Fix subtracting types from union template types

src/Type/Generic/TemplateTypeTrait.php

@@ -337,11 +337,18 @@ public function traverseSimultaneously(Type $right, callable $cb): Type
 
 	public function tryRemove(Type $typeToRemove): ?Type
 	{
-		if ($this->getBound()->isSuperTypeOf($typeToRemove)->yes()) {
-			return $this->subtract($typeToRemove);
+		$bound = TypeCombinator::remove($this->getBound(), $typeToRemove);
+		if ($this->getBound() === $bound) {
+			return null;
 		}
 
-		return null;
+		return TemplateTypeFactory::create(
+			$this->getScope(),
+			$this->getName(),
+			$bound,
+			$this->getVariance(),
+			$this->getStrategy(),
+		);
 	}
 
 	public function toPhpDocNode(): TypeNode

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1342,6 +1342,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/nullsafe-vs-scalar.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-8517.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Functions/data/bug-9803.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9939.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-9939.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace Bug9939;
+
+use function PHPStan\Testing\assertType;
+
+enum Combinator
+{
+	case NEXT_SIBLING;
+	case CHILD;
+	case FOLLOWING_SIBLING;
+
+    public function getText(): string
+    {
+        return match ($this) {
+            self::NEXT_SIBLING => '+',
+            self::CHILD => '>',
+            self::FOLLOWING_SIBLING => '~',
+        };
+    }
+}
+
+/**
+ * @template T of string|\Stringable|array<string|\Stringable>|Combinator|null
+ */
+class CssValue
+{
+	/**
+	 * @param T $value
+	 */
+	public function __construct(private readonly mixed $value)
+	{
+	}
+
+    /**
+     * @return T
+     */
+    public function getValue(): mixed
+    {
+        return $this->value;
+    }
+
+    public function __toString(): string
+    {
+		assertType('T of array<string|Stringable>|Bug9939\Combinator|string|Stringable|null (class Bug9939\CssValue, argument)', $this->value);
+
+        if ($this->value instanceof Combinator) {
+			assertType('T of Bug9939\Combinator (class Bug9939\CssValue, argument)', $this->value);
+            return $this->value->getText();
+        }
+
+		assertType('T of array<string|Stringable>|string|Stringable|null (class Bug9939\CssValue, argument)', $this->value);
+
+        if (\is_array($this->value)) {
+			assertType('T of array<string|Stringable> (class Bug9939\CssValue, argument)', $this->value);
+            return implode($this->value);
+        }
+
+		assertType('T of string|Stringable|null (class Bug9939\CssValue, argument)', $this->value);
+
+        return (string) $this->value;
+    }
+}