Do not create conditional expressions for non-Variable expressions absent from the other branch

- In `MutatingScope::createConditionalExpressions()`, skip creating a
  conditional expression when the target expression (e.g. an array dim
  fetch like `$R['aa']`) is not tracked in the other branch, the
  expression is not a Variable, and the guard type overlaps with the
  other branch's guard type.
- This prevents incorrect type narrowing where an array dim fetch or
  property fetch from an `elseif` condition leaks into a subsequent
  `if` block that checks a variable set in multiple branches.
- The Variable exception preserves the existing behavior for variable
  certainty tracking (e.g. a variable defined in only one branch
  correctly gets Yes certainty via conditional expressions).
- Tested with array dim fetch, nested array dim fetch, property fetch,
  and multiple elseif variants.

Author: VincentLanglet

src/Analyser/MutatingScope.php

@@ -3780,6 +3780,15 @@ private function createConditionalExpressions(
 				) {
 					continue;
 				}
+				if (
+					!array_key_exists($exprString, $theirExpressionTypes)
+					&& !$holder->getExpr() instanceof Variable
+					&& array_key_exists($guardExprString, $theirExpressionTypes)
+					&& $theirExpressionTypes[$guardExprString]->getCertainty()->yes()
+					&& !$guardHolder->getType()->isSuperTypeOf($theirExpressionTypes[$guardExprString]->getType())->no()
+				) {
+					continue;
+				}
 				$conditionalExpression = new ConditionalExpressionHolder([$guardExprString => $guardHolder], $holder);
 				$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
 			}

tests/PHPStan/Analyser/nsrt/bug-14469.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Bug14469Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+function t(array $R, bool $var1, object $user): void {
+	$aa = null;
+
+	if ($var1) {
+		$aa = $user->id === 10 ? 2 : null;
+	} elseif ($R['aa']) {
+		$aa = $R['aa'];
+	}
+
+	if ($aa) {
+		assertType('mixed', $R['aa']);
+	}
+}

tests/PHPStan/Rules/Comparison/BooleanNotConstantConditionRuleTest.php

@@ -234,6 +234,12 @@ public function testBug6702(): void
 		$this->analyse([__DIR__ . '/data/bug-6702.php'], []);
 	}
 
+	public function testBug14469(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-14469.php'], []);
+	}
+
 	public function testBug12852(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;

tests/PHPStan/Rules/Comparison/data/bug-14469.php

@@ -0,0 +1,73 @@
+<?php
+
+namespace Bug14469;
+
+function t(array $R, bool $var1, object $user, bool $is): array {
+    $aa = null;
+
+    if ($var1) {
+        $aa = $user->id  === 10 ? 2 : null;
+    } elseif ($R['aa']) {
+        $aa = $R['aa'];
+    }
+
+    if ($aa) {
+        if (!$R['aa']) {
+            return [];
+        }
+    }
+	return $R;
+}
+
+/** Property fetch variant */
+function propertyFetch(object $obj, bool $var1, object $user): void {
+    $aa = null;
+
+    if ($var1) {
+        $aa = $user->id === 10 ? 2 : null;
+    } elseif ($obj->prop) {
+        $aa = $obj->prop;
+    }
+
+    if ($aa) {
+        if (!$obj->prop) {
+            return;
+        }
+    }
+}
+
+/** Nested array fetch variant */
+function nestedArrayFetch(array $R, bool $var1, object $user): void {
+    $aa = null;
+
+    if ($var1) {
+        $aa = $user->id === 10 ? 2 : null;
+    } elseif ($R['a']['b']) {
+        $aa = $R['a']['b'];
+    }
+
+    if ($aa) {
+        if (!$R['a']['b']) {
+            return;
+        }
+    }
+}
+
+/** Multiple elseif branches */
+function multipleElseif(array $R, bool $var1, bool $var2, object $user): void {
+    $aa = null;
+
+    if ($var1) {
+        $aa = $user->id === 10 ? 2 : null;
+    } elseif ($var2) {
+        $aa = 5;
+    } elseif ($R['aa']) {
+        $aa = $R['aa'];
+    }
+
+    if ($aa) {
+        if (!$R['aa']) {
+            return;
+        }
+    }
+}