[TASK] Test :only-child

And updated README to indicate it is supported.

Also removed ‘support’ for `:only-child` from `Emogrifier` class by adjusting
the `PSEUDO_CLASS_MATCHER` regex, so that rules with such selectors will be
copied to a `<style>` element.  (It is not supported in that class.)

Closes #747.

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## x.y.z
 
 ### Added
+- Support and test `:only-child`
+  ([#747](https://github.com/MyIntervals/emogrifier/issues/747),
+  [#754](https://github.com/MyIntervals/emogrifier/pull/754))
 - Support and test `:nth-last-of-type`
   ([#747](https://github.com/MyIntervals/emogrifier/issues/747),
   [#751](https://github.com/MyIntervals/emogrifier/pull/751))

README.md

@@ -354,6 +354,7 @@ Emogrifier currently supports the following
      `*:nth-last-of-type(2n)` which will behave as `*:nth-last-child(2n)`)
    * [nth-of-type()](https://developer.mozilla.org/en-US/docs/Web/CSS/:nth-of-type)
      (with a type)
+   * [only-child](https://developer.mozilla.org/en-US/docs/Web/CSS/:only-child)
 
 The following selectors are not implemented yet:
 

src/Emogrifier.php

@@ -77,7 +77,7 @@ class Emogrifier
      *
      * @var string
      */
-    const PSEUDO_CLASS_MATCHER = '(?:first|last|nth|only)-child|nth-of-type|not\\([[:ascii:]]*\\)';
+    const PSEUDO_CLASS_MATCHER = '(?:first|last|nth)-child|nth-of-type|not\\([[:ascii:]]*\\)';
 
     /**
      * @var string

tests/Unit/CssInlinerTest.php

@@ -510,6 +510,12 @@ public function matchedCssDataProvider()
                 'body > :last-child { %1$s }',
                 '<p class="p-7" style="%1$s">',
             ],
+            ':only-child => element without siblings' => [':only-child { %1$s }', '<span style="%1$s">'],
+            'type & :only-child => element without siblings' => ['span:only-child { %1$s }', '<span style="%1$s">'],
+            'child combinator & :only-child => element without siblings' => [
+                'p > :only-child { %1$s }',
+                '<span style="%1$s">',
+            ],
             ':nth-child(even) => 2nd of many' => [':nth-child(even) { %1$s }', '<p class="p-2" style="%1$s">'],
             ':nth-child(even) => 4th of many' => [':nth-child(even) { %1$s }', '<p class="p-4" id="p4" style="%1$s">'],
             ':nth-child(2n) => 2nd of many' => [':nth-child(2n) { %1$s }', '<p class="p-2" style="%1$s">'],
@@ -799,6 +805,12 @@ public function nonMatchedCssDataProvider()
             'type & :last-child => not 2nd of many' => ['p:last-child { %1$s }', '<p class="p-2">'],
             'child combinator & :last-child => not 1st of many' => ['body > :last-child { %1$s }', '<p class="p-1">'],
             'child combinator & :last-child => not 2nd of many' => ['body > :last-child { %1$s }', '<p class="p-2">'],
+            ':only-child => not element with siblings' => [':only-child { %1$s }', '<p class="p-1">'],
+            'type & :only-child => not element with siblings' => ['p:only-child { %1$s }', '<p class="p-1">'],
+            'child combinator & :only-child => not element with siblings' => [
+                'body > :only-child { %1$s }',
+                '<p class="p-1">',
+            ],
             ':nth-child(even) => not 1st of many' => [':nth-child(even) { %1$s }', '<p class="p-1">'],
             ':nth-child(even) => not 3rd of many' => [':nth-child(even) { %1$s }', '<div class="div-3">'],
             ':nth-child(2n) => not 1st of many' => [':nth-child(2n) { %1$s }', '<p class="p-1">'],

tests/Unit/EmogrifierTest.php

@@ -731,6 +731,7 @@ public function matchedCssDataProvider()
             'type & :first-child => 1st of many' => ['p:first-child { %1$s }', '<p class="p-1" style="%1$s">'],
             // broken: last-child => last of many
             'type & :last-child => last of many' => ['p:last-child { %1$s }', '<p class="p-7" style="%1$s">'],
+            // broken: only-child
             // broken: nth-child without preceding component - OK if preceded by universal selector
             ':nth-child(even) => 2nd of many' => ['*:nth-child(even) { %1$s }', '<p class="p-2" style="%1$s">'],
             ':nth-child(even) => 4th of many' => ['*:nth-child(even) { %1$s }', '<p class="p-4" id="p4" style="%1$s">'],