Description:
------------
It seems that in PHP7 the '/' flag has had it's meaning reversed. It is documented as:

"'/' - This indicates that the preceding parameter should be separated from the calling parameter, in case you wish to modify it locally in the function without modifying the original calling parameter."

i.e. if you want a function to accept a parameter by reference you should _not_ use this flag, so that when you set the variable inside the function, the new value is seen outside by any reference to the variable outside the function.


However it is now _required_ to set the '/' flag to pass a variable by reference.


Example code from - https://github.com/mkoppanen/imagick/blob/phpseven/imagick_class.c#L11636


This code works to set the parameter in 5.x:

zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "O|zz", &reference_obj, php_imagick_sc_entry, &z_best_match_offset, &z_similarity);
if (z_similarity) {
    ZVAL_DOUBLE(z_similarity, similarity);
}

That code needs to be changed to this in 7:
zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "O|z/z/", &reference_obj, php_imagick_sc_entry, &z_best_match_offset, &z_similarity);
if (z_similarity) {
    ZVAL_DOUBLE(z_similarity, similarity);
}

It appears this change was done in this commit:
https://github.com/php/php-src/commit/c1965f58d4dd3970912dcd6a63ccd5860bae1a97



Test script:
---------------
<?php

$imagick = new \Imagick();
$imagick->newPseudoImage(640, 480, "magick:logo");
$imagick2 = clone $imagick;
$imagick2->cropimage(40, 40, 250, 110);
$imagick2->vignetteimage(0, 1, 3, 3);

$similarity = 'not set';
$bestMatch = 'not set';
$comparison = $imagick->subImageMatch($imagick2, $bestMatch, $similarity);

var_dump($similarity);

Expected result:
----------------
float(0.90996121310752)

Actual result:
--------------
string(7) "not set"