gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-1.c

/*
  { dg-options "-Wuninitialized -ftrack-macro-expansion=0" }
  { dg-do compile }
*/

void f (unsigned);

#define CODE_WITH_WARNING \
  int a;		  \
  f (a)

#pragma GCC diagnostic ignored "-Wuninitialized"

void
g (void)
{
  CODE_WITH_WARNING;
}

#pragma GCC diagnostic push

#pragma GCC diagnostic error "-Wuninitialized"

void
h (void)
{
  CODE_WITH_WARNING;		/* { dg-error "uninitialized" } */
}

/*
  { dg-message "some warnings being treated as errors" "" {target *-*-*} 0 }
*/