Quote proposals in error message

packages/babel-parser/src/plugin-utils.js

@@ -62,7 +62,7 @@ export function validatePlugins(plugins: PluginList) {
   ) {
     throw new Error(
       "'pipelineOperator' requires 'proposal' option whose value should be one of: " +
-        PIPELINE_PROPOSALS.join(", "),
+        PIPELINE_PROPOSALS.map(p => `'${p}'`).join(", "),
     );
   }
 }

packages/babel-parser/test/fixtures/experimental/pipeline-operator/invalid-proposal/options.json

@@ -2,5 +2,5 @@
   "plugins": [
     ["pipelineOperator", { "proposal": "invalid" }]
   ],
-  "throws": "'pipelineOperator' requires 'proposal' option whose value should be one of: minimal, smart"
+  "throws": "'pipelineOperator' requires 'proposal' option whose value should be one of: 'minimal', 'smart'"
 }