From 6d9684c04d2d6146799b0bd86b77bd4b91941172 Mon Sep 17 00:00:00 2001
From: phpstan-bot <79867460+phpstan-bot@users.noreply.github.com>
Date: Sun, 7 Jun 2026 16:20:31 +0000
Subject: [PATCH] Treat `decimal-int-string` as a numeric string in
 `looseCompare()` instead of assuming inequality with non-decimal strings

- `AccessoryDecimalIntegerStringType::looseCompare()` wrongly returned `false` whenever the other operand was a string that is not a `decimal-int-string`. Numeric strings compare numerically in PHP, so `'2' == '02'` and `'2' == '2.0'` are `true`.
- For the non-inverse case (an actual `decimal-int-string`), mirror `AccessoryNumericStringType::looseCompare()`: a decimal-int-string is a numeric, non-empty string, so it is never loosely equal to `null` or to a non-numeric string, but may equal any numeric value.
- For the inverse case (`non-decimal-int-string`), always return `bool`: such a value may still be numeric (`"02"`, `"2.0"`, `"1e1"`) or empty (`""`), so it can be loosely equal to a decimal-int-string, another numeric value, or `null` (`'' == null` is `true`).
- Probed sibling accessory string types: `AccessoryNumericStringType`, `AccessoryNonEmptyStringType`, `AccessoryLowercaseStringType`/`AccessoryUppercaseStringType` already guard numeric-string loose comparison correctly; no change needed there.
---
 .../AccessoryDecimalIntegerStringType.php     | 21 ++++++----
 tests/PHPStan/Analyser/nsrt/bug-14793.php     | 40 +++++++++++++++++++
 2 files changed, 53 insertions(+), 8 deletions(-)
 create mode 100644 tests/PHPStan/Analyser/nsrt/bug-14793.php

diff --git a/src/Type/Accessory/AccessoryDecimalIntegerStringType.php b/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
index d965eb0ebc..98c6b2d7bb 100644
--- a/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
+++ b/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
@@ -411,18 +411,23 @@ public function isScalar(): TrinaryLogic
 
 	public function looseCompare(Type $type, PhpVersion $phpVersion): BooleanType
 	{
+		if ($this->inverse) {
+			// A non-decimal-int-string may still be numeric ("02", "2.0", "1e1")
+			// or empty (""), so it can be loosely equal to a decimal-int-string,
+			// another numeric value or null. Nothing can be decided here.
+			return new BooleanType();
+		}
+
+		// A decimal-int-string is a numeric string, so it compares like one:
+		// numerically against other numeric strings (and numbers), and never
+		// loosely equal to null (it is always non-empty) or to a non-numeric
+		// string (that would be a byte-wise comparison that cannot match).
 		if ($type->isNull()->yes()) {
 			return new ConstantBooleanType(false);
 		}
 
-		if ($type->isString()->yes()) {
-			if ($this->inverse) {
-				if ($type->isDecimalIntegerString()->yes()) {
-					return new ConstantBooleanType(false);
-				}
-			} elseif ($type->isDecimalIntegerString()->no()) {
-				return new ConstantBooleanType(false);
-			}
+		if ($type->isString()->yes() && $type->isNumericString()->no()) {
+			return new ConstantBooleanType(false);
 		}
 
 		return new BooleanType();
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14793.php b/tests/PHPStan/Analyser/nsrt/bug-14793.php
new file mode 100644
index 0000000000..9c7c7c4154
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14793.php
@@ -0,0 +1,40 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14793;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param decimal-int-string $a
+ * @param non-decimal-int-string $b
+ * @param numeric-string $n
+ */
+function foo(string $a, string $b, string $n): void
+{
+	// '2' == '02' and '2' == '2.0' are true in PHP, so these cannot be decided.
+	assertType('bool', $a == $b);
+	assertType('bool', $b == $a);
+	assertType('bool', $a == $n);
+	assertType('bool', $a == '2.0');
+	assertType('bool', $a == '02');
+}
+
+/**
+ * @param decimal-int-string $a
+ */
+function decimalAlwaysFalse(string $a): void
+{
+	// A decimal-int-string is numeric and non-empty: comparing it to a
+	// non-numeric string or to null can never be loosely equal.
+	assertType('false', $a == 'foo');
+	assertType('false', $a == null);
+}
+
+/**
+ * @param non-decimal-int-string $b
+ */
+function nonDecimalVsNull(string $b): void
+{
+	// '' is a valid non-decimal-int-string and '' == null is true.
+	assertType('bool', $b == null);
+}