For example, the following error message is generated for the piglit test tests/spec/glsl-1.30/compiler/switch-statement/switch-case-const-int-expression.vert (copied below).  The compiler should never see 'two' because it should be replaced with the digit 2 by the preprocessor.

0:23(14): error: `two' undeclared
0:23(14): error: Operands to arithmetic operators must be numeric


// [config]
// expect_result: pass
// glsl_version: 1.30
// [end config]
//
// From page 57 (page 63 of the PDF) of the GLSL 1.30 spec:
//
//     "The type of init-expression in a switch statement must be a scalar
//     integer.  If a case label has a constant- expression of equal value,
//     then execution will continue after that label."
//
// The spec doesn't actually say anything about the type of cases.  It only
// says "constant-expression".

#version 130

#define one 1
#define two 2

void main() {
   int tmp = 0;
   switch (1) {
   case one + two:
      tmp = 1;
   }

   gl_Position = vec4(0.0);
}