Sql AST: avg/min/max/count can get null on empty result sets (#579)

Author: staabm

.phpstan-dba-mysqli.cache

@@ -161,15 +161,17 @@ private function stringifyResult(Type $type): Type
 
     private function stringifyType(Type $type): Type
     {
+        $containsNull = TypeCombinator::containsNull($type);
+
         $numberType = new UnionType([new IntegerType(), new FloatType()]);
 
-        if ($numberType->isSuperTypeOf($type)->yes()) {
+        if ($numberType->isSuperTypeOf(TypeCombinator::removeNull($type))->yes()) {
             $stringified = new IntersectionType([
                 new StringType(),
                 new AccessoryNumericStringType(),
             ]);
 
-            if (TypeCombinator::containsNull($type)) {
+            if ($containsNull) {
                 return TypeCombinator::addNull($stringified);
             }
 

.phpstan-dba-pdo-mysql.cache

@@ -27,10 +27,6 @@ public function getReturnType(FunctionCall $expression, QueryScope $scope): ?Typ
         $argType = $scope->getType($args[0]);
         $numberType = $argType->toNumber();
 
-        if (TypeCombinator::containsNull($argType)) {
-            return TypeCombinator::addNull($numberType);
-        }
-
-        return $numberType;
+        return TypeCombinator::addNull($numberType);
     }
 }

src/QueryReflection/QueryReflection.php

@@ -6,6 +6,7 @@
 
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 use SqlFtw\Sql\Expression\BuiltInFunction;
 use SqlFtw\Sql\Expression\FunctionCall;
 
@@ -30,6 +31,12 @@ public function isFunctionSupported(FunctionCall $expression): bool
 
     public function getReturnType(FunctionCall $expression, QueryScope $scope): Type
     {
-        return IntegerRangeType::fromInterval(0, null);
+        $positiveInt = IntegerRangeType::fromInterval(0, null);
+
+        if ($expression->getFunction()->getName() === BuiltInFunction::COUNT) {
+            return TypeCombinator::addNull($positiveInt);
+        }
+
+        return $positiveInt;
     }
 }