From b8bf62b60a63e4af4be0cfdd7b4e0d4b424af45c Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 11 Mar 2021 10:35:04 -0800
Subject: [PATCH] On MS-Windows, fflush stderr after newline

Problem reported by Ioannis Kappas (Bug#46388).
* src/sysdep.c (errputc) [WINDOWSNT]: Flush stderr after newline.
---
 src/sysdep.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/sysdep.c b/src/sysdep.c
index 24d8832b2f3..d940acc4e05 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -2670,6 +2670,13 @@ void
 errputc (int c)
 {
   fputc_unlocked (c, errstream ());
+
+#ifdef WINDOWSNT
+  /* Flush stderr after outputting a newline since stderr is fully
+     buffered when redirected to a pipe, contrary to POSIX.  */
+  if (c == '\n')
+    fflush_unlocked (stderr);
+#endif
 }
 
 void
-- 
2.39.2