i believe where is a typo in :

slang_typeinfo.c

allowing "float to int" conversation instead of "int to float":

this :
slang_type_specifier_compatible(const slang_type_specifier * x,
                                const slang_type_specifier * y)
{
   /* special case: float == int */
   if (x->type == SLANG_SPEC_INT && y->type == SLANG_SPEC_FLOAT) {
      return GL_TRUE;
   }
should be replaced with :
   if (x->type == SLANG_SPEC_FLOAT && y->type == SLANG_SPEC_INT) {