[cfe-commits] [PATCH] Add -Wknr-promoted-parameter option

Dimitry Andric dimitry at andric.com
Sun Dec 18 12:44:45 PST 2011


While compiling a certain unnamed piece of mail server software, that is
a sort of mix of C99-like constructs and an extremely old K&R core, I
repeatedly received the following type of warning:

  int foo(char x, int y);

  int foo(x, y)
  char x;
  int y;
    return x * y;

  // $ clang -c knrpromo.c
  // knrpromo.c:4:6: warning: promoted type 'int' of K&R function parameter is not compatible with the parameter type 'char' declared in a previous prototype
  // char x;
  //      ^
  // knrpromo.c:1:14: note: previous declaration is here
  // int foo(char x, int y);
  //              ^
  // 1 warning generated.

Apparently, this is because of the promotion rules for K&R function
parameters, which are always converted to int.

While this warning is fine in itself, it cannot be turned off, which is
a nuisance, as it would be very disruptive to edit all the dozens, if
not hundreds, of prototypes and definitions in the program to fix these

Therefore, I propose the attached patch, which adds a new warning option
(-Wknr-promoted-parameter) for turning it on or off.  This runs through
the standard tests just fine.
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