[cfe-commits] [PATCH] Fix crash printing diagnostic range spanning macros

Eli Friedman eli.friedman at gmail.com
Thu Oct 25 14:57:00 PDT 2012

On Thu, Oct 25, 2012 at 1:27 PM, Chandler Carruth <chandlerc at google.com> wrote:
> On Thu, Oct 25, 2012 at 9:38 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>> I think that's the best we can do. Even if the range had the beginning
>> before the end (say, by trying to highlight the entirety of both macros), it
>> wouldn't be "correct".  We should not show ranges that don't correspond to
>> something meaningful in the text.
> I actually think we can do a bit better.

Yes, we could completely change what we display, but I'm not really
interested in embarking on a large architectural project at the

>> ...though arguably we could show a line with all macros expanded, and put
>> the range there. But that's a big change in what you expect from diagnostic
>> printing, and it wouldn't work in IDEs anyway.
> We get pretty close with the macro backtrace. I have sometimes
> wondered if we should start the error with a synthetic preprocessed
> snippet, and then give the code the user wrote in the first note, and
> descend through the macro expansions in subsequent notes.
> Alternatively, we could add a final note to the macro backtrace that
> shows the fully preprocessed source, but that seems more likely to be
> ignored.

Hmm, interesting; please file a bug. :)

>> Jordan
>> On Oct 24, 2012, at 19:36 , Eli Friedman <eli.friedman at gmail.com> wrote:
>> Patch attached.  Fixes a crash on a testcase like the following:
>> +#define BAD_CONDITIONAL_OPERATOR (2<3)?4:5
>> We try to print a source range which starts at the 5 in the first
>> expansion, and ends just after the 3 in the second expansion.
> My suggestion would be this:
> When you have a source range to highlight, and it's start or stop
> location occurs within a macro, grow it to the start (or stop, resp.)
> of the macro info's expansion location. This should be the start of
> where the macro got expanded into the code.
> Then, if there the diagnostic location itself is inside a macro, as
> you do the macro backtrace walk you'll need to address the fixme in
> the diagnostic code to actually walk the source ranges back through
> the macro backtrace as well, and at each level to the analogous
> transform to grow the range at that level.

We already do this; we just don't do it correctly for the case where
the start and/or end locations come from a different expansion than
the caret.


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