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.

1 files changed, 60 insertions, 0 deletions

diff --git a/gdb/unittests/utils-selftests.c b/gdb/unittests/utils-selftests.c
new file mode 100644
index 0000000..70609aa
--- /dev/null
+++ b/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);
+}