Ignore unused function params prefixed with _ (#6743)

Author: bpfoley

src/Rules/UnusedParametersCheck.php

@@ -14,6 +14,7 @@
 use function is_string;
 use function ltrim;
 use function sprintf;
+use function str_starts_with;
 
 /**
  * The per-parameter half of the unused-parameter rules, on top of the
@@ -61,6 +62,9 @@ public function getUnusedParameterErrors(
 			if (!$parameter->var instanceof Variable || !is_string($parameter->var->name)) {
 				continue;
 			}
+			if (str_starts_with($parameter->var->name, '_')) {
+				continue;
+			}
 			if (isset($contractParameterNames[$parameter->var->name])) {
 				continue;
 			}

tests/PHPStan/Rules/Functions/data/unused-function-parameters.php

@@ -113,3 +113,25 @@ function observedByFuncGetArg(int $x): array
 
 	return [func_get_arg(0), $x];
 }
+
+function completelyUnusedIgnore(int $used, $_ignoredUnused): int
+{
+	return $used;
+}
+
+function byRefUnusedIgnore(int &$_ignoredX): void
+{
+	echo 'no use of the reference';
+}
+
+function variadicIgnoredUnusedIgnore(int $used, int ...$_ignoredRest): int
+{
+	return $used;
+}
+
+function usedViaResolvedVariableVariableIgnore(int $secret, int $_ignoredOther): int
+{
+	$name = 'secret';
+
+	return $$name;
+}

tests/PHPStan/Rules/Functions/data/unused-input-value-flow.php

@@ -57,3 +57,9 @@ function overwrittenParameter(int $input): int
 	$input = 1;
 	return $input;
 }
+
+function overwrittenParameterIgnore(int $_ignoredInput): int
+{
+	$_ignoredInput = 1;
+	return $_ignoredInput;
+}