Add Support for Roslyn LSP (Csharp Language Server) by Digni · Pull Request #11 · zed-extensions/csharp

Digni · 2025-05-26T13:36:58Z

This adds support for the (newer) Roslyn LSP from Microsoft (Microsoft.CodeAnalysis.LanguageServer).

The current Implementation is using a wrapper provided by: https://github.com/SofusA/csharp-language-server.
This is because the Roslyn LSP expects one of the following notifications after "initialize":

{
  "method": "solution/open",
  "params": {
    "solution" : "filepathUri_to_solution" (.sln, .slnx)
  }
}

{
  "method": "project/open",
  "params": {
    "projects" : [ "filePathUri_to_Project" ,  ....] (list of .csproj files)
  }
}

The csharp-language-server reacts on the initialize notification to get the working directory and then scans it for solution and project files.
If it finds a solution file it picks the first one it finds, this could lead to some unintended reference issues if there are more than one solution file in the working directory.
The VsCode Extension handles this by asking the user which solution should be opened.

I would like to implement something similar and run the roslyn lsp directly (dotnet Microsoft.CodeAnalysis.LanguageServer.dll).
But for that to work I need to be able to send these notifications to the lsp server (and if possible ask the user which solution he wants to open) and I currently don't know how this would be possible with the extension api.

Maybe someone could help me with that.

Update

Added Workspace Configuration Options for Roslyn lsp.
Server expects the following format:

{language}|{grouping}.name for language specific options or {grouping}.{name} for general options.

Example

"csharp|inlay_hints.csharp_enable_inlay_hints_for_implicit_object_creation": true,
"csharp|inlay_hints.csharp_enable_inlay_hints_for_implicit_variable_types": true,

In the settings json I made it nested:

  "lsp": {
    "roslyn": {
      "settings": {
        "csharp|inlay_hints": {
          "csharp_enable_inlay_hints_for_implicit_object_creation": true,
          "csharp_enable_inlay_hints_for_implicit_variable_types": true,
          "csharp_enable_inlay_hints_for_lambda_parameter_types": true,
          "csharp_enable_inlay_hints_for_types": true,
          "dotnet_enable_inlay_hints_for_indexer_parameters": true,
          "dotnet_enable_inlay_hints_for_literal_parameters": true,
          "dotnet_enable_inlay_hints_for_object_creation_parameters": true,
          "dotnet_enable_inlay_hints_for_other_parameters": true,
          "dotnet_enable_inlay_hints_for_parameters": true,
          "dotnet_suppress_inlay_hints_for_parameters_that_differ_only_by_suffix": true,
          "dotnet_suppress_inlay_hints_for_parameters_that_match_argument_name": true,
          "dotnet_suppress_inlay_hints_for_parameters_that_match_method_intent": true
        }
      }
    }
  }

This will get translated to the valid format described above.
Which leads to something like this (configured inlay_hints):

Fixes #1
Fixes #7
Fixes #8
Fixes #9
Fixes #10
Fixes #13
Fixes #14
Fixes #20
Fixes #29
Fixes zed-industries/zed#8352
Fixes zed-industries/zed#11104
Fixes zed-industries/zed#22002
Fixes zed-industries/zed#31014
Fixes zed-industries/zed#33135

Vlaaaaaaad · 2025-05-27T00:13:13Z

CC @fminkowski, @dibarbet, @CyrusNajmabadi, and @maxbrunsfeld since they were involved in the initial implementation of the Zed C# extension and thus might or might not have thoughts

Digni · 2025-05-29T12:05:36Z

Seems like I made that PR to early... I did try Completion, Code Action etc.
But I missed a really crucial part.
The diagnostics are not working, even with that hack of @SofusA. (Force Diagnostics Pull)
I did try the hack that is used in nvim:

    capabilities = {
        textDocument = {
            -- HACK: Doesn't show any diagnostics if we do not set this to true
            diagnostic = {
                dynamicRegistration = true,
            },
        },
    },

Via intercepting the notification and adding it, but that did not work.

So I think here we need the support from the Zed Team.

SofusA · 2025-05-29T14:14:31Z

I also get no diagnostics. A simple way to reproduce is overriding the path for omnisharp:

"lsp": {
    "omnisharp": {
      "binary": {
        "path": "csharp-language-server"
      }
    }
  }

Do you know if zed supports pull diagnostics?

Digni · 2025-05-29T17:45:43Z

I do not, but my guess at the moment seems no.

Just tried dotrush to see if the diagnostics are working with that, but its the same. No Diagnostics

SofusA · 2025-05-30T05:39:23Z

ruby configuration states that pull diagnostics are not supported, under setting up ruby-lsp

Digni · 2025-05-30T07:17:35Z

You are right, here is the issue tracking that: zed-industries/zed#13107
Roslyn switched to only pull diagnostics some time ago, so it seems we need to wait on that for working rolyn support.

SofusA · 2025-06-03T16:14:26Z

Thanks to @MoaidHathot for pointing this out. It looks like utilizing csharp-language-server outside of Visual Studio Code goes against the Dev Kit license making this usage illegal in Zed.

The tool only utilises code from Roslyn which is licensed under MIT Licence. It does do use anything from C# DevKit.

C# DevKit utilises the same underlying language server from Roslyn, Microsoft.CodeAnalysis.LanguageServer, but csharp-language-server has nothing to do with C# DevKit.

Digni · 2025-06-03T16:16:43Z

@SofusA was quicker to respond. And that is true, the server uses the Microsoft.CodeAnalysis.LanguageServer. This can be found here: https://github.com/dotnet/roslyn.
And that is MIT License, so no DevKit is used.

Co-authored-by: Dylan Hackworth <drhackworth@pm.me>

dylhack · 2025-06-03T16:35:39Z

Ah okay looks like a misinterpretation of csharp-language-server and the DevKit license. Love it so far! Great work.

Digni · 2025-06-03T17:32:24Z

Well they are though:
https://dev.azure.com/azure-public/vside/_artifacts/feed/vs-impl/NuGet/Microsoft.CodeAnalysis.LanguageServer.osx-arm64/overview/5.0.0-1.25302.10
https://dev.azure.com/azure-public/vside/_artifacts/feed/vs-impl/NuGet/Microsoft.CodeAnalysis.LanguageServer.linux-x64/overview/5.0.0-1.25302.10
https://dev.azure.com/azure-public/vside/_artifacts/feed/vs-impl/NuGet/Microsoft.CodeAnalysis.LanguageServer.win-x64/overview/5.0.0-1.25302.10

They are all MIT Licensed, as can be seen in the nuget Feed.

julionav · 2025-06-03T19:13:50Z

@Digni any chance that this can be run alongside omnisharp? to have the diagnostics. Right now the omnisharp ls doesn't work when decompiling sources (go to definition)

Digni · 2025-06-03T19:29:42Z

@Digni any chance that this can be run alongside omnisharp? to have the diagnostics. Right now the omnisharp ls doesn't work when decompiling sources (go to definition)

Yeah, Zed supports running several lsp's for one language.
https://zed.dev/docs/configuring-languages

  "languages": {
    "CSharp": {
      "language_servers": ["roslyn", "omnisharp", "..."]
    }
  }

But as written in the ruby extension (https://zed.dev/docs/languages/ruby) they would provide similar functionality. So we probably need to turn off autocompletion, code-actions from omnisharp.

https://github.com/OmniSharp/omnisharp-roslyn/wiki/Configuration-Options

I did not look into that yet.

AleksaBajat · 2025-06-11T22:47:12Z

@SofusA @Digni It seems that Zed closed this PR. Let me know if I can help out in pursuing this LSP.

Digni · 2025-06-12T06:03:07Z

I just did a quick check on Zed Preview and diagnostics seems to be working now.

julionav · 2025-06-13T10:51:02Z

@Digni i tried this but I couldn't make the go to definition with decompiling work. Do you know if that should work? E.g go to the definition of a installed package

SofusA · 2025-06-19T13:37:03Z

@Digni i tried this but I couldn't make the go to definition with decompiling work. Do you know if that should work? E.g go to the definition of a installed package

I get working decompiling using the the config mentioned in my previous comment.

fallenwood · 2025-10-18T04:25:55Z

I am able to make diagnostic work on my fork(?) with an workaround, to enrich the textDocument/diagnostic request in the wrapper with range

moheladwy · 2025-10-30T22:28:19Z

any updates on this PR?

reflectronic · 2025-10-30T22:32:37Z

I am planning on tackling the Zed bugs that are blocking this PR next week

reflectronic · 2025-11-11T13:20:59Z

We have a patch that fixes the diagnostics: zed-industries/zed@main...pull-diagnostics-registrations

It requires some cleanup before we merge it, but it's working reliably:

vavans · 2025-11-15T08:08:14Z

So close guys... I have like 10 friends of mine waiting for this PR to be merged to drop the lagy vscode for .net core dev ! 🥳

reflectronic · 2025-11-24T19:08:32Z

Roslyn issues with LSP specification conformance have been resolved: dotnet/roslyn#81174

I will try to get the Zed fixes merged this week.

reflectronic

zed-industries/zed#43703 has fixed the issue with diagnostics in Zed. As such, I think this PR is good to go.

v0.217 (the preview that'll be released on Wednesday) will be the first version with these fixes. We'll change the default settings in Zed so that versions without the fix will use OmniSharp and versions with the fix will use Roslyn.

Additionally, a new release of csharp-language-server which has the latest Roslyn fixes will need to be released before we can publish a new version of the extension.

SofusA · 2025-12-09T11:09:13Z

zed-industries/zed#43703 has fixed the issue with diagnostics in Zed. As such, I think this PR is good to go.

v0.217 (the preview that'll be released on Wednesday) will be the first version with these fixes. We'll change the default settings in Zed so that versions without the fix will use OmniSharp and versions with the fix will use Roslyn.

Additionally, a new release of csharp-language-server which has the latest Roslyn fixes will need to be released before we can publish a new version of the extension.

Great work!
How would you prefer updates to and releases of sofusa/csharp-language-server?

Currently I update and do manual tests every months before releasing. Simple automatic tests is on the way.

I have considered that the server version should be a cli argument or to follow the version of the vscode extension.

I personally don’t have any preferences, I am happy to follow requests. Only that we can share as much as possible between editors (mainly helix and zed).

In preparation for zed-extensions/csharp#11. Do not merge before that PR is published. Release Notes: - Added support for Roslyn in C# files. Roslyn will now be the default language server for C#

reflectronic · 2025-12-16T16:53:29Z

We found an issue with the Zed fixes that were causing stale diagnostics with other language servers. We had to revert the patch, so the stable release for v0.217 won't support Roslyn. v0.218 will support Roslyn. Sorry for any inconvenience

In preparation for zed-extensions/csharp#11. Do not merge before that PR is published. Release Notes: - Added support for Roslyn in C# files. Roslyn will now be the default language server for C#

Adds [csharp-ls](https://github.com/razzmatazz/csharp-language-server) as a third language server option alongside OmniSharp and Roslyn. csharp-ls is an F#-based C# language server distributed as a `dotnet tool` NuGet package; it is unrelated to the deprecated `SofusA/csharp-language-server` wrapper referenced by [#11](#11) and [#57](#57). The naming overlap is unfortunate: the upstream project markets itself as `csharp-ls` precisely to reduce that confusion. The use case is different from Roslyn. csharp-ls is a leaner alternative: cold start is faster, memory footprint is lower, and it stays responsive on small projects or quick edits where spinning up a full Roslyn workspace is overkill. Roslyn remains the right choice for the deepest Microsoft tooling; csharp-ls is for the case when you want something snappy. To use it: ```json { "languages": { "CSharp": { "language_servers": ["csharp-ls", "!omnisharp", "!roslyn"] } } } ``` It partially addresses #62, it is running better on my own M3 mac for smaller projects. --------- Co-authored-by: MrSubidubi <dev@bahn.sh> Co-authored-by: Finn Evers <finn@zed.dev>

In preparation for zed-extensions/csharp#11. Do not merge before that PR is published. Release Notes: - Added support for Roslyn in C# files. Roslyn will now be the default language server for C#

Digni added 3 commits May 25, 2025 14:03

refactor: move omnisharp to language servers

a52140c

add roslyn language server via binary config

8ff3168

feat: add download for language server

8affb73

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chore: removing comment

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cla-bot Bot added the cla-signed label May 26, 2025

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Digni mentioned this pull request May 26, 2025

[Feature] Support Roslyn LSP #10

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feat: add implementation for workspace configuration options for roslyn

ed8aca7

dylhack suggested changes Jun 3, 2025

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Comment thread src/language_servers/roslyn.rs Outdated

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Update src/language_servers/roslyn.rs

f346ea1

Co-authored-by: Dylan Hackworth <drhackworth@pm.me>

reflectronic mentioned this pull request Sep 22, 2025

Downloaded C# OmniSharp language server does not start zed-industries/zed#8352

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1 task done

MrSubidubi assigned reflectronic Sep 29, 2025

AdeAttwood mentioned this pull request Oct 2, 2025

[Feature] Support csharp-ls #22

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AdamWawrzynkowskiGF mentioned this pull request Oct 20, 2025

Diagnostics not working in Zed marcptrs/csharp_roslyn#2

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S222em mentioned this pull request Nov 6, 2025

Csharp omnisharp code actions stop working (Error snapshot not found for buffer) zed-industries/zed#31014

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vavans mentioned this pull request Nov 15, 2025

Something is lacked in your zed extension. #29

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reflectronic added 2 commits December 6, 2025 11:36

Merge branch 'main' into Digni/main

3eb5fd3

Fix configuration when custom LSP binary is used

098364f

MrSubidubi mentioned this pull request Dec 8, 2025

Disable OmniSharp by default for C# files zed-industries/zed#44427

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Add default settings for inlay hints and code lenses

d02d35a

reflectronic approved these changes Dec 8, 2025

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reflectronic merged commit a39a06b into zed-extensions:main Dec 10, 2025
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rbstp mentioned this pull request May 5, 2026

Add csharp-ls as a new option #77

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rbstp mentioned this pull request May 23, 2026

Add csharp-ls language server zed-industries/extensions#6205

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