Fix of default lookup for "this" symbol.

Using the default lookup for the symbol "this" might lead to segmentation
fault in GDB.
Some languages, e.g. Fortran, use as default lookup routine the C++
routines.
For those languages "this" can be the instance of a class or even the
definition of a class.
When an instance of a class having the name "this" is evaluated
in GDB a segmentation fault was observed.

As example of the issue take into consideration the Fortran code:
  type foo
    real :: a
    type(bar) :: x
    character*7 :: b
  end type foo
  type(foo) :: this

Issue appears when evaluating the variable "this" in GDB.

Within the language definition structure there is a field that represents
the name of the special symbol used for the C++ "this" for the language
being described.
The fix presented here takes into account the aforementioned field. In the
case the aforementioned field is NULL "this" is not represented in the
language described and the lookup should return a null_block_symbol.

Tests: Performed tests with gfortran and ifort.

Reviewed:
https://sourceware.org/ml/gdb-patches/2016-04/msg00068.html

After the commited patch:
https://sourceware.org/ml/gdb-patches/2016-06/msg00364.html
Patch can be applied.

2016-06-16  Walfred Tedeschi  <walfred.tedeschi@intel.com>

gdb/ChangeLog:

	* cp-namespace.c (cp_lookup_bare_symbol): Use language passed as
	parameter to look for the symbol "this".

gdb/testsuite/ChangeLog:

	* gdb.fortran/derived-types.exp (result_line, result_line_2):
	New variables.
	(print this%a, print this%b, print this): New tests.
	* gdb.fortran/derived-types.f90 (this): New object and
	initialization.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2016-07-07  Walfred Tedeschi  <walfred.tedeschi@intel.com>
+
+	* cp-namespace.c (cp_lookup_bare_symbol): Use language passed as
+	parameter to look for the symbol "this".
+
+
 2016-07-06  John Baldwin  <jhb@FreeBSD.org>
 
 	* h8300-tdep.c (h8300_print_register): Remove extraneous parentheses.

gdb/cp-namespace.c

@@ -206,10 +206,13 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
       struct block_symbol lang_this;
       struct type *type;
 
-      lang_this = lookup_language_this (language_def (language_cplus), block);
+      if (langdef != NULL)
+	lang_this = lookup_language_this (langdef, block);
+
       if (lang_this.symbol == NULL)
 	return null_block_symbol;
 
+
       type = check_typedef (TYPE_TARGET_TYPE (SYMBOL_TYPE (lang_this.symbol)));
       /* If TYPE_NAME is NULL, abandon trying to find this symbol.
 	 This can happen for lambda functions compiled with clang++,

gdb/testsuite/ChangeLog

@@ -1,3 +1,11 @@
+2016-07-07  Walfred Tedeschi  <walfred.tedeschi@intel.com>
+
+	* gdb.fortran/derived-types.exp (result_line, result_line_2):
+	New variables.
+	(print this%a, print this%b, print this): New tests.
+	* gdb.fortran/derived-types.f90 (this): New object and
+	initialization.
+
 2016-07-06  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* gdb.ada/arraydim.exp: Remove extra directory level in build

gdb/testsuite/gdb.fortran/derived-type.exp

@@ -73,14 +73,45 @@ gdb_test_multiple $test $test {
 gdb_test "print q%x%c" "\\$\[0-9\]+ = 1"
 gdb_test "print q%x%d" "\\$\[0-9\]+ = 2\\.375"
 
+set result_line "= \\( a = 3.125, x = \\( c = 1, d = 2\\.375 \\),\
+b = 'abcdefg' \\)\r\n$gdb_prompt $"
+
+# Used in case compiler generates an array of characters.
+set result_line_2 " = \\( a = 3.125, x = \\( 1, 2\\.375 \\),\
+b = \\('abcdefg'\\) \\)\r\n$gdb_prompt $"
+
 set test "print q"
 gdb_test_multiple $test $test {
-    -re "\\$\[0-9\]+ = \\( a = 3.125, x = \\( c = 1, d = 2\\.375 \\), b = 'abcdefg' \\)\r\n$gdb_prompt $" {
+    -re $result_line {
 	pass $test
     }
-    -re "\\$\[0-9\]+ = \\( a = 3.125, x = \\( 1, 2\\.375 \\), b = \\('abcdefg'\\) \\)\r\n$gdb_prompt $" {
+    -re $result_line_2 {
 	# Compiler should produce string, not an array of characters.
 	setup_xfail "*-*-*"
 	fail $test
     }
 }
+
+gdb_test "print this%a" " = 3\\.125"
+
+set test "print this%b"
+gdb_test_multiple $test $test {
+    -re " = 'abcdefg'\r\n$gdb_prompt $" {
+        pass $test
+    }
+    -re $result_line_2 {
+        setup_xfail "*-*-*"
+        fail $test
+    }
+}
+
+set test "print this"
+gdb_test_multiple $test $test {
+    -re $result_line {
+        pass $test
+    }
+    -re $result_line_2 {
+         setup_xfail "*-*-*"
+         fail $test
+    }
+}

gdb/testsuite/gdb.fortran/derived-type.f90

@@ -29,12 +29,17 @@ program main
   end type foo
   type(foo) :: q
   type(bar) :: p
+  type(foo) :: this
 
   p = bar(1, 2.375)
   q%a = 3.125
   q%b = "abcdefg"
   q%x%c = 1
   q%x%d = 2.375
-  print *,p,q 
+  this%a = 3.125
+  this%b = "abcdefg"
+  this%x%c = 1
+  this%x%d = 2.375
+  print *,p,q,this
 
 end program main