rfc:null_coercion_consistency

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rfc:null_coercion_consistency [2022/05/11 10:59] – Add note about adding types to userland libraries without BC breaks (thanks Aleksander) craigfrancisrfc:null_coercion_consistency [2022/10/16 07:37] – Note that Rector can now "help" with this problem. craigfrancis
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 </code> </code>
  
-Arrays, Resources, and Objects (without //__toString()//) cannot be coerced (for fairly obvious reasons).+Arrays, Resources, and Objects (without toString) cannot be coerced (for fairly obvious reasons).
  
 String/Int/Float/Bool can be coerced. String/Int/Float/Bool can be coerced.
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   - 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 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.   - PHP 8.1 updated internal function parameters to work in the same way.
 +
 +==== Scalar Types ====
 +
 +[[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". 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).
 +
 +The RFC also 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:
 +
 +<code php>
 +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);
 +}
 +
 +function my_function(string $s, int $i, float $f, bool $b) {
 +  var_dump($s, $i, $f, $b);
 +}
 +
 +my_function(NULL, NULL, NULL, NULL);
 +</code>
 +
 +Some developers view NULL as a missing/invalid value, and passing NULL to a function like //htmlspecialchars()// could indicate a problem (can a be useful check for static analysis, or in the context of //strict_types=1//).
  
 ==== Examples ==== ==== Examples ====
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 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), expect thousands of changes to be made; and note how this does not improve code quality.
  
 ==== Temporary Solutions ==== ==== Temporary Solutions ====
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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 automatically, but I have no idea how this improves code quality.
  
 ===== Proposal ===== ===== Proposal =====
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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). In theory "it should be possible for existing userland libraries to add scalar type declarations without breaking compatibility", but this was not the case, because of NULL. Talking to developers, the only reason mentioned (noted above) is 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]]).
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   - //$method// in [[https://php.net/method_exists|method_exists()]]   - //$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 =====
rfc/null_coercion_consistency.txt · Last modified: 2023/10/18 11:57 by craigfrancis

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