Fix void cannot be changed to null and never/void cannot be used in a union

Fix #1773

Author: kkmuffme

SlevomatCodingStandard/Sniffs/TypeHints/ReturnTypeHintSniff.php

@@ -406,9 +406,12 @@ private function checkFunctionTypeHint(
 				return;
 			}
 
-			$typeHintsWithConvertedUnion[$typeHintNo] = TypeHintHelper::isVoidTypeHint($typeHint)
-				? 'null'
-				: TypeHintHelper::convertLongSimpleTypeHintToShort($typeHint);
+			if (TypeHintHelper::isVoidTypeHint($typeHint) || TypeHintHelper::isNeverTypeHint($typeHint)) {
+				$this->reportUselessSuppress($phpcsFile, $functionPointer, $isSuppressedNativeTypeHint, $suppressNameNativeTypeHint);
+				return;
+			}
+
+			$typeHintsWithConvertedUnion[$typeHintNo] = TypeHintHelper::convertLongSimpleTypeHintToShort($typeHint);
 		}
 
 		if ($originalReturnTypeNode instanceof NullableTypeNode) {

tests/Sniffs/TypeHints/ReturnTypeHintSniffTest.php

@@ -137,7 +137,7 @@ public function testWithUnionErrors(): void
 			'traversableTypeHints' => ['Traversable', '\ArrayIterator'],
 		]);
 
-		self::assertSame(17, $report->getErrorCount());
+		self::assertSame(15, $report->getErrorCount());
 
 		self::assertSniffError($report, 7, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
 		self::assertSniffError($report, 11, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
@@ -155,8 +155,6 @@ public function testWithUnionErrors(): void
 		self::assertSniffError($report, 55, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
 		self::assertSniffError($report, 59, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
 		self::assertSniffError($report, 63, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
-		self::assertSniffError($report, 67, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
-		self::assertSniffError($report, 71, ReturnTypeHintSniff::CODE_MISSING_NATIVE_TYPE_HINT);
 
 		self::assertAllFixedInFile($report);
 	}

tests/Sniffs/TypeHints/data/returnTypeHintWithUnionErrors.fixed.php

@@ -59,14 +59,6 @@ private function numericNullable(): int|float|string|null
 	private function scalarAndnumericNullable(): string|int|float|bool|null
 	{}
 
-	/** */
-	private function objectAndVoid(): object|null
-	{}
-
-	/** */
-	private function mixedAndVoid(): mixed
-	{}
-
 	/** @return non-empty-array|null */
 	public function returnNonEmptyArray(): ?array
 	{}

tests/Sniffs/TypeHints/data/returnTypeHintWithUnionErrors.php

@@ -59,14 +59,6 @@ private function numericNullable()
 	private function scalarAndnumericNullable()
 	{}
 
-	/** @return object|void */
-	private function objectAndVoid()
-	{}
-
-	/** @return mixed|void */
-	private function mixedAndVoid()
-	{}
-
 	/** @return non-empty-array|null */
 	public function returnNonEmptyArray()
 	{}

tests/Sniffs/TypeHints/data/returnTypeHintWithUnionNoErrors.php

@@ -43,4 +43,12 @@ public function returnCallableArray(): ?callable
 	{
 	}
 
+	/** @return bool|never */
+	public function neverUnion() {
+	}
+
+	/** @return bool|void */
+	public function voidUnion() {
+	}
+
 }