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

[phpstan-bot]

Summary

When a constant with value null (or empty array []) was listed in dynamicConstantNames, PHPStan still treated it as having its literal type because NullType::generalize() returns $this — there is no broader "null family" type to generalize to. This made dynamicConstantNames ineffective for null-valued constants.

Changes

• Modified ConstantResolver::resolveConstantType() in src/Analyser/ConstantResolver.php to check whether generalize() actually widened the type; if the result still reports isConstantValue()->yes(), return MixedType instead
• Applied the same fix to ConstantResolver::resolveClassConstantType() for class constants
• Added test cases for null-valued class constants, null-valued global constants, and empty-array class constants in tests/PHPStan/Analyser/data/dynamic-constant.php
• Added corresponding dynamicConstantNames entries in tests/PHPStan/Analyser/dynamic-constants.neon

Analogous cases probed

• true/false constants: Already generalize correctly to bool — confirmed with tests (already passing)
• String/integer/float constants: Already generalize correctly to their parent scalar types — not affected
• Empty ConstantArrayType ([]): generalize() returns $this for empty arrays — was broken, now fixed by the same check
• EnumCaseObjectType: Reports isConstantