Last elseif can be exhaustive and no else branch is not needed

Author: ondrejmirtes

src/Analyser/NodeScopeResolver.php

@@ -784,7 +784,7 @@ private function processStmtNode(
 			}
 
 			if ($stmt->else === null) {
-				if (!$ifAlwaysTrue) {
+				if (!$ifAlwaysTrue && !$lastElseIfConditionIsTrue) {
 					$finalScope = $scope->mergeWith($finalScope);
 					$alwaysTerminating = false;
 				}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1165,6 +1165,7 @@ public function dataFileAsserts(): iterable
 		if (PHP_VERSION_ID >= 80000) {
 			yield from $this->gatherAssertTypes(__DIR__ . '/data/pathinfo-php8.php');
 		}
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/always-true-elseif.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/pathinfo.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-8568.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/DeadCode/data/bug-8620.php');

tests/PHPStan/Analyser/data/always-true-elseif.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace AlwaysTrueElseif;
+
+use PHPStan\TrinaryLogic;
+use function PHPStan\Testing\assertVariableCertainty;
+
+class Foo
+{
+
+	/**
+	 * @param 'a'|'b'|'c' $s
+	 * @return void
+	 */
+	public function doFoo(string $s): void
+	{
+		if ($s === 'a') {
+			$a = true;
+		} elseif ($s === 'b') {
+			$a = false;
+		} elseif ($s === 'c') {
+			$a = true;
+		}
+
+		assertVariableCertainty(TrinaryLogic::createYes(), $a);
+	}
+
+}