codemirror-cel

codemirror-cel

A CodeMirror 6 extension that adds full language support for CEL (Common Expression Language) — powered by a WASM language server running in a Web Worker.

Live demo

Features

• Diagnostics — real-time error checking as you type
• Autocompletion — variables, functions, methods, and field access
• Hover — type information on hover
• Semantic highlighting — full token-level highlighting that integrates with your CodeMirror theme

All of this runs entirely in the browser — no server required.

Quick start

npm install codemirror-cel

import { cel } from "codemirror-cel";
import { basicSetup } from "codemirror";
import { EditorState } from "@codemirror/state";
import { EditorView } from "@codemirror/view";

const worker = new Worker(
  new URL("codemirror-cel/worker", import.meta.url),
  { type: "module" },
);

const celExtensions = await cel({
  worker,
  variables: [
    { name: "user", type: { kind: "map", keyType: "string", valueType: "dyn" } },
    { name: "now", type: "timestamp" },
  ],
  functions: [
    {
      name: "isEmail",
      params: [{ name: "value", type: "string" }],
      returnType: "bool",
    },
  ],
});

new EditorView({
  parent: document.getElementById("editor")!,
  state: EditorState.create({
    doc: 'user.email.endsWith("@acme.com") && isEmail(user.email)',
    extensions: [basicSetup, ...celExtensions],
  }),
});

Configuration

The cel() function accepts a CelConfig object:

Option	Type	Default	Description
worker	Worker	(required)	A Web Worker running the celsp WASM language server.
variables	VariableDeclaration[]	[]	Variables available in the CEL environment.
functions	FunctionDeclaration[]	[]	Custom function declarations for the type-checker.
rootUri	string	"file:///"	LSP workspace root URI.
documentUri	string	"file:///cel.cel"	URI for the document being edited.
languageId	string	"cel"	Language ID sent to the LSP server.
hoverShowErrors	boolean	false	Include check-error details in hover tooltips.

Types

Variables use CEL's type system:

// Primitive types
{ name: "active", type: "bool" }
{ name: "count", type: "int" }
{ name: "score", type: "double" }
{ name: "name", type: "string" }
{ name: "now", type: "timestamp" }
{ name: "ttl", type: "duration" }

// List type
{ name: "tags", type: { kind: "list", elementType: "string" } }

// Map type
{ name: "headers", type: { kind: "map", keyType: "string", valueType: "string" } }

// Nested types
{ name: "matrix", type: { kind: "list", elementType: { kind: "list", elementType: "int" } } }

Functions declare parameter names, types, and a return type:

{
  name: "clamp",
  params: [
    { name: "value", type: "double" },
    { name: "min", type: "double" },
    { name: "max", type: "double" },
  ],
  returnType: "double",
}

How it works

The extension runs a fork of celsp by ponix-dev — a CEL language server written in Rust — compiled to WebAssembly inside a Web Worker. LSP messages are bridged between the worker and CodeMirror via postMessage.

Semantic highlighting is handled through a custom side-channel (since the upstream CodeMirror LSP plugin doesn't support semantic tokens) and integrates with whatever HighlightStyle you have active (e.g. oneDark).

License

Unlicense — public domain.