Change gdb_realpath to return a unique_xmalloc_ptr

This changes gdb_realpath to return a unique_xmalloc_ptr and fixes up
the callers.  This allows removing some cleanups.  This change by
itself caused xfullpath.exp to fail; and attempting to fix that ran
into various problems (like .get() being optimized out); so this patch
also rewrites xfullpath.exp to be a C++ selftest instead.

ChangeLog
2017-08-22  Tom Tromey  <tom@tromey.com>

	* exec.c (exec_file_attach): Update.
	* linux-thread-db.c (try_thread_db_load): Update.
	* guile/scm-safe-call.c (gdbscm_safe_source_script): Update.
	* utils.c (gdb_realpath): Change return type.
	(gdb_realpath_keepfile): Update.
	(gdb_realpath_check_trailer, gdb_realpath_tests): New functions.
	(_initialize_utils): Register the new self test.
	* source.c (openp): Update.
	(find_and_open_source): Update.
	* nto-tdep.c (nto_find_and_open_solib): Update.
	* main.c (set_gdb_data_directory): Update.
	(captured_main_1): Update.
	* dwarf2read.c (dwarf2_get_dwz_file): Update
	(dw2_map_symbol_filenames): Update.
	* auto-load.c (auto_load_safe_path_vec_update): Update.
	(filename_is_in_auto_load_safe_path_vec): Change type of
	"filename_realp".
	(auto_load_objfile_script): Update.
	(file_is_auto_load_safe): Update.  Use std::string.
	* utils.h (gdb_realpath): Return a gdb::unique_xmalloc_ptr.

testsuite/ChangeLog
2017-08-22  Tom Tromey  <tom@tromey.com>

	* gdb.gdb/xfullpath.exp: Remove.

gdb/utils.c

@@ -66,6 +66,7 @@
 #include "interps.h"
 #include "gdb_regex.h"
 #include "job-control.h"
+#include "common/selftest.h"
 
 #if !HAVE_DECL_MALLOC
 extern PTR malloc ();		/* ARI: PTR */
@@ -2662,7 +2663,7 @@ string_to_core_addr (const char *my_string)
   return addr;
 }
 
-char *
+gdb::unique_xmalloc_ptr<char>
 gdb_realpath (const char *filename)
 {
 /* On most hosts, we rely on canonicalize_file_name to compute
@@ -2698,21 +2699,57 @@ gdb_realpath (const char *filename)
        we might not be able to display the original casing in a given
        path.  */
     if (len > 0 && len < MAX_PATH)
-      return xstrdup (buf);
+      return gdb::unique_xmalloc_ptr<char> (xstrdup (buf));
   }
 #else
   {
     char *rp = canonicalize_file_name (filename);
 
     if (rp != NULL)
-      return rp;
+      return gdb::unique_xmalloc_ptr<char> (rp);
   }
 #endif
 
   /* This system is a lost cause, just dup the buffer.  */
-  return xstrdup (filename);
+  return gdb::unique_xmalloc_ptr<char> (xstrdup (filename));
 }
 
+#if GDB_SELF_TEST
+
+static void
+gdb_realpath_check_trailer (const char *input, const char *trailer)
+{
+  gdb::unique_xmalloc_ptr<char> result = gdb_realpath (input);
+
+  size_t len = strlen (result.get ());
+  size_t trail_len = strlen (trailer);
+
+  SELF_CHECK (len >= trail_len
+	      && strcmp (result.get () + len - trail_len, trailer) == 0);
+}
+
+static void
+gdb_realpath_tests ()
+{
+  /* A file which contains a directory prefix.  */
+  gdb_realpath_check_trailer ("./xfullpath.exp", "/xfullpath.exp");
+  /* A file which contains a directory prefix.  */
+  gdb_realpath_check_trailer ("../../defs.h", "/defs.h");
+  /* A one-character filename.  */
+  gdb_realpath_check_trailer ("./a", "/a");
+  /* A file in the root directory.  */
+  gdb_realpath_check_trailer ("/root_file_which_should_exist",
+			      "/root_file_which_should_exist");
+  /* A file which does not have a directory prefix.  */
+  gdb_realpath_check_trailer ("xfullpath.exp", "xfullpath.exp");
+  /* A one-char filename without any directory prefix.  */
+  gdb_realpath_check_trailer ("a", "a");
+  /* An empty filename.  */
+  gdb_realpath_check_trailer ("", "");
+}
+
+#endif /* GDB_SELF_TEST */
+
 /* Return a copy of FILENAME, with its directory prefix canonicalized
    by gdb_realpath.  */
 
@@ -2721,7 +2758,6 @@ gdb_realpath_keepfile (const char *filename)
 {
   const char *base_name = lbasename (filename);
   char *dir_name;
-  char *real_path;
   char *result;
 
   /* Extract the basename of filename, and return immediately 
@@ -2749,13 +2785,13 @@ gdb_realpath_keepfile (const char *filename)
   /* Canonicalize the directory prefix, and build the resulting
      filename.  If the dirname realpath already contains an ending
      directory separator, avoid doubling it.  */
-  real_path = gdb_realpath (dir_name);
+  gdb::unique_xmalloc_ptr<char> path_storage = gdb_realpath (dir_name);
+  const char *real_path = path_storage.get ();
   if (IS_DIR_SEPARATOR (real_path[strlen (real_path) - 1]))
     result = concat (real_path, base_name, (char *) NULL);
   else
     result = concat (real_path, SLASH_STRING, base_name, (char *) NULL);
 
-  xfree (real_path);
   return gdb::unique_xmalloc_ptr<char> (result);
 }
 
@@ -3283,4 +3319,8 @@ _initialize_utils (void)
   add_internal_problem_command (&internal_error_problem);
   add_internal_problem_command (&internal_warning_problem);
   add_internal_problem_command (&demangler_warning_problem);
+
+#if GDB_SELF_TEST
+  selftests::register_test (gdb_realpath_tests);
+#endif
 }