[META] PHP 8 backward incompatible changes detection

[mglaman]

Feature request

We are starting to work on PHP 8 compatibility detection for the Drupal ecosystem. Currently, Drupal 9 and eventual Drupal 10 are PHP 8 compatible, but we have a wide array of an ecosystem and client code that needs inspection.

Some initial discussion started here: #5265. While some of it was Drupal specific "we only want to report PHP 8 specific errors", we discovered some PHP 8 incompatibilities were not discovered (or needed a different error message when phpVersion: 80000.

Having these rules makes it easy to check your PHP 7.4 code before running it on PHP 8 and hitting a bunch of errors.

List of the backward incompatible changes: https://www.php.net/manual/en/migration80.incompatible.php

Progress

• match is now a reserved keyword.
• Methods with the same name as the class are no longer interpreted as constructors. The __construct() method should be used instead.
• The ability to call non-static methods statically has been removed. Thus is_callable() will fail when checking for a non-static method with a classname (must check with an object instance).
• The ability to define case-insensitive constants has been removed. The third argument to define() may no longer be true.
• The ability to specify an autoloader using an __autoload() function has been removed. spl_autoload_register() should be used instead.
• create_function() has been removed. Anonymous functions may be used instead.
• each() has been removed. foreach or ArrayIterator should be used instead.
• The ability to use array_key_exists() with objects has been removed. isset() or property_exists() may be used instead.
• Using parent inside a class that has no parent will now result in a fatal compile-time error.
• #[ is no longer interpreted as the start of a comment, as this syntax is now used for attributes.
• The signature of abstract methods defined in traits is now checked against the implementing class method:
• Support for deprecated curly braces for offset access has been removed.
• Magic Methods will now have their arguments and return types checked if they have them declared. The signatures should match the following list:

Notes

I figure we can use this to organize rules that need to be written. My original notes are here: https://impossible-tangerine-e23.notion.site/Drupal-PHP-8-Readiness-53094cf842df424899d83d20bfd9fba4

match is now a reserved keyword.

I don't know if this is possible to handle. When the parser runs across the following code we get a syntax error and the file stops parsing.

https://phpstan.org/r/cae8e1b1-2d0d-4ee0-8e2c-b9c9a5796535

Methods with the same name as the class are no longer interpreted as constructors. The __construct() method should be used instead.

This was deprecated in PHP 7, so who knows if anyone hits this. But PHPStan doesn't warn of its deprecation on PHP 7 nor report it as an error in PHP 8. All we get is a warning about the return type.

https://phpstan.org/r/1d412d9d-76a1-440e-a65c-809b03250974

The ability to call non-static methods statically has been removed. Thus is_callable() will fail when checking for a non-static method with a classname (must check with an object instance).

This seems like a good rule/check regardless of PHP. I didn't know is_callable could invoke a non-static method on a class this way.

https://phpstan.org/r/ef91bba8-d5eb-441b-91d8-60866e2af6e6

The ability to define case-insensitive constants has been removed. The third argument to define() may no longer be true.

https://phpstan.org/r/a303a478-e979-48f7-92fb-d56b0cd121b7

The ability to specify an autoloader using an __autoload() function has been removed. spl_autoload_register() should be used instead.

No idea how relevant

https://phpstan.org/r/f914387f-6e8f-4ee6-b601-75baa728084a

create_function() has been removed. Anonymous functions may be used instead.

Seems like a good generic rule of "Don't use create_function, use anonymous instead" for PHP 7 would be great. And in PHP 8 handle function is not found for backward incompat error.

https://phpstan.org/r/7b7db20f-8b1d-411d-9d9e-41dbec9bae4d

Links: #5373, phpstan/phpstan-src#588

each() has been removed. foreach or ArrayIterator should be used instead.

No idea how relevant. But there is some ancient Drupal code out there.

https://phpstan.org/r/a00f7a19-f467-450c-9991-2ef41cd5d441

The ability to use array_key_exists() with objects has been removed. isset() or property_exists() may be used instead.

https://phpstan.org/r/a964496a-9929-4aaa-9c78-7dbc144c4d7b

I think "Call to function array_key_exists() with 'foo' and stdClass will always evaluate to false." just needs to be updated to match what happens in PHP8. I haven't tried directly to see if there is a runtime error versus always returning false.

Using parent inside a class that has no parent will now result in a fatal compile-time error.

I think phpstan-src/src/Rules/Classes/InstantiationRule.php just needs to have PHP8 specific checks. Instead of just Bar::__construct() calls parent::__construct() but Bar does not extend any class. we need an error on PHP8

#[ is no longer interpreted as the start of a comment, as this syntax is now used for attributes.

This might just cause a syntax error with php-parser and nothing we can do.

https://phpstan.org/r/e384296a-be57-4282-8621-be46c7865f44

The signature of abstract methods defined in traits is now checked against the implementing class method

https://phpstan.org/r/3eb722f0-eba2-49ef-9222-a717994d38af

Support for deprecated curly braces for offset access has been removed.

https://phpstan.org/r/41e34db1-9124-4233-8351-1e565a2b0093

Magic Methods will now have their arguments and return types checked if they have them declared. The signatures should match the following list:

Need to have a mapping of the defined return types + magic methods; defined in the page.

https://phpstan.org/r/617bee17-0fb8-4ee6-bec4-04118853506d

parse_str() can no longer be used without specifying a result array.

This works. but we don't verify the type of the 2nd param

https://phpstan.org/r/d98ba1b6-6dd2-4ec4-ade2-aae0837f575a

[ondrejmirtes]

Hi, please create a Markdown checklist in your post from the todo items 😊

[ondrejmirtes]

Funny - there's almost no overlap between your list and my list 😊 I'll add mine once I get the chance from a computer.

