Re: [PATCH] gdb/rust: Handle printing structures containing strings

[Tom Tromey <tom@tromey.com>]

>>>>> "Andrew" == Andrew Burgess <andrew.burgess@embecosm.com> writes:

Andrew> When printing a rust structure that contains a string GDB can
Andrew> currently fail to read the fields that define the string. This is
Andrew> because GDB mistakenly treats a value that is the parent structure as
Andrew> though it is the structure that defines the string, and then fails to
Andrew> find the fields needed to extract a string.

Andrew> The solution is to create a new value to represent the string field of
Andrew> the parent value.

Thank you for doing this.

Andrew>    if (rust_slice_type_p (type) && strcmp (TYPE_NAME (type), "&str") == 0)
Andrew>      {
Andrew> +      /* If what we are printing here is actually a string within a
Andrew> +	 structure then VAL will be the original parent value, while TYPE
Andrew> +	 will be the type of the structure representing the string we want
Andrew> +	 to print.
Andrew> +	 However, RUST_VAL_PRINT_STR looks up the fields of the string
Andrew> +	 inside VAL, assuming that VAL is the string.
Andrew> +	 So, recreate VAL as a value representing just the string.  */
Andrew> +      val = value_at_lazy (type, value_address (val) + embedded_offset);
Andrew>        rust_val_print_str (stream, val, options);
Andrew>        return;

It took me a while to understand this, but I get it now.  At first it
looked like this code was misplaced, but what's going on is that
rust_val_print_str only takes a value, so in a "val_print" context we
must reconstruct one.

We really ought to get rid of the val_print / value_print distinction
someday.  It doesn't provide any benefit and it leads to bugs like this.

Andrew> +gdb_test "print st" " = simple::StringAtOffset {field1: \"hello\", field2: 1, field3: \"world\"}"

I think this line should probably be split after the first argument.
Ok with this change.

Tom