Unify error handling for reading directories.

* m4/path.c (m4_path_search): Factor open attempts...
(m4_fopen): ...into new function, to reject directories.
* tests/others.at (directory): Enhance test.
* doc/m4.texinfo (Include): Document that directories cannot be
input files.

Signed-off-by: Eric Blake <ebb9@byu.net>
(cherry picked from commit eed62f0d2729c243d7c081c48d789f9d86fa340f)

4 files changed, 46 insertions, 10 deletions

diff --git a/ChangeLog b/ChangeLog
index 8b0f04a8..fd85259a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2008-09-25  Eric Blake  <ebb9@byu.net>
 
+	Unify error handling for reading directories.
+	* m4/path.c (m4_path_search): Factor open attempts...
+	(m4_fopen): ...into new function, to reject directories.
+	* tests/others.at (directory): Enhance test.
+	* doc/m4.texinfo (Include): Document that directories cannot be
+	input files.
+
 	Avoid bugs on platforms that mishandle trailing /.
 	* ltdl/m4/gnulib-cache.m4: Import fopen module.
 	* tests/others.at (directory): New test.
diff --git a/doc/m4.texinfo b/doc/m4.texinfo
index ad0b2d47..9f523e5e 100644
--- a/doc/m4.texinfo
+++ b/doc/m4.texinfo
@@ -5729,7 +5729,8 @@ the previous input file.
 The expansion of @code{include} and @code{sinclude} is therefore the
 contents of @var{file}.
 
-If @var{file} does not exist (or cannot be read), the expansion is void,
+If @var{file} does not exist, is a directory, or cannot otherwise be
+read, the expansion is void,
 and @code{include} will fail with an error while @code{sinclude} is
 silent.  The empty string counts as a file that does not exist.
 
diff --git a/m4/path.c b/m4/path.c
index 91991e00..bf151935 100644
--- a/m4/path.c
+++ b/m4/path.c
@@ -123,6 +123,29 @@ m4_add_include_directory (m4 *context, const char *dir, bool prepend)
 #endif
 }
 
+/* Attempt to open FILE; if it opens, verify that it is not a
+   directory, and ensure it does not leak across execs.  */
+static FILE *
+m4_fopen (m4 *context, const char *file, const char *mode)
+{
+  FILE *fp = fopen (file, "r");
+  if (fp)
+    {
+      struct stat st;
+      int fd = fileno (fp);
+      if (fstat (fd, &st) == 0 && S_ISDIR (st.st_mode))
+	{
+	  fclose (fp);
+	  errno = EISDIR;
+	  return NULL;
+	}
+      if (set_cloexec_flag (fileno (fp), true) != 0)
+	m4_error (context, 0, errno, NULL,
+		  _("cannot protect input file across forks"));
+    }
+  return fp;
+}
+
 /* Search for FILE according to -B options, `.', -I options, then
    M4PATH environment.  If successful, return the open file, and if
    RESULT is not NULL, set *RESULT to a malloc'd string that
@@ -152,12 +175,9 @@ m4_path_search (m4 *context, const char *file, char **expanded_name)
      lookup will do the trick.  */
   if (IS_ABSOLUTE_FILE_NAME (file) || m4_get_posixly_correct_opt (context))
     {
-      fp = fopen (file, "r");
+      fp = m4_fopen (context, file, "r");
       if (fp != NULL)
 	{
-	  if (set_cloexec_flag (fileno (fp), true) != 0)
-	    m4_error (context, 0, errno, NULL,
-		      _("cannot protect input file across forks"));
 	  if (expanded_name != NULL)
 	    *expanded_name = xstrdup (file);
 	  return fp;
@@ -174,16 +194,12 @@ m4_path_search (m4 *context, const char *file, char **expanded_name)
       xfprintf (stderr, "path_search (%s) -- trying %s\n", file, name);
 #endif
 
-      fp = fopen (name, "r");
+      fp = m4_fopen (context, name, "r");
       if (fp != NULL)
 	{
 	  m4_debug_message (context, M4_DEBUG_TRACE_PATH,
 			    _("path search for `%s' found `%s'"),
 			    file, name);
-	  if (set_cloexec_flag (fileno (fp), true) != 0)
-	    m4_error (context, 0, errno, NULL,
-		      _("cannot protect input file across forks"));
-
 	  if (expanded_name != NULL)
 	    *expanded_name = name;
 	  else
diff --git a/tests/others.at b/tests/others.at
index 666409ee..71a1ee05 100644
--- a/tests/others.at
+++ b/tests/others.at
@@ -135,6 +135,10 @@ AT_DATA([in1.m4],
 ]])
 AT_DATA([in2.m4],
 [[sinclude(`in2.m4/')
+sinclude(`.')
+]])
+AT_DATA([in3.m4],
+[[include(`.')
 ]])
 
 AT_CHECK_M4([in1.m4/], [1], [], [stderr])
@@ -151,6 +155,14 @@ AT_CHECK([sed 's/Invalid argument/Not a directory/' stderr], [0],
 ]])
 
 AT_CHECK_M4([in2.m4], [0], [[
+
+]])
+
+AT_CHECK_M4([in3.m4], [1], [[
+]], [stderr])
+dnl mingw fails with EACCES rather than the expected EISDIR
+AT_CHECK([sed 's/Permission denied/Is a directory/' stderr], [0],
+[[m4:in3.m4:1: include: cannot open `.': Is a directory
 ]])
 
 AT_CLEANUP