separable loaders as opt-in feature, fixes #16

in future separable loaders may run in a
  sperate process for performance reasons

README.md

@@ -409,6 +409,7 @@ You can also save this options object in a JSON file and use it with the shell c
  //  "module"           (module, filename) before a module is loaded
  //  "context"          (module, dirname) before a context is loaded
  //  "dependency"       (filename) before a dependency is loaded
+ //  "static-dependency"(filename) after a dependency is flagged as not recompile-able
  //  "loader"           (filename) before a loader is required
  //  -- events for progress --
  //  "task"             (name?) start of a task

lib/execLoaders.js

@@ -30,15 +30,21 @@ module.exports = function(context, request, loaders, filenames, contents, cacheE
 				var loaderFilename = require.resolve(name);
 				options.events.emit("loader", loaderFilename);
 
-				// require loader in fresh context
-				var oldCache = {};
-				for(var entry in require.cache) {
-					oldCache[entry] = require.cache[entry];
-					delete require.cache[entry];
-				}
 				var loader = require(loaderFilename);
-				for(var entry in oldCache) {
-					require.cache[entry] = oldCache[entry];
+
+				if(loader.separable) {
+					// require loader in fresh context
+					var oldCache = {};
+					for(var entry in require.cache) {
+						oldCache[entry] = require.cache[entry];
+						delete require.cache[entry];
+					}
+					loader = require(loaderFilename);
+					for(var entry in oldCache) {
+						require.cache[entry] = oldCache[entry];
+					}
+				} else {
+					options.events.emit("static-dependency", loaderFilename);
 				}
 
 				loaderFunctions.push(loader);

lib/webpack.js

@@ -165,6 +165,7 @@ module.exports = function(context, moduleName, options, callback) {
 		var isRunning = true;
 		var isWaiting = false;
 		var runAgain = false;
+		var staticChanges = [];
 
 		// Start the timeout again
 		function startAgain() {
@@ -179,6 +180,11 @@ module.exports = function(context, moduleName, options, callback) {
 				});
 				watchers.length = 0;
 
+				if(staticChanges.length > 0)
+					return callback(new Error(
+						"Files (" + staticChanges.join(", ") +
+						") changed. Webpack cannot recompile in this watch step."));
+
 				runAgain = false;
 				isRunning = true;
 				isWaiting = false;
@@ -229,6 +235,16 @@ module.exports = function(context, moduleName, options, callback) {
 			}));
 		});
 
+		// on before a static dependency is read
+		options.events.on("static-dependency", function(filename) {
+			if(!filename) return;
+			watchers.push(fs.watch(filename, function() {
+				if(staticChanges.indexOf(filename) == -1)
+					staticChanges.push(filename);
+				change();
+			}));
+		});
+
 		// on user defines the bundle as invalid
 		options.events.on("invalid", function() {
 			change();

test/browsertest/build.js

@@ -39,5 +39,5 @@ libary1.on("exit", function(code) {
 	}
 });
 var libary2 = cp.spawn("node", join(["../../bin/webpack.js", "--colors", "--libary", "libary2",
-									"--script-src-prefix", "js/", "--options", "libary2config.js", "node_modules/libary2", "js/libary2.js"], extraArgs));
+									"--script-src-prefix", "js/", "--options", "libary2config.js", "node_modules/libary2", "js/libary2.js"], extraArgsNoWatch));
 bindOutput(libary2);