ILSpy 9.x is based on .NET 8.0. All artifacts except the self-contained distribution are built framework-dependent, which means .NET 8.0.x or later must be installed prior to starting ILSpy.

Generic themes of this release were refactoring the old WPF code base and moving away from platform-dependent implementations to make reuse easier via our ILSpyX package.

A few notable picks from the "What's new" department for you to check out: WebCIL and standalone ECMA-335 metadata support, as well as diagramming (either via ilspycmd or assembly context menu). And in general quality-of-life improvements like the ability to disable automatic assembly loading, performance improvements via DATAS and future-proofing for .NET 10.

New Language Features

• Add support for C# 12 primary constructors.
• Add support for C# 12 'ref readonly' parameters
• Added support for switch on (ReadOnly)Span<char> using a compiler-generated hash function.
• Added new a.GetValueOrDefault(b) -> a ?? b transform for side-effect-free default values.
• Support types that provide DisposeAsync without implementing IAsyncDisposable.
• Updated pattern detection to Roslyn 4.12

Enhancements

• Added support for reading WebCIL assemblies (IL embedded in WASM) (see #3184)
• Added support for reading standalone ECMA-335 metadata (portable PDB and other metadata blobs) (see #3149)
• #3118: Add "Clear assembly list" menu item.
• #2893: Add option to disable automatic assembly loading.
• Allow implicit conversions in switch
• IL output: Add indentation level to make it easier to see custom attributes belonging to interface implementations.
• IL output: Print metadata token of custom attribute.
• Replace native interop CommandLineToArgvW with parsing in Process.Unix.cs from System.Diagnostics.Process #3201
• Natural Sort without interop #3196
• AOT and x-plat changes #3203
• Allow running tests on ARM64 (see #3231)
• Alow collecting analyzers annotated with ExportAnalyzerAttribute (see #3239)
• Fix #3237: Use ref readonly locals for readonly.ldelema
• Fix #3001: Support new resources format in ResourcesFile/ResXResourceWriter
• Fix #3134: Include newobj, initobj and call instructions in TypeInstantiatedByAnalyzer
• Fix #3089: Add comment regarding .constraint prefix expressed as cast in C#
• Fix #3372: Fix loading a DLL that contains byte sequences matching ZIP central directory
• Use Microsoft.Sbom.Targets in NuGets #3346

Contributions

• Diagramming feature by @h0lg (see #3324)
• Various WPF-related refactorings by @tom-englert (see #3257, #3266, #3274, #3283, #3285, #3291, #3292, #3294, #3295, #3297, #3298, #3299, #3302, #3308, #3314, #3325 and #3335)
• High DPI fixes by @CreateAndInject (see #3348 and #3350)
• TreeView: Add referenced types, members and exported types under references (#3092, @fowl2)
• Adjust colors of AvalonEdit built-in highlightings for dark themes (#3138, @ltrzesniewski)
• Add support for Mono C# compiler 2.6.4 pinned region with array variable (#3110, @ElektroKill)
• Add smooth scrolling to settings panels and DecompilerTextView (see #3244 by @tom-englert)
• Ignore empty version directories of dotnet (#3265 by @Herrmel)
• Missing DecompilerSettings by @naratteu (see #3356)
• Fix metadata display of DynamicLocalVariable and DefaultNamespace custom debug information (#3111, @ElektroKill)
• Read and use tuple element names and dynamic type information from PDBs (#3114, @ElektroKill)
• Bugfix: infinite loop in DetermineEffectiveAccessibility (#3164, @yzdeveloper)
• Decompiler Settings: Checkbox in group header does not reflect state of the group (see #3252 by @tom-englert)
• Fix Derived Types Node always being empty (#3280 by @Applesauce314)

Performance

• Activate Dynamic Adaptation To Application Sizes (DATAS) (#3122).
• RDP hardware acceleration (#3122): Enabling hardware acceleration for Remote Desktop Protocol (RDP) to boost performance.
• Performance: Initialize ToolPanes in DockWorkspace.InitializeLayout() instead of the property getter to avoid WPF seeing them in InitializeComponent() and rendering all panes docked at the right before the layout is properly initialized.

Breaking Changes

• ICSharpCode.Decompiler: Added MetadataFile base class for PEFile
• ICSharpCode.Decompiler: IModule.PEFile is now named IModule.MetadataFile
• ICSharpCode.Decompiler/ILSpyX: Added IFileLoader API to allow for easier extensibility of supported file formats (see #3191)
• ILSpy: Split BAML decompiler into library and add-in (see #3178)
• ILSpy/ILSpyX: Moved non-UI analyzer API to ILSpyX (see #3186)
• ICSharpCode.Decompiler: IProjectFileWriter and IProjectInfoProvider APIs are now public (see #3151 and #3191)
• @file support with breaking changes to command line options #3205
• New single instance handling #3212
• Remove IsRef, IsOut and IsIn flags from IParameter
• Replace ParameterModifiers with ReferenceKind.

Bug fixes

• Fix #3072: Ignoring resources with the same name as a namespace.
• Fix bug in UnknownType: Ensuring that the FullName of nested unknown types contains the outer type name(s), not just the namespace and nested type name.
• Fix #3153: Always using SHA1 for public key tokens.
• Fix ILSpy for ZIP files/VSIX with bundle signatures: Enabling ILSpy to open ZIP files and VSIX packages containing bundle signatures.
• Omit package entries from the treeview that denote the directory.
• Fix #3142: Exception when analyzing source of library with global assembly attributes
• Fix #3113: Remove GetAlternativeName and instead reuse existing names, if there are no conflicts.
• Fix #3197: Bug when trying to read a bundle/archive file
• Fix #3189: Support primitive types in Expression.Constant(object) pattern in Expression Trees
• Fix #3209: Ensure using directives are added for extension methods in higher level patterns such as: foreach -> GetEnumerator(), collection initializer -> Add() and deconstruction -> Deconstruct().
• Fix #3255: Ignore exceptions while decoding sequence point blobs.
• Fix #2166: Unnecessary uint casts/conversions for certain bitwise operations
• Fix #3310: Filter out copy-constructor only if it's an actual record type.
• Fix #3319: KeyDownEvent field reference was replaced with KeyDown event reference.
• Fix #3349: Make ILSpy ready for .NET 10
• Fix #3361: switch-value conversion was losing its target type.

And many other fixes, for a full list click here.