implement case-expression inference (#522)

Author: staabm

.phpstan-dba-mysqli.cache

@@ -12,7 +12,9 @@
 use PHPStan\Type\MixedType;
 use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 use SqlFtw\Sql\Expression\BoolValue;
+use SqlFtw\Sql\Expression\CaseExpression;
 use SqlFtw\Sql\Expression\ExpressionNode;
 use SqlFtw\Sql\Expression\FunctionCall;
 use SqlFtw\Sql\Expression\Identifier;
@@ -112,6 +114,15 @@ public function getType($expression): Type
             throw new ShouldNotHappenException('Unable to resolve column '.$expression->getName());
         }
 
+        if ($expression instanceof CaseExpression) {
+            $resultTypes = [];
+            foreach ($expression->getResults() as $result) {
+                $resultTypes[] = $this->getType($result);
+            }
+
+            return TypeCombinator::union(...$resultTypes);
+        }
+
         if ($expression instanceof FunctionCall) {
             foreach ($this->extensions as $extension) {
                 if (!$extension->isFunctionSupported($expression)) {