feature #28969 [Form] deprecate using invalid names for buttons (xabbuh)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[Form] deprecate using invalid names for buttons

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #28964
| License       | MIT
| Doc PR        |

Commits
-------

405aa548eb deprecate using invalid names for buttons

Author: fabpot

ButtonBuilder.php

@@ -63,6 +63,18 @@ public function __construct(?string $name, array $options = [])
 
         $this->name = $name;
         $this->options = $options;
+
+        if (\preg_match('/^([^a-z0-9_].*)?(.*[^a-zA-Z0-9_\-:].*)?$/D', $name, $matches)) {
+            if (isset($matches[1])) {
+                @trigger_error(sprintf('Using names for buttons that do not start with a letter, a digit, or an underscore is deprecated since Symfony 4.3 and will throw an exception in 5.0 ("%s" given).', $name), E_USER_DEPRECATED);
+            }
+            if (isset($matches[2])) {
+                @trigger_error(sprintf('Using names for buttons that do not contain only letters, digits, underscores ("_"), hyphens ("-") and colons (":") ("%s" given) is deprecated since Symfony 4.3 and will throw an exception in 5.0.', $name), E_USER_DEPRECATED);
+            }
+        }
+
+        // to be added in 5.0
+        // FormConfigBuilder::validateName($name);
     }
 
     /**

CHANGELOG.md

@@ -4,6 +4,10 @@ CHANGELOG
 4.3.0
 -----
 
+ * Using names for buttons that do not start with a letter, a digit, or an underscore is deprecated and will lead to an
+   exception in 5.0.
+ * Using names for buttons that do not contain only letters, digits, underscores, hyphens, and colons is deprecated and
+   will lead to an exception in 5.0.
  * deprecated using the `date_format`, `date_widget`, and `time_widget` options of the `DateTimeType` when the `widget`
    option is set to `single_text`
  * added `block_prefix` option to `BaseType`.

Tests/ButtonBuilderTest.php

@@ -28,7 +28,6 @@ public function getValidNames()
             ['foo'],
             ['0'],
             [0],
-            ['button[]'],
         ];
     }
 
@@ -40,6 +39,14 @@ public function testValidNames($name)
         $this->assertInstanceOf('\Symfony\Component\Form\ButtonBuilder', new ButtonBuilder($name));
     }
 
+    /**
+     * @group legacy
+     */
+    public function testNameContainingIllegalCharacters()
+    {
+        $this->assertInstanceOf('\Symfony\Component\Form\ButtonBuilder', new ButtonBuilder('button[]'));
+    }
+
     public function getInvalidNames()
     {
         return [