fclose: Fix test failure on AIX 7.2

fclose: Fix test failure on AIX 7.2

[Bruno Haible]

On AIX 7.2, I see this test failure:

FAIL: test-fclose
=================

../../gltests/test-fclose.c:74: assertion 'lseek (fd, 0, SEEK_CUR) == 3' failed
FAIL test-fclose (exit status: 134)

The cause is that while POSIX specify a certain behaviour regarding the
position of the underlying file descriptor for fflush() and fclose(),
most systems
  - either do it right for both — like musl libc —
  - or wrong for both — like glibc (at least up to version 2.32) —,
whereas AIX gets it right for fflush() but wrong for fclose().

This patch fixes it.


2021-01-05  Bruno Haible  <bruno@clisp.org>

	fclose: Fix test failure on AIX 7.2.
	* m4/fclose.m4 (gl_FUNC_FCLOSE_STDIN): New macro.
	(gl_FUNC_FCLOSE): Invoke it. Set REPLACE_FCLOSE accordingly.
	* doc/posix-functions/fclose.texi: Update platform information.
	* doc/posix-functions/fflush.texi: Likewise.

diff --git a/doc/posix-functions/fclose.texi b/doc/posix-functions/fclose.texi
index d3606b4..fb83f6a 100644
--- a/doc/posix-functions/fclose.texi
+++ b/doc/posix-functions/fclose.texi
@@ -11,7 +11,7 @@ Portability problems fixed by Gnulib:
 @item
 On some platforms, this function fails to set the file position of a
 seekable input stream to the byte after the last one actually read:
-glibc 2.13, FreeBSD.
+glibc 2.32, FreeBSD, AIX 7.2.
 @item
 This function crashes if the stream's file descriptor has already been
 closed on some platforms:
diff --git a/doc/posix-functions/fflush.texi b/doc/posix-functions/fflush.texi
index 1964da4..665951d 100644
--- a/doc/posix-functions/fflush.texi
+++ b/doc/posix-functions/fflush.texi
@@ -11,7 +11,8 @@ Portability problems fixed by Gnulib:
 @item
 @code{fflush} followed by @code{fseek} or @code{fseeko}, applied to an input
 stream, should have the effect of positioning the underlying file descriptor.
-It doesn't do this on some platforms.
+It doesn't do this on some platforms:
+glibc 2.32 and others.
 @item
 @code{fflush} on an input stream changes the position of the stream to the
 end of the previous buffer, on some platforms: mingw, MSVC 14.
diff --git a/m4/fclose.m4 b/m4/fclose.m4
index 13e1799..74a04e1 100644
--- a/m4/fclose.m4
+++ b/m4/fclose.m4
@@ -1,4 +1,4 @@
-# fclose.m4 serial 8
+# fclose.m4 serial 9
 dnl Copyright (C) 2008-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -23,4 +23,76 @@ AC_DEFUN([gl_FUNC_FCLOSE],
   case "$host_os" in
     openedition) REPLACE_FCLOSE=1 ;;
   esac
+
+  if test $REPLACE_FCLOSE = 0; then
+    gl_FUNC_FCLOSE_STDIN
+    case "$gl_cv_func_fclose_stdin" in
+      *yes) ;;
+      *) REPLACE_FCLOSE=1 ;;
+    esac
+  fi
+])
+
+dnl Determine whether fclose works on input streams.
+dnl Sets gl_cv_func_fclose_stdin.
+
+AC_DEFUN([gl_FUNC_FCLOSE_STDIN],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CHECK_HEADERS_ONCE([unistd.h])
+  AC_CACHE_CHECK([whether fclose works on input streams],
+    [gl_cv_func_fclose_stdin],
+    [echo hello world > conftest.txt
+     AC_RUN_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <fcntl.h>
+            #include <stdio.h>
+            #if HAVE_UNISTD_H
+            # include <unistd.h>
+            #else /* on Windows with MSVC */
+            # include <io.h>
+            #endif
+           ]GL_MDA_DEFINES],
+          [[int fd;
+            int fd2;
+            FILE *fp;
+            fd = open ("conftest.txt", O_RDONLY);
+            if (fd < 0)
+              return 1;
+            if (lseek (fd, 1, SEEK_SET) != 1)
+              return 2;
+            fd2 = dup (fd);
+            if (fd2 < 0)
+              return 3;
+            fp = fdopen (fd2, "r");
+            if (fp == NULL)
+              return 4;
+            if (fgetc (fp) != 'e')
+              { fclose (fp); return 5; }
+            /* This fclose() call should reposition the underlying file
+               descriptor.  */
+            if (fclose (fp) != 0)
+              return 6;
+            if (lseek (fd2, 0, SEEK_CUR) != -1) /* should fail with EBADF */
+              return 7;
+            /* Verify the file position.  */
+            if (lseek (fd, 0, SEEK_CUR) != 2)
+              return 8;
+            return 0;
+          ]])],
+       [gl_cv_func_fclose_stdin=yes],
+       [gl_cv_func_fclose_stdin=no],
+       [case "$host_os" in
+                         # Guess no on glibc systems.
+          *-gnu* | gnu*) gl_cv_func_fclose_stdin="guessing no" ;;
+                         # Guess yes on musl systems.
+          *-musl*)       gl_cv_func_fclose_stdin="guessing yes" ;;
+                         # Guess no on native Windows.
+          mingw*)        gl_cv_func_fclose_stdin="guessing no" ;;
+                         # If we don't know, obey --enable-cross-guesses.
+          *)             gl_cv_func_fclose_stdin="$gl_cross_guess_normal" ;;
+        esac
+       ])
+     rm conftest.txt
+    ])
 ])