rfc:null_coercion_consistency

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rfc:null_coercion_consistency [2022/05/05 11:51] – Add note about html templating engines craigfrancisrfc:null_coercion_consistency [2023/10/18 11:57] (current) craigfrancis
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 ===== Introduction ===== ===== Introduction =====
  
-PHP 8.1 introduced [[https://wiki.php.net/rfc/deprecate_null_to_scalar_internal_arg|Deprecate passing null to non-nullable arguments of internal functions]]. While the consistency is welcome (user-defined vs internal functions), for those **not** using strict Static Analysis or //strict_types=1//, the breaking of NULL coercion creates an upgrade problem.+PHP 8.1 introduced [[https://wiki.php.net/rfc/deprecate_null_to_scalar_internal_arg|Deprecate passing null to non-nullable arguments of internal functions]]. While the consistency is welcome (user-defined vs internal functions), for those **not** using strict Static Analysis or //strict_types=1//, the breaking of NULL coercion creates a difficult BC problem.
  
-This RFC does **not** change anything for //strict_types=1// (or strict static analysis), as strict type checks can be useful. For example, developers can view NULL as a missing/invalid value (not as a value in itself), and passing NULL to a function like //htmlspecialchars()// could indicate a problem.+This RFC does **not** change anything for //strict_types=1// (or static analysis), as strict type checks can be useful. For example, some developers view NULL as a missing/invalid value (not as a value in itself), and passing NULL to a function like //htmlspecialchars()// might indicate a problem.
  
-Roughly **15%** of scripts use //strict_types=1// (calculation below).+There was a [[https://externals.io/message/112327|short discussion]] about the original RFC, but with the exception of Craig Duncan, there was no discussion about the BC problems, or the inconsistency of NULL coercion compared to string/int/float/bool coercion, or other contexts like string concatenation, == comparisons, arithmetics, sprintf, print, echo, array keys, etc.
  
-Roughly **33%** of developers use static analysis (realistically it's less than this, details below). +The intention is to also keep [[https://github.com/Girgias/unify-typing-modes-rfc|Unify PHP's typing modes]] by George Peter Banyard in mind, with coercions like //substr($string, "offset")// and //htmlspecialchars(array())// as being clearly problematic; whereas the following is common:
- +
-There was a [[https://externals.io/message/112327|short discussion]] about the original RFC, but with the exception of Craig Duncan, there was no consideration for the problems this creates with existing code (or the inconsistency of NULL coercion compared to string/int/float/bool coercion; or other contexts like string concatenation, == comparisons, arithmetics, sprintf, etc). +
- +
-The intention is to also keep [[https://github.com/Girgias/unify-typing-modes-rfc|Unify PHP's typing modes]] by George Peter Banyard in mind, with coercions like //substr($string, "offset")// and //htmlspecialchars(array())// as being clearly problematic; whereas the following is common, and has been fine:+
  
 <code php> <code php>
-$search = filter_input(INPUT_GET, 'q'); // Or similar (examples below)+$search = ($_GET['q'] ?? NULL); // Or similar (examples below)
  
-echo 'Results for ' . htmlspecialchars($search);+echo 'Results for ' . htmlspecialchars($search); // Fatal Error?!?
 </code> </code>
 +
 +Roughly **15%** of scripts use //strict_types=1// (calculation below).
 +
 +Roughly **33%** of developers use static analysis (realistically it's less than this, details below).
  
 ===== Problem ===== ===== Problem =====
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   - [[https://www.php.net/manual/en/language.types.boolean.php|To Boolean]]: "When converting to bool, the following values are considered false [...] the special type NULL"   - [[https://www.php.net/manual/en/language.types.boolean.php|To Boolean]]: "When converting to bool, the following values are considered false [...] the special type NULL"
  
-For example:+String/Int/Float/Bool can be coerced; Arrays, Resources, and Objects (without toString) cannot be coerced (for fairly obvious reasons). 
 + 
 +Or, NULL "can be coerced to the type requested by the hint without data loss and without creation of likely unintended data" ([[https://wiki.php.net/rfc/coercive_sth|ref]]). 
 + 
 +PHP 7.0 introduced the ability for user-defined functions to specify parameter types via the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations RFC]], where the implementation triggered Type Errors for those using //strict_types=1//, and otherwise used coercion for string/int/float/bool, but not NULL, PHP 8.1 updated internal function parameters to work in the same way. 
 + 
 +==== Current State ====
  
