From 9a2f02df6655f65e5a7892e853cc2112e28b89e8 Mon Sep 17 00:00:00 2001
From: varkor <github@varkor.com>
Date: Mon, 29 Jan 2018 12:50:36 +0000
Subject: [PATCH] Warn when `-C extra-filename` flag is used with `-o`

---
 src/librustc_driver/driver.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs
index 1ab5f19c2e2a..df8860823add 100644
--- a/src/librustc_driver/driver.rs
+++ b/src/librustc_driver/driver.rs
@@ -1378,6 +1378,9 @@ pub fn build_output_filenames(input: &Input,
             if *odir != None {
                 sess.warn("ignoring --out-dir flag due to -o flag.");
             }
+            if !sess.opts.cg.extra_filename.is_empty() {
+                sess.warn("ignoring -C extra-filename flag due to -o flag.");
+            }
 
             let cur_dir = Path::new("");