src/parser/parseSync.js in prettier-1.5.3 vs src/parser/parseSync.js in prettier-1.5.4

@@ -2,12 +2,27 @@
 
 // Formats and sends a request to the parser server. We use netcat (or something
 // like it) here since Prettier requires the results of `parse` to be
 // synchronous and Node.js does not offer a mechanism for synchronous socket
 // requests.
-function parseSync(parser, source) {
-  const { stdout, stderr, status } = requestParse(parser, source);
+function parseSync(parser, source, opts) {
+  const { stdout, stderr, status } = requestParse(parser, source, opts);
 
+  // We need special handling in case the user's version of nc doesn't support
+  // using unix sockets.
+  if (stderr.includes("invalid option -- U")) {
+    throw new Error(`
+      @prettier/plugin-ruby uses netcat to communicate over unix sockets between
+      the node.js process running prettier and an underlying Ruby process used
+      for parsing. Unfortunately the version of netcat that you have installed
+      (GNU netcat) does not support unix sockets. To solve this either uninstall
+      GNU netcat and use a different implementation, or change the value of the
+      rubyNetcatCommand option in your prettier configuration.
+    `);
+  }
+
+  // If we didn't receive anything over stdout or we have a bad exit status,
+  // then throw whatever we can.
   if (stdout.length === 0 || (status !== null && status !== 0)) {
     throw new Error(stderr || "An unknown error occurred");
   }
 
   const parsed = JSON.parse(stdout);