Fix false positive nullsafe.neverNull on left side of ??

The nullsafe operator ?-> on the left side of ?? was unconditionally reported as unnecessary. This is correct for isset()/empty() which handle null objects natively, but wrong for ?? which does not catch TypeError from property access on null objects.

Author: kemo

src/Rules/IssetCheck.php

@@ -252,6 +252,16 @@ static function (Type $type) use ($typeMessageCallback): ?string {
 		}
 
 		if ($expr instanceof Expr\NullsafePropertyFetch) {
+			// For ?? the nullsafe operator is needed when the object can be null,
+			// because ?? does not catch TypeError from property access on null.
+			// isset()/empty() handle null objects natively so ?-> is truly redundant there.
+			if ($identifier === 'nullCoalesce') {
+				$varType = $this->treatPhpDocTypesAsCertain ? $scope->getScopeType($expr->var) : $scope->getScopeNativeType($expr->var);
+				if (!$varType->isNull()->no()) {
+					return null;
+				}
+			}
+
 			if ($expr->name instanceof Node\Identifier) {
 				return RuleErrorBuilder::message(sprintf('Using nullsafe property access "?->%s" %s is unnecessary. Use -> instead.', $expr->name->name, $operatorDescription))
 					->identifier('nullsafe.neverNull')

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -253,22 +253,10 @@ public function testBug5933(): void
 	public function testBug7109(): void
 	{
 		$this->analyse([__DIR__ . '/../Properties/data/bug-7109.php'], [
-			[
-				'Using nullsafe property access "?->aaa" on left side of ?? is unnecessary. Use -> instead.',
-				17,
-			],
-			[
-				'Using nullsafe property access "?->aaa" on left side of ?? is unnecessary. Use -> instead.',
-				28,
-			],
 			[
 				'Expression on left side of ?? is not nullable.',
 				40,
 			],
-			[
-				'Using nullsafe property access "?->aaa" on left side of ?? is unnecessary. Use -> instead.',
-				66,
-			],
 			[
 				'Expression on left side of ?? is not nullable.',
 				73,
@@ -372,4 +360,14 @@ public function testBug13921(): void
 		]);
 	}
 
+	public function testNullsafeCoalesceNullableObject(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-nullsafe-coalesce-nullable-object.php'], [
+			[
+				'Expression on left side of ?? is not nullable.',
+				66,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Variables/data/bug-nullsafe-coalesce-nullable-object.php

@@ -0,0 +1,68 @@
+<?php // lint >= 8.0
+
+namespace BugNullsafeCoalesceNullableObject;
+
+class TransactionVoucher
+{
+	public string $code;
+
+	public function __construct(string $code)
+	{
+		$this->code = $code;
+	}
+}
+
+class Transaction
+{
+	private ?TransactionVoucher $voucher;
+
+	public function __construct(?TransactionVoucher $voucher)
+	{
+		$this->voucher = $voucher;
+	}
+
+	public function getTransactionVoucher(): ?TransactionVoucher
+	{
+		return $this->voucher;
+	}
+}
+
+class Disbursement
+{
+	private ?Transaction $transaction;
+
+	public function __construct(?Transaction $transaction)
+	{
+		$this->transaction = $transaction;
+	}
+
+	public function getTransaction(): ?Transaction
+	{
+		return $this->transaction;
+	}
+}
+
+class Foo
+{
+	public function doFoo(Disbursement $disbursement): void
+	{
+		// Both ?-> are needed: getTransaction() and getTransactionVoucher() return nullable types.
+		// Without ?->, null->prop on left of ?? throws TypeError (not caught by ??).
+		$a = $disbursement->getTransaction()?->getTransactionVoucher()?->code ?? '';
+
+		// Single nullable method in chain
+		$b = $disbursement->getTransaction()?->getTransactionVoucher()?->code ?? '';
+	}
+
+	public function nonNullableObject(Transaction $transaction): void
+	{
+		// getTransactionVoucher() returns nullable, so ?->code is needed
+		$a = $transaction->getTransactionVoucher()?->code ?? '';
+	}
+
+	public function allNonNullable(TransactionVoucher $voucher): void
+	{
+		// ?->code is unnecessary here: $voucher is non-null, code is non-null string
+		$a = $voucher?->code ?? '';
+	}
+}