Slingshot - SystemVerilog LSP

Important

This is BETA quality software; bugs may be present. Please file issues on the issue tracker.

Slingshot is a language server for the SystemVerilog hardware description language, with a focus on stability, performance, and accuracy in autocomplete. The overarching goal is to make SystemVerilog as intuitive to edit as C++ or Rust.

Compared to other SV LSPs, the main feature that Slingshot brings to the table is a completion-first approach, using the powerful Slang frontend. The intent is to provide fast, accurate and robust completion even in complex projects. Slingshot also features a relatively advanced multi-threaded indexing system, to power this completion system, that features graph-based dependency resolution.

The trade-off is this does mean that features such as "go-to-reference" take somewhat of a backseat; though the plan is to implement them eventually.

Slingshot is (now) written in C++23. Previously, it was written in Kotlin and used ANTLR. This new rewrite aims to:

• Improve speed and utility by using a proper SystemVerilog parser (Slang)
• Reduce memory usage

Features

• Diagnostics
  • Based on the Slang SystemVerilog frontend, which is considered best in its class
• Completion system
  • Context-sensitive completion, based off the Slang parse tree, a "best-effort" approach to only recommend valid completions
• Advanced indexing system
  • Graph-based (backwards BFS) automatic dependency tracking between SV documents
    • Improves performance by only compiling the documents necessary to index a file
  • Multi-threaded for theoretically higher-performance on large codebases
• Simple configuration
  • Slingshot is configured through a simple .slingshot.toml file declared in the project's root directory
  • This format is documented in docs/config.md
• Compatible with Ubuntu 22.04+ and similar Linux distributions

Future features are planned on the issue tracker.

Current state

Slingshot is somewhat stable and is ready for testing in larger projects. Please keep me posted!

Timeline

Slingshot is being developed in my free time during my PhD. I do not always have time to work on this project.

Known supported editors

• Neovim v0.11+
• Helix

Building and running

Building and environment

You will need:

• CMake 3.21+
• A C++23 compiler (Clang 20+ recommended)
• Ninja
• ccache (optional)
• Just (optional)
• mold (optional)
• Something compatible with Ubuntu 22.04+ (I develop on Arch, btw)
• Abseil (e.g. libabsl-dev or similar)

The simplest way to build, with Just, is to run just build and/or just build_debug.

If that doesn't work, you can do it yourself:

# remove references to ccache if you don't have it
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=1 \
    -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DCMAKE_C_COMPILER_LAUNCHER=ccache
cd build
ninja

C++ dependency management is a fucking disaster, as is the language itself, as I have complained extensively about 1, 2, 3. This project uses the CMake CPM package manager, which is basically a thin wrapper around FetchContent.

We vendor all our dependencies. This should mean, by the grace of god, it'll compile on your system. The price to pay is that you have to compile all your deps from scratch each time, sorry. Use ccache.

Running

Currently, I have only tested Slingshot in Neovim.

When Slingshot is a more capable LSP, it will (hopefully) be available in upstream LSP projects like mason.nvim and nvim-lspconfig; although both of these projects are surprisingly quite restrictive about what LSPs they allow, and it's possible Slingshot may never make the cut.

Until then, you can manually add Slingshot as a nvim-lspconfig server by inserting the following into init.lua:

vim.lsp.config("sv-slingshot", {
    cmd = { "<PATH_TO_SLINGSHOT_ROOT>/build/slingshot" },
    root_markers = { ".git", ".slingshot.toml" },
    filetypes = {
        "systemverilog",
        "verilog",
    },
})

vim.lsp.enable("sv-slingshot")

This is the setup I use for development as well.

Important: Please read docs/config.md for instructions on how to create a .slingshot.toml file to configure the server. This is mandatory for multi-file (read: most) projects.

Troubleshooting

Slingshot issues can be diagnosed by reading the LSP log file. This is located in ~/.local/share/slingshot/slingshot.log.

If the LSP does nothing at all, please make sure you have read docs/config.md and created your .slingshot.toml file. Then, read the log to make sure that Slingshot has the correct root directory. The best way to ensure this is invoking Neovim by typing nvim . in the project's root directory - don't edit individual files.

If the above steps do not resolve your issue, please open a bug ticket in the GitHub issue tracker. You must include your log file, detailed description of the issue, and also a SystemVerilog code example if possible. As my time is extremely limited, I may not be able to respond to or fix bug tickets. Pull requests are welcome as well, but may take some time to review.

Design philosophy and goals

Slingshot's primary goals across the board are stability, performance and accuracy. Stability is always difficult in an unsafe language like C++, but we try as much as we can, including through the use of ASan and UBSan.

For its feature set, Slingshot prioritises these features and all the infrastructure necessary to make them stable and performant:

• Autocompletion
• Diagnostics (error checking)
• Niceties (e.g. progress bars and simple configuration)

This is a pretty small set of features, but is the minimum set to have a reasonably nice editing experience. Once those features are stabilised, I plan to eventually move out into more advanced features such as go-to-definition, but importantly only after the core features are sufficiently stable.

Implementation details

See docs/impl_details.md

Contributing guidelines

No AI policy

As part of Slingshot's design philosophy, as well as the tenuous copyright and ethical situation around the use of LLMs, I will not accept any pull requests or issues that are written in whole or in part using LLMs. I also do not use any LLMs in any way when working on Slingshot. All bugs are 100% proudly human generated.

Slingshot's mission in this AI-age (bubble?) is to assist human developers writing good SystemVerilog code through rigorous, disciplined and explainable syntax-tree analysis.

Important

Submitting a PR or issue that is reasonably believed to be written using AI will result in it being immediately closed without exception.

This is based on precedent from Zig, QEMU, LibreOffice, and others.

Licence

Copyright (c) 2023-2026 M. L. Young. Available under the Mozilla Public License v2.0.

This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.

Third party libraries

Slingshot uses the following 3rd party libraries:

• spdlog: MIT licence
• fmt: MIT licence
• Slang: MIT licence
• ankerl::unordered_dense: MIT licence
• nlohmann::json: MIT licence
• lsp-framework: MIT licence
• BS::thread_pool: MIT licence
• TOML++: MIT licence
• sockpp: BSD 3-Clause licence
• Graaf: MIT licence
• moodycamel::ConcurrentQueue: BSD 3-Clause licence/BSL 1.0