# AGENTS.md - tia-lsp

A standalone LSP server for Siemens TIA Portal languages. Currently supports **SCL**; planned support for STL/AWL, LAD, FBD. This repo is the server only (`src/` + tree-sitter grammar). The companion Neovim plugin lives in `tia-lsp.nvim`.

## 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

# Unit Tests
lua test/run_tests.lua       # Run all server tests
lua test/test_formatter.lua  # Run formatter tests
lua test/test_plc_json.lua   # Run plc_json tests

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

## Project Structure

```
tia-lsp/
├── src/                     # LSP server (uses dofile)
│   ├── main.lua            # Entry point, JSON-RPC protocol
│   ├── parser.lua          # SCL parser (will become parser_scl.lua + dispatch)
│   ├── diagnostics.lua     # Linter (source = "tia_lsp")
│   ├── formatter.lua       # Document formatter
│   ├── treesitter.lua      # Tree-sitter integration
│   ├── plc_json.lua        # External UDT/DB loading (language-agnostic)
│   ├── builtin_instructions.lua  # TIA Portal built-in types
│   └── json.lua            # JSON encoder/decoder
├── grammar.js               # Tree-sitter grammar (language name: 'scl')
└── test/                    # Server tests
```

## Naming Convention

- **Project name** (repo, LSP server, mason package): `tia-lsp` / `tia_lsp` — umbrella for all TIA languages.
- **Language name** (filetype, tree-sitter parser, grammar): `scl` — stays as-is. Future languages (`stl`, `lad`, `fbd`) get their own names.
- **LSP client name**: `tia_lsp` (one client handles all TIA languages; dispatches by `filetype` / `languageId`).
- **Diagnostic source**: `tia_lsp`.

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

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

### Comments
Add comments to explain non-obvious code sections, complex logic, and public API functions. Keep comments concise and relevant.

### 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:
```
~/Documenta/siemens/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
- Workspace type scanning