 <code php> <code php>
-// echo(string ...$expressions): void 
-// print(string $expression): int 
 print('A'); print('A');
 print(1); print(1);
 print(1.2); print(1.2);
 print(false); print(false);
-print(NULL); // Fine, coerced to empty string.+print(NULL); // Fine, still coerced to empty string. 
 + 
 +echo NULL; // Fine, still coerced to empty string.
  
 var_dump(3 + '5' + NULL); // Fine, int(8) var_dump(3 + '5' + NULL); // Fine, int(8)
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 $o[] = ('' == ''); $o[] = ('' == '');
-$o[] = ('' == NULL); // Fine, coerced to empty string.+$o[] = ('' == NULL); // Fine, still coerced to empty string.
  
 $o[] = 'ConCat ' . 'A'; $o[] = 'ConCat ' . 'A';
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 $o[] = 'ConCat ' . 1.2; $o[] = 'ConCat ' . 1.2;
 $o[] = 'ConCat ' . false; $o[] = 'ConCat ' . false;
-$o[] = 'ConCat ' . NULL; // Fine, coerced to empty string.+$o[] = 'ConCat ' . NULL; // Fine, still coerced to empty string.
  
 $o[] = sprintf('%s', 'A'); $o[] = sprintf('%s', 'A');
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 $o[] = sprintf('%s', 1.2); $o[] = sprintf('%s', 1.2);
 $o[] = sprintf('%s', false); $o[] = sprintf('%s', false);
-$o[] = sprintf('%s', NULL); // Fine, coerced to empty string.+$o[] = sprintf('%s', NULL); // Fine, still coerced to empty string.
  
 $o[] = htmlspecialchars('A'); $o[] = htmlspecialchars('A');
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 </code> </code>
  
-With user-defined functions, while there hasn't been a backwards compatibility issue, it still highlights the coercion inconsistency, in an environment that does not expect type checking, despite NULL being a value that "can be coerced to the type requested by the hint without data loss and without creation of likely unintended data":+With user-defined functions, this inconsistency is also noted:
  
 <code php> <code php>
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 user_function(3.3, 3.3, 3.3, 3.3); user_function(3.3, 3.3, 3.3, 3.3);
-  // string(3) "3.3" / int(3) / float(3.3) / bool(true)+  // string(3) "3.3" / int(3), lost precision / float(3.3) / bool(true)
  
 user_function(false, false, false, false); user_function(false, false, false, false);
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 user_function(NULL, NULL, NULL, NULL); user_function(NULL, NULL, NULL, NULL);
-  // Uncaught TypeError x4?+  // Fatal error, Uncaught TypeError x4!
 </code> </code>
  
-Arrays, Resources, and Objects (without //__toString()//) cannot be coerced (for fairly obvious reasons).+==== Scalar Types ====
  
-String/Int/Float/Bool can be coerced. +The [[https://wiki.php.net/rfc/scalar_type_hints_v5|Scalar Type Declarations]] RFC says "it should be possible for existing userland libraries to add scalar type declarations without breaking compatibility", but this is not the case, because of NULL. This has made adoption of type declarations harder, as it does not work like the following:
- +
-NULL can usually be coerced (e.g. string concatenation, == comparisons, arithmetics, sprintf, print, echo, array keys), but... +
- +
-  - PHP 7.0 introduced the ability for user-defined functions to specify parameter types via the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations RFC]], where the implementation triggered Type Errors for those using //strict_types=1//, and otherwise used coercion for string/int/float/bool, but not NULL. +
-  - PHP 8.1 updated internal function parameters to work in the same way. +
- +
-==== Examples ==== +
- +
-A simple search page:+
  
 <code php> <code php>
-$name = $request->get('name');+function my_function($s, $i, $f, $b) { 
 +  $s strval($s); 
 +  $i = intval($i); 
 +  $f = floatval($f); 
 +  $b = boolval($b); 
 +  var_dump($s, $i, $f, $b); 
 +}
  
