rectorphp/rector · error · ShouldNotHappenException

"%s" is deprecated as it produces too many false positives.

Error message

"%s" is deprecated as it produces too many false positives. Add the type manually where needed instead

What it means

Rector\TypeDeclaration\Rector\ClassMethod\StrictStringParamConcatRector is deprecated: refactor() throws Rector\Exception\ShouldNotHappenException on the first ClassMethod, Function_ or Closure node. The rule added `string` parameter types to parameters that get concatenated with strings, but that heuristic produced too many false positives (non-string values concatenated via __toString, mixed input, casts). The rule targets PHP 7.0+ (PhpVersionFeature::SCALAR_TYPES).

Source

Thrown at rules/TypeDeclaration/Rector/ClassMethod/StrictStringParamConcatRector.php:60

)]);
    }
    /**
     * @return array<class-string<Node>>
     */
    public function getNodeTypes(): array
    {
        return [ClassMethod::class, Function_::class, Closure::class];
    }
    public function provideMinPhpVersion(): int
    {
        return PhpVersionFeature::SCALAR_TYPES;
    }
    /**
     * @param ClassMethod|Function_|Closure $node
     */
    public function refactor(Node $node): ?Node
    {
        throw new ShouldNotHappenException(sprintf('"%s" is deprecated as it produces too many false positives. Add the type manually where needed instead', self::class));
    }
}

View on GitHub (pinned to 408fcb0ff1)

Solutions

Remove StrictStringParamConcatRector from rector.php.
Add `string` parameter types manually where the value really is always a string, verifying with PHPStan first.
Use phpstan level-driven type coverage reports instead of the concatenation heuristic.

Example fix

// before (rector.php)
->withRules([StrictStringParamConcatRector::class])

// after (rector.php) - removed; add types by hand

// before                          // after
function greet($name, $suffix)     function greet(string $name, string $suffix)
{
    return $name . $suffix;
}

Defensive patterns

Strategy: validation

Validate before calling

use Rector\TypeDeclaration\Rector\ClassMethod\StrictStringParamConcatRector;

$rules = [/* your list */ StrictStringParamConcatRector::class];
if (in_array(StrictStringParamConcatRector::class, $rules, true)) {
    throw new InvalidArgumentException('Rule deprecated due to false positives; add string types manually');
}

Try / catch

try {
    exit($rectorApplication->run());
} catch (\Rector\Exception\ShouldNotHappenException $e) {
    if (str_contains($e->getMessage(), 'StrictStringParamConcatRector')) {
        fwrite(STDERR, 'Remove the rule; derive parameter types from PHPStan knowledge, not concatenation.' . PHP_EOL);
        exit(1);
    }
    throw $e;
}

Prevention

Add parameter types guided by PHPStan reports on call sites rather than by usage heuristics.
Watch for Stringable/int values in concatenating code before typing a param as string.
Prune deprecated TypeDeclaration rules from rector.php whenever rector is updated.

When it happens

Trigger: The rule is still present in rector.php and the analyzed code contains any closure, function or method; refactor() throws on the first visited node, before any type analysis happens.

Common situations: Old 'strict types' rector configs; CI failing immediately after a rector upgrade; codebases where the rule previously mis-typed parameters that receive int/float/Stringable values.

Related errors

AI-assisted analysis of rectorphp/rector@408fcb0ff1 (2026-08-21). Data as JSON: /api/errors/533f1a73de67af43. Report an issue: GitHub.