Another issue with diagnostic format-checker

[Gabriel Dos Reis]

"Kaveh R. Ghazi" <ghazi@caip.rutgers.edu> writes:

|  > The diagnostic framework does already some check at run-time.  If a front
|  > end does not register a format specifier, it halts compilation if the
|  > execution path uses it.  So we do have some consistency check.
|  > 
|  > What the format specifiers checker buys us is the ability to tell
|  > whether a given pair  of format specifier and argument are used
|  > consistently.  It does NOT check whether a format specifier is
|  > *effectively* handled -- that check is done at run-time.
|  > 
|  > Both are complimentary, and NOT mutually exclusive.
| 
| Well, the consistency check at gcc runtime calls abort if it
| encounters a non-valid specifier.  That is a "bad user experience"
| IMHO.  Better to catch these and fix them at gcc compile-time with the
| static format checker.  If the format checker is doing its job, the
| runtime check is redundant. 

No, it is not redondant.  The format checker does not know whether
there is a code to effectively handle a given format specifier.  The
only thing it knows is that some set of format specifiers is
*intended* (or acceptable) for use. 

It is like having an abstract base class

    struct formatter {
      virtual handle_D(...) = 0;
      virtual hanlde_E(...) = 0;

      void operator()(...);
    };

used as follows:

   struct c_diagnostic_reporter : formatter {
     // ...
   };

if you don't declare a handler (listed in formatter) in c_formatter,
then the format checker will catch you because, then you cannot have

    c_diagnostic_reporter warning;

    warning(...);

The format specifier won't say anything, but that does not guarantee
that you do have an actual implementation for any handled declared in
c_diagnostic_reporter.  In really, you'll get a link error (at best)
or obscure "call to pure virtual function" failure at run-time.
That is part of the check is what run-time check in the current
diagnostic framework does.  As you can see, it is not redundant.

-- Gaby