Throw better errors for failing (not missing) plugins (#243)

index.js

@@ -34,7 +34,10 @@ const cliConfig = {
         try {
           return require(plugin)()
         } catch (e) {
-          return error(`Plugin Error: Cannot find module '${plugin}'`)
+          const msg = e.message || `Cannot find module '${plugin}'`
+          let prefix = msg.includes(plugin) ? '' : ` (${plugin})`
+          if (e.name && e.name !== 'Error') prefix += `: ${e.name}`
+          return error(`Plugin Error${prefix}: ${msg}'`)
         }
       })
     : []

test/error.js

@@ -40,7 +40,7 @@ test.failing('invalid --config', t => {
   })
 })
 
-test('PluginError', t => {
+test('plugin not found', t => {
   return cli(['test/fixtures/a.css', '-u', 'postcss-plugin', '-o', tmp()]).then(
     ({ err, code }) => {
       t.is(code, 1, 'expected non-zero error code')
@@ -52,6 +52,19 @@ test('PluginError', t => {
   )
 })
 
+test('plugin throws on require', t => {
+  return cli([
+    'test/fixtures/a.css',
+    '-u',
+    './test/fixtures/bad-plugin',
+    '-o',
+    tmp()
+  ]).then(({ err, code }) => {
+    t.is(code, 1, 'expected non-zero error code')
+    t.regex(err.toString(), /Plugin Error \(.*bad-plugin\): This fails/)
+  })
+})
+
 test('CssSyntaxError', t => {
   return cli(['test/fixtures/a.css', '--parser', 'sugarss', '-o', tmp()]).then(
     ({ err, code }) => {

test/fixtures/bad-plugin.js

@@ -0,0 +1 @@
+throw new Error('This fails')