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

Chandler Carruth chandlerc at google.com
Thu Oct 25 15:32:58 PDT 2012

On Thu, Oct 25, 2012 at 2:57 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> 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
> moment.
>>> ...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.

Yes, but do we do the first paragraph correctly? I think we can do the
first paragraph and fix the crash/misbehavior you're talking about.

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