Generalize dynamicConstantNames constants whose type cannot be widened by generalize() to mixed

- NullType::generalize() returns $this because null has no broader type
  family, so dynamicConstantNames had no effect on null-valued constants
- After calling generalize(), check if the result is still a constant
  value; if so, return MixedType instead
- Fix applies to both resolveConstantType (global constants) and
  resolveClassConstantType (class constants)
- Also fixes the analogous case for empty ConstantArrayType ([]),
  whose generalize() also returns $this

Author: ondrejmirtes

src/Analyser/ConstantResolver.php

@@ -424,7 +424,11 @@ public function resolveConstantType(string $constantName, Type $constantType): T
 				return $constantType;
 			}
 			if (in_array($constantName, $this->dynamicConstantNames, true)) {
-				return $constantType->generalize(GeneralizePrecision::lessSpecific());
+				$generalized = $constantType->generalize(GeneralizePrecision::lessSpecific());
+				if ($generalized->isConstantValue()->yes()) {
+					return new MixedType();
+				}
+				return $generalized;
 			}
 		}
 
@@ -455,7 +459,11 @@ public function resolveClassConstantType(string $className, string $constantName
 			}
 
 			if ($constantType->isConstantValue()->yes()) {
-				return $constantType->generalize(GeneralizePrecision::lessSpecific());
+				$generalized = $constantType->generalize(GeneralizePrecision::lessSpecific());
+				if ($generalized->isConstantValue()->yes()) {
+					return new MixedType();
+				}
+				return $generalized;
 			}
 		}
 

tests/PHPStan/Analyser/data/dynamic-constant.php

@@ -7,12 +7,17 @@
 define('GLOBAL_PURE_CONSTANT', 123);
 define('GLOBAL_DYNAMIC_CONSTANT', false);
 define('GLOBAL_DYNAMIC_CONSTANT_WITH_EXPLICIT_TYPES', null);
+define('GLOBAL_DYNAMIC_NULL_CONSTANT', null);
 
 class DynamicConstantClass
 {
 	const DYNAMIC_CONSTANT_IN_CLASS = 'abcdef';
 	const DYNAMIC_CONSTANT_WITH_EXPLICIT_TYPES_IN_CLASS = 'xyz';
 	const PURE_CONSTANT_IN_CLASS = 'abc123def';
+	const DYNAMIC_NULL_CONSTANT = null;
+	const DYNAMIC_TRUE_CONSTANT = true;
+	const DYNAMIC_FALSE_CONSTANT = false;
+	const DYNAMIC_EMPTY_ARRAY_CONSTANT = [];
 }
 
 class NoDynamicConstantClass
@@ -29,5 +34,16 @@ private function rip()
 		assertType('bool', GLOBAL_DYNAMIC_CONSTANT);
 		assertType('123', GLOBAL_PURE_CONSTANT);
 		assertType('string|null', GLOBAL_DYNAMIC_CONSTANT_WITH_EXPLICIT_TYPES);
+
+		// Bug 9218: dynamicConstantNames with null value
+		assertType('mixed', DynamicConstantClass::DYNAMIC_NULL_CONSTANT);
+		assertType('mixed', GLOBAL_DYNAMIC_NULL_CONSTANT);
+
+		// Bool constants should generalize properly
+		assertType('bool', DynamicConstantClass::DYNAMIC_TRUE_CONSTANT);
+		assertType('bool', DynamicConstantClass::DYNAMIC_FALSE_CONSTANT);
+
+		// Empty array constant should generalize to mixed
+		assertType('mixed', DynamicConstantClass::DYNAMIC_EMPTY_ARRAY_CONSTANT);
 	}
 }

tests/PHPStan/Analyser/dynamic-constants.neon

@@ -4,6 +4,11 @@ includes:
 parameters:
 	dynamicConstantNames:
 		- DynamicConstants\DynamicConstantClass::DYNAMIC_CONSTANT_IN_CLASS
+		- DynamicConstants\DynamicConstantClass::DYNAMIC_NULL_CONSTANT
+		- DynamicConstants\DynamicConstantClass::DYNAMIC_TRUE_CONSTANT
+		- DynamicConstants\DynamicConstantClass::DYNAMIC_FALSE_CONSTANT
+		- DynamicConstants\DynamicConstantClass::DYNAMIC_EMPTY_ARRAY_CONSTANT
 		- GLOBAL_DYNAMIC_CONSTANT
+		- GLOBAL_DYNAMIC_NULL_CONSTANT
 		DynamicConstants\DynamicConstantClass::DYNAMIC_CONSTANT_WITH_EXPLICIT_TYPES_IN_CLASS: 'string|null'
 		GLOBAL_DYNAMIC_CONSTANT_WITH_EXPLICIT_TYPES: 'string|null'