multiply by zero is always zero

src/Analyser/MutatingScope.php

@@ -1040,6 +1040,34 @@ private function resolveType(Expr $node): Type
 			return new StringType();
 		}
 
+		if (
+			$node instanceof Node\Expr\BinaryOp\Mul
+			|| $node instanceof Node\Expr\AssignOp\Mul
+		) {
+			if ($node instanceof Node\Expr\AssignOp) {
+				$leftType = $this->getType($node->var)->toNumber();
+				$rightType = $this->getType($node->expr)->toNumber();
+			} else {
+				$leftType = $this->getType($node->left)->toNumber();
+				$rightType = $this->getType($node->right)->toNumber();
+			}
+
+			$floatType = new FloatType();
+
+			if ($leftType instanceof ConstantIntegerType && $leftType->getValue() === 0) {
+				if ($floatType->isSuperTypeOf($rightType)->yes()) {
+					return new ConstantFloatType(0.0);
+				}
+				return new ConstantIntegerType(0);
+			}
+			if ($rightType instanceof ConstantIntegerType && $rightType->getValue() === 0) {
+				if ($floatType->isSuperTypeOf($leftType)->yes()) {
+					return new ConstantFloatType(0.0);
+				}
+				return new ConstantIntegerType(0);
+			}
+		}
+
 		if (
 			$node instanceof Node\Expr\BinaryOp\Div
 			|| $node instanceof Node\Expr\AssignOp\Div

tests/PHPStan/Analyser/data/math.php

@@ -109,4 +109,34 @@ public function doSit(int $i, int $j): void
 		assertType('int', $i - $j);
 	}
 
+	/**
+	 * @param int<-5, 5> $range
+	 */
+	public function multiplyZero(int $i, float $f, $range): void
+	{
+		assertType('0', $i * false);
+		assertType('0.0', $f * false);
+		assertType('0', $range * false);
+
+		assertType('0', $i * '0');
+		assertType('0.0', $f * '0');
+		assertType('0', $range * '0');
+
+		assertType('0', $i * 0);
+		assertType('0.0', $f * 0);
+		assertType('0', $range * 0);
+
+		assertType('0', 0 * $i);
+		assertType('0.0', 0 * $f);
+		assertType('0', 0 * $range);
+
+		$i *= 0;
+		$f *= 0;
+		$range *= 0;
+		assertType('0', $i);
+		assertType('0.0', $f);
+		assertType('0', $range);
+
+	}
+
 }