[PATCH] Use __fpurge when fpurge is undeclared

[Mike Gilbert <floppym@xxxxxxxxxx>]

glibc neither declares nor defines fpurge(). Instead, it provides an
equivalent function __fpurge() in stdio_ext.h.

musl defines fpurge as an alias for __fpurge, but does not declare the
former in stdio.h.

Checking for the fpurge symbol breaks building on musl since the
function is not declared in headers. Check for the declaration instead.

Bug: https://bugs.gentoo.org/963567
---
 Src/utils.c      | 23 ++++++++++++++++-------
 Src/zsh_system.h |  3 +++
 configure.ac     |  6 +++++-
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/Src/utils.c b/Src/utils.c
index 4ea7b8e93..332d5db66 100644
--- a/Src/utils.c
+++ b/Src/utils.c
@@ -2011,6 +2011,17 @@ movefd(int fd)
     return fd;
 }
 
+static void
+invoke_fpurge(FILE *fp)
+{
+#if HAVE_DECL_FPURGE
+    fpurge(fp);
+#elif HAVE_DECL___FPURGE
+    /* glibc and musl do not declare fpurge, use __fpurge instead */
+    __fpurge(fp);
+#endif
+}
+
 /*
  * Move fd x to y.  If x == -1, fd y is closed.
  * Returns y for success, -1 for failure.
@@ -2022,7 +2033,6 @@ redup(int x, int y)
 {
     int ret = y;
 
-#ifdef HAVE_FPURGE
     /* Make sure buffers are cleared when changing descriptor for a
      * FILE object.  No fflush() here because the only way anything
      * can legitimately be left in the buffer is when an error has
@@ -2030,18 +2040,17 @@ redup(int x, int y)
      * and at worst squirt out something unexpected.
      */
     if (stdout && y == fileno(stdout))
-	fpurge(stdout);
+	invoke_fpurge(stdout);
     if (stderr && y == fileno(stderr))
-	fpurge(stderr);
+	invoke_fpurge(stderr);
     if (shout && y == fileno(shout))
-	fpurge(shout);
+	invoke_fpurge(shout);
     if (xtrerr && y == fileno(xtrerr))
-	fpurge(xtrerr);
+	invoke_fpurge(xtrerr);
 #ifndef _IONBF
     /* See init.c setupshin() -- stdin otherwise unbuffered */
     if (stdin && y == fileno(stdin))
-	fpurge(stdin);
-#endif
+	invoke_fpurge(stdin);
 #endif
 
     if(x < 0)
diff --git a/Src/zsh_system.h b/Src/zsh_system.h
index 21446a9b1..2b9e9deee 100644
--- a/Src/zsh_system.h
+++ b/Src/zsh_system.h
@@ -136,6 +136,9 @@ char *alloca (size_t);
 #endif
 
 #include <stdio.h>
+#ifdef HAVE_STDIO_EXT_H
+# include <stdio_ext.h>
+#endif
 #include <ctype.h>
 #include <sys/stat.h>
 #include <signal.h>
diff --git a/configure.ac b/configure.ac
index 13895bb1d..8d9198a4d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1250,7 +1250,7 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       select poll \
 	       readlink faccessx fchdir ftruncate \
 	       fstat lstat lchown fchown fchmod \
-	       fpurge fseeko ftello \
+	       fseeko ftello \
 	       mkfifo _mktemp mkstemp \
 	       waitpid wait3 \
 	       sigqueue \
@@ -1292,6 +1292,10 @@ AC_CHECK_FUNCS(strftime strptime mktime timelocal \
 	       setutxent getutxent endutxent getutent)
 AC_FUNC_STRCOLL
 
+AC_CHECK_DECLS([fpurge])
+AC_CHECK_HEADERS([stdio_ext.h])
+AC_CHECK_DECLS([__fpurge], , , [#include <stdio_ext.h>])
+
 # isinf() and isnan() can exist as either functions or macros.
 AH_TEMPLATE([HAVE_ISINF],
   [Define to 1 if you have the `isinf' macro or function.])
-- 
2.51.0