Perl: while with no conditional

Question

According to the doc, the while statement executes the block as long as the expression is true. I wonder why it becomes an infinite loop with an empty expression:

Answer 1

This is a special case of the concept of Vacuous Truth. If there is no condition, the statement while the condition is true is itself vacuously true.

If I am reading this correctly, the relevant piece of code seems to be around line 5853 of op.c in 5.14.1:

5853     if (expr) {
5854         scalar(listop);
5855         o = new_logop(OP_AND, 0, &expr, &listop);
5856         if (o == expr && o->op_type == OP_CONST && !SvTRUE(cSVOPo->op_sv)) {
5857             op_free(expr);              /* oops, it's a while (0) */
5858             op_free((OP*)loop);
5859             return NULL;                /* listop already freed by new_logop */
5860         }
5861         if (listop)
5862             ((LISTOP*)listop)->op_last->op_next =
5863                 (o == listop ? redo : LINKLIST(o));
5864     }
5865     else
5866         o = listop;

I am assuming with no expr in the condition, we reach o = listop. listop was previously defined as listop = op_append_list(OP_LINESEQ, block, cont);.