Improve config loading error handling

3 files changed, 136 insertions, 20 deletions

diff --git a/luacov-scm-1.rockspec b/luacov-scm-1.rockspec
index 5df14bc..3e4d79b 100644
--- a/luacov-scm-1.rockspec
+++ b/luacov-scm-1.rockspec
@@ -30,6 +30,7 @@ build = {
     ["luacov.stats"] = "src/luacov/stats.lua",
     ["luacov.tick"] = "src/luacov/tick.lua",
     ["luacov.hook"] = "src/luacov/hook.lua",
+    ["luacov.util"] = "src/luacov/util.lua"
   },
   install = {
     bin = {
diff --git a/src/luacov/runner.lua b/src/luacov/runner.lua
index d7f150b..160cc95 100644
--- a/src/luacov/runner.lua
+++ b/src/luacov/runner.lua
@@ -9,9 +9,11 @@ local runner = {}
 runner.version = "0.11.0"
 
 local stats = require("luacov.stats")
+local util = require("luacov.util")
 runner.defaults = require("luacov.defaults")
 
 local debug = require("debug")
+local raw_os_exit = os.exit
 
 local new_anchor = newproxy or function() return {} end -- luacheck: compat
 
@@ -146,16 +148,6 @@ local function on_exit()
    end
 end
 
--- Returns true if the given filename exists.
-local function file_exists(fname)
-   local f = io.open(fname)
-
-   if f then
-      f:close()
-      return true
-   end
-end
-
 local dir_sep = package.config:sub(1, 1)
 local wildcard_expansion = "[^/]+"
 
@@ -315,6 +307,31 @@ local function set_config(configuration)
    runner.tick = runner.tick or runner.configuration.tick
 end
 
+local function die(error_msg)
+   io.stderr:write(("Error: %s\n"):format(error_msg))
+   raw_os_exit(1)
+end
+
+local function load_config_file(name, is_default)
+   local ok, conf, error_msg = util.load_config(name, _G)
+
+   if ok then
+      if type(conf) ~= "table" then
+         die("config is not a table")
+      end
+
+      return conf
+   end
+
+   local error_type = conf
+
+   if error_type == "read" and is_default then
+      return nil
+   end
+
+   die(("couldn't %s config file %s: %s"):format(error_type, name, error_msg))
+end
+
 local default_config_file = ".luacov"
 
 ------------------------------------------------------
@@ -327,14 +344,10 @@ local default_config_file = ".luacov"
 function runner.load_config(configuration)
    if not runner.configuration then
       if not configuration then
-         -- nothing provided, load from default location if possible
-         if file_exists(default_config_file) then
-            set_config(dofile(default_config_file))
-         else
-            set_config(runner.defaults)
-         end
+         -- Nothing provided, load from default location if possible.
+         set_config(load_config_file(default_config_file, true) or runner.defaults)
       elseif type(configuration) == "string" then
-         set_config(dofile(configuration))
+         set_config(load_config_file(configuration))
       elseif type(configuration) == "table" then
          set_config(configuration)
       else
@@ -406,10 +419,9 @@ function runner.init(configuration)
 
    -- metatable trick on filehandle won't work if Lua exits through
    -- os.exit() hence wrap that with exit code as well
-   local rawexit = os.exit
    os.exit = function(...) -- luacheck: no global
       on_exit()
-      rawexit(...)
+      raw_os_exit(...)
    end
 
    debug.sethook(runner.debug_hook, "l")
@@ -518,7 +530,7 @@ local function getfilename(name)
          error("Bad argument: " .. tostring(name))
       end
 
-      if file_exists(name) then
+      if util.file_exists(name) then
          return name
       end
 
diff --git a/src/luacov/util.lua b/src/luacov/util.lua
new file mode 100644
index 0000000..9f8e6f9
--- /dev/null
+++ b/src/luacov/util.lua
@@ -0,0 +1,103 @@
+---------------------------------------------------
+-- Utility module.
+-- @class module
+-- @name luacov.util
+local util = {}
+
+--- Removes a prefix from a string if it's present.
+-- @param str a string.
+-- @param prefix a prefix string.
+-- @return original string if does not start with prefix
+-- or string without prefix.
+function util.unprefix(str, prefix)
+   if str:sub(1, #prefix) == prefix then
+      return str:sub(#prefix + 1)
+   else
+      return str
+   end
+end
+
+-- Returns contents of a file or nil + error message.
+local function read_file(name)
+   local f, open_err = io.open(name, "rb")
+
+   if not f then
+      return nil, util.unprefix(open_err, name .. ": ")
+   end
+
+   local contents, read_err = f:read("*a")
+   f:close()
+
+   if contents then
+      return contents
+   else
+      return nil, read_err
+   end
+end
+
+--- Loads a string.
+-- @param str a string.
+-- @param[opt] env environment table.
+-- @param[opt] chunkname chunk name.
+function util.load_string(str, env, chunkname)
+   if _VERSION:find("5%.1") then
+      local func, err = loadstring(str, chunkname)
+
+      if not func then
+         return nil, err
+      end
+
+      if env then
+         setfenv(func, env)
+      end
+
+      return func
+   else
+      return load(str, chunkname, "bt", env or _ENV)
+   end
+end
+
+--- Load a config file.
+-- Reads, loads and runs a Lua file in an environment.
+-- @param name file name.
+-- @param env environment table.
+-- @return true and the first return value of config on success,
+-- nil + error type + error message on failure, where error type
+-- can be "read", "load" or "run".
+function util.load_config(name, env)
+   local src, read_err = read_file(name)
+
+   if not src then
+      return nil, "read", read_err
+   end
+
+   local func, load_err = util.load_string(src, env, "@config")
+
+   if not func then
+      return nil, "load", "line " .. util.unprefix(load_err, "config:")
+   end
+
+   local ok, ret = pcall(func)
+
+   if not ok then
+      return nil, "run", "line " .. util.unprefix(ret, "config:")
+   end
+
+   return true, ret
+end
+
+--- Checks if a file exists.
+-- @param name file name.
+-- @return true if file can be opened, false otherwise.
+function util.file_exists(name)
+   local f = io.open(name)
+
+   if f then
+      f:close()
+      return true
+   else
+      return false
+   end
+end
+
+return util