DevKit updates (sonata-project#3906)

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Sonata project contribution
 
-Thanks for you interest onto Sonata projects!
+Thanks for your interest in Sonata projects!
 
 ## Summary
 
@@ -15,18 +15,18 @@ you using the latest patch version?
 
 If you are not sure this is a bug, consider posting your question on [Stack
 Overflow](http://stackoverflow.com), using one of the sonata tags.
-If you happen to find a bug, we kindly request you to report it. However,
+If you happen to find a bug, we kindly request you report it. However,
 before submitting it, please check the [project documentation available
 online](https://sonata-project.org/bundles/).
 
 Then, if it appears that it is indeed a real bug, you may report it using
 Github by following these points are taken care of:
 
 * Check if the bug is not already reported!
-* A clear title to sum up the issue
+* The title sums up the issue with clarity.
 * A description of the workflow needed to reproduce the bug. Please try to make
-  sentence, dumping an error message by itself is not great.
-* If your issue is an error page, you must provide us with a stack trace.  With
+  sentences, dumping an error message by itself is frowned upon.
+* If your issue is an error page, you must provide us with a stack trace. With
   recent versions of Symfony, you can even get stack traces as plain text at the
 end of the page. Just look for "Stack Trace (Plain Text)", and copy/paste what
 you see. **Do not** make a screenshot of the stack trace, as screenshots are
@@ -42,7 +42,7 @@ When you feel the code is to long, use external code pastebin like
 https://gist.github.com/ or http://hastebin.com/ . If this is not sufficient,
 just create a repository to show the issue.
 
-> _NOTE:_ Don't hesitate giving as much information as you can (OS, PHP
+> _NOTE:_ Don't hesitate to give as much information as you can (OS, PHP
 > version, extensions...)
 
 ## Pull Requests
@@ -86,7 +86,7 @@ Some rules have to be respected about the test:
   * `@coversNothing`
   * `@codeCoverageIgnore`
   * `@codeCoverageIgnoreStart`
-  * `codeCoverageIgnoreEnd`
+  * `@codeCoverageIgnoreEnd`
 * All test methods should be prefixed by `test`. Example: `public function testItReturnsNull()`.
 * As opposed, the `@test` annotation is prohibited.
 * Most of the time, the test class should have the same name as the targeted class, suffixed by `Test`.
@@ -99,10 +99,10 @@ Ideally, a Pull Request should concern one and **only one** subject, so that it
 remains clear, and independent changes can be merged quickly.
 
 If you want to fix a typo and improve the performance of a process, you should
-try as much as possible to it in a **separate** PR, so that we can quickly
+try as much as possible to do it in a **separate** PR, so that we can quickly
 merge one while discussing the other.
 
-The goal is to have a clear commit history and make possible revert easier.
+The goal is to have a clear commit history and make a possible revert easier.
 
 If you found an issue/typo while writing your change that is not related to
 your work, please do another PR for that. In some rare cases, you might be
@@ -155,9 +155,9 @@ Notes:
   * Branch `3.x` is the branch of the **latest stable** minor release and
   has to be used for Backward compatible PRs.
   * If you PR is not **Backward Compatible** but can be, it **must** be:
-    * Changing a function/method signature? Prefer create a new one and deprecated the old one.
+    * Changing a function/method signature? Prefer create a new one and deprecate the old one.
     * Code deletion? Don't. Please deprecate it instead.
-    * If your BC PR is accepted, you can do a new one on the `master` branch which remove the deprecated code.
+    * If your BC PR is accepted, you can do a new one on the `master` branch which removes the deprecated code.
     * SYMFONY DOC REF (same logic)?
 
 If you have a non-BC PR to propose, please try to create a related BC PR first.
@@ -186,10 +186,29 @@ interface BarInterface
 }
 ```
 
-Be aware that pull requests with BC breaks could be not accepted
-or reported for next major release if BC is not possible.
+In some cases, you will have the possibility to warn the user that things will change,
+and recommend a new way of doing things. You can do so by triggering the dedicated kind of error, like this:
 
-If you are not sure of what to do, don't hesitate to open an issue about your PR project.
+```php
+<?php
+if (/* some condition showing the user is using the legacy way */) {
+    @trigger_error(
+        'The '.__METHOD__.' method is deprecated since 42.x, to be removed in 43.0. '.
+        'Use FooClass::barMethod() instead.',
+        E_USER_DEPRECATED
+    );
+} else {
+    // new way of doing things
+}
+```
+
+In that case, unit tests might show your deprecation notice. You must mark such tests with the `@group legacy` annotation,
+and if need be, isolate them in a new test method that can simply be removed in the non-BC PR.
+
+Be aware that pull requests with BC breaks could be rejected
+or postponed to next major release if BC is not possible.
+
+If you are not sure what should be done, don't hesitate to open an issue about your PR project.
 
 #### The commit message
 
@@ -225,7 +244,7 @@ Document how to install the project
 
 Also, when you specify what you did avoid commit message subjects with "Fix bug
 in such and such feature". Saying you are fixing something implies the previous
-implementation was wrong and yours is right, which might not be even true.
+implementation was wrong and yours is right, which might not even be true.
 Instead, state unquestionable technical facts about your changes, not opinions.
 Then, in the commit description, explain why you did that and how it fixes
 something.