chandlerc

Most of the cases we ran into were metaprogramming techniques which test whether an expression is a valid null pointer constants. These got innocently applied to 'false' and trigger the warning needlessly.

GCC definitely has a warning for 0.5 -> int (likely -Wconversion, but I've not checked). It also has a warning for setting a pointer to "false" (-Wconversion-null). However, turning that warning on in a codebase where every warning breaks the build was challenging because of false positives. We're able to remove false positives and narrow the scope of the warning to just the buggy code in many cases with Clang, and that allows us to turn these warnings on much more aggressively.

That's the whole point. =] This is a surprising aspect of C++: the shift expression doesn't have the type of the declared variable.

The integer literals we are shifting are of 'int' type, and the shift occurs at that type (based on the usual arithmetic conversions). There is stack overflow question with explanations and a good blog post here about it:

http://stackoverflow.com/questions/836544/usual-arithmetic-c...

http://blogs.msdn.com/b/oldnewthing/archive/2004/03/10/87247...

Also, you can look through the C++98 standard to understand all the details. Relevant sections are [expr]p9 and [expr.shift].

Doh! Good catch, comment updated. =[ Maybe we do need Clang-for-comments as well as Clang-for-C++ code.... ;]

I would expect many of these tools to catch these types of bugs. The challenging thing for us has been to catch only bugs, and to catch them very fast during normal compilation.

A lot of the static analyses we've looked into (and I'm hoping for more detailed blog posts about that in the future) find plenty of bugs, but also find lots of non-bugs. Combine that with being too slow to run during the normal build, and you can't break the build when such a bug is found.

I think one of the most interesting aspects of this is how we catch the bugs early, and force developers to fix them immediately by breaking the build.