php / php/php-src

Possible regression with spreading nested arrays into a function call and references

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Bug Category: Engine Status: Verified
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Description

Description

I've noticed the following possible regression:

$args = [1];
$ref = [&$args];
function test(&$v) {
	$v = 7;
};
test(...$ref[0]);
var_dump($args[0]);

Starting with PHP 7.3, the output of the above code has changed:

$ docker run --rm php:7.2.34 -r "$args = [1]; $ref = [&$args]; function test(&$v) { $v = 7; }; test(...$ref[0]); var_dump($args[0]);"
int(7)

$ docker run --rm php:7.3    -r "$args = [1]; $ref = [&$args]; function test(&$v) { $v = 7; }; test(...$ref[0]); var_dump($args[0]);"
int(1)

$ docker run --rm php:8.3.7  -r "$args = [1]; $ref = [&$args]; function test(&$v) { $v = 7; }; test(...$ref[0]); var_dump($args[0]);"
int(1)

The only entry I've found within PHP 7.3's release notes that might be related is References returned by Array and Property Accesses are immediately unwrapped. But I'm not sure whether this does actually describe the behavior change in the code snippet above.

I'm also not really sure whether the code is valid or not. In case it is not, it might be helpful to display a message.

There exists a workaround to get the old result by introducing another variable:

$temp = &$ref[0];
test(...$temp);
PHP Version

PHP 7.3.0 - PHP 8.3.7

Operating System

No response

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the nested-array spread and reference example on PHP 7.2, 7.3, and 8.3, then compare it with the PHP 7.3 reference-unwrapping migration note. Determine whether the changed result is valid; done means documenting the expected semantics and adding a correction or diagnostic if the behavior is erroneous.

Written by the indexing model from the issue text.

Assessment

Tech stack
php
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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