# AGENTS.md - SCL Language Server

A Neovim/LazyVim plugin for Siemens SCL language support providing LSP, linting, formatting, syntax highlighting, and auto-completion.

## Build/Lint/Test Commands

```bash
# LSP Server
make start                    # Start LSP server
make test                     # Run LSP in test mode
lua src/main.lua --test       # Direct test execution

# Tree-sitter Parser
tree-sitter generate          # Generate parser from grammar.js
tree-sitter test              # Run all parser tests
tree-sitter parse <file.scl>  # Parse single SCL file

# Lua Linting
luacheck src/                 # Lint LSP server code
luacheck lua/scl/             # Lint plugin modules

# Unit & Integration Tests
lua test/run_tests.lua       # Run all tests
lua test/test_udt.lua        # Run UDT parser tests
lua test/test_db.lua         # Run DB parser tests
lua test/test_fb.lua         # Run FB parser tests
lua test/test_formatter.lua  # Run formatter tests
lua test/test_plc_json.lua   # Run plc_json tests
lua test/test_integration.lua # Run integration tests

# Reference Project
# Tests use files from: ~/dev/siemens/projects/scl_lang_support_lazyvim_ref_project/
# Override with: SCL_REF_PROJECT=/path/to/ref lua tests/run_tests.lua
```

## Project Structure

```
scl_lsp/
├── src/                     # LSP server (uses dofile)
│   ├── main.lua            # Entry point, JSON-RPC protocol
│   ├── parser.lua          # SCL parser
│   ├── diagnostics.lua     # Linter
│   ├── formatter.lua       # Document formatter
│   ├── treesitter.lua      # Tree-sitter integration
│   ├── plc_json.lua        # External UDT/DB loading
│   ├── builtin_instructions.lua  # TIA Portal built-in types
│   └── json.lua            # JSON encoder/decoder
├── lua/scl/                 # Neovim plugin (uses require)
│   ├── init.lua            # Main plugin setup
│   ├── udt_parser.lua      # UDT parser
│   ├── db_parser.lua       # Global DB parser
│   ├── fb_parser.lua       # Function Block parser
│   ├── variables.lua       # Variable extraction
│   ├── workspace_types.lua # Workspace scanning
│   ├── multiline_params.lua
│   ├── auto_prefix.lua
│   └── attr_toggle.lua
├── queries/                 # Tree-sitter queries
└── grammar.js               # Tree-sitter grammar
```

## Filetype Detection

Required in Neovim config (ftdetect/scl.vim):
```vim
au BufRead,BufNewFile *.scl set filetype=scl
au BufRead,BufNewFile *.udt set filetype=scl
au BufRead,BufNewFile *.db set filetype=scl
```

## Code Style Guidelines

### Module Pattern
```lua
local M = {}

local cache = {}

function M.public_function()
end

local function private_function()
end

return M
```

### Naming Conventions
- Functions/variables: `snake_case` (e.g., `get_udt_members`)
- Constants: `UPPER_SNAKE_CASE` (e.g., `PROJECT_MARKERS`)
- Private functions: declare as `local function` before public functions
- Booleans: prefix with `is_`, `has_` (e.g., `is_udt`, `has_members`)

### Imports
- `lua/scl/` modules: `require("scl.module_name")`
- `src/` modules: `dofile(script_path .. "/module.lua")`
- External dependencies: wrap in `pcall()` for safety

### Code Formatting
- `lua/scl/`: 2 spaces indentation
- `src/`: tab-based indentation
- Max line length: 120 characters
- No trailing whitespace

### Comments
**DO NOT ADD COMMENTS** in code unless explicitly requested by the user.

### Parser Module API
All parser modules must implement:
- `parse_*_file(filepath)` - Parse and cache
- `parse_*_content(content, filename)` - Parse string
- `get_*(name)` - Get cached item
- `get_all_*_names()` - List all cached names
- `get_*_members(name)` - Get members/fields
- `is_*_type(name)` - Check if known type
- `clear_cache()` - Clear cached data
- `get_cache_count()` - Return cache size

### Cache Management
```lua
local cache = {}

function M.clear_cache()
  for k in pairs(cache) do
    cache[k] = nil
  end
end
```

### Error Handling
```lua
function M.parse_file(filepath)
  local file = io.open(filepath, "r")
  if not file then
    return nil, "Cannot open file: " .. filepath
  end
  return result
end

-- External dependencies
local ok, module = pcall(require, "some_module")
if ok and module then
  module.do_something()
end
```

## Lua Reserved Keywords

Cannot use reserved keywords as table keys directly:
```lua
-- WRONG
local range = { start = pos1, end = pos2 }

-- CORRECT
local range = { start = pos1, ["end"] = pos2 }
```

Critical for LSP range objects with `end` field.

## Type System

The LSP validates data types and provides warnings for unknown types:
- **Elementary**: BOOL, BYTE, WORD, DWORD, INT, DINT, REAL, TIME, STRING, etc.
- **Timer/counter**: IEC_TIMER, TON_TIME, TOF_TIME, CTU, CTD, CTUD
- **Built-in FBs**: TON, TOF, TP, R_TRIG, F_TRIG, etc.
- **Built-in functions**: ADD, SUB, MUL, DIV, SIN, COS, SQRT, etc.
- **Workspace types**: UDTs from `.udt` files, DBs from `.db` files

## Testing

Use the reference project for testing:
```
~/dev/siemens/projects/scl_lang_support_lazyvim_ref_project/
```

Contains `.scl`, `.db`, `.udt`, and `.xml` files for comprehensive testing of:
- LSP features (hover, completion, go-to-definition)
- Formatter (`:SCLFormat`)
- Attribute block toggle
- Workspace type scanning