Resolve ConditionalType when subject-target relationship is deterministic despite containing template types

src/Type/ConditionalType.php

@@ -113,7 +113,13 @@
 
 	public function isResolvable(): bool
 	{
-		return !TypeUtils::containsTemplateType($this->subject) && !TypeUtils::containsTemplateType($this->target);
+		if (!TypeUtils::containsTemplateType($this->subject) && !TypeUtils::containsTemplateType($this->target)) {
+			return true;
+		}
+
+		$isSuperType = $this->target->isSuperTypeOf($this->subject);
+
+		return $isSuperType->yes() || $isSuperType->no();
 	}
 
 	protected function getResult(): Type

tests/PHPStan/Analyser/nsrt/bug-11894.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11894Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is string ? string : T)
+ */
+function conditionalReturn(mixed $a): mixed
+{
+	if (!is_string($a)) {
+		return $a;
+	}
+	return trim($a);
+}
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function testNarrowedToString(mixed $a): void
+{
+	if (!is_string($a)) {
+		return;
+	}
+	assertType('string', conditionalReturn($a));
+}
+
+/**
+ * @template T of int|null
+ * @param T $a
+ */
+function testNarrowedToNonMatchingType(mixed $a): void
+{
+	if (!is_int($a)) {
+		return;
+	}
+	assertType('T of int (function Bug11894Nsrt\testNarrowedToNonMatchingType(), argument)', conditionalReturn($a));
+}
+
+/**
+ * @template T of string|int
+ * @param T $a
+ */
+function testNotFullyNarrowable(mixed $a): void
+{
+	assertType('string|T of int (function Bug11894Nsrt\testNotFullyNarrowable(), argument)', conditionalReturn($a));
+}

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -2871,4 +2871,9 @@ public function testBug3842(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-3842.php'], []);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Functions/data/bug-11894.php

@@ -0,0 +1,70 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11894;
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function test(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+	return conditionalReturn($a);
+}
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is string ? string : T)
+ */
+function conditionalReturn(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+    return trim($a);
+}
+
+/**
+ * @template T of string|null
+ * @param T $a
+ */
+function testNegated(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+	return conditionalReturnNegated($a);
+}
+
+/**
+ * @template T
+ * @param T $a
+ * @return (T is not string ? T : string)
+ */
+function conditionalReturnNegated(mixed $a): mixed
+{
+    if (!is_string($a)) {
+        return $a;
+    }
+
+    return trim($a);
+}
+
+/**
+ * @template T of int|null
+ * @param T $a
+ */
+function testNoRelation(mixed $a): mixed
+{
+    if (!is_int($a)) {
+        return $a;
+    }
+
+	return conditionalReturn($a);
+}

tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php

@@ -4062,4 +4062,12 @@ public function testBug14549(): void
 		]);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkNullables = true;
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php

@@ -1015,4 +1015,10 @@ public function testPipeOperator(): void
 		]);
 	}
 
+	public function testBug11894(): void
+	{
+		$this->checkThisOnly = false;
+		$this->analyse([__DIR__ . '/data/bug-11894.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-11894.php

@@ -0,0 +1,62 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11894Methods;
+
+class Converter
+{
+	/**
+	 * @template T
+	 * @param T $a
+	 * @return (T is string ? string : T)
+	 */
+	public function conditionalReturn(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+		return trim($a);
+	}
+
+	/**
+	 * @template T
+	 * @param T $a
+	 * @return (T is string ? string : T)
+	 */
+	public static function conditionalReturnStatic(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+		return trim($a);
+	}
+}
+
+class Consumer
+{
+	/**
+	 * @template T of string|null
+	 * @param T $a
+	 */
+	public function testMethod(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+
+		$c = new Converter();
+		return $c->conditionalReturn($a);
+	}
+
+	/**
+	 * @template T of string|null
+	 * @param T $a
+	 */
+	public function testStaticMethod(mixed $a): mixed
+	{
+		if (!is_string($a)) {
+			return $a;
+		}
+
+		return Converter::conditionalReturnStatic($a);
+	}
+}