[BUGFIX] Allow selector combinators in pseudo-class functions (#1537)

The bug was introduced by #1496 and related changes that split selector
representation and parsing into compound selectors and combinators.

The regex for `CompoundSelector::isValid()` now matches that for
`Selector::isValid()`.

Fixes #1533

Author: JakeQZ

CHANGELOG.md

@@ -27,7 +27,7 @@ Please also have a look at our
   `getPropertyName()` (#1506)
 - `Selector` is now represented as a sequence of `Selector\Component` objects
   which can be accessed via `getComponents()`, manipulated individually, or set
-  via `setComponents()` (#1478, #1486, #1487, #1488, #1494, #1496, #1536)
+  via `setComponents()` (#1478, #1486, #1487, #1488, #1494, #1496, #1536, #1537)
 - `Selector::setSelector()` and `Selector` constructor will now throw exception
   upon provision of an invalid selectior (#1498, #1502)
 - Clean up extra whitespace in CSS selector (#1398)

src/Property/Selector/CompoundSelector.php

@@ -48,7 +48,7 @@ class CompoundSelector implements Component
             (?:
                 (?:
                     # any sequence of valid unescaped characters, except quotes
-                    [a-zA-Z0-9\\x{00A0}-\\x{FFFF}_^$|*~=\\[\\]()\\-\\.:#,\\s]++
+                    [a-zA-Z0-9\\x{00A0}-\\x{FFFF}_^$|*=~\\[\\]()\\-\\s\\.:#+>,]++
                     |
                     # one or more escaped characters
                     (?:\\\\.)++

tests/Unit/Property/Selector/CompoundSelectorTest.php

@@ -68,6 +68,16 @@ public static function provideCompoundSelectorAndSpecificity(): array
             'attribute with case insensitive modifier' => ['a[href*="insensitive" i]', 12],
             // TODO, broken: specificity should be 21, but the calculator doesn't realize the `.` is in a string.
             'multiple attributes' => ['a[href^="https://"][href$=".org"]', 31],
+            // TODO, broken: specificity should be 11, but the calculator is treating the `n` as a type selector.
+            'nth-last-child' => ['li:nth-last-child(2n+3)', 12],
+            // TODO, maybe broken: specificity should probably be 2 (1 for `p` and 1 for `span`).
+            '`not` with descendent combinator' => [':not(p span)', 1],
+            // TODO, maybe broken: specificity should probably be 2 (1 for `p` and 1 for `span`).
+            '`not` with child combinator' => [':not(p > span)', 1],
+            // TODO, maybe broken: specificity should probably be 2 (1 for `h1` and 1 for `p`).
+            '`not` with next-sibling combinator' => [':not(h1 + p)', 1],
+            // TODO, maybe broken: specificity should probably be 2 (1 for `h1` and 1 for `p`).
+            '`not` with subsequent-sibling combinator' => [':not(h1 ~ p)', 1],
         ];
     }