[Bug mi/18282] New: Pretty Printers - prints string value as char[] from children()

[Bug mi/18282] New: Pretty Printers - prints string value as char[] from children()

[david.docteur at intel dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

            Bug ID: 18282
           Summary: Pretty Printers - prints string value as char[] from
                    children()
           Product: gdb
           Version: 7.3
            Status: NEW
          Severity: normal
          Priority: P2
         Component: mi
          Assignee: unassigned at sourceware dot org
          Reporter: david.docteur at intel dot com

Created attachment 8255
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8255&action=edit
Unable to create variable object issue

Hi guys,

I am using Eclipse Kepler, GDB 7.3.1 and working on a project with pretty
printers (Python 2.7).

The problem is that I am trying to display a "prettyfied" object having
children and the string type is displayed as characters array.
Types such as int or long are displayed properly.
Those children are obtained from a Python list object such as follow:



class TestPrinter:
    "Print a test printer"

    def __init__(self, val):
        self.val = val

    def to_string(self):
        return "map"

    def children(self):

        streetno = {"1":"testing", "2":"Dravid", "3":"Sehwag", 
                    "4":"Laxman","5":"Kohli"}

        for field in sorted(streetno.keys()):
            if field is not None:
                yield field, str(streetno[field])


def str_lookup_function(val):
       lookup_tag = val.type.tag
       if lookup_tag == None:
           return None
       regex = re.compile("^test$")
       if regex.match(lookup_tag):
         return TestPrinter(val)


If I return a simple string from to_string() (without calling the children()
function) then it works well, and displayed as a string within Eclipse in the
"Value" column.

But in this case, the children of my object are displayed as char[].
I can expand the content of each, which displays character by character and its
ASCII value. Then, once I click on the child itself I get the following error:

1    char [33]    Error: Multiple errors reported.\ Failed to execute MI
command: -var-create - * &((((this)->test_object)).1) Error message from
debugger back end: -var-create: unable to create variable object\ Failed to
execute MI command: -var-create - * &((((this)->test_object)).1) Error message
from debugger back end: -var-create: unable to create variable object\ Unable
to create variable object


The expected behavior would be, of course, to see the full string instead of
"Error: Failed to execute MI ..."

Thank you very much for your help !

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[Bug mi/18282] Pretty Printers - unable to create variable object (string value from children())

[david.docteur at intel dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

David Docteur <david.docteur at intel dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Pretty Printers - prints    |Pretty Printers - unable to
                   |string value as char[] from |create variable object
                   |children()                  |(string value from
                   |                            |children())

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[Bug mi/18282] Pretty Printers - unable to create variable object (string value from children())

[xdje42 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Doug Evans <xdje42 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xdje42 at gmail dot com

--- Comment #1 from Doug Evans <xdje42 at gmail dot com> ---
This is related to bug 17529.
There may even be an existing bug for this (Eclipse printing value as a char
array).  Not sure about the MI errors though.

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[Bug mi/18282] Pretty Printers - unable to create variable object (string value from children())

[david.docteur at intel dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

--- Comment #3 from David Docteur <david.docteur at intel dot com> ---
Created attachment 8258
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8258&action=edit
using same name as in class attributes

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[Bug mi/18282] Pretty Printers - unable to create variable object (string value from children())

[alex.zhigay at yandex dot ru]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Alex <alex.zhigay at yandex dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alex.zhigay at yandex dot ru

--- Comment #4 from Alex <alex.zhigay at yandex dot ru> ---
Any workaround for this problem? How to return string from children()?

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[Bug mi/18282] Pretty Printers - unable to create variable object (string value from children())

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
This seems to be two different bugs.

First, if children returns strings, they don't seem to appear.
I get this from my test:

^done,numchild="5",children=[child={name="tval.1",exp="1",numchild="8",value="[8]",type="char
[8]"},child={name="tval.2",exp="2",numchild="7",value="[7]",type="char
[7]"},child={name="tval.3",exp="3",numchild="7",value="[7]",type="char
[7]"},child={name="tval.4",exp="4",numchild="7",value="[7]",type="char
[7]"},child={name="tval.5",exp="5",numchild="6",value="[6]",type="char
[6]"}],has_more="0"

The string values don't appear at all, instead for some reason
we're getting map "indices".


Second, the name returned by the printer doesn't necessarily
correspond to any kind of sub-object.  This is the part that is
bug#17529.

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[Bug varobj/18282] Pretty Printers - unable to create variable object (string value from children())

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|mi                          |varobj

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[Bug varobj/18282] Pretty Printers - unable to create variable object (string value from children())

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
This turns out to be this code in c_value_of_variable:

    case TYPE_CODE_ARRAY:
      return string_printf ("[%d]", var->num_children);

i.e., the weird short-circuiting thing strikes again.

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[Bug varobj/18282] Pretty Printers - unable to create variable object (string value from children())

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

--- Comment #7 from Tom Tromey <tromey at sourceware dot org> ---
I have a mildly hacky (given varobj, what else) patch for this.

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[Bug varobj/18282] Pretty Printers - unable to create variable object (string value from children())

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

--- Comment #8 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=aa15623fe68b3151ed54a7365b5a5226b538851a

commit aa15623fe68b3151ed54a7365b5a5226b538851a
Author: Tom Tromey <tromey@adacore.com>
Date:   Thu Aug 31 13:01:00 2023 -0600

    Allow pretty-printer 'children' method to return strings

    A user noticed that, while a pretty-printer can return Python strings
    from its "children" method, this does not really work for MI.  I
    tracked this down to my_value_of_variable calling into
    c_value_of_variable, which specially handles arrays and structures --
    not using the actual contents of the string.

    Now, this part of MI seems bad to me, but rather than change that,
    this applies the fix to only dynamic varobjs, which is the only
    scenario where a string like this can really be returned.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=18282
    Reviewed-by: Keith Seitz <keiths@redhat.com>

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[Bug varobj/18282] Pretty Printers - unable to create variable object (string value from children())

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18282

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.1
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #9 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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