[cfe-dev] Assertion on valid use of highlighting whitespace

[Tom Care]

I think there might be other things broken in this function too.

I'm having problems trying to get highlighting/fixits working for parts of printf statements (rather than the whole thing).

Currently, if I give a SourceLocation within a printf formatting string, it will highlight it from the beginning until the end of the format string (rather than the end I specified). For example:

/tmp/fixit.c:13:15: warning: precision used with 'n' conversion specifier,
      resulting in undefined behavior [-Wformat]
  printf("%100.100n", (int*) 0);
              ^~~~~

When what I expect is:
/tmp/fixit.c:13:15: warning: precision used with 'n' conversion specifier,
      resulting in undefined behavior [-Wformat]
  printf("%100.100n", (int*) 0);
              ^~~~

This ends up breaking the fixits, which delete the rest of the format string rather than the invalid part.

The offending line is lib/Frontend/TextDiagnosticPrinter.cpp:116
      // Add in the length of the token, so that we cover multi-char tokens.
      EndColNo += Lexer::MeasureTokenLength(End, SM, *LangOpts);

I'm sure this line has importance, but I don't think it is correct.

I'm a bit lost in this section! Does anyone have any ideas?

Tom
On Jun 17, 2010, at 12:05 PM, Tom Care wrote:

> Hi all,
> 
> Whilst fixing bug 7377, I ran into an assertion when trying to highlight code in the following warning:
> 
> flag ' ' results in undefined behavior in 'p' conversion specifier
> 
> triggered by: printf("% p", p);
> 
> Assertion failed: (StartColNo <= EndColNo && "Trying to highlight whitespace??"), function HighlightRange, file /Volumes/Data/Users/tcare/Projects/llvm/tools/clang/lib/Frontend/TextDiagnosticPrinter.cpp, line 138.
> 
> The assertion is triggered by trying to highlight the format specifier ("% p")
> 
> This assertion seems valid, except for this rare case. Maybe there are others?
> 
> Any ideas on how to fix this?
> 
> Tom
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