Tell users what's going on in postinstall

Author: taion

npm-scripts/postinstall.js

@@ -1,11 +1,27 @@
-var execSync = require('child_process').execSync
 var stat = require('fs').stat
 
-function exec(command) {
-  execSync(command, { stdio: [0, 1, 2] })
-}
-
 stat('lib', function (error, stat) {
-  if (error || !stat.isDirectory())
-    exec('npm run build')
+  if (error || !stat.isDirectory()) {
+    console.warn(
+      '-'.repeat(79) + '\n' +
+'Built output not found. It looks like you might be attempting to install React\n' +
+'Router from GitHub. React Router sources need to be transpiled before use. We\n'+
+'will now make a best-efforts attempt to transpile the code. This will only work\n' +
+'if your development environment is set up appropriately.\n' +
+      '-'.repeat(79)
+    )
+
+    try {
+      var execSync = require('child_process').execSync
+      execSync('npm run build', { stdio: [ 0, 1, 2 ] })
+    } catch (e) {
+      console.error(
+        '-'.repeat(79) + '\n' +
+'Failed to build React Router automatically. Please install React Router from\n' +
+'npm, or clone the repo locally and build the library manually.\n' +
+        '-'.repeat(79)
+      )
+      throw(e)
+    }
+  }
 })