[mglaman]

@ondrejmirtes :) sounds good. I'll keep updating and adding playground examples.

[mglaman]

@ondrejmirtes okay, my list is added. I went through the top of the page and left off at https://www.php.net/manual/en/migration80.incompatible.php#migration80.incompatible.standard

[mglaman]

I just saw this in the PhpStorm stubs:

#[Deprecated(reason: "Use anonymous functions instead", since: "7.2")]
function create_function (string $args, string $code): false|string
{}

I think we'll need to update phpstan/phpstan-deprecation-rules to read this Deprecated attribute.

[ondrejmirtes]

I'll comment briefly on your items:

match is now a reserved keyword.

Doesn't need any handling, as you said, it's already a parse error.

Methods with the same name as the class are no longer interpreted as constructors. The __construct() method should be used instead.

I think PHPStan handles this correctly too: https://phpstan.org/r/23861f3c-652e-44c6-817f-7054529e88fa

The ability to call non-static methods statically has been removed. Thus is_callable() will fail when checking for a non-static method with a classname (must check with an object instance).

Should be handled in ConstantArrayType::getCallableParametersAcceptors();

 The ability to define case-insensitive constants has been removed. The third argument to define() may no longer be true.

This needs a custom rule.

The ability to specify an autoloader using an __autoload() function has been removed. spl_autoload_register() should be used instead.

This needs a custom rule.

create_function() has been removed. Anonymous functions may be used instead.

Not action needed, already reported by PHPStan.

each() has been removed. foreach or ArrayIterator should be used instead.

Not action needed, already reported by PHPStan.

The ability to use array_key_exists() with objects has been removed. isset() or property_exists() may be used instead.

Not action needed, already reported by PHPStan: Parameter #2 $array of function array_key_exists expects array, stdClass given.

Using parent inside a class that has no parent will now result in a fatal compile-time error.

Not action needed, already reported by PHPStan: https://phpstan.org/r/7cbe058c-7c72-4349-b54f-3b7300f55457

#[ is no longer interpreted as the start of a comment, as this syntax is now used for attributes.

Not action needed, already reported by PHPStan.

The signature of abstract methods defined in traits is now checked against the implementing class method

Needs handling in OverridingMethodRule. Getting to the overridden trait method through reflection might be challenging.

Support for deprecated curly braces for offset access has been removed.

No idea if this is different in the AST.

Magic Methods will now have their arguments and return types checked if they have them declared. The signatures should match the following list:

Needs a new rule.

parse_str() can no longer be used without specifying a result array.

That's because the array is defined as passed by reference. PHPStan doesn't enforce types on that, because functions simply behave in a weird way around this.

[ondrejmirtes]

I'll add my items:

• call_user_func_array can break because of named parameters: https://3v4l.org/A2MGD
• min() and max() should require non-empty array
• RFC: Remove inappropriate inheritance signature checks on private methods
• Constant of null value does not make parameter nullable (https://3v4l.org/pOQgF)
• Non-absolute trait method references in trait alias adaptations are now required to be unambiguous: https://3v4l.org/kkPJp
• Report boolean, integer typehints: https://3v4l.org/u1mMu
• Removed constants: FILTER_FLAG_SCHEME_REQUIRED, FILTER_FLAG_HOST_REQUIRED, FILTER_VALIDATE_URL, INPUT_REQUEST, INPUT_SESSION, MB_OVERLOAD_MAIL, MB_OVERLOAD_STRING, MB_OVERLOAD_REGEX
• Check __set_state signature: [#79521] Check __set_state structure php/php-src#5462
• final private is no longer allowed: https://3v4l.org/TR37P
• Optional before required parameter: https://3v4l.org/Zd1Eg (but it's not reported in this case: https://3v4l.org/ltiTs)

[ondrejmirtes]

And to comment on those:

call_user_func_array can break because of named parameters

It could be a very useful couple of rules to actually check call_user_func and call_user_func_array whether they call the functions correctly.

min() and max() should require non-empty array

This might just work if we add 'min' => ['', '...arg1'=>'non-empty-array'], to functionMap_php80delta.php

RFC: Remove inappropriate inheritance signature checks on private methods

I'd like to make sure PHPStan behaves correctly on both PHP 7 and PHP 8.

Constant of null value does not make parameter nullable (https://3v4l.org/pOQgF)

This needs handling in https://github.com/ondrejmirtes/BetterReflection

Non-absolute trait method references in trait alias adaptations are now required to be unambiguous

This needs a new rule.

Report boolean, integer typehints

This needs handling in FunctionDefinitionCheck.

Removed constants

Looks like this is already handled: https://phpstan.org/r/dd7faf4c-0aae-4d3c-aa9f-fc04ad562594 but it needs to be checked whether all of these constants have the @removed tag in phpstorm-stubs.

Check __set_state signature

Needs a new rule

final private is no longer allowed

Needs a new rule

Optional before required parameter

Needs a new rule Already implemented.

[ondrejmirtes]

Also please - any discussion of any of these specific items warrants a new separate thread (new issue) so that this issue with the list isn't diluted any further :) Thanks.

[phpstan-bot]

@mglaman After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
 PHP 7.1 – 7.4 (1 error)
 ==========
 
-3: Function match() has no return typehint specified.
+3: Function match() has no return type specified.

Full report

PHP 8.0 (1 error)

Line	Error
3	Syntax error, unexpected T_MATCH, expecting T_STRING or '(' on line 3

PHP 7.1 – 7.4 (1 error)

Line	Error
3	Function match() has no return type specified.

[phpstan-bot]

@mglaman After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-7: Method Foo::foo() has no return typehint specified.
+7: Method Foo::foo() has no return type specified.

Full report

Line	Error
7	Method Foo::foo() has no return type specified.