Revert "Simplify auto_load_expand_dir_vars and remove substitute_path_component"

This reverts commit 02601231fdd91a7bd4837ce202906ea2ce661489.

This commit was a refactoring to remove an xrealloc and simplify
utils.[ch].  However, it has a flaw -- it mishandles a substitution
like "$datadir/subdir".

I am backing out the patch in the interests of fixing the regression
before GDB 14.  It can be reinstated (with modifications) later if we
like.

Regression tested on x86-64 Fedora 36.

gdb/Makefile.in

@@ -490,6 +490,7 @@ SELFTESTS_SRCS = \
 	unittests/ui-file-selftests.c \
 	unittests/unique_xmalloc_ptr_char.c \
 	unittests/unpack-selftests.c \
+	unittests/utils-selftests.c \
 	unittests/vec-utils-selftests.c \
 	unittests/xml-utils-selftests.c
 

gdb/auto-load.c

@@ -173,33 +173,24 @@ static std::string auto_load_safe_path = AUTO_LOAD_SAFE_PATH;
    counterpart.  */
 static std::vector<gdb::unique_xmalloc_ptr<char>> auto_load_safe_path_vec;
 
-/* Expand $datadir and $debugdir in STRING.  */
+/* Expand $datadir and $debugdir in STRING according to the rules of
+   substitute_path_component.  */
 
 static std::vector<gdb::unique_xmalloc_ptr<char>>
 auto_load_expand_dir_vars (const char *string)
 {
-  std::vector<gdb::unique_xmalloc_ptr<char>> result
-    = dirnames_to_char_ptr_vec (string);
+  char *s = xstrdup (string);
+  substitute_path_component (&s, "$datadir", gdb_datadir.c_str ());
+  substitute_path_component (&s, "$debugdir", debug_file_directory.c_str ());
 
-  for (auto &elt : result)
-    {
-      if (strcmp (elt.get (), "$datadir") == 0)
-	{
-	  elt = make_unique_xstrdup (gdb_datadir.c_str ());
-	  if (debug_auto_load)
-	    auto_load_debug_printf ("Expanded $datadir to \"%s\".",
-				    gdb_datadir.c_str ());
-	}
-      else if (strcmp (elt.get (), "$debugdir") == 0)
-	{
-	  elt = make_unique_xstrdup (debug_file_directory.c_str ());
-	  if (debug_auto_load)
-	    auto_load_debug_printf ("Expanded $debugdir to \"%s\".",
-				    debug_file_directory.c_str ());
-	}
-    }
+  if (debug_auto_load && strcmp (s, string) != 0)
+    auto_load_debug_printf ("Expanded $-variables to \"%s\".", s);
 
-  return result;
+  std::vector<gdb::unique_xmalloc_ptr<char>> dir_vec
+    = dirnames_to_char_ptr_vec (s);
+  xfree(s);
+
+  return dir_vec;
 }
 
 /* Update auto_load_safe_path_vec from current AUTO_LOAD_SAFE_PATH.  */

gdb/unittests/utils-selftests.c

@@ -0,0 +1,60 @@
+/* Unit tests for the utils.c file.
+
+   Copyright (C) 2018-2023 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "utils.h"
+#include "gdbsupport/selftest.h"
+
+namespace selftests {
+namespace utils {
+
+static void
+test_substitute_path_component ()
+{
+  auto test = [] (std::string s, const char *from, const char *to,
+		  const char *expected)
+    {
+      char *temp = xstrdup (s.c_str ());
+      substitute_path_component (&temp, from, to);
+      SELF_CHECK (strcmp (temp, expected) == 0);
+      xfree (temp);
+    };
+
+  test ("/abc/$def/g", "abc", "xyz", "/xyz/$def/g");
+  test ("abc/$def/g", "abc", "xyz", "xyz/$def/g");
+  test ("/abc/$def/g", "$def", "xyz", "/abc/xyz/g");
+  test ("/abc/$def/g", "g", "xyz", "/abc/$def/xyz");
+  test ("/abc/$def/g", "ab", "xyz", "/abc/$def/g");
+  test ("/abc/$def/g", "def", "xyz", "/abc/$def/g");
+  test ("/abc/$def/g", "abc", "abc", "/abc/$def/g");
+  test ("/abc/$def/g", "abc", "", "//$def/g");
+  test ("/abc/$def/g", "abc/$def", "xyz", "/xyz/g");
+  test ("/abc/$def/abc", "abc", "xyz", "/xyz/$def/xyz");
+}
+
+}
+}
+
+void _initialize_utils_selftests ();
+void
+_initialize_utils_selftests ()
+{
+  selftests::register_test ("substitute_path_component",
+			    selftests::utils::test_substitute_path_component);
+}

gdb/utils.c

@@ -3346,6 +3346,51 @@ parse_pid_to_attach (const char *args)
   return pid;
 }
 
+/* Substitute all occurrences of string FROM by string TO in *STRINGP.  *STRINGP
+   must come from xrealloc-compatible allocator and it may be updated.  FROM
+   needs to be delimited by IS_DIR_SEPARATOR or DIRNAME_SEPARATOR (or be
+   located at the start or end of *STRINGP.  */
+
+void
+substitute_path_component (char **stringp, const char *from, const char *to)
+{
+  char *string = *stringp, *s;
+  const size_t from_len = strlen (from);
+  const size_t to_len = strlen (to);
+
+  for (s = string;;)
+    {
+      s = strstr (s, from);
+      if (s == NULL)
+	break;
+
+      if ((s == string || IS_DIR_SEPARATOR (s[-1])
+	   || s[-1] == DIRNAME_SEPARATOR)
+	  && (s[from_len] == '\0' || IS_DIR_SEPARATOR (s[from_len])
+	      || s[from_len] == DIRNAME_SEPARATOR))
+	{
+	  char *string_new;
+
+	  string_new
+	    = (char *) xrealloc (string, (strlen (string) + to_len + 1));
+
+	  /* Relocate the current S pointer.  */
+	  s = s - string + string_new;
+	  string = string_new;
+
+	  /* Replace from by to.  */
+	  memmove (&s[to_len], &s[from_len], strlen (&s[from_len]) + 1);
+	  memcpy (s, to, to_len);
+
+	  s += to_len;
+	}
+      else
+	s++;
+    }
+
+  *stringp = string;
+}
+
 #ifdef HAVE_WAITPID
 
 #ifdef SIGALRM

gdb/utils.h

@@ -136,6 +136,9 @@ private:
 extern int gdb_filename_fnmatch (const char *pattern, const char *string,
 				 int flags);
 
+extern void substitute_path_component (char **stringp, const char *from,
+				       const char *to);
+
 std::string ldirname (const char *filename);
 
 extern int count_path_elements (const char *path);