yield without value in reference generator function does not create notice

[ohyeaah]

Description

The following code:

<?php
error_reporting(E_ALL);
function &y()
{
  yield null; // warning
  yield; // no warning
}
foreach (y() as &$y);

Resulted in this output:

PHP Notice:  Only variable references should be yielded by reference in /home/user10/test.php on line 5

But I expected this output instead:

PHP Notice:  Only variable references should be yielded by reference in /home/user10/test.php on line 5
PHP Notice:  Only variable references should be yielded by reference in /home/user10/test.php on line 6

PHP Version

PHP 8.2.24 (cli) (built: Sep 27 2024 04:16:10) (NTS)

Operating System

Debian GNU/Linux 12 (bookworm)

[bwoebi]

I'm not sure whether that's a bug or not. Maybe the bare yield; is just a $tmp = null; yield &$tmp; in disguise.

[nielsdos]

Err, unless I misunderstand, the yield; line receives a value from outside the generator, it does not generate a value. Hence, this does not seem like a bug to me.
See https://3v4l.org/PZlBb

[cmb69]

the yield; line receives a value from outside the generator, it does not generate a value.

A yield without argument is basically the same as yield null. ::send() would override the given value anyway (https://3v4l.org/Kk31R).

[nielsdos]

TIL, not very intuitive.
In that case I think this is a bug.

[cmb69]

In that case I think this is a bug.

I agree:

php-src/Zend/zend_vm_def.h

Lines 8315 to 8380 in 33ba1a4

	if (OP1_TYPE != IS_UNUSED) {
	if (UNEXPECTED(EX(func)->op_array.fn_flags & ZEND_ACC_RETURN_REFERENCE)) {
	/* Constants and temporary variables aren't yieldable by reference,
	* but we still allow them with a notice. */
	if (OP1_TYPE & (IS_CONST|IS_TMP_VAR)) {
	zval *value;
	zend_error(E_NOTICE, "Only variable references should be yielded by reference");
	value = GET_OP1_ZVAL_PTR(BP_VAR_R);
	ZVAL_COPY_VALUE(&generator->value, value);
	if (OP1_TYPE == IS_CONST) {
	if (UNEXPECTED(Z_OPT_REFCOUNTED(generator->value))) {
	Z_ADDREF(generator->value);
	}
	}
	} else {
	zval *value_ptr = GET_OP1_ZVAL_PTR_PTR(BP_VAR_W);
	/* If a function call result is yielded and the function did
	* not return by reference we throw a notice. */
	do {
	if (OP1_TYPE == IS_VAR) {
	ZEND_ASSERT(value_ptr != &EG(uninitialized_zval));
	if (opline->extended_value == ZEND_RETURNS_FUNCTION
	&& !Z_ISREF_P(value_ptr)) {
	zend_error(E_NOTICE, "Only variable references should be yielded by reference");
	ZVAL_COPY(&generator->value, value_ptr);
	break;
	}
	}
	if (Z_ISREF_P(value_ptr)) {
	Z_ADDREF_P(value_ptr);
	} else {
	ZVAL_MAKE_REF_EX(value_ptr, 2);
	}
	ZVAL_REF(&generator->value, Z_REF_P(value_ptr));
	} while (0);
	FREE_OP1();
	}
	} else {
	zval *value = GET_OP1_ZVAL_PTR(BP_VAR_R);
	/* Consts, temporary variables and references need copying */
	if (OP1_TYPE == IS_CONST) {
	ZVAL_COPY_VALUE(&generator->value, value);
	if (UNEXPECTED(Z_OPT_REFCOUNTED(generator->value))) {
	Z_ADDREF(generator->value);
	}
	} else if (OP1_TYPE == IS_TMP_VAR) {
	ZVAL_COPY_VALUE(&generator->value, value);
	} else if ((OP1_TYPE & (IS_VAR|IS_CV)) && Z_ISREF_P(value)) {
	ZVAL_COPY(&generator->value, Z_REFVAL_P(value));
	FREE_OP1_IF_VAR();
	} else {
	ZVAL_COPY_VALUE(&generator->value, value);
	if (OP1_TYPE == IS_CV) {
	if (Z_OPT_REFCOUNTED_P(value)) Z_ADDREF_P(value);
	}
	}
	}
	} else {
	/* If no value was specified yield null */
	ZVAL_NULL(&generator->value);
	}

For UNUSED_UNUSED the last else branch is taken, but there is no check for the generator returning by ref.