-if (trim($name) === '') { // Contains non-whitespace characters; so not """ "NULLetc +function my_function(string $sint $ifloat $fbool $b) { 
-  $where_sql[] = 'name LIKE ?'; +  var_dump($s, $i, $f, $b);
-  $where_val[] = $name;+
 } }
  
-echo ' +my_function(NULL, NULL, NULL, NULL);
-  <form action="./" method="get"> +
-    <label> +
-      Search +
-      <input type="search" name="name" value="' . htmlspecialchars($name) . '"> +
-    </label> +
-    <input type="submit" value="Go"> +
-  </form>'; +
- +
-if ($name !== NULL) +
-  $register_url = '/admin/accounts/add/?name=' . urlencode($name); +
-  echo ' +
-    <p><a href="' . htmlspecialchars($register_url) . '">Add Account</a></p>'; +
-}+
 </code> </code>
  
-Regarding the source of //$name// (line 1); while frameworks could change their default to an Empty String, or an automated tool could cast the variable to a string, doing so would break the "Add Accountlink.+[[https://news-web.php.net/php.internals/117523|George Peter Banyard]] notes that "Userland scalar types [...] did not include coercion from NULL for //very// good reasons".
  
-HTML Templating engines like [[https://github.com/laravel/framework/blob/ab1506091b9f166b312b3990d07b2e21d971f2e6/src/Illuminate/Support/helpers.php#L119|Laravel Blade]] will now suppress this deprecation via null-coalescing ([[https://github.com/laravel/framework/pull/36262/files#diff-15b0a3e2eb2d683222d19dfacc04c616a3db4e3d3b3517e96e196ccbf838f59eR118|patch]]); or [[https://github.com/twigphp/Twig/blob/b4d6723715da57667cca851051eba3786714290d/src/Extension/EscaperExtension.php#L195|Symphony Twig]] will preserve NULL, where it's usually passed to //echo// (despite the [[https://www.php.net/echo|echo documentation]] saying it only accepts non-nullable strings).+The [[https://wiki.php.net/rfc/scalar_type_hints_v5|Scalar Type Declarations]] RFC says "The only exception to this is the handling of NULL: in order to be consistent with our existing type declarations for classes, callables and arrays, NULL is not accepted by default, unless it is a parameter and is explicitly given a default value of NULL", which goes against the documentation (as noted abovewhere the coercion from NULL is well defined (i.e. NULL is more like a string/int/float/bool, rather than an object/callable/array).
  
-I'd argue a very strict level of type checking (that prevents all forms of coercion) is best done by Static Analysis, which can check if a variable can be nullable, and it can decide if this is a problem, in the same way that a string (e.g. '15') being provided to integer parameter could be seen as a problem.+==== Examples ====
  
 Common sources of NULL: Common sources of NULL:
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 $value = array_pop($empty_array); $value = array_pop($empty_array);
 $value = mysqli_fetch_row($result); $value = mysqli_fetch_row($result);
-$value = json_decode($json); // Invalid JSON, or nesting limit. 
 </code> </code>
  
-Examples functions, often working with user input, where NULL has been fine:+Examples functions, often working with user input, where NULL has always been accepted/coerced:
  
 <code php> <code php>
 +$rounded_value = round($value);
 +
 $search_trimmed = trim($search); $search_trimmed = trim($search);
  
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 mail('nobody@example.com', 'subject', 'message', NULL, '-fwebmaster@example.com'); mail('nobody@example.com', 'subject', 'message', NULL, '-fwebmaster@example.com');
 </code> </code>
 +
 +HTML Templating engines like [[https://github.com/laravel/framework/blob/ab1506091b9f166b312b3990d07b2e21d971f2e6/src/Illuminate/Support/helpers.php#L119|Laravel Blade]] suppress this deprecation with null-coalescing ([[https://github.com/laravel/framework/pull/36262/files#diff-15b0a3e2eb2d683222d19dfacc04c616a3db4e3d3b3517e96e196ccbf838f59eR118|patch]]); or [[https://github.com/twigphp/Twig/blob/b4d6723715da57667cca851051eba3786714290d/src/Extension/EscaperExtension.php#L195|Symphony Twig]] which preserves NULL, but it's often passed to //echo// (which accepts it, despite the [[https://www.php.net/echo|echo documentation]] saying it accepts non-nullable strings).
 +
 +I'd argue strict type checking (that prevents all forms of coercion) should be done via Static Analysis or via //strict_types=1// opt-in, like how a string (e.g. '15') being provided to integer parameter could identify a problem in some development environments.
  
