gdb: allow use of ~ in 'save gdb-index' command

Add a call to gdb_tilde_expand in the save_gdb_index_command function,
this means that we can now do:

  (gdb) save gdb-index ~/blah/

Previous this wouldn't work.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/dwarf2/index-write.c

@@ -39,6 +39,7 @@
 #include "objfiles.h"
 #include "ada-lang.h"
 #include "dwarf2/tag.h"
+#include "gdbsupport/gdb_tilde_expand.h"
 
 #include <algorithm>
 #include <cmath>
@@ -1548,6 +1549,8 @@ save_gdb_index_command (const char *arg, int from_tty)
   if (!*arg)
     error (_("usage: save gdb-index [-dwarf-5] DIRECTORY"));
 
+  std::string directory (gdb_tilde_expand (arg));
+
   for (objfile *objfile : current_program_space->objfiles ())
     {
       /* If the objfile does not correspond to an actual file, skip it.  */
@@ -1567,8 +1570,8 @@ save_gdb_index_command (const char *arg, int from_tty)
 	      if (dwz != NULL)
 		dwz_basename = lbasename (dwz->filename ());
 
-	      write_dwarf_index (per_objfile->per_bfd, arg, basename,
-				 dwz_basename, index_kind);
+	      write_dwarf_index (per_objfile->per_bfd, directory.c_str (),
+				 basename, dwz_basename, index_kind);
 	    }
 	  catch (const gdb_exception_error &except)
 	    {

gdb/testsuite/gdb.dwarf2/gdb-index-tilde.exp

@@ -0,0 +1,91 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test that tilde expansion works for the 'save gdb-index' command.
+
+# This test relies on using the $HOME directory.  We could make this
+# work for remote hosts, but right now, this isn't supported.
+require {!is_remote host}
+
+# Can't save an index with readnow.
+require !readnow
+
+standard_testfile main.c
+
+# Create a directory to generate an index file into.
+set full_dir [standard_output_file "index_files"]
+remote_exec host "mkdir -p ${full_dir}"
+
+# The users home directory.
+set home $::env(HOME)
+
+# Check that FULL_DIR is within the $HOME directory.  If it's not, then
+# that's fine, but we can't test tilde expansion in this case.
+if { [string compare -length [string length $home] $full_dir $home] != 0 } {
+    unsupported "test not run within home directory"
+    return -1
+}
+
+# Convert the $HOME prefix in to ~.
+set dir "~[string range $full_dir [string length $home] end]"
+
+# Build the test executable.
+if { [prepare_for_testing "failed to prepare" "${testfile}" ${srcfile}] } {
+    return -1
+}
+
+# Start GDB and load in the executable.
+clean_restart ${binfile}
+
+# If the executable was built with an index, or lacks the debug
+# information required to create an index, then we'll not be able to
+# generate an index, so lets not even try.
+set has_index false
+set can_dump_index false
+gdb_test_multiple "maint print objfile $binfile" "check we can generate an index" {
+    -re "\r\n\\.gdb_index: version ${decimal}(?=\r\n)" {
+	set has_index true
+	gdb_test_lines "" $gdb_test_name ".*"
+    }
+    -re "\r\n\\.debug_names: exists(?=\r\n)" {
+	set has_index true
+	gdb_test_lines "" $gdb_test_name ".*"
+    }
+    -re "\r\n(Cooked index in use:|Psymtabs)(?=\r\n)" {
+	set can_dump_index true
+	gdb_test_lines "" $gdb_test_name ".*"
+    }
+    -re -wrap "" {
+    }
+}
+
+if { $has_index } {
+    unsupported "already have an index"
+    return -1
+}
+
+if { !$can_dump_index } {
+    unsupported "lacks debug information needed to dump index"
+    return -1
+}
+
+# Generate an index file.
+gdb_test_no_output "save gdb-index $dir"
+gdb_exit
+
+# Confirm that the index file exists.
+set index_filename "${full_dir}/${gdb_test_file_name}.gdb-index"
+gdb_assert { [remote_file host exists $index_filename] } \
+    "confirm the index file exists"