ftw: throw exception on failure.

The ftw function just returns -1 if, for instance, given a bad
path (nonexistent or no permissions).  The documentation also
has issues.

* ftw.c (ftw_wrap): If the return value is -1, convert it to a
file-error using errno_to_file_error and throw a diagnostic
exception. This situation can, of course, arise if the
callback function returns -1, in which case it should prepare
a value in errno.

* txr.1: Return value of callbackfn documented better.
Documented exception throwing behavior, and failed termination
if the callback returns -1.

1 files changed, 7 insertions, 1 deletions

diff --git a/ftw.c b/ftw.c
index 27b8e790..537e6d4f 100644
--- a/ftw.c
+++ b/ftw.c
@@ -30,6 +30,8 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <stddef.h>
+#include <string.h>
+#include <errno.h>
 #include <ftw.h>
 #include "config.h"
 #include "alloca.h"
@@ -122,7 +124,11 @@ val ftw_wrap(val dirpath, val fn, val flags_in, val nopenfd_in)
     case 0:
       return t;
     case -1:
-      return nil;
+      {
+        int eno = errno;
+        uw_throwf(errno_to_file_error(eno), lit("ftw ~a: ~d/~s"),
+                  dirpath, num(eno), string_utf8(strerror(eno)), nao);
+      }
     default:
       return num(res);
     }