Fix latent bug in .debug_names file-name handling

An internal Ada test case showed that the .debug_names code does not
compute the same list of file names as the partial symbol reader.  In
particular, the partial symbol reader uses the DW_AT_name of the CU:

  /* Allocate a new partial symbol table structure.  */
  filename = dwarf2_string_attr (comp_unit_die, DW_AT_name, cu);
  if (filename == NULL)
    filename = "";

  pst = create_partial_symtab (per_cu, filename);

This patch changes the .debug_names reader to follow.

gdb/ChangeLog
2019-09-10  Tom Tromey  <tromey@adacore.com>

	* dwarf2read.c (dw2_get_file_names_reader): Add the
	CU's file name to the results.

gdb/testsuite/ChangeLog
2019-09-10  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/dgopt.exp: New file.
	* gdb.ada/dgopt/x.adb: New file.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2019-09-10  Tom Tromey  <tromey@adacore.com>
+
+	* dwarf2read.c (dw2_get_file_names_reader): Add the
+	CU's file name to the results.
+
 2019-09-10  Tom Tromey  <tromey@adacore.com>
 
 	* ada-lang.c (add_nonlocal_symbols): Combine calls to

gdb/dwarf2read.c

@@ -3692,11 +3692,17 @@ dw2_get_file_names_reader (const struct die_reader_specs *reader,
 
   file_and_directory fnd = find_file_and_directory (comp_unit_die, cu);
 
-  qfn->num_file_names = lh->file_names.size ();
+  int offset = 0;
+  if (strcmp (fnd.name, "<unknown>") != 0)
+    ++offset;
+
+  qfn->num_file_names = offset + lh->file_names.size ();
   qfn->file_names =
-    XOBNEWVEC (&objfile->objfile_obstack, const char *, lh->file_names.size ());
+    XOBNEWVEC (&objfile->objfile_obstack, const char *, qfn->num_file_names);
+  if (offset != 0)
+    qfn->file_names[0] = xstrdup (fnd.name);
   for (i = 0; i < lh->file_names.size (); ++i)
-    qfn->file_names[i] = file_full_name (i + 1, lh.get (), fnd.comp_dir);
+    qfn->file_names[i + offset] = file_full_name (i + 1, lh.get (), fnd.comp_dir);
   qfn->real_names = NULL;
 
   lh_cu->v.quick->file_names = qfn;

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2019-09-10  Tom Tromey  <tromey@adacore.com>
+
+	* gdb.ada/dgopt.exp: New file.
+	* gdb.ada/dgopt/x.adb: New file.
+
 2019-09-08  Tom Tromey  <tom@tromey.com>
 
 	* gdb.tui/resize.exp: Remove setup_xfail.

gdb/testsuite/gdb.ada/dgopt.exp

@@ -0,0 +1,34 @@
+# Copyright 2019 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 case using the -gnatDG option.
+
+load_lib "ada.exp"
+
+standard_ada_testfile x
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable \
+	 {debug additional_flags=-gnatDG}] != "" } {
+  return -1
+}
+
+clean_restart ${testfile}
+
+# The bug occurs with .debug_names, but here we don't check whether
+# the appropriate target board is in use.  The problem was that the
+# .adb file did not end up in the file table, but did show up in the
+# DWARF, which the psymtab reader handled, but which the .debug_names
+# reader did not.
+gdb_test "list x.adb:16, 16" "16.*procedure X is"

gdb/testsuite/gdb.ada/dgopt/x.adb

@@ -0,0 +1,19 @@
+--  Copyright 2019 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/>.
+
+procedure X is
+begin
+   null;
+end X;