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 function, FB, DB, or UDT definition
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 with :SCLFormat
Multi-line Assignments	Preserves and formats multi-line expressions with proper alignment
FB Call Formatting	Formats function block calls in multiline style
Indentation	Proper block indentation
Keyword Casing	Maintains SCL keyword casing

Syntax Highlighting

• Full SCL syntax support via tree-sitter
• Block definitions: ORGANIZATION_BLOCK, FUNCTION_BLOCK, FUNCTION
• Variable sections: VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR_TEMP, VAR_CONSTANT
• Control structures: IF/THEN/ELSIF/ELSE/END_IF, CASE/OF/END_CASE, FOR/TO/BY/DO/END_FOR, WHILE/END_WHILE, REPEAT/UNTIL/END_REPEAT
• Built-in data types: BOOL, INT, DINT, REAL, STRING, TIME, etc.
• Function block instances highlighted in calls
• FB parameter names (IN, PT, CU, etc.) highlighted as properties
• # prefix for local variables highlighted
• Operators: AND, OR, NOT, XOR, MOD
• Comments: line (//), block ((* *)), C-style (/* */)

Additional Features

Feature	Description
Auto-Prefix	Automatically adds # prefix to local variables (like TIA Portal)
Multiline Parameters	Fill FB/Function call parameters across multiple lines with <Space>mp or :SCLMultilineParams
Tab Navigation	Jump between parameters with <Tab> in insert mode
Workspace UDT Scanner	Scans project for user-defined types (.udt files)
Workspace Global DB Scanner	Scans project for global data blocks (.db files)
blink.cmp Integration	Smart completion source for blink.cmp
Attribute Block Toggle	Interactive expand/collapse of {...} blocks with <Leader>xa

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, FBs, and Global DBs count
:SCLRescanWorkspaceTypes	Rescan workspace for types and DBs
:SCLPrefixWord	Manually prefix current word with #
:SCLMultilineParams	Fill multiline parameters for FB/Function call
:SCLFormat	Format current SCL file
:SCLToggleAttrBlock	Toggle attribute block under cursor
:SCLExpandAllAttrBlocks	Expand all {...} blocks in buffer
:SCLCollapseAllAttrBlocks	Collapse all matching attribute blocks

Keybindings

Key	Action
K	Hover (show variable info)
gd	Go to Definition
<leader>s	Document Symbols
<leader>w	Workspace Symbols
<Space>mp	Fill multiline FB/Function parameters (insert mode)
<Tab>	Jump to next parameter (insert mode)
<Leader>xa	Toggle attribute block under cursor
<Leader>xae	Expand all attribute blocks
<Leader>xac	Collapse all attribute blocks
<leader>fw	Workspace Symbols (Telescope)
<leader>ca	Code Actions

Attribute Block Toggle

Interactive expand/collapse of SCL variable attribute blocks:

-- Before: Verbose attributes
statCounter{EXTERNALACCESSIBLE := 'false'; EXTERNALVISIBLE := 'false'} : Int;

-- After: Collapsed
statCounter{...} : Int;

Usage:

• Place cursor inside any {...} block
• Press <Leader>xa to toggle expand/collapse
• Use <Leader>xae to expand all blocks in buffer
• Use <Leader>xac to collapse all blocks

Note: Collapsed blocks are automatically expanded before saving to preserve full content on disk. Use :SCLFormat to format, then :SCLCollapseAllAttrBlocks to collapse while preserving the ability to expand later.

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

Global Data Block Support

The plugin automatically scans for .db files in the workspace and provides auto-completion for global data blocks and their members.

How it works

1. Workspace Scanning: When opening a .scl file, the plugin scans the project for .db files
2. DB Parsing: Parses DATA_BLOCK definitions and extracts members from VAR sections
3. Auto-completion: Provides smart completion for DB names and members

Usage

• Type a space or # to trigger completion - global DB names appear alongside local variables
• Type " followed by a DB name to get member completions
• Access nested members: "MyDB".member.submember

Example

// Access global DB members
"HmiData".units
"Parameter".machine.unit100.paramTimeStampApplied

// Inside FB call parameter
#instParameterManager(hmiInterface:="HmiData".units, ...)

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
            ├── db_parser.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

Architecture

The plugin uses a standalone LSP server (src/main.lua) that communicates via JSON-RPC over stdio. The server handles:

• Text document synchronization
• Diagnostics (linting)
• Formatting
• Completion, hover, go-to-definition
• Semantic tokens

The Neovim plugin (lua/scl_lsp/init.lua) manages:

• LSP client lifecycle via vim.lsp.start()
• FileType autocmd for lazy loading
• blink.cmp integration
• Workspace scanning for UDTs/DBs

Requirements

• Neovim 0.11+ (uses vim.lsp.start())
• nvim-treesitter - Syntax highlighting
• blink.cmp - Optional, for completion
• Lua 5.1+ - LSP server runtime