More precise mixed-type subtraction

src/Type/MixedType.php

@@ -27,6 +27,7 @@
 use PHPStan\Type\Accessory\OversizedArrayType;
 use PHPStan\Type\Constant\ConstantArrayType;
 use PHPStan\Type\Constant\ConstantBooleanType;
+use PHPStan\Type\Constant\ConstantIntegerType;
 use PHPStan\Type\Generic\TemplateMixedType;
 use PHPStan\Type\Generic\TemplateType;
 use PHPStan\Type\Traits\NonGeneralizableTypeTrait;
@@ -471,10 +472,10 @@ public function toBoolean(): BooleanType
 
 	public function toNumber(): Type
 	{
-		return new UnionType([
+		return TypeCombinator::union(
 			$this->toInteger(),
 			$this->toFloat(),
-		]);
+		);
 	}
 
 	public function toAbsoluteNumber(): Type
@@ -484,6 +485,24 @@ public function toAbsoluteNumber(): Type
 
 	public function toInteger(): Type
 	{
+		$castsToZero = new UnionType([
+			new NullType(),
+			new ConstantBooleanType(false),
+			new ConstantIntegerType(0),
+			new ConstantArrayType([], []),
+			new StringType(),
+			new FloatType(),
+		]);
+		if (
+			$this->subtractedType !== null
+			&& $this->subtractedType->isSuperTypeOf($castsToZero)->yes()
+		) {
+			return new UnionType([
+				IntegerRangeType::fromInterval(null, -1),
+				IntegerRangeType::fromInterval(1, null),
+			]);
+		}
+
 		return new IntegerType();
 	}
 

tests/PHPStan/Analyser/nsrt/integer-range-types.php

@@ -446,3 +446,44 @@ public function zeroIssues($positive, $negative)
 	}
 
 }
+
+function subtract($m) {
+	if ($m != 0) {
+		assertType("mixed", $m); // could be "mixed~0|0.0|''|'0'|array{}|false|null"
+		assertType('int', (int) $m);
+	}
+	if ($m !== 0) {
+		assertType("mixed~0", $m);
+		assertType('int', (int) $m); // mixed could still contain falsey values, which cast to 0
+	}
+	if (!is_int($m)) {
+		assertType("mixed~int", $m);
+		assertType('int', (int) $m); // mixed could still contain falsey values, which cast to 0
+	}
+
+	if ($m != true) {
+		assertType("0|0.0|''|'0'|array{}|false|null", $m);
+		assertType('0', (int) $m);
+	}
+	if ($m !== true) {
+		assertType("mixed~true", $m);
+		assertType('int', (int) $m);
+	}
+
+	if ($m != false) {
+		assertType("mixed~0|0.0|''|'0'|array{}|false|null", $m);
+		assertType('int', (int) $m);
+	}
+	if ($m !== false) {
+		assertType("mixed~false", $m);
+		assertType('int', (int) $m); // mixed could still contain falsey values, which cast to 0
+	}
+	if (!is_string($m) && !is_float($m)) {
+		assertType("mixed~float|string", $m);
+		assertType('int', (int) $m);
+		if ($m != false) {
+			assertType("mixed~0|array{}|float|string|false|null", $m);
+			assertType('int<min, -1>|int<1, max>', (int) $m);
+		}
+	}
+}