Scanning over what is being proposed here and in D27514, I have just a couple of comments.

Implemented comments.

Ok, I've removed support for nested parentheses. Can this go through now?

Updated patch according to the comments made. Also spotted a corner-case where a double-diagnostic was produced, for example in the following where one string has too few arguments and the other string too many:

Second bump :o)

Patch additionally re-based off r261522.

Revised patch coming shortly...

I've removed CheckFormatString from Sema.h and make it a static function inside SemaChecking.cpp in r261522. I'll submit a new diff here with the remaining requested changes for this patch when I have a moment.

Bump :o)

Richard, are you happy with this latest version? Can I proceed to commit it?

To be honest, the simple answer is because it was just as easy to do with nesting as without (the code would still need to track the appearance of left and right parentheses in order to correctly parse to the closing right-parenthesis of the macro invocation in any case).

Test comment -- just to see whether email notifications are sending properly (it seems, for example, that cfe-commits wasn't notified of this patch...)

All strings matching the highest uncovered argument are now highlighted in the diagnostic.

In your case, the first string would be highlighted only. Yes, I see what you mean. Is it possible to have multiple ranges for the diagnostic? By which I mean, to produce the following:

Thoughts? Am I good to go?

Yes, but only for the "data argument not used" warning. All other warnings are unaffected by the change, for example:

Hi Richard,

Richard, you have been recommended to me as a suitable reviewer by David. If that's not ok with you, please could you recommend another! Thanks, Andy.

Bump! :o)

Sorry, I've added you as reviewers by proximity to recent relevant changes in SemaChecking.cpp. Hope you don't mind. Please tell me who to redirect to, if there are more applicable reviewers.