Improve inference on FuncCall === FuncCall

src/Analyser/TypeSpecifier.php

@@ -2242,13 +2242,40 @@ public function resolveEqual(Expr\BinaryOp\Equal $expr, Scope $scope, TypeSpecif
 
 	public function resolveIdentical(Expr\BinaryOp\Identical $expr, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
 	{
-		// Normalize to: fn() === expr
 		$leftExpr = $expr->left;
 		$rightExpr = $expr->right;
+
+		// Normalize to: fn() === expr
 		if ($rightExpr instanceof FuncCall && !$leftExpr instanceof FuncCall) {
-			[$leftExpr, $rightExpr] = [$rightExpr, $leftExpr];
+			$specifiedTypes = $this->resolveNormalizedIdentical(new Expr\BinaryOp\Identical(
+				$rightExpr,
+				$leftExpr,
+			), $scope, $context);
+		} else {
+			$specifiedTypes = $this->resolveNormalizedIdentical(new Expr\BinaryOp\Identical(
+				$leftExpr,
+				$rightExpr,
+			), $scope, $context);
+		}
+
+		// merge result of fn1() === fn2() and fn2() === fn1()
+		if ($rightExpr instanceof FuncCall && $leftExpr instanceof FuncCall) {
+			return $specifiedTypes->unionWith(
+				$this->resolveNormalizedIdentical(new Expr\BinaryOp\Identical(
+					$rightExpr,
+					$leftExpr,
+				), $scope, $context),
+			);
 		}
 
+		return $specifiedTypes;
+	}
+
+	private function resolveNormalizedIdentical(Expr\BinaryOp\Identical $expr, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
+	{
+		$leftExpr = $expr->left;
+		$rightExpr = $expr->right;
+
 		$unwrappedLeftExpr = $leftExpr;
 		if ($leftExpr instanceof AlwaysRememberedExpr) {
 			$unwrappedLeftExpr = $leftExpr->getExpr();

tests/PHPStan/Analyser/nsrt/bug-13749.php

@@ -0,0 +1,69 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13749;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	/**
+	 * @param non-empty-string $nonES
+	 */
+	public function sayNonEmpty(string $s, string $nonES): void
+	{
+		if (strlen($nonES) === strlen($s)) {
+			assertType('non-empty-string', $s);
+		}
+		if (strlen($nonES) >= strlen($s)) {
+			assertType('string', $s); // could be non-empty-string
+		}
+
+		if (strlen($s) === strlen($nonES)) {
+			assertType('non-empty-string', $s);
+		}
+		if (strlen($s) >= strlen($nonES)) {
+			assertType('non-empty-string', $s);
+		}
+	}
+
+	/**
+	 * @param non-falsy-string $nonFalsy
+	 */
+	public function sayNonFalsy(string $s, string $nonFalsy): void
+	{
+		if (strlen($nonFalsy) === strlen($s)) {
+			assertType('non-empty-string', $s);
+		}
+		if (strlen($nonFalsy) >= strlen($s)) {
+			assertType('string', $s); // could be non-empty-string
+		}
+
+		if (strlen($s) === strlen($nonFalsy)) {
+			assertType('non-empty-string', $s);
+		}
+		if (strlen($s) >= strlen($nonFalsy)) {
+			assertType('non-empty-string', $s);
+		}
+	}
+
+	/**
+	 * @param non-empty-array $nonEmptyArr
+	 */
+	public function sayCount(array $arr, array $nonEmptyArr): void
+	{
+		if (count($arr) === count($nonEmptyArr)) {
+			assertType('non-empty-array', $arr);
+			assertType('non-empty-array', $nonEmptyArr);
+		}
+		assertType('array', $arr);
+		assertType('non-empty-array', $nonEmptyArr);
+
+		if (count($nonEmptyArr) === count($arr)) {
+			assertType('non-empty-array', $arr);
+			assertType('non-empty-array', $nonEmptyArr);
+		}
+		assertType('array', $arr);
+		assertType('non-empty-array', $nonEmptyArr);
+	}
+
+}