[WIP] Use the Symfony event dispatcher for hooks and callbacks

[leofeyer]

This is the PR for #97. Can you please confirm that this is the way to go, so I can adjust the other hooks as well?

[Toflar]

Looks good to me!! My input: I would place all hook listeners in an extra subnamespace so it becomes Contao\CoreBundle\EventListener\Hooks\InitializeSystemListener. Otherwise the EventListener namespace containing new code already becomes really cluttered with listeners that only provide support for old hooks and will get removed in v5 anyway :)

[leofeyer]

Good point, will change it accordingly.

[aschempp]

I would suggest to use one class for all hook events. That will make the old stuff much cleaner. Also we only need one service with just a lot of tags.

[leofeyer]

I don't think Insights and Scrutinizer would like that. They already don't like that we have only two controllers with too many methods.

[Toflar]

Well, Scruitinizer should not be the issue for code that only provides BC layers. https://scrutinizer-ci.com/docs/reviews/excluding_files_from_analysis

[leofeyer]

I know. Still we should always follow the best practices, because people will look at how we've done things.

[Toflar]

Of course and I prefer your variant.

[leofeyer]

This will also solve our arguments order problem:

// Call
$strTemp = $this->$callback[0]->$callback[1]($row, $blnWriteToFile, $vars, $parent);

// Usage
public function compileDefinition($row, $blnWriteToFile, $vars, $parent)
{
    // do something
}

But if we are using events, it will all be in the event object:

// Call
$event = new CompileDefinitionEvent();
$event->setRow($row);
$event->setWriteToFile($blnWriteToFile);
$event->setVars($vars);
$event->setParent($parent);

$this->container->get('event_dispatcher')->dispatch('contao.initialize_system', $event);

// Usage
public function compileDefinition(CompileDefinitionEvent $event)
{
    print_r($event->getRow());
}

If we ever want to add or remove parameters, we don't have to stick to an argument order anymore :)

[Toflar]

Did you only realize this now? :D

[leofeyer]

No, I just wanted to mention it :)

[aschempp]

I'm still for one class, also using event subscribers (see http://symfony.com/doc/current/components/event_dispatcher/introduction.html#using-event-subscribers). Let's discuss that later today.

[leofeyer]

Yes. I have still added another example to my POC to see how it works with parameters.

[discordier]

You might want to have a look how we did it in dc-general.

[aschempp]

Looks like a setter method is missing here.

[leofeyer]

There is no setter method. The variable is only injected to include the initialize.php file.

[aschempp]

In addition to setting the event variables from hook references, you also need to set the variables where the event is fired. Otherwise the variables could still not be changed by reference. Example:

// Trigger the getPageLayout hook (see #4736)
$event = new PageEvent($objPage, $objLayout, $this);
$kernel->getContainer()->get('event_dispatcher')->dispatch(ContaoEvents::GENERATE_PAGE, $event);
$objPage = $event->getPage();
$objLayout = $event->getLayout();

[leofeyer]

No, I found a better solution. Check my latest commit :)

[aschempp]

Not sure if that's not a problem. Now we are deciding wether the variables are passed by reference, instead of the hook developer…

[leofeyer]

The developer will still have to put an ampersand before the argument, otherwise they will not receive the reference. Here's how you can test:

// vendor/contao/calendar-bundle/src/Resources/config.php
$GLOBALS['TL_HOOKS']['modifyFrontendPage'][] = function ($page, $template, $handler) {
    $template = 'fe_foo';

    return $page;
};

The template name will not be changed, therefore fe_page is rendered. However, if you add the ampersand and make $template a reference:

// vendor/contao/calendar-bundle/src/Resources/config.php
$GLOBALS['TL_HOOKS']['modifyFrontendPage'][] = function ($page, &$template, $handler) {
    $template = 'fe_foo';

    return $page;
};

Then you get a Could not find template "fe_foo" exception.

[leofeyer]

I'm going to write the tests tonight.

[bytehead]

👍 Is it still realistic for 4.1? :)

[leofeyer]

Here is the list of the currently available hooks in the core distribution:

1. activateAccount
2. activateRecipient
3. addComment
4. addCustomRegexp
5. addFileMetaInformationToRequest
6. addLogEntry
7. checkCredentials
8. closeAccount
9. colorizeLogEntries
10. compareThemeFiles
11. compileArticle
12. compileDefinition
13. compileFormFields
14. createDefinition
15. createNewUser
16. customizeSearch
17. executePostActions
18. executePreActions
19. executeResize
20. exportTheme
21. extractThemeFiles
22. generateBreadcrumb
23. generateFrontendUrl
24. generatePage
25. generateXmlFiles
26. getAllEvents
27. getArticle
28. getArticles
29. getAttributesFromDca
30. getCacheKey
31. getCombinedFile
32. getContentElement
33. getCountries
34. getForm
35. getFrontendModule
36. getImage
37. getLanguages
38. getPageIdFromUrl
39. getPageLayout
40. getPageStatusIcon
41. getRootPageFromUrl
42. getSearchablePages
43. getSystemMessages
44. getUserNavigation
45. importUser
46. indexPage
47. initializeSystem
48. insertTagFlags
49. isAllowedToEditComment
50. isVisibleElement
51. listComments
52. loadDataContainer
53. loadFormField
54. loadLanguageFile
55. modifyFrontendPage
56. newsListCountItems
57. newsListFetchItems
58. outputBackendTemplate
59. outputFrontendTemplate
60. parseBackendTemplate
61. parseDate
62. parseFrontendTemplate
63. parseTemplate
64. parseWidget
65. postAuthenticate
66. postDownload
67. postLogin
68. postLogout
69. postUpload
70. prepareFormData
71. printArticleAsPdf
72. processFormData
73. removeOldFeeds
74. removeRecipient
75. replaceDynamicScriptTags
76. replaceInsertTags
77. reviseTable
78. sendNewsletter
79. setCookie
80. setNewPassword
81. sqlCompileCommands
82. sqlGetFromDB
83. sqlGetFromDca
84. sqlGetFromFile
85. storeFormData
86. updatePersonalData
87. validateFormField

The highlighted ones have been added already in the PR.

[leofeyer]

As discussed on Mumble, @aschempp wants to try to set up a general service which allows to map events to hooks. If he succeeds, we do not need this PR at all.

[leofeyer]

Closed in favor of #376.