[PR c/52952] More precise locations within format strings

[Joseph Myers]

On Fri, 7 Nov 2014, Manuel López-Ibáñez wrote:

> This patch allows format warnings to point within the format string
> for simple strings. There are a few limitations:
> 
> * It does not handle 'const char *' because the location of the
> initializer is not available. The result is the same before and after
> this patch.
> 
> * It does not handle non-concatenated tokens, since the preprocessor
> does not keep their location yet. The result after the patch is that
> we point to some arbitrary place between the first " and the first
> newline. This is slightly worse than the current behavior (which
> points to the first "), but I could not figure out a way to detect
> this case and not generate an offset. It is a matter of implementing
> this idea: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52952#c13 as a
> follow-up. The line pointed at is the same before and after the patch,
> only the column number is affected.
> 
> * It does not handle macros, but the behavior before and after this
> patch is the same (and there is work-in-progress on this:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52952#c33)

Does it also not handle escape sequences in the strings?  You appear to 
compute offsets in terms of the number of bytes after the start of the 
string, then pass this to functions commented to take an offset in 
columns, and escape sequences before the point where the warning is being 
given are another case where those would differ.

Anyway, the front-end changes are OK with appropriate comments that make 
clear what the interface is at each point and where the (missing) 
conversion from a byte offset within a string to a column offset in the 
source file should take place, though someone else ought to review the 
line-map changes.

-- 
Joseph S. Myers
joseph@codesourcery.com