Server externals are complicated. Abstract away with features?

To summarize:
- Short-circuit anything in `node_modules`
- Skip relative paths or non-valid names (e.g. `webpack/hot/poll?1000`)
- Folder or file (`.js`) has to exist in `node_modules`

This solves any problems with server-side `externals` and `alias`.

``` diff
diff --git a/webpack.config.test.js b/webpack.config.test.js
index 87af92b..094abbb 100644
--- a/webpack.config.test.js
+++ b/webpack.config.test.js
@@ -1,3 +1,17 @@
+/* eslint-disable no-var */
+var fs = require("fs");
+var path = require("path");
+
+function nodeModuleExists(request) {
+ try {
+ fs.accessSync(path.resolve(process.cwd(), "node_modules", request));
+ } catch (e) {
+ return false;
+ }
+
+ return true;
+}
+
module.exports = require("./webpack.config.defaults")
.externals(
/^@?\w[a-z\-0-9\./]+$/,
@@ -6,7 +20,24 @@ module.exports = require("./webpack.config.defaults")
"react/lib/ReactContext"
)
.loader("babel", ".js", {
- exclude: /node_modules/,
+ function(context, request, callback) {
+ if (
+ /node_modules/.test(context)
+ || (
+ /^@?\w[a-z\-0-9\./]+$/.test(request)
+ &&
+ (
+ nodeModuleExists(request)
+ ||
+ nodeModuleExists(`${request}.js`)
+ )
+ )
+ ) {
+ return callback(null, `commonjs ${request}`);
+ }
+
+ callback();
+ },
query: { cacheDirectory: true },
})
.loader("null", ".css")
```

Start with webpack.config.test.js and the existing externals and loader configuration. Check how server-side externals and aliases are currently handled, then compare the proposed node_modules checks and request filtering against the stated requirements. Done means those cases are abstracted into the project’s configuration without breaking valid module resolution.

Written by the indexing model from the issue text.