Normalize constant-string member access ($obj->{'n'}) to bareword form when printing expression keys

src/Node/Printer/Printer.php

@@ -2,6 +2,9 @@
 
 namespace PHPStan\Node\Printer;
 
+use Override;
+use PhpParser\Node;
+use PhpParser\Node\Scalar\String_;
 use PhpParser\PrettyPrinter\Standard;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Node\BooleanAndNode;
@@ -31,6 +34,7 @@
 use PHPStan\Node\MethodCallableNode;
 use PHPStan\Node\StaticMethodCallableNode;
 use PHPStan\Type\VerbosityLevel;
+use function preg_match;
 use function sprintf;
 
 /**
@@ -40,6 +44,25 @@
 final class Printer extends Standard
 {
 
+	/**
+	 * Normalize curly-brace member access with a constant string name to the
+	 * bareword form, so that e.g. `$obj->{'n'}` and `$obj->n` (or `$obj->{'n'}()`
+	 * and `$obj->n()`) produce identical expression keys and are treated as the
+	 * same member by the analyser.
+	 */
+	#[Override]
+	protected function pObjectProperty(Node $node): string
+	{
+		if (
+			$node instanceof String_
+			&& preg_match('/^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$/', $node->value) === 1
+		) {
+			return $node->value;
+		}
+
+		return parent::pObjectProperty($node);
+	}
+
 	protected function pPHPStan_Node_TypeExpr(TypeExpr $expr): string // phpcs:ignore
 	{
 		return sprintf('__phpstanType(%s)', $expr->getExprType()->describe(VerbosityLevel::precise()));

tests/PHPStan/Analyser/nsrt/bug-14847.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14847;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	public ?string $n = null;
+
+	public static ?string $s = null;
+
+}
+
+function narrowFromBareword(Foo $obj): void
+{
+	if ($obj->n !== null) {
+		assertType('string', $obj->n);
+		assertType('string', $obj->{'n'});
+	}
+}
+
+function narrowFromCurly(Foo $obj): void
+{
+	if ($obj->{'n'} !== null) {
+		assertType('string', $obj->{'n'});
+		assertType('string', $obj->n);
+	}
+}
+
+function narrowStaticProperty(): void
+{
+	if (Foo::$s !== null) {
+		assertType('string', Foo::$s);
+		assertType('string', Foo::${'s'});
+	}
+
+	if (Foo::${'s'} !== null) {
+		assertType('string', Foo::${'s'});
+		assertType('string', Foo::$s);
+	}
+}
+
+function narrowNullsafe(?Foo $obj): void
+{
+	if ($obj?->n !== null) {
+		assertType('string', $obj->n);
+		assertType('string', $obj->{'n'});
+	}
+}

tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php

@@ -1244,4 +1244,18 @@ public function testBug14791(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-14791.php'], []);
 	}
 
+	public function testBug14847(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-14847.php'], [
+			[
+				'Strict comparison using === between string and null will always evaluate to false.',
+				18,
+			],
+			[
+				'Strict comparison using === between string and null will always evaluate to false.',
+				29,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-14847.php

@@ -0,0 +1,32 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14847Comparison;
+
+class Foo
+{
+
+	public ?string $n = null;
+
+}
+
+function f(Foo $obj): void
+{
+	if ($obj->n === null) {
+		return;
+	}
+
+	if ($obj->{'n'} === null) {
+		echo 'dead';
+	}
+}
+
+function g(Foo $obj): void
+{
+	if ($obj->{'n'} === null) {
+		return;
+	}
+
+	if ($obj->n === null) {
+		echo 'dead';
+	}
+}