Re: [PATCH, doc RFA] Fix lazy string type docs

[Doug Evans <dje at google dot com>]

On Thu, Nov 3, 2016 at 10:46 AM, Doug Evans <dje@google.com> wrote:
> Hi.
>
> I was trying to understand a problem I was having with python lazy strings.
> It turns out the docs are wrong, and the "type" attribute of a lazy
> string is the character type, not a pointer to the character's type.

... Unless the thing we're making a lazy string out of is an array
instead of a pointer.

const char* foo = "Dave";
const char bar[] = "No, man, I'm Dave.";

(gdb) py print gdb.parse_and_eval("foo").lazy_string().type
const char
(gdb) py print gdb.parse_and_eval("bar").lazy_string().type
const char [19]

I don't have a strong opinion on what the correct answer is, but there
is certainly a bug here.

Phil, do you remember why this code exists in valpy_lazy_string():

      if (TYPE_CODE (value_type (value)) == TYPE_CODE_PTR)
        value = value_ind (value);

[lazy string support went in in commit be759fcf]

I kinda like the type of the lazy string version of a char array still
being a char array.

OTOH, when I look at the definition of a lazy string, recording the
character type makes more sense
(to me anyway: e.g., length would be redundant for the case where type
is a char array)

typedef struct {
  PyObject_HEAD
  /*  Holds the address of the lazy string.  */
  CORE_ADDR address;

  /*  Holds the encoding that will be applied to the string
      when the string is printed by GDB.  If the encoding is set
      to None then GDB will select the most appropriate
      encoding when the sting is printed.  */
  char *encoding;

  /* Holds the length of the string in characters.  If the
     length is -1, then the string will be fetched and encoded up to
     the first null of appropriate width.  */
  long length;

  /*  This attribute holds the type that is represented by the lazy
      string's type.  */
  struct type *type;
} lazy_string_object;

To fix this bug we're going to have to break one or the other, or add
a knob (bleah) to control the old, broken, behaviour.
Or mark the "type" LazyString attribute as broken/deprecated and
provide a new attribute with correct behaviour.

Opinions?