feat(lsp): add goto declaration for FB, DB, and UDT types

- Add declaration provider (gD) that finds definitions for:
  - Functions in .scl files
  - Function Blocks (FB) in .scl files
  - Data Blocks (DB) in .scl and .db files
  - User-Defined Types (UDT) in .scl and .udt files
- Implement project root detection for cross-directory searches
- Add duplicate location filtering to prevent multiple results
- Load UDT types from .udt files in plc_json
- Update documentation with goto declaration feature

AGENTS.md

@@ -235,6 +235,17 @@ Rules are checked in order; first match wins.
 | `:SCLExpandAllAttrBlocks` | Expand all `{...}` blocks in buffer |
 | `:SCLCollapseAllAttrBlocks` | Collapse all matching attribute blocks |
 
+## LSP Features
+
+### Goto Declaration (`gD`)
+The LSP supports goto declaration functionality for:
+- **Functions** - Jump to function definition in `.scl` files
+- **Function Blocks (FB)** - Jump to FB definition in `.scl` files
+- **Data Blocks (DB)** - Jump to DB definition in `.scl` and `.db` files
+- **User-Defined Types (UDT)** - Jump to type definition in `.scl` and `.udt` files
+
+Usage: Place cursor on a variable or type name and press `gD` (or use LSP client command).
+
 ## Keybindings (SCL/UDT files)
 
 ### Attribute Block Toggle

src/main.lua

@@ -62,6 +62,7 @@ local capabilities = {
 	},
 	definitionProvider = true,
 	referencesProvider = true,
+	declarationProvider = true,
 	documentSymbolProvider = true,
 	diagnosticProvider = { relatedDocuments = {} },
 	textDocumentSync = 1,
@@ -99,7 +100,7 @@ local function scan_scl_files(root_dir)
 	if not root_dir or root_dir == "" then
 		return files
 	end
-	local result = run_command("find " .. root_dir .. ' -type f -name "*.scl" 2>/dev/null')
+	local result = run_command('find "' .. root_dir .. '" -type f -name "*.scl" 2>/dev/null')
 	if result then
 		for f in result:gmatch("[^\n]+") do
 			if f and f ~= "" then
@@ -165,6 +166,45 @@ function handlers.shutdown(params)
 	return nil
 end
 
+local project_markers = {
+	"Program blocks",
+	"PLC data types",
+	"PLC tags",
+	"program blocks",
+	"plc data types",
+	"plc tags",
+	".git",
+}
+
+local function find_project_root(start_path)
+	if not start_path or start_path == "" then
+		return nil
+	end
+	local current = start_path
+	local depth = 0
+	while current and current ~= "/" and current ~= "" and depth < 20 do
+		local handle = io.popen('ls -a "' .. current .. '" 2>/dev/null')
+		if handle then
+			local entries = {}
+			for line in handle:lines() do
+				table.insert(entries, line)
+			end
+			handle:close()
+			local found_marker = false
+			for _, marker in ipairs(project_markers) do
+				for _, entry in ipairs(entries) do
+					if entry == marker then
+						return current
+					end
+				end
+			end
+		end
+		current = current:match("(.*)/") or ""
+		depth = depth + 1
+	end
+	return nil
+end
+
 function handlers.exit(params)
 	os.exit(0)
 end
@@ -173,7 +213,8 @@ function handlers.textDocument_didOpen(params)
 	local uri = params.textDocument.uri
 	local content = params.textDocument.text
 	local path = uri_to_path(uri)
-	local root_dir = path:match("(.*/)") or "."
+	local file_dir = path:match("(.*/)") or "."
+	local root_dir = find_project_root(file_dir) or file_dir
 
 	local variables, var_positions = parser.extract_variables(content)
 	local functions = parser.extract_functions(content)
@@ -457,6 +498,226 @@ function handlers.textDocument_definition(params)
 	return nil
 end
 
+function handlers.textDocument_declaration(params)
+	local uri = params.textDocument.uri
+	local doc = documents[uri]
+	if not doc then
+		return nil
+	end
+
+	local lines = {}
+	for line in doc.content:gmatch("([^\n]*)\n") do
+		table.insert(lines, line)
+	end
+	if params.position.line + 1 > #lines then
+		return nil
+	end
+
+	local line = lines[params.position.line + 1]
+	local col = params.position.character + 1
+
+	local word_start = col
+	while word_start > 1 and line:sub(word_start - 1, word_start - 1):match("[%w_]") do
+		word_start = word_start - 1
+	end
+
+	local word_end = col
+	while word_end <= #line and line:sub(word_end, word_end):match("[%w_]") do
+		word_end = word_end + 1
+	end
+
+	local word = line:sub(word_start, word_end - 1):gsub("^#", "")
+	if not word or word == "" then
+		return nil
+	end
+
+	local function make_location(doc_uri, doc_line, doc_col, name_len)
+		name_len = name_len or 0
+		return {
+			uri = doc_uri,
+			range = {
+				start = { line = doc_line, character = doc_col },
+				["end"] = { line = doc_line, character = doc_col + name_len },
+			},
+		}
+	end
+
+	local locations = {}
+	local seen_locations = {}
+	local search_names = { word }
+
+	local function add_location(loc)
+		local key = loc.uri .. ":" .. tostring(loc.range.start.line) .. ":" .. tostring(loc.range.start.character)
+		if not seen_locations[key] then
+			seen_locations[key] = true
+			table.insert(locations, loc)
+		end
+	end
+
+	if doc.variables and doc.variables[word] then
+		local var_type = doc.variables[word].data_type
+		if var_type then
+			var_type = var_type:gsub("%s*;.*$", ""):gsub("%s*:=.*$", ""):gsub("^%s+", ""):gsub("%s+$", "")
+			local type_name = var_type:match("([%w_]+)")
+			if type_name and type_name ~= word then
+				table.insert(search_names, type_name)
+			end
+		end
+	end
+
+	for check_uri, check_doc in pairs(documents) do
+		if check_doc.functions then
+			for _, func in ipairs(check_doc.functions) do
+				for _, search_name in ipairs(search_names) do
+					if func.name == search_name then
+						add_location(make_location(check_uri, func.start, 0, #search_name))
+					end
+				end
+			end
+		end
+	end
+
+	local root_dirs = {}
+	for _, d in pairs(documents) do
+		if d.root_dir and d.root_dir ~= "" then
+			root_dirs[d.root_dir] = true
+		end
+	end
+
+	for root_dir, _ in pairs(root_dirs) do
+		local scl_files = scan_scl_files(root_dir)
+		for _, filepath in ipairs(scl_files) do
+			local cached = workspace_symbol_cache[":file:" .. filepath]
+			if not cached then
+				local variables, functions, types = parse_scl_file(filepath)
+				cached = { functions = functions, types = types }
+				workspace_symbol_cache[":file:" .. filepath] = cached
+			end
+
+			if cached.functions then
+				for _, func in ipairs(cached.functions) do
+					for _, search_name in ipairs(search_names) do
+						if func.name == search_name then
+							local file_uri = path_to_uri(filepath)
+							add_location(make_location(file_uri, func.start, 0, #search_name))
+						end
+					end
+				end
+			end
+
+			local handle = io.open(filepath, "r")
+			if handle then
+				local content = handle:read("*a")
+				handle:close()
+				for _, search_name in ipairs(search_names) do
+					local fb_pattern = 'FUNCTION_BLOCK%s+"' .. search_name .. '"'
+					local fb_plain = "^FUNCTION_BLOCK%s+" .. search_name .. "$"
+					if content:match(fb_pattern) or content:match(fb_plain) then
+						for line in content:gmatch("([^\n]*)\n") do
+							if line:match(fb_pattern) or line:match(fb_plain) then
+								local file_uri = path_to_uri(filepath)
+								add_location(make_location(file_uri, 0, 0, #search_name))
+								break
+							end
+						end
+					end
+
+					local db_pattern = 'DATA_BLOCK%s+"' .. search_name .. '"'
+					local db_plain = "^DATA_BLOCK%s+" .. search_name .. "$"
+					if content:match(db_pattern) or content:match(db_plain) then
+						for line in content:gmatch("([^\n]*)\n") do
+							if line:match(db_pattern) or line:match(db_plain) then
+								local file_uri = path_to_uri(filepath)
+								add_location(make_location(file_uri, 0, 0, #search_name))
+								break
+							end
+						end
+					end
+				end
+			end
+
+			if cached.types then
+				for type_name, type_info in pairs(cached.types) do
+					for _, search_name in ipairs(search_names) do
+						if type_name == search_name then
+							local file_uri = path_to_uri(filepath)
+							local start_line = type_info.start_line or 0
+							add_location(make_location(file_uri, start_line, 0, #search_name))
+						end
+					end
+				end
+			end
+		end
+	end
+
+	for root_dir, _ in pairs(root_dirs) do
+		local udt_result = run_command('find "' .. root_dir .. '" -type f -name "*.udt" 2>/dev/null')
+		if udt_result then
+			for filepath in udt_result:gmatch("[^\n]+") do
+				if filepath and filepath ~= "" then
+					local handle = io.open(filepath, "r")
+					if handle then
+						local file_content = handle:read("*a")
+						handle:close()
+						for _, search_name in ipairs(search_names) do
+							local type_line = file_content:match('TYPE%s+"' .. search_name .. '"')
+							if not type_line then
+								type_line = file_content:match("TYPE%s+" .. search_name)
+							end
+							if type_line then
+								local line_num = 1
+								for line in file_content:gmatch("([^\n]*)\n?") do
+									if line:match('TYPE%s+"' .. search_name .. '"') or line:match("TYPE%s+" .. search_name) then
+										local file_uri = path_to_uri(filepath)
+										add_location(make_location(file_uri, line_num - 1, 0, #search_name))
+										break
+									end
+									line_num = line_num + 1
+								end
+							end
+						end
+					end
+				end
+			end
+		end
+
+		local db_result = run_command('find "' .. root_dir .. '" -type f -name "*.db" 2>/dev/null')
+		if db_result then
+			for filepath in db_result:gmatch("[^\n]+") do
+				if filepath and filepath ~= "" then
+					local handle = io.open(filepath, "r")
+					if handle then
+						local file_content = handle:read("*a")
+						handle:close()
+						for _, search_name in ipairs(search_names) do
+							local db_line = file_content:match('DATA_BLOCK%s+"' .. search_name .. '"')
+							if not db_line then
+								db_line = file_content:match("DATA_BLOCK%s+" .. search_name)
+							end
+							if db_line then
+								local line_num = 1
+								for line in file_content:gmatch("([^\n]*)\n?") do
+									if line:match('DATA_BLOCK%s+"' .. search_name .. '"') or line:match("DATA_BLOCK%s+" .. search_name) then
+										local file_uri = path_to_uri(filepath)
+										add_location(make_location(file_uri, line_num - 1, 0, #search_name))
+										break
+									end
+									line_num = line_num + 1
+								end
+							end
+						end
+					end
+				end
+			end
+		end
+	end
+
+	if #locations > 0 then
+		return locations
+	end
+	return nil
+end
+
 function handlers.textDocument_references(params)
 	local uri = params.textDocument.uri
 	local doc = documents[uri]
@@ -923,6 +1184,7 @@ local function handle_message(message)
 	if message.method == "$/cancelRequest" then
 		return nil
 	end
+
 	-- Convert method name from "textDocument/didOpen" to "textDocument_didOpen"
 	local method_name = message.method:gsub("/", "_")
 	local handler = handlers[method_name]

src/parser.lua

@@ -17,22 +17,22 @@ function M.extract_variables(content)
   local function process_line(line, line_num)
     local trimmed = line:gsub("^%s+", ""):gsub("%s+$", "")
 
-    -- Detect block start
+    -- Detect block start (with or without quotes)
-    local fb_name = trimmed:match('FUNCTION_BLOCK%s+"([^"]+)"')
+    local fb_name = trimmed:match('FUNCTION_BLOCK%s+"([^"]+)"') or trimmed:match("^FUNCTION_BLOCK%s+([%w_]+)")
     if fb_name then
       current_block = { name = fb_name, kind = "function_block" }
       in_var_section = false
       return
     end
 
-    local ob_name = trimmed:match('ORGANIZATION_BLOCK%s+"([^"]+)"')
+    local ob_name = trimmed:match('ORGANIZATION_BLOCK%s+"([^"]+)"') or trimmed:match("^ORGANIZATION_BLOCK%s+([%w_]+)")
     if ob_name then
       current_block = { name = ob_name, kind = "organization_block" }
       in_var_section = false
       return
     end
 
-    local fn_name = trimmed:match('FUNCTION%s+"([^"]+)"')
+    local fn_name = trimmed:match('FUNCTION%s+"([^"]+)"') or trimmed:match("^FUNCTION%s+([%w_]+)")
     if fn_name then
       current_block = { name = fn_name, kind = "function" }
       in_var_section = false
@@ -239,7 +239,7 @@ function M.extract_functions(content)
   end
 
   for i, line in ipairs(lines) do
-    local func_name = line:match('FUNCTION%s+"([^"]+)"')
+    local func_name = line:match('FUNCTION%s+"([^"]+)"') or line:match("^FUNCTION%s+([%w_]+)")
     if func_name then
       local end_line = find_block_end(i, "END_FUNCTION", { "END_FUNCTION" })
       table.insert(functions, {
@@ -250,7 +250,7 @@ function M.extract_functions(content)
       })
     end
 
-    local fb_name = line:match('FUNCTION_BLOCK%s+"([^"]+)"')
+    local fb_name = line:match('FUNCTION_BLOCK%s+"([^"]+)"') or line:match("^FUNCTION_BLOCK%s+([%w_]+)")
     if fb_name then
       local end_line = find_block_end(i, "END_FUNCTION_BLOCK", { "END_FUNCTION_BLOCK" })
       table.insert(functions, {
@@ -261,7 +261,7 @@ function M.extract_functions(content)
       })
     end
 
-    local ob_name = line:match('ORGANIZATION_BLOCK%s+"([^"]+)"')
+    local ob_name = line:match('ORGANIZATION_BLOCK%s+"([^"]+)"') or line:match("^ORGANIZATION_BLOCK%s+([%w_]+)")
     if ob_name then
       local end_line = find_block_end(i, "END_ORGANIZATION_BLOCK", { "END_ORGANIZATION_BLOCK" })
       table.insert(functions, {

src/plc_json.lua

@@ -198,6 +198,21 @@ function M.load_types_from_workspace(root_dir)
     end
   end
 
+  -- Also scan for .udt files
+  local udt_files = scan_files_recursive(root_dir, "*.udt")
+  for _, filepath in ipairs(udt_files) do
+    local content = run_command("cat " .. filepath:gsub(" ", "\\ "))
+    if content then
+      local udt_types = parse_scl_type_file(content)
+      for name, typ in pairs(udt_types) do
+        typ.source = "udt_file"
+        if not types[name] then
+          types[name] = typ
+        end
+      end
+    end
+  end
+
   return types
 end