[Ada] print null array pointer as 0x0' rather than (null)'

Trying to print a variable defined as an access to an unconstrained
array:

       type String_Access is access String;
       S1 : String_Access;

If that variable is null, then GDB prints its value in an odd way:

    (gdb) print S1
    $1 = (string_bug.string_access) (null)
                                    ^^^^^^

This patch changes the debugger behavior to print the pointer using
the same output we'd use for any null pointer:

    (gdb) print S1
    $1 = (string_bug.string_access) 0x0

It also adds an assert, helping us verify an assumption.

gdb/ChangeLog:

        * ada-valprint.c (ada_val_print_1): Print null array pointers as
        `0x0' rather than `(null)'.  Add assertion.

gdb/testsuite/ChangeLog:

        * gdb.ada/arrayptr/foo.adb: Add new local variable Null_String.
        * gdb.ada/arrayptr.exp: Add test printing that new variable.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2010-12-29  Joel Brobecker  <brobecker@adacore.com>
+
+	* ada-valprint.c (ada_val_print_1): Print null array pointers as
+	`0x0' rather than `(null)'.  Add assertion.
+
 2010-12-29  Joel Brobecker  <brobecker@adacore.com>
 
 	* ada-lang.h (ada_coerce_to_simple_array): Add declaration.

gdb/ada-valprint.c

@@ -690,7 +690,8 @@ ada_val_print_1 (struct type *type, const gdb_byte *valaddr0,
 	val = ada_coerce_to_simple_array (val);
       if (val == NULL)
 	{
-	  fprintf_filtered (stream, "(null)");
+	  gdb_assert (TYPE_CODE (type) == TYPE_CODE_TYPEDEF);
+	  fprintf_filtered (stream, "0x0");
 	  retn = 0;
 	}
       else

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2010-12-29  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.ada/arrayptr/foo.adb: Add new local variable Null_String.
+	* gdb.ada/arrayptr.exp: Add test printing that new variable.
+
 2010-12-29  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.ada/lang_switch.exp: Correct expected parameter value.

gdb/testsuite/gdb.ada/arrayptr.exp

@@ -44,3 +44,4 @@ gdb_test "print string_p" \
          "= \\(foo\\.string_access\\) 0x\[0-9a-zA-Z\]+" \
          "print string_p"
 
+gdb_test "print null_string" "= \\(foo\\.string_access\\) 0x0"

gdb/testsuite/gdb.ada/arrayptr/foo.adb

@@ -19,6 +19,8 @@ procedure Foo is
    type String_Access is access String;
 
    String_P : String_Access := new String'("Hello");
+   Null_String : String_Access := null;
 begin
    Do_Nothing (String_P'Address);  -- STOP
+   Do_Nothing (Null_String'Address);
 end Foo;