Adding a fully-bootstrapped Mono:

• In 2016, a Mono package was introduced but later removed due to prebuilt binaries. A new Mono package was added in 2024 via a patch series.
• The author started working on a Mono package to meet the dependency of a C# package requiring C# 12.0 features.

History:

• Mono and Portable.NET were competing free software implementations in the early 2000s with different goals, licenses, and methods.
• Portable.NET was decommissioned in 2012 but its source is still available. The author used pnet-git for bootstrap efforts.

The start:

• Mono-1.2.6 initially failed due to C# and Java's compile-time library dependency issue. The runtime in mono-1.9.1 was modified to allow version override.
• From there, it was a trial-and-error process to identify bitrotted areas and switch to Mono's homebrewed sgen garbage collector.

A concerning development:

• Mono started using git submodules with the git:// protocol in mono-2.11.4, which GitHub dropped support for in 2021.
• This led to issues with recursive clones and update processes, but the transparency of git mitigates the security risk.

Meanwhile, in reality:

• Mono added a roslyn-binaries submodule in 2016, which contained binary blobs for Microsoft's Roslyn compiler.
• This raised concerns about potential security risks and the importance of bootstrappability.

Another note on roslyn-binaries:

• Writing a self-hosting compiler and relying on Microsoft's C# compiler is a bittersweet situation.
• The dependencies on new C# features are in Mono's standard library, not the compiler.

More binary submodules:

• There were binary-reference-assemblies and xunit-binaries submodules containing prebuilt blobs.
• Debian only runs tests in certain subdirectories due to these binary blobs.

The long march through the 5.0s:

• The 5.0 series was challenging due to Mono's acquisition by Microsoft and its dependency on Microsoft's corefx library.
• It took many versions and nontrivial patching to get through the 5.0 series.

The final stretch:

• The author realized the dependencies on new features were from corefx and cherry-picked mcs commits to jump to building 6.12.0.

The finishing touches:

• The author patched Mono's xbuild condition parser and added a <runpath> element to per-assembly config files.

Future work:

• Dotnet builds heavily depend on binary blobs and there are portability issues with the current bootstrap path.
• Porting mcs to Portable.NET could solve these issues and make the bootstrap path more appealing.

Closing thoughts:

• The maintenance of Mono was transferred to WineHQ. The author disputes Mono's claim of being the first.NET implementation on Linux.
• The author thanks the DotGNU project, Adam Faiz, and the Mono project.