When dispatch is disabled via a constant, it should not be dispatched (#14034)

* When dispatch is disabled via a constant, it should not be dispatched

Eg when Matomo is not installed, it would still dispatch the request in https://github.com/matomo-org/matomo/blob/3.8.1-b1/plugins/Installation/Installation.php#L111 even when `PIWIK_ENABLE_DISPATCH` is disabled. 

Will set it to WIP for now as I'm not sure if we want to have this actually merged or not.

* Update Installation.php

* Use correct exception class

* throw exception if one is given

* adding a test

* fix tests

* trying to fix test

2 files changed, 13 insertions, 1 deletions

diff --git a/plugins/Installation/Installation.php b/plugins/Installation/Installation.php
index aa4ff1c6df..a1d2964343 100644
--- a/plugins/Installation/Installation.php
+++ b/plugins/Installation/Installation.php
@@ -107,8 +107,13 @@ class Installation extends \Piwik\Plugin
 
         $action = Common::getRequestVar('action', 'welcome', 'string');
 
-        if ($this->isAllowedAction($action)) {
+        if ($this->isAllowedAction($action) && (!defined('PIWIK_ENABLE_DISPATCH') || PIWIK_ENABLE_DISPATCH)) {
             echo FrontController::getInstance()->dispatch('Installation', $action, array($message));
+        } elseif (defined('PIWIK_ENABLE_DISPATCH') && !PIWIK_ENABLE_DISPATCH) {
+            if ($exception && $exception instanceof \Exception) {
+                throw $exception;
+            }
+            return;
         } else {
             Piwik::exitWithErrorMessage($this->getMessageToInviteUserToInstallPiwik($message));
         }
diff --git a/plugins/Installation/tests/System/APITest.php b/plugins/Installation/tests/System/APITest.php
index d8ae5523c8..887e5e17ba 100644
--- a/plugins/Installation/tests/System/APITest.php
+++ b/plugins/Installation/tests/System/APITest.php
@@ -61,6 +61,13 @@ class APITest extends SystemTestCase
         $this->assertContains('Access denied', $data);
     }
 
+    public function test_shouldReturnEmptyResultWhenNotInstalledAndDispatchIsDisabled()
+    {
+        $url = Fixture::getTestRootUrl() . 'nodispatchnotinstalled.php';
+        $response = $this->sendHttpRequest($url);
+        $this->assertSame('', $response['data']);
+    }
+
     private function getUrl()
     {
         return Fixture::getRootUrl() . 'tests/PHPUnit/proxy/index.php?module=API&method=API.getPiwikVersion';