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Re: [PATCH] MI: Allow non-raw varobj evaluation
- From: "Leszek Swirski via gdb-patches" <gdb-patches at sourceware dot org>
- To: Simon Marchi <simon dot marchi at polymtl dot ca>
- Cc: gdb-patches at sourceware dot org
- Date: Thu, 25 Jan 2018 11:11:00 +0000
- Subject: Re: [PATCH] MI: Allow non-raw varobj evaluation
- Authentication-results: sourceware.org; auth=none
- References: <20180124173223.213808-1-leszeks@google.com> <9bc195e52123f5d878778ebebd074ee4@polymtl.ca>
- Reply-to: Leszek Swirski <leszeks at google dot com>
On Thu, Jan 25, 2018 at 2:53 AM, Simon Marchi <simon.marchi@polymtl.ca> wrote:
>
> Could you give an example to reproduce this problem? I tried with a vector of vector, but -var-evaluate-expression just prints "{...}":
>
> -var-evaluate-expression var1
> ^done,value="{...}"
>
> so I am not sure what problem you are after.
Hi Simon,
So, this is a bit of an edge case, which I encountered with the
chromium pretty printers. Effectively, it's when a pretty printer
returns another object in its to_string, rather than a string.
Consider the following code:
struct Foo { int val; };
struct Wrapper { Foo foo; };
int main() {
Wrapper w;
w.foo.val = 23;
}
and this pretty printer file:
import gdb.printing
class FooPrinter:
def __init__(self, val):
self.val = val
def to_string(self):
return "Foo" + str(self.val["val"])
class WrapperPrinter:
def __init__(self, val):
self.val = val
def to_string(self):
return self.val["foo"]
test_printer = gdb.printing.RegexpCollectionPrettyPrinter("test")
test_printer.add_printer('Foo', '^Foo$', FooPrinter)
test_printer.add_printer('Wrapper', '^Wrapper$', WrapperPrinter)
gdb.printing.register_pretty_printer(None, test_printer)
Setting a breakpoint at the end of the function, we call the following commands:
-enable-pretty-printing
^done
-var-create var_w @ w
^done,name="var_w",numchild="0",value="{val =
23}",type="Wrapper",dynamic="1",has_more="0"
-var-create var_w_foo @ w.foo
^done,name="var_w_foo",numchild="0",value="Foo23",type="Foo",dynamic="1",has_more="0"
-var-evaluate-expression var_w
^done,value="{val = 23}"
-var-evaluate-expression var_w_foo
^done,value="Foo23"
-data-evaluate-expression w
^done,value="Foo23"
-data-evaluate-expression w.foo
^done,value="Foo23"
So, in the -var-evaluate-expression var_w case, we print the "raw"
value of w.foo, while in the -data-evaluate-expression w case, we
print the pretty printed w.foo value. After my patch, all of the above
print "Foo23".
Note that this isn't encountered very often, probably because it
disappears if I replace `return self.val["foo"]` with `return
str(self.val["foo"])`. But, it does feel like the wrong behaviour.
- Leszek