From 3324bb013cdd5e835bd8374d5c31f037948f89f0 Mon Sep 17 00:00:00 2001
From: rxi <rxi@users.noreply.github.com>
Date: Sun, 2 Mar 2014 17:13:18 +0000
Subject: [PATCH] Added error handling to lume.hotswap()

Changed lume.hotswap() to return an error and restore the global
environment if an error occurs when requiring the new package
---
 README.md | 14 ++++++++------
 lume.lua  | 28 ++++++++++++++++++----------
 2 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/README.md b/README.md
index bcdc7ad..17fb766 100644
--- a/README.md
+++ b/README.md
@@ -5,8 +5,8 @@ A collection of functions for Lua, geared towards game development.
 
 ## Installation
 
-The [lume.lua](lume.lua?raw=1) file should be dropped into an existing project and
-required by it:
+The [lume.lua](lume.lua?raw=1) file should be dropped into an existing project
+and required by it:
 
 ```lua
 lume = require "lume"
@@ -205,12 +205,14 @@ lume.dostring("print('Hello!')") -- Prints "Hello!"
 ```
 
 ### lume.hotswap(modname)
-Reloads an already loaded module in place; `modname` should be the same string
-used when loading the module with require(). This function can be used to
-immediatly see the effects of code changes without having to restart the
-program.
+Reloads an already loaded module in place, allowing you to immediatly see the
+effects of code changes without having to restart the program. `modname` should
+be the same string used when loading the module with require(). In the case of
+an error the global environment is restored and `nil` plus an error message is
+returned.
 ```lua
 lume.hotswap("lume") -- Reloads the lume module
+assert(lume.hotswap("inexistant_module")) -- Raises an error
 ```
 
 ### lume.rgba(color)
diff --git a/lume.lua b/lume.lua
index 274f7dd..1ccd563 100644
--- a/lume.lua
+++ b/lume.lua
@@ -229,6 +229,7 @@ end
 
 
 function lume.hotswap(modname)
+  local oldglobal = lume.clone(_G)
   local updated = {}
   local function update(old, new)
     if updated[old] then return end 
@@ -239,18 +240,25 @@ function lume.hotswap(modname)
       if type(v) == "table" then update(old[k], v) else old[k] = v end
     end
   end
-  local oldglobal = lume.clone(_G)
   local oldmod = require(modname)
-  package.loaded[modname] = nil
-  local newmod = require(modname)
-  package.loaded[modname] = oldmod
-  if type(oldmod) == "table" then update(oldmod, newmod) end
-  for k, v in pairs(oldglobal) do
-    if v ~= _G[k] and type(v) == "table" then 
-      update(v, _G[k])
-      _G[k] = v
-    end
+  local err = nil
+  local function onerror(e)
+    for k, v in pairs(_G) do _G[k] = oldglobal[k] end
+    err = lume.trim(e)
   end
+  xpcall(function()
+    package.loaded[modname] = nil
+    local newmod = require(modname)
+    if type(oldmod) == "table" then update(oldmod, newmod) end
+    for k, v in pairs(oldglobal) do
+      if v ~= _G[k] and type(v) == "table" then 
+        update(v, _G[k])
+        _G[k] = v
+      end
+    end
+  end, onerror)
+  package.loaded[modname] = oldmod
+  if err then return nil, err end
   return oldmod
 end