Report null coalesce errors on the last line of the left operand

- `??` and `??=` errors used the start line of the whole expression, which is the first line of
  the left operand. When the left operand spans several lines, the error landed above the
  operator.
- The AST does not keep the operator token, so the error now uses the last line of the left
  operand: the operator is on that line or below it, so a line that was already correct stays.
- When `??` starts its own line, the error is still one line above the operator.

Author: Cayan

src/Rules/Variables/NullCoalesceRule.php

@@ -68,6 +68,11 @@ static function (Type $type): ?string {
 			return [];
 		}
 
+		$error = RuleErrorBuilder::message($error->getMessage())
+			->identifier($error->getIdentifier())
+			->line($this->getOperatorLine($node))
+			->build();
+
 		if ($scope->isInTrait()) {
 			// The error messages already distinguish the possible outcomes,
 			// so the contexts only need to be told apart by error/no error.
@@ -78,6 +83,24 @@ static function (Type $type): ?string {
 		return [$error];
 	}
 
+	/**
+	 * The AST does not keep the operator token. The left side ends on the operator's
+	 * line or above it, so its last line is the closest one that never overshoots.
+	 */
+	private function getOperatorLine(CoalesceExpressionNode $node): int
+	{
+		$originalExpr = $node->getOriginalExpr();
+		if ($originalExpr instanceof Node\Expr\BinaryOp\Coalesce) {
+			return $originalExpr->left->getEndLine();
+		}
+
+		if ($originalExpr instanceof Node\Expr\AssignOp\Coalesce) {
+			return $originalExpr->var->getEndLine();
+		}
+
+		return $node->getStartLine();
+	}
+
 	private function checkUnnecessaryNullCoalesce(CoalesceExpressionNode $node, Scope $scope): ?IdentifierRuleError
 	{
 		if (!$this->unnecessaryNullCoalesce) {

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -711,6 +711,36 @@ public function testBug12780(): void
 		$this->analyse([__DIR__ . '/data/bug-12780.php'], []);
 	}
 
+	public function testBug10714(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10714.php'], [
+			[
+				'Expression on left side of ?? is not nullable.',
+				12,
+			],
+			[
+				'Variable $a on left side of ?? always exists and is not nullable.',
+				18,
+			],
+			[
+				'Variable $a on left side of ?? always exists and is not nullable.',
+				24,
+			],
+			[
+				'Variable $a on left side of ?? always exists and is not nullable.',
+				30,
+			],
+			[
+				'Variable $a on left side of ??= always exists and is not nullable.',
+				35,
+			],
+			[
+				'Offset \'k\' on array{k: string} on left side of ??= always exists and is not nullable.',
+				48,
+			],
+		]);
+	}
+
 	#[RequiresPhp('>= 8.2.0')]
 	public function testReadonlyPropertyOnNullableReceiver(): void
 	{

tests/PHPStan/Rules/Variables/data/bug-10714.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace Bug10714;
+
+/**
+ * @param array<string, string> $info
+ */
+function issueLayout(array $info, string $other): string
+{
+	return strtolower(
+		($info['test'] ?? 'default') . '-' .
+		$other ?? 'other'
+	);
+}
+
+function operatorStartsTheLine(string $a): string
+{
+	return $a
+		?? 'b';
+}
+
+function operatorEndsTheLine(string $a): string
+{
+	return $a ??
+		'b';
+}
+
+function singleLine(string $a): string
+{
+	return $a ?? 'b';
+}
+
+function assignOperatorStartsTheLine(string $a): string
+{
+	$a
+		??= 'b';
+
+	return $a;
+}
+
+/**
+ * @param array{k: string} $s
+ */
+function assignOperatorAfterMultiLineLeftSide(array $s): string
+{
+	$s[
+		'k'
+	] ??= 'b';
+
+	return $s['k'];
+}