[RFA] fix gdb.ada/null_record.exp

[Joel Brobecker <brobecker at adacore dot com>]

Hello,

Daniel reported that null_record.exp was failing. The test was failing
on my side as well, although not the same way (I was so intent on
finding out what the cause was that I didn't pay enough attention to
what Daniel posted - sorry).

Here is what I observed:

    ptype empty
    type = <void>
    (gdb) FAIL: gdb.ada/null_record.exp: ptype on null record

The output is not a surprise when you look at what ada_evaluate_subexp
returns for OP_TYPE expressions:

    case OP_TYPE:
      /* The value is not supposed to be used.  This is here to make it
         easier to accommodate expressions that contain types.  */
      (*pos) += 2;
      if (noside == EVAL_SKIP)
        goto nosideret;
      else if (noside == EVAL_AVOID_SIDE_EFFECTS)
!!!->   return allocate_value (builtin_type_void);
      else
        error (_("Attempt to use a type name as an expression"));

The reason this was good enough is that, in GDB 6.4 (we are still
using this as our baseline), ptype_command was not doing a full
evaluation of the expression to get the type description. Rather,
it used a short-cut:

        static struct type *
        ptype_eval (struct expression *exp)
        {
          if (exp->elts[0].opcode == OP_TYPE)
            {
              return (exp->elts[1].type);
            }
          else
          [...]
        }

This was changed since then to call evaluate_type (expr) instead,

Knowing this, I discovered that calling ptype on probably any type
name would return this "<void>" type. I reproduced this with a non-
null record too, for instance.

The proposed fix is attached:

2007-01-02  Joel Brobecker  <brobecker@adacore.com>

        * ada-lang.c (ada_evaluate_subexp) [OP_TYPE]: Return a value with
        the appropriate type rather than a bogus void type.

Tested on x86-linux, no regression. Fixes the null_record.exp on my side.
OK to apply?

Thanks,
-- 
Joel

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