17.4. I still have all the feature flags around in case we see something catastrophic happen I can remotely disable it for the world 😄