Improve input preprocessor failure diagnostics (#328)

This fixes gwsw/less issue #327.
* configure.ac: Check for sys/wait.h and for strsignal.
* edit.c: Include <sys/wait.h> if available.
(close_pipe): Always diagnose internal error with pclose.
On POSIX-compatible systems, generate better diagnostics
that distinguish between ordinary exit and signals,
and do not diagnose SIGPIPE after the user types 'q'
as that is normal and expected.
* os.c (signal_message): New function.

configure.ac

@@ -36,7 +36,7 @@ AC_CHECK_LIB(termlib, tgetent, [have_termlib=yes], [have_termlib=no])
 AC_SEARCH_LIBS([regcmp], [gen intl PW])
 
 # Checks for header files.
-AC_CHECK_HEADERS_ONCE([ctype.h errno.h fcntl.h limits.h stdio.h stdlib.h string.h termcap.h termio.h termios.h time.h unistd.h values.h linux/magic.h sys/ioctl.h sys/stream.h sys/types.h time.h wctype.h])
+AC_CHECK_HEADERS_ONCE([ctype.h errno.h fcntl.h limits.h stdio.h stdlib.h string.h termcap.h termio.h termios.h time.h unistd.h values.h linux/magic.h sys/ioctl.h sys/stream.h sys/types.h sys/wait.h time.h wctype.h])
 
 # Checks for typedefs, structures, and compiler characteristics.
 AC_HEADER_STAT
@@ -264,7 +264,7 @@ AC_MSG_CHECKING(for ANSI function prototypes)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[int f(int a) { return a; }]])],[AC_MSG_RESULT(yes); AC_DEFINE(HAVE_ANSI_PROTOS)],[AC_MSG_RESULT(no)])
 
 # Checks for library functions.
-AC_CHECK_FUNCS([fchmod fsync nanosleep poll popen realpath _setjmp sigprocmask sigsetmask snprintf stat system ttyname usleep])
+AC_CHECK_FUNCS([fchmod fsync nanosleep poll popen realpath _setjmp sigprocmask sigsetmask snprintf stat strsignal system ttyname usleep])
 
 # AC_CHECK_FUNCS may not work for inline functions, so test these separately.
 AC_MSG_CHECKING(for memcpy)

edit.c

@@ -13,6 +13,9 @@
 #if HAVE_STAT
 #include <sys/stat.h>
 #endif
+#if HAVE_SYS_WAIT_H
+#include <sys/wait.h>
+#endif
 #if OS2
 #include <signal.h>
 #endif
@@ -262,6 +265,7 @@ static void check_modelines(void)
 static void close_pipe(FILE *pipefd)
 {
  int status;
+ PARG parg;
 
  if (pipefd == NULL)
  return;
@@ -273,9 +277,37 @@ static void close_pipe(FILE *pipefd)
  kill(pipefd->_pid, SIGINT);
 #endif
  status = pclose(pipefd);
- if (status != 0 && show_preproc_error)
+ if (status == -1)
  {
- PARG parg;
+ /* An internal error in 'less', not a preprocessor error. */
+ parg.p_string = errno_message("pclose");
+ error("%s", &parg);
+ free(parg.p_string);
+ return;
+ }
+ if (!show_preproc_error)
+ return;
+#if defined WIFEXITED && defined WEXITSTATUS
+ if (WIFEXITED(status)) {
+ int s = WEXITSTATUS(status);
+ if (s != 0) {
+ parg.p_int = s;
+ error("Input preprocessor failed (status %d)", &parg);
+ }
+ return;
+ }
+#endif
+#if defined WIFSIGNALED && defined WTERMSIG && HAVE_STRSIGNAL
+ if (WIFSIGNALED(status)) {
+ int sig = WTERMSIG(status);
+ if (sig != SIGPIPE || ch_length() != NULL_POSITION) {
+ parg.p_string = signal_message(sig);
+ error("Input preprocessor terminated: %s", &parg);
+ }
+ return;
+ }
+#endif
+ if (status != 0) {
  parg.p_int = status;
  error("Input preprocessor exited with status %x", &parg);
  }

os.c

@@ -338,6 +338,22 @@ public char * errno_message(char *filename)
  return (m);
 }
 
+/*
+ * Return a description of a signal.
+ * The return value is good until the next call to this function.
+ */
+public char * signal_message(int sig)
+{
+ static char sigbuf[sizeof "signal " + INT_STRLEN_BOUND(sig)];
+#if HAVE_STRSIGNAL
+ char *description = strsignal(sig);
+ if (description)
+ return description;
+#endif
+ sprintf(sigbuf, "Signal %d", sig);
+ return sigbuf;
+}
+
 /* #define HAVE_FLOAT 0 */
 
 static POSITION muldiv(POSITION val, POSITION num, POSITION den)