Re: Shadowed local variables in "info locals"

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2021-06-29 10:21 a.m., Aktemur, Tankut Baris via Gdb-patches wrote:
> Hi,
> 
> Suppose we have the following program:
> 
>      1  int
>      2  main ()
>      3  {
>      4    int x = 42;
>      5    {
>      6      int x = 99;
>      7      x = 99;
>      8    }
>      9    return 0;
>     10  }
> 
> The "info locals" command, when stopped at line 7, gives
> 
>   (gdb) info locals
>   x = 99
>   x = 42
> 
> Is this a bug or an (un)intentional feature?
> 
> From one perspective, only one "x" is available for use in our context, and
> thus only one "x" should be printed by "info locals".  This is the "bug" view.
> 
> From another perspective, the outer "x" and inner "x" are two different
> variables that are located in separate locations but they just happen to have
> the same name.  Therefore, displaying both is giving valuable information.
> This is the "feature" view.
> 
> Displaying both names could be confusing for the user in particular if the 
> values of the variables come from complex execution flows and if the user cannot
> tell which "x" is which.  A potential improvement to the current state is
> annotating the outer scope variable for clarity.  E.g.
> 
>   (gdb) info locals
>   x = 99
>   x = 42 <shadowed>
> 
> What are your thoughts?

I don't have a strong opinion.  I maybe lean more towards the side of
showing all the information, but making it clearer which variable is
which (i.e. the example above).

But I just wanted to note that a change for MI's -stack-list-locals
command may also be desirable.  It could be a new attribute in the
shadowed variable's record that says it is shadowed, that would not
break backwards compatibility.

Simon