 There are approximately [[https://github.com/craigfrancis/php-allow-null-rfc/blob/main/functions-change.md|335 parameters affected by this deprecation]]. There are approximately [[https://github.com/craigfrancis/php-allow-null-rfc/blob/main/functions-change.md|335 parameters affected by this deprecation]].
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 The only realistic way for developers to find when NULL is passed to these internal functions is to use the deprecation notices (not ideal). The only realistic way for developers to find when NULL is passed to these internal functions is to use the deprecation notices (not ideal).
 +
 +And this does not stop new issues being introduced, as developers may not consider when variables might be NULL (e.g. a browser extension or network issues affecting GET/POST variables).
  
 It is possible to use very strict Static Analysis, to follow every variable from source to sink (to check if a variable could be NULL), but most developers are not in a position to do this (i.e. not using static analysis, or not at a high enough level, or they are using a baseline to ignore). It is possible to use very strict Static Analysis, to follow every variable from source to sink (to check if a variable could be NULL), but most developers are not in a position to do this (i.e. not using static analysis, or not at a high enough level, or they are using a baseline to ignore).
  
-In the last JetBrains developer survey (with 67% regularly using Laravel), **only 33% used Static Analysis** ([[https://www.jetbrains.com/lp/devecosystem-2021/php/#PHP_do-you-use-static-analysis|source]]); where it's fair to many still would still not be identify these possible NULL values (too low level, and/or using a baseline).+In the last JetBrains developer survey (with 67% regularly using Laravel), **only 33% used Static Analysis** ([[https://www.jetbrains.com/lp/devecosystem-2021/php/#PHP_do-you-use-static-analysis|source]]); where it's fair to say many of these developers would //still// not identify these possible NULL values (too low level, and/or using a baseline).
  
 As an example, take this simple script: As an example, take this simple script:
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 </code> </code>
  
-Even that is considered fine today by the relevant tools: +This is considered fine by these tools:
- +
-<code cli> +
-composer require --dev rector/rector +
-./vendor/bin/rector init +
-./vendor/bin/rector process ./src/ +
-[OK] Rector is done! +
-</code>+
  
 <code cli> <code cli>
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 </code> </code>
 Note: Psalm can detect this at [[https://psalm.dev/docs/running_psalm/error_levels/|levels 1, 2, and 3]] (don't use a baseline). Note: Psalm can detect this at [[https://psalm.dev/docs/running_psalm/error_levels/|levels 1, 2, and 3]] (don't use a baseline).
 +
 +==== One Solution ====
 +
 +Since [[https://github.com/rectorphp/rector-src/pull/2543|21st June 2022]], Rector can modify 362 function arguments via //NullToStrictStringFuncCallArgRector//:
 +
 +<code cli>
 +mkdir -p rector/src;
 +
 +cd rector/;
 +
 +composer require --dev rector/rector;
 +
 +echo '<?= htmlspecialchars($var) ?>' > src/index.php;
 +
 +echo '<?php
 +
 +use Rector\Php81\Rector\FuncCall\NullToStrictStringFuncCallArgRector;
 +use Rector\Config\RectorConfig;
 +
 +return static function (RectorConfig $rectorConfig): void {
 +    $rectorConfig->paths([__DIR__ . "/src"]);
 +    $rectorConfig->rule(NullToStrictStringFuncCallArgRector::class);
 +};
 +' > rector.php;
 +
 +./vendor/bin/rector process;
 +</code>
 +
 +This will litter the code with the use of //(string)// type casting, e.g.
 +
 +<code diff>
 +-<?= htmlspecialchars($var) ?>
 ++<?= htmlspecialchars((string) $var) ?>
 +</code>
 +
 +For a typical project (which won't be using //strict_types=1//), expect thousands of changes to be made; and note how this does not improve code quality.
  
 ==== Temporary Solutions ==== ==== Temporary Solutions ====
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 ==== Updating ==== ==== Updating ====
  
-While making each change is fairly easy - they are difficult to find, there are many of them (time consuming), and the updates used are often pointless, e.g.+While making each change is fairly easy - they are still difficult to find, there are many of them, and the updates used are often pointless, e.g.
  
   * //urlencode(strval($name));//   * //urlencode(strval($name));//
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   * //urlencode($name ?? "");//   * //urlencode($name ?? "");//
  
-One example diff didn't exactly make the code easier to read:+And often do not make the code easier to read:
  
 <code diff> <code diff>
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 </code> </code>
  
-As noted above - PHPCompatibility, CodeSniffer, Rector, etc are unable to find or update these cases.+As noted above - Rector can add //(string)// type casting automaticallybut this does not improve code quality.
  
 ===== Proposal ===== ===== Proposal =====
  
-Revert the NULL deprecation for parameters (when **not** using //strict_types=1//), so it continues to work (as NULL coercion does in other contexts)to avoid the upgrade problems (i.e. Fatal Errors in PHP 9.0).+Revert the NULL deprecation for parameters (when **not** using //strict_types=1//), so NULL coercion continues to work (as it does in other contexts) to avoid the upgrade problems (i.e. Fatal Errors in PHP 9.0).
  
 And, in the spirit of the original RFC to keep user-defined and internal functions consistent, also change user-defined functions so NULL is coerced for non-nullable parameters (when **not** using //strict_types=1//). And, in the spirit of the original RFC to keep user-defined and internal functions consistent, also change user-defined functions so NULL is coerced for non-nullable parameters (when **not** using //strict_types=1//).
  
-This means the type "//?int//" will allow NULL or an integer to be provided to the function; whereas the non-nullable type "//int//" would coerce NULL to 0in the same way the string "0" would be.+This means the type "//?int//" will allow NULL or an integer to be provided to the function; whereas the non-nullable type "//int//" would coerce NULL to 0in exactly the same way the string "0" or the boolean false would be.
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
  
-None+While the intention of this RFC is to avoid a BC break; for user defined functions to be updated to also coerce NULL (instead of throwing a Type Error), while unlikely, it is possible some non //strict_types// code may rely the TypeError being thrown, for example: 
 + 
 +<code php> 
 +function my_function(string $my_string) { 
 +  var_dump($my_string); 
 +
 + 
 +try { 
 +  my_function('A');   // string(1) "A" 
 +  my_function(1);     // string(1) "1" 
 +  my_function(1.2);   // string(3) "1.2" 
 +  my_function(true);  // string(1) "1" 
 +  my_function(false); // string(0) "" 
 +  my_function(NULL);  // Throw Type Error 
 +} catch (TypeError $e) { 
 +  // Do something important? 
 +
 +</code>
  
 ===== Proposed PHP Version(s) ===== ===== Proposed PHP Version(s) =====
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 "it's a bit late" - We only have a deprecation at the moment (which can and is being ignored), it will be "too late" when PHP 9.0 uses Fatal Errors. "it's a bit late" - We only have a deprecation at the moment (which can and is being ignored), it will be "too late" when PHP 9.0 uses Fatal Errors.
- 
-"Userland scalar types [...] did not include coercion from NULL for //very// good reasons." - The only reason mentioned in [[https://wiki.php.net/rfc/scalar_type_hints_v5|Scalar Type Declarations]] is "to be consistent with our existing type declarations" (no further details given). Talking to developers, the only reason mentioned is noted above, where NULL can be viewed as a missing/invalid value, and passing NULL to a function like //htmlspecialchars()// could indicate a problem (which can a be useful check for static analysis, or in the context of //strict_types=1//). 
  
 The function //mt_rand()// can be called with no arguments, or with min and max integer arguments. A developer may call //mt_rand(NULL, NULL)// and expect it to work the same as no arguments (returning a random number between 0 and //mt_getrandmax()//), but the NULL's would be coerced to 0, so it would always return 0. That said, I cannot find any public examples of this happening ([[https://grep.app/search?q=mt_rand%28NULL&filter%5Blang%5D%5B0%5D=PHP|1]], [[https://grep.app/search?q=mt_rand%5Cs%2A%5C%28%5Cs%2ANULL&regexp=true&filter[lang][0]=PHP|2]], [[https://www.google.com/search?q=%22mt_rand+NULL+NULL%22|3]]). The function //mt_rand()// can be called with no arguments, or with min and max integer arguments. A developer may call //mt_rand(NULL, NULL)// and expect it to work the same as no arguments (returning a random number between 0 and //mt_getrandmax()//), but the NULL's would be coerced to 0, so it would always return 0. That said, I cannot find any public examples of this happening ([[https://grep.app/search?q=mt_rand%28NULL&filter%5Blang%5D%5B0%5D=PHP|1]], [[https://grep.app/search?q=mt_rand%5Cs%2A%5C%28%5Cs%2ANULL&regexp=true&filter[lang][0]=PHP|2]], [[https://www.google.com/search?q=%22mt_rand+NULL+NULL%22|3]]).
Line 379: Line 419:
   - //$method// in [[https://php.net/method_exists|method_exists()]]   - //$method// in [[https://php.net/method_exists|method_exists()]]
   - //$json// in [[https://php.net/json_decode|json_decode()]]   - //$json// in [[https://php.net/json_decode|json_decode()]]
 +
 +It might be appropriate for coercion and explicit casting/converting to work in the same way, even if they were to become stricter in the values they accept; e.g. //intval("")// and //((int) "")// currently return int(0), whereas //(5 + "")// results in a TypeError.
  
 ===== Voting ===== ===== Voting =====
Line 396: Line 438:
 ===== Notes ===== ===== Notes =====
  
-The **15%** of scripts that do not use //strict_types=1// was calculated using [[https://grep.app/|grep.app]], to "search across a half million git repos", were each result is a script (not a count of matches,  [[https://grep.app/search?q=defuse/php-encryption&filter[lang][0]=PHP|example]]). We can see [[https://grep.app/search?q=strict_types&filter[lang][0]=PHP|272,871]] scripts using //strict_types=1//, out of [[https://grep.app/search?q=php&filter[lang][0]=PHP|1,842,666]]. And keep in mind that [[https://grep.app/search?q=class%20wpdb%20%7B&filter[lang][0]=PHP|WordPress only really appears once]], it is [[https://make.wordpress.org/core/2022/01/10/wordpress-5-9-and-php-8-0-8-1/#php-8-1-deprecation-passing-null-to-non-nullable-php-native-functions-parameters|affected by this deprecation]], and is installed/used by many.+The **15%** of scripts that use //strict_types=1// was calculated using [[https://grep.app/|grep.app]], to "search across a half million git repos", were each result is a script (not a count of matches,  [[https://grep.app/search?q=defuse/php-encryption&filter[lang][0]=PHP|example]]). We can see [[https://grep.app/search?q=strict_types&filter[lang][0]=PHP|272,871]] scripts using //strict_types=1//, out of [[https://grep.app/search?q=php&filter[lang][0]=PHP|1,842,666]]. And keep in mind that [[https://grep.app/search?q=class%20wpdb%20%7B&filter[lang][0]=PHP|WordPress only really appears once]], it is [[https://make.wordpress.org/core/2022/01/10/wordpress-5-9-and-php-8-0-8-1/#php-8-1-deprecation-passing-null-to-non-nullable-php-native-functions-parameters|affected by this deprecation]], and is installed/used by many.
  
 In the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations]] RFC for PHP 7.0, scalar types were defined as "int, float, string and bool" - but, despite NULL also being a simple value (i.e. not an array/object/resource), it was not included in this definition. For backwards compatibility reasons this definition is unlikely to change. In the [[https://wiki.php.net/rfc/scalar_type_hints_v5#behaviour_of_weak_type_checks|Scalar Type Declarations]] RFC for PHP 7.0, scalar types were defined as "int, float, string and bool" - but, despite NULL also being a simple value (i.e. not an array/object/resource), it was not included in this definition. For backwards compatibility reasons this definition is unlikely to change.
rfc/null_coercion_consistency.1651751483.txt.gz · Last modified: 2022/05/05 11:51 by craigfrancis