Treat decimal-int-string as a numeric string in looseCompare() instead of assuming inequality with non-decimal strings

src/Type/Accessory/AccessoryDecimalIntegerStringType.php

@@ -411,18 +411,19 @@
 
 	public function looseCompare(Type $type, PhpVersion $phpVersion): BooleanType
 	{
+		if ($this->inverse) {
+			// may be numeric ("02", "2.0") or empty (""), so nothing is decidable
+			return new BooleanType();
+		}
+
+		// a decimal-int-string is a non-empty numeric string, so it compares
+		// like one: never loosely equal to null or to a non-numeric string
 		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();
@@ -433,7 +434,7 @@
 		return $this;
 	}
 
 	public function traverseSimultaneously(Type $right, callable $cb): Type
 	{
 		return $this;
 	}

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);
+}