Fix false positives on existing-offsets after assign

Author: staabm

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -856,6 +856,13 @@ public function testBug12406(): void
 		$this->analyse([__DIR__ . '/data/bug-12406.php'], []);
 	}
 
+	public function testBug12406b(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12406b.php'], []);
+	}
+
 	public function testBug11679(): void
 	{
 		$this->reportPossiblyNonexistentGeneralArrayOffset = true;

tests/PHPStan/Rules/Arrays/data/bug-12406b.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Bug12406_2;
+
+final class Foo
+{
+
+	public function sayHello(string $s): void
+	{
+		$stats = [];
+		preg_match_all('~
+			commit[ ][a-z0-9]{40}\\n
+			Author:\s+(.+)\s+<[^>]+>\\n
+			AuthorDate:[^\\n]+\\n
+			Commit:[^\\n]+\\n
+			CommitDate:[^\\n]+\\n\\n
+			(\s+(?:[^\n]+\n)+)\n
+			[ ](\\d+)[ ]files?[ ]changed,(?:[ ](\\d+)[ ]insertions?\\(\\+\\),?)?(?:[ ](\\d+)[ ]deletions?\\(-\\))?
+		~mx', $s, $matches, PREG_SET_ORDER);
+
+		for ($i = 0; $i < count($matches); $i++) {
+			$author = $matches[$i][1];
+			$files = (int) $matches[$i][3];
+
+			$stats[$author]['commits']
+				= ($stats[$author]['commits'] ?? 0) + 1;
+			$stats[$author]['files']
+				= ($stats[$author]['files'] ?? 0) + $files;
+		}
+	}
+
+}