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

Eli Friedman eli.friedman at gmail.com
Mon Oct 29 16:07:00 PDT 2012

On Thu, Oct 25, 2012 at 6:09 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Thu, Oct 25, 2012 at 3:32 PM, Chandler Carruth <chandlerc at google.com> wrote:
>> 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.
> I see what you mean.  New patch attached.



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