Narrow regex subject to decimal-int-string when every alternation branch is a decimal integer

src/Type/Regex/RegexGroupParser.php

@@ -617,7 +617,7 @@ private function walkGroupAst(
 				->onlyLiterals($newLiterals)
 				->nonEmpty($walkResult->isNonEmpty()->or($nonEmpty))
 				->nonFalsy($walkResult->isNonFalsy()->or($nonFalsy))
-				->decimalInteger($walkResult->isDecimalInteger()->and($decimalInteger));
+				->decimalInteger(TrinaryLogic::maxMin($walkResult->isDecimalInteger(), $decimalInteger));
 		}
 
 		// [^0-9] should not parse as decimal-int-string, and [^list-everything-but-numbers] is technically

tests/PHPStan/Analyser/nsrt/bug-14784.php

@@ -0,0 +1,46 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14784;
+
+use function PHPStan\Testing\assertType;
+
+function doFoo(string $str): void
+{
+	if (preg_match('/^(?:0|-?[1-9][0-9]*)$/', $str)) {
+		assertType('decimal-int-string', $str);
+	}
+
+	// capturing group variant
+	if (preg_match('/^(0|-?[1-9][0-9]*)$/', $str, $matches)) {
+		assertType('decimal-int-string', $str);
+		assertType("array{decimal-int-string, '0'|(decimal-int-string&non-falsy-string)}", $matches);
+	}
+
+	// alternation of two decimal literals
+	if (preg_match('/^(?:0|123)$/', $str)) {
+		assertType('decimal-int-string', $str);
+	}
+
+	// alternation without a leading sign
+	if (preg_match('/^(?:0|[1-9][0-9]*)$/', $str)) {
+		assertType('decimal-int-string', $str);
+	}
+
+	// alternation digits prefixed by required digits stays decimal
+	if (preg_match('/^[0-9]+(?:0|5)$/', $str)) {
+		assertType('decimal-int-string', $str);
+	}
+
+	// an alternation branch that is not decimal breaks the narrowing
+	if (preg_match('/^(?:0|abc)$/', $str)) {
+		assertType('non-empty-string', $str);
+	}
+	if (preg_match('/^(?:2|abc)$/', $str)) {
+		assertType('non-falsy-string', $str);
+	}
+
+	// a capturing decimal alternation keeps the group decimal too
+	if (preg_match('/^(0|[1-9][0-9]*)$/', $str, $matches)) {
+		assertType("'0'|(decimal-int-string&non-falsy-string)", $matches[1]);
+	}
+}