[gdb/symtab] Handle named DW_TAG_unspecified_type DIE

With the test-case included in the patch, we run into:
...
(gdb) info types -q std::nullptr_t^M
During symbol reading: unsupported tag: 'DW_TAG_unspecified_type'^M
^M
File /usr/include/c++/7/x86_64-suse-linux/bits/c++config.h:^M
2198:   typedef decltype(nullptr) std::nullptr_t;^M
(gdb) FAIL: gdb.dwarf2/nullptr_t.exp: info types -q std::nullptr_t \
  without complaint
...

Fix the complaint by handling DW_TAG_unspecified_type in new_symbol, and verify
in the test-case using "maint print symbols" that the symbol exists.

Tested on x86_64-linux, with gcc 7.5.0 and clang 13.0.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17271

3 files changed, 69 insertions, 0 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 29ccd00..0a3c292 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -21066,6 +21066,7 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	case DW_TAG_base_type:
 	case DW_TAG_subrange_type:
 	case DW_TAG_generic_subrange:
+	case DW_TAG_unspecified_type:
 	  sym->set_aclass_index (LOC_TYPEDEF);
 	  sym->set_domain (VAR_DOMAIN);
 	  list_to_add = cu->list_in_scope;
diff --git a/gdb/testsuite/gdb.dwarf2/nullptr_t.cc b/gdb/testsuite/gdb.dwarf2/nullptr_t.cc
new file mode 100644
index 0000000..85fe801
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/nullptr_t.cc
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 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/>.  */
+
+#include <cstddef>
+
+void
+foo (std::nullptr_t)
+{
+}
+
+int
+main (void)
+{
+  foo (nullptr);
+}
diff --git a/gdb/testsuite/gdb.dwarf2/nullptr_t.exp b/gdb/testsuite/gdb.dwarf2/nullptr_t.exp
new file mode 100644
index 0000000..c597c66
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/nullptr_t.exp
@@ -0,0 +1,39 @@
+# Copyright 2022 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/>.
+
+if {[skip_cplus_tests]} { continue }
+
+standard_testfile .cc
+
+if [prepare_for_testing "failed to prepare" $testfile $srcfile {debug c++}] {
+    return -1
+}
+
+set cmd "info types -q std::nullptr_t"
+
+set re \
+    [multi_line \
+	 "$cmd" \
+	 "" \
+	 "File .*:" \
+	 "$decimal:\ttypedef decltype\\(nullptr\\) std::nullptr_t;"]
+
+with_complaints 5 {
+    gdb_test $cmd $re "$cmd without complaints"
+}
+
+gdb_test "maint print symbols -source $srcfile" \
+    "typedef void decltype\\(nullptr\\); \r\n.*" \
+    "decltype(nullptr) symbol"