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Jan Jones

@janjones.me
82 followers 24 following 21 posts

C# (Roslyn) compiler dev at Microsoft github.com/jjonescz

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Jan Jones @janjones.me · 28/02/2026
Bound trees (internal Roslyn representation of executable code) can now be displayed on .NET Lab. This includes ref safety escape scopes. Makes investigation of compiler bugs easier. #dotnet #csharp #roslyn #dotnetlab
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Jan Jones @janjones.me · 22/12/2025
.NET Lab can now display disassembled machine code. It's taken directly from JIT, hence only supported on desktop for now. #dotnet #csharp #roslyn #asm #dotnetlab
Screenshot of .NET Lab with disassembled machine code
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Jan Jones @janjones.me · 17/12/2025
Tired of waiting for the WebAssembly version of .NET Lab to load? There is now .NET Lab Desktop for Windows which is much faster thanks to running on full .NET: apps.microsoft.com/detail/9PCPM... ⚡
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Reposted by Jan Jones
nohwnd @jakubjares.com · 08/12/2025
Getting ready for our last .NET meetup Prague of the year. This time with a holiday vibe! #dotnet aka.ms/DotnetMeetup...
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Jan Jones @janjones.me · 14/11/2025
Great feature I've got a chance to work on in .NET 10
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Jan Jones @janjones.me · 05/10/2025
Fully revamped the tree view 🌳 in .NET Lab. Now with cursor syncing. Can display syntax, IOperation, and symbol info. #dotnet #csharp #roslyn #dotnetlab
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Reposted by Jan Jones
Damian Edwards @damianedwards.com · 11/09/2025
Big improvements to the performance of developing C# file-based incoming. Subsequent builds/runs will cache MSBuild outputs & directly invoke the C# compiler if inputs don't change. This in addition to the work in rc.1 to avoid MSBuild completely for simple file-based apps github.com/dotnet/sdk/p...
github.com
Reuse CSC arguments in file-based app runs by jjonescz · Pull Request #50635 · dotnet/sdk
Part of #48011. This optimization saves CSC arguments when MSBuild runs and then reuses them in subsequent runs so dotnet run file.cs can skip MSBuild and invoke only the compiler. In my simple exp...
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Jan Jones @janjones.me · 06/09/2025
Added a small but useful feature to copy the current URL in .NET Lab (lab.razor.fyi). It has a keyboard shortcut too: Ctrl+; 📋 #dotnet #csharp #roslyn #dotnetlab
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Jan Jones @janjones.me · 26/07/2025
.NET Lab (lab.razor.fyi) just gained new configuration options inspired by `dotnet run app.cs`. Reference any NuGet packages via `#:package` or quickly change config via `#:property` (with editor suggestions to guide you). 🚀⚙️
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Reposted by Jan Jones
Damian Edwards @damianedwards.com · 15/07/2025
Check out all the improvements to file-based apps (dotnet run app.cs) in preview.6 that went out today! github.com/dotnet/core/...
github.com
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Reposted by Jan Jones
Andrew Lock "Sock" @andrewlock.bsky.social · 08/07/2025
Blogged: Behind the scenes of dotnet run app.cs - Exploring the .NET 10 preview - Part 2 andrewlock.net/exploring-do... In this post I looks at how the new single-file .NET run experience is implemented inside the .NET SDK, focusing on how the virtual-project file is built. #dotnet #csharp
andrewlock.net
Behind the scenes of dotnet run app.cs: Exploring the .NET 10 preview - Part 2
In this post I looks at how the new single-file .NET run experience is implemented inside the .NET SDK, focusing on how the virtual-project file is built
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Jan Jones @janjones.me · 28/06/2025
.NET Lab (lab.razor.fyi) now has Code Actions 🚀 Very useful when you paste some code snippet and want to add missing usings. But it can do much more - all Roslyn code fixes are included.
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Jan Jones @janjones.me · 22/06/2025
Added semantic highlighting to .NET Lab (lab.razor.fyi)
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Reposted by Jan Jones
Mattias Karlsson @devlead.se · 14/06/2025
And soon just dotnet app.cs 😎 github.com/dotnet/sdk/p...
github.com
Add support for `dotnet file.cs` (without explicit `run` subcommand) by jjonescz · Pull Request #48387 · dotnet/sdk
Resolves #49202.
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Jan Jones @janjones.me · 16/05/2025
Completions and live diagnostics are now much improved and enabled by default in .NET Lab (lab.razor.fyi). Stay tuned for more enhancements to the editing experience coming soon.
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Jan Jones @janjones.me · 02/03/2025
Shared lab.razor.fyi snippets are now cached, so you can see the output even before the compiler is initialized. (Nevertheless, more optimizations of loading times are coming.) Example: lab.razor.fyi#47Lm4gooyk8v...
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Jan Jones @janjones.me · 21/02/2025
Added this cool loading animation to lab.razor.fyi. Suddenly the loading feels faster ⚡
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Jan Jones @janjones.me · 20/12/2024
Updated lab.razor.fyi to use Microsoft Fluent UI. Quite happy with the result. Also got dark mode for free.
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