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Siegfried Pammer
8ab3f93f5e
A dynamic call site that names a type passes typeof(T) as its target. When a later argument contains control flow, the compiler stores that typeof in a temporary. ILInlining does not undo this: it inlines a store only into the immediately following instruction, so an intervening statement leaves the typeof behind, and the expression builder printed the temporary instead of the type. Substituting the typeof back into the target slot is not an option either, because a call there has side effects and blocks inlining of the remaining arguments. The type is therefore stored on the instruction. Object creation already did this, but kept the field private, so the expression builder re-derived the type from the target argument and failed on the spilled form. Member invocation gets the same field. Both drop the target from Arguments, so the dead-argument handling removes the store; ArgumentInfo keeps its entry for the target, because the invocation symbol is built from it. The type of an object creation is not nullable: the transform returns before constructing the instruction when it cannot match the typeof, and substitutes the unknown type otherwise. An unresolvable type therefore reaches the expression builder as the unresolved type it is, and prints as `?` like any other, rather than being indistinguishable from a missing one. Those two are also the only binder method kinds that ever see CSharpArgumentInfoFlags.IsStaticType. Every other way of naming a type as the receiver binds statically and leaves only a conversion of the dynamic operand behind. Assisted-by: Claude:claude-opus-5[1m]:Claude Code
ILSpy 
ILSpy is the open-source, cross-platform .NET assembly browser and decompiler. The desktop UI runs on Windows, Linux, and macOS (built on Avalonia).
Download: latest release | latest CI build (master) | Microsoft Store (RTM versions only)
Decompiler Frontends
Aside from the cross-platform desktop UI ILSpy (downloadable via Releases, see also plugins), the following other frontends are available:
- Visual Studio 2022/2026 ship with decompilation support for F12 enabled by default (using our engines v8.2 and v9.1 respectively).
- Our Visual Studio 2022 extension marketplace (works with VS 2026 as well)
- Our Visual Studio Code Extension repository | marketplace | open-vsx
- Our dotnet tool for Linux/Mac/Windows - check out ILSpyCmd in this repository | dotnet tool install
- C# for Visual Studio Code ships with decompilation support as well. To enable, activate the setting "Enable Decompilation Support".
- In Visual Studio 2019, you have to manually enable F12 support. Go to Tools / Options / Text Editor / C# / Advanced and check "Enable navigation to decompiled source"
- Our ICSharpCode.Decompiler and ILSpyX NuGet packages for your own projects
- Our Linux/Mac/Windows PowerShell cmdlets in this repository
Features
- Decompilation to C# (check out the language support status)
- Whole-project decompilation
- Open from NuGet feed, open from running process in addition to disk and GAC (Windows-only)
- Search for types/methods/properties (learn about the options)
- Hyperlink-based type/method/property navigation, bookmarks
- Base/Derived types navigation, history
- Assembly metadata explorer (feature walkthrough)
- BAML to XAML decompiler, !AvaloniaResources support
- ReadyToRun binary support for .NET Core (see the tutorial)
- Extensible via plugins
- Additional features in DEBUG builds (for the devs)
License
ILSpy is distributed under the MIT License. Please see the About doc for details, as well as third party notices for included open-source libraries.
How to build
Windows:
- Make sure Windows PowerShell (at least version) 5.0 or PowerShell 7+ is installed.
- Clone the ILSpy repository using git.
- Execute
git submodule update --init --recursiveto download the ILSpy-Tests submodule (used by some test cases). - Install Visual Studio (documented version: 18.0/2026). You need the following workload components:
- Workload ".NET Desktop Development". This workload includes the .NET Framework 4.8 SDK and the .NET Framework 4.7.2 targeting pack, as well as the .NET 10.0 SDK (ILSpy.csproj targets .NET 10.0, but we have net472 projects too). Our unit tests require .NET 11.0 SDK.
- Workload "Visual Studio extension development" (Note: ILSpy.VSExtensions.slnx is separate from ILSpy.sln and thus this workload is optional)
- Individual Component "MSVC v143 - VS 2022 C++ x64/x86 build tools" (or similar)
- The VC++ toolset is optional; if present it is used for
editbin.exeto modify the stack size used by ILSpy.exe from 1MB to 16MB, because the decompiler makes heavy use of recursion, where small stack sizes lead to problems in very complex methods.
- The VC++ toolset is optional; if present it is used for
- Open ILSpy.sln in Visual Studio.
- NuGet package restore will automatically download further dependencies
- Run project "ILSpy" for the ILSpy UI
- Use the Visual Studio "Test Explorer" to see/run the tests
- If you are only interested in a specific subset of ILSpy, you can also use
- ILSpy.Desktop.slnf: for the cross-platform Avalonia UI and its tests
- ILSpy.XPlat.slnf: for the cross-platform CLI (ilspycmd) or PowerShell cmdlets
- ILSpy.VSExtensions.slnx: for the Visual Studio extensions
Note: Visual Studio includes a version of the .NET SDK that is managed by the Visual Studio installer - once you update, it may get upgraded too. Please note that ILSpy is only compatible with the .NET 11.0 SDK and Visual Studio will refuse to load some projects in the solution (and unit tests will fail). If this problem occurs, please manually install the .NET 11.0 SDK from here.
Unix / Mac:
- Make sure .NET 10.0 SDK (for run) and .NET 11.0 SDK (for tests) is installed.
- Make sure PowerShell is installed (formerly known as PowerShell Core)
- Clone the repository using git.
- Execute
git submodule update --init --recursiveto download the ILSpy-Tests submodule (used by some test cases). - Use
dotnet build ILSpy.Desktop.slnfto build the cross-platform Avalonia desktop UI; run it withdotnet run --project ILSpy. - Use
dotnet build ILSpy.XPlat.slnfto build only the CLI tool (ilspycmd) and PowerShell cmdlets.
How to contribute
- Report bugs
- If you want to contribute a pull request, please add https://github.com/icsharpcode/ILSpy/blob/master/BuildTools/pre-commit to your
.git/hooksto prevent checking in code with wrong formatting. We use tabs and not spaces. The build server runs the same script, so any pull requests using wrong formatting will fail.
Current and past contributors.
Privacy Policy for ILSpy
ILSpy does not collect any personally identifiable information, nor does it send user files to 3rd party services. ILSpy does not use any APM (Application Performance Management) service to collect telemetry or metrics.