CSL Language Server

Inofficial language server for Cerebras Software Language (CSL), providing rich editor features beyond syntax highlighting.

Required Setup

Before using the extension, set csl.systemModuleSif to point to the .sif file in the Cerebras SDK. The language server extracts system modules from that container to resolve imports with angle bracket syntax (<...>). Alternatively, you can set csl.systemImportPath to a directory containing the extracted system modules.

This is required so system module imports (<...>) can be resolved correctly.

Features

Diagnostics -- real-time error and warning reporting as you type
Hover -- type information and documentation on hover
Go to Definition -- jump to definitions of functions, variables, and imports
Auto-completion -- context-aware code completion suggestions
Dot completion -- member/field completions after .
Function signature help -- call argument hints with active parameter highlighting
Document Symbols -- outline view and symbol search within a file

Why this language server exists

The frontend used by this language server was originally developed for the CSL transpiler that we are building in a research project at TU Darmstadt. That transpiler performs whole-program transformations, including lowering coroutine-style code into explicit FSM-style code.

Those transformations depend on accurate static types for the full program.
In CSL (similar to Zig), types are first-class values, and thus infering static type information requires comptime evaluation of the complete program.

For that reason, comptime-related analysis in this extension is intended to model CSL semantics fully, not as a best-effort approximation for editor tooling.

If you observe a mismatch with the official CSL compiler (especially after SDK updates), please open an issue and include a minimal repro.

Settings

Configure the extension under csl.* in your VS Code settings:

Setting	Description	Default
`csl.systemModuleSif`	Path to a `.sif` container providing system modules. Required for resolving imports with angle bracket syntax (`<...>`).	(empty)
`csl.systemImportPath`	Search path for system module imports (`<...>` syntax).	`/cb/toolchains/cslang///csl-libs/` if `csl.systemModuleSif` is set, otherwise empty
`csl.arch`	Target architecture (optional).	`wse2`
`csl.params`	Parameter bindings as key-value pairs (optional). Numbers containing `.` are `comptime_float`, otherwise `comptime_int`.	`{}`
`csl.rectangle`	Rectangle size as `width,height` for `@get_rectangle`.	`100,100`
`csl.fabricDims`	Fabric dimensions as `width,height`.	`100,100`
`csl.fabricOffsets`	Fabric offsets as `x,y`.	`3,3`
`csl.serverArgs`	Additional CLI arguments passed to the server.	`[]`
`csl.trace.server`	Trace LSP communication (`off`, `messages`, `verbose`).	`off`

Example Configuration

{
  "csl.systemModuleSif": "/opt/Cerebras-SDK-1.4.0-202505230211-4-d9070058/sdk-cbcore-202505230211-4-9382352f.sif",
  "csl.arch": "wse3",
  "csl.params": {
    "M": 4,
    "N": 4,
    "width": 8
  }
}

About

This extension is part of a research project at TU Darmstadt (Embedded Systems and Applications Group) that builds MLIR-based compiler infrastructure for Cerebras Wafer-Scale Engines (WSE).

Feedback and Contact

Bug reports and feature requests can be filed on the GitHub issue tracker.

If you are interested in the project or in collaborating, feel free to reach out by email: noack@esa.tu-darmstadt.de

Note

If you have the official "Cerebras Software Language (CSL)" extension installed, you can keep it -- both extensions work side by side without conflicts. That extension provides syntax highlighting only; this extension includes syntax highlighting plus full language server features.

Language Server for CSL

Embedded Systems and Applications Group