testsuite: Fix false FAIL in gdb.cp/casts.exp

gcc-6.2.1-1.fc26.x86_64

gdb compile failed, /home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:10: error: expected primary-expression before 'int'
 decltype(int x)
          ^~~
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:10: error: expected ')' before 'int'
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:40:1: error: expected unqualified-id before 'decltype'
 decltype(int x)
 ^~~~~~~~
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc: In function 'int main(int, char**)':
/home/jkratoch/redhat/gdb-clean/gdb/testsuite/gdb.cp/casts.cc:59:14: error: expected primary-expression before 'decltype'
   double y = decltype(2);
              ^~~~~~~~

'decltype' is a registered keyword since C++11 which is now a default for GCC.

On Thu, 15 Sep 2016 14:06:56 +0200, Pedro Alves wrote:

Seems to be exercising the FLAG_SHADOW bits:

...
    {"__typeof__", TYPEOF, OP_TYPEOF, 0 },
    {"__typeof", TYPEOF, OP_TYPEOF, 0 },
    {"typeof", TYPEOF, OP_TYPEOF, FLAG_SHADOW },
    {"__decltype", DECLTYPE, OP_DECLTYPE, FLAG_CXX },
    {"decltype", DECLTYPE, OP_DECLTYPE, FLAG_CXX | FLAG_SHADOW },
...

/* This is used to associate some attributes with a token.  */

enum token_flag
{
...
  /* If this bit is set, the token is conditional: if there is a
     symbol of the same name, then the token is a symbol; otherwise,
     the token is a keyword.  */

  FLAG_SHADOW = 2
};

So perhaps a better fix is to move that particular test to a
separate testcase that force-compiles with -std=c++03.

gdb/testsuite/ChangeLog
2016-09-16  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.cp/casts.cc (decltype): Move it ...
	(main): ... with its call to ...
	* gdb.cp/casts03.cc: ... a new file.
	* gdb.cp/casts.exp: Add new file casts03.cc, move decltype test to it.

3 files changed, 53 insertions, 15 deletions

diff --git a/gdb/testsuite/gdb.cp/casts.cc b/gdb/testsuite/gdb.cp/casts.cc
index 43f112f..543db89 100644
--- a/gdb/testsuite/gdb.cp/casts.cc
+++ b/gdb/testsuite/gdb.cp/casts.cc
@@ -34,14 +34,6 @@ struct DoublyDerived : public VirtuallyDerived,
 {
 };
 
-// Confuse a simpler approach.
-
-double
-decltype(int x)
-{
-  return x + 2.0;
-}
-
 int
 main (int argc, char **argv)
 {
@@ -56,7 +48,5 @@ main (int argc, char **argv)
   Alpha *ad = &derived;
   Alpha *add = &doublyderived;
 
-  double y = decltype(2);
-
   return 0;  /* breakpoint spot: casts.exp: 1 */
 }
diff --git a/gdb/testsuite/gdb.cp/casts.exp b/gdb/testsuite/gdb.cp/casts.exp
index 34a2492..57a56b8 100644
--- a/gdb/testsuite/gdb.cp/casts.exp
+++ b/gdb/testsuite/gdb.cp/casts.exp
@@ -27,7 +27,7 @@
 
 if { [skip_cplus_tests] } { continue }
 
-standard_testfile .cc
+standard_testfile .cc casts03.cc
 
 if [get_compiler_info "c++"] {
     return -1
@@ -110,10 +110,6 @@ gdb_test "print reinterpret_cast<void> (b)" "Invalid reinterpret_cast" \
 gdb_test "print reinterpret_cast<A &> (*b)" " = \\(A \\&\\) @$hex: {a = 42}" \
     "reinterpret_cast to reference type"
 
-# Test that keyword shadowing works.
-
-gdb_test "whatis decltype(5)" " = double"
-
 # Basic tests using typeof.
 
 foreach opname {__typeof__ __typeof __decltype} {
@@ -176,3 +172,23 @@ gdb_test "print dynamic_cast<DoublyDerived *> (add)" \
 gdb_test "print dynamic_cast<Gamma *> (add)" \
     " = \\(Gamma \\*\\) $nonzero_hex" \
     "dynamic_cast to sibling"
+
+if {[prepare_for_testing $testfile.exp ${testfile}03 $srcfile2 \
+			 {debug c++ additional_flags=-std=c++03}]} {
+    return -1
+}
+
+if ![runto_main] then {
+    perror "couldn't run to breakpoint"
+    continue
+}
+
+# Prevent symbol on address 0x0 being printed.
+gdb_test_no_output "set print symbol off"
+
+gdb_breakpoint [gdb_get_line_number "casts.exp: 1" $srcfile2]
+gdb_continue_to_breakpoint "end of casts03"
+
+# Test that keyword shadowing works.
+
+gdb_test "whatis decltype(5)" " = double"
diff --git a/gdb/testsuite/gdb.cp/casts03.cc b/gdb/testsuite/gdb.cp/casts03.cc
new file mode 100644
index 0000000..58d9a42
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/casts03.cc
@@ -0,0 +1,32 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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/>.  */
+
+// Confuse a simpler approach.
+
+double
+decltype(int x)
+{
+  return x + 2.0;
+}
+
+int
+main (int argc, char **argv)
+{
+  double y = decltype(2);
+
+  return 0;  /* breakpoint spot: casts.exp: 1 */
+}