fix: Occur error when can't detect language (#27)

lua/js-i18n/config.lua

@@ -18,7 +18,7 @@ function M.default_detect_language(path)
   local abs_path = vim.fn.fnamemodify(path, ":p")
   local split = vim.split(abs_path, "[/.]")
 
-  local lang = nil
+  local lang = "unknown"
 
   for _, part in ipairs(vim.fn.reverse(split)) do
     if LangSet[normalize_lang(part)] then

lua/js-i18n/utils.lua

@@ -23,10 +23,13 @@ end
 --- @return string|nil ライブラリの識別子
 function M.detect_library(bufnr)
   local root = M.get_workspace_root(bufnr)
-  local package_json = root .. "/package.json"
 
-  local package = vim.fn.json_decode(vim.fn.readfile(package_json))
+  local ok, package_json = pcall(vim.fn.readfile, root .. "/package.json")
+  if not ok then
+    return nil
+  end
 
+  local package = vim.fn.json_decode(package_json)
   if package == nil then
     return nil
   end

tests/js-i18n/config_spec.lua

@@ -5,12 +5,12 @@ describe("js-i18n.config", function()
     local tests = {
       { path = "/path/to/locals/en/trans.json", expected = "en" },
       { path = "/path/to/locals/ja/trans.json", expected = "ja" },
-      { path = "/path/to/locals/hoge/trans.json", expected = nil },
+      { path = "/path/to/locals/hoge/trans.json", expected = "unknown" },
 
       -- Test cases to verify that it is sufficient for the languagee name to be included somewhere.
       { path = "/path/to/locals/sub/en.json", expected = "en" },
       { path = "/path/to/en/locals/trans.json", expected = "en" },
-      { path = "/path/to/locals/en-trans.json", expected = nil },
+      { path = "/path/to/locals/en-trans.json", expected = "unknown" },
 
       -- Test cases for language names with any case and separating characters.
       { path = "/path/to/locals/en-us/trans.json", expected = "en-us" },