SCL Language Server - Unified Plugin for Siemens SCL

A comprehensive Neovim/LazyVim plugin providing Language Server Protocol (LSP), Linting, Formatting, and Syntax Highlighting for Siemens SCL (Structured Control Language) used in Siemens TIA Portal.

Features

LSP (Language Server Protocol)

Feature	Description
Hover	Press K to see variable type and struct fields
Completion	# for variables, . for struct fields, ( for functions
Go to Definition	gd jump to variable declaration
Document Symbols	Shows functions, variables, types
Workspace Symbols	Search across all .scl files with fuzzy matching
Semantic Tokens	Keywords, variables highlighted
Inlay Hints	Shows variable types after declaration
External UDT	Load types from .plc.json or data_types/ folder

Linter (Diagnostics)

Feature	Description
Undefined Variables	Detects variables used without declaration
Invalid # Prefix	Detects # prefix in VAR sections
Unknown Types	Warns about unknown data types
Type Validation	Basic type checking

Formatter

Feature	Description
Document Formatting	Format entire SCL files
Indentation	Proper block indentation
Keyword Casing	Maintains SCL keyword casing

Syntax Highlighting

• Full SCL syntax support via tree-sitter
• ORGANIZATION_BLOCK, FUNCTION_BLOCK, FUNCTION definitions
• Variable declarations (VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR_TEMP, etc.)
• Control structures (IF/THEN/ELSE, CASE, FOR, WHILE, REPEAT)
• Code regions and comments
• All SCL data types and operators

Additional Features

Feature	Description
Auto-Prefix	Automatically adds # prefix to local variables (like TIA Portal)
Workspace UDT Scanner	Scans project for user-defined types
blink.cmp Integration	Smart completion source for blink.cmp

Installation

LazyVim

-- ~/.config/nvim/lua/plugins/scl.lua
return {
  "lazar/scl_lsp",
  ft = "scl",
  lazy = true,
  dependencies = {
    "neovim/nvim-lspconfig",
    "nvim-treesitter/nvim-treesitter",
    "saghen/blink.cmp",
  },
  config = function()
    require("scl_lsp").setup({
      -- LSP options
      lsp = {
        on_attach = function(client, bufnr)
          -- custom keymaps
        end,
      },
      cmp = true,              -- Enable blink.cmp integration
      workspace_types = true,  -- Enable workspace UDT scanning
      auto_prefix = true,      -- Enable auto-# prefixing
      debug = false,
    })
  end,
}

Manual Setup

-- In your init.lua or plugin file
require("scl_lsp").setup({
  server_path = "/path/to/scl_lsp/src/main.lua",
  cmp = true,
  workspace_types = true,
  auto_prefix = true,
})

Configuration Options

Option	Type	Default	Description
server_path	string	~/dev/scl_lsp/src/main.lua	Path to LSP server
lsp.on_attach	function	nil	Custom LSP attach callback
lsp.formatting	boolean	false	Enable format command
cmp	boolean	true	Enable blink.cmp integration
workspace_types	boolean	true	Enable workspace UDT scanning
auto_prefix	boolean	true	Enable auto-# prefixing
project_root	string	nil	Custom project root
library_paths	table	{}	Additional library paths
debug	boolean	false	Enable debug logging

Commands

Command	Description
:SCLShowVariables	Show local variables in current file
:SCLShowWorkspaceTypes	Show workspace UDTs and FB count
:SCLRescanWorkspaceTypes	Rescan workspace for types
:SCLPrefixWord	Manually prefix current word with #
:LspSCLFormat	Format current SCL file
:SCLGeneratePlcJson	Generate plc.data.json from data_types/

Keybindings

Key	Action
K	Hover (show variable info)
gd	Go to Definition
<leader>s	Document Symbols
<leader>w	Workspace Symbols
<leader>fw	Workspace Symbols (Telescope)
<leader>ca	Code Actions

External UDT Support

Option 1: Create .plc.json

{
  "dataTypes": [
    {
      "name": "equipmentData",
      "struct": [
        {"name": "id", "dataTypeName": "INT"},
        {"name": "status", "dataTypeName": "BOOL"},
        {"name": "temperature", "dataTypeName": "REAL"}
      ]
    }
  ]
}

Option 2: Auto-scan data_types/ folder

The LSP automatically scans for SCL files in data_types/ folder and extracts TYPE definitions.

Option 3: Generate .plc.json

lua /home/lazar/dev/scl_lsp/src/plc_json.lua --generate

Project Structure

scl_lsp/
├── README.md                    # This file
├── package.json                 # NPM scripts (tree-sitter)
├── Makefile                     # Build commands
├── grammar.js                   # Tree-sitter grammar
├── tree-sitter.json            # Parser config
├── queries/                    # Tree-sitter queries
│   ├── highlights.scm         # Syntax highlighting
│   ├── indents.scm            # Indentation
│   ├── folds.scm              # Code folding
│   ├── locals.scm             # Variable scoping
│   └── tags.scm               # Navigation tags
├── src/                        # LSP server
│   ├── main.lua               # Main entry point
│   ├── parser.lua             # Regex-based parser
│   ├── treesitter.lua         # Tree-sitter integration
│   ├── json.lua               # JSON encoder/decoder
│   ├── plc_json.lua           # External UDT loading
│   ├── diagnostics.lua        # Linter diagnostics
│   └── formatter.lua          # Document formatter
└── lua/
    └── scl_lsp/
        ├── init.lua           # Main plugin setup
        ├── plugins/
        │   └── scl.lua        # LazyVim plugin spec
        └── scl/               # Syntax/completion modules
            ├── init.lua
            ├── auto_prefix.lua
            ├── blink_cmp_source.lua
            ├── fb_parser.lua
            ├── udt_parser.lua
            ├── variables.lua
            └── workspace_types.lua

Building Tree-sitter Parser

# Generate parser from grammar.js
npm run build
# or: tree-sitter generate

# Run tests
npm test
# or: tree-sitter test

SCL Code Example

FUNCTION_BLOCK "Em101Sequence"
VAR
    x : INT;
    myVar : equipmentData;  // User-defined type
END_VAR

IF x > 5 THEN
    myVar.id := 10;
END_IF

myVar.status := TRUE;
myVar.temperature := 25.5;

END_FUNCTION_BLOCK

Requirements

• Neovim 0.9+
• nvim-lspconfig - LSP client
• nvim-treesitter - Syntax highlighting
• blink.cmp - Optional, for completion
• Lua 5.1+ - LSP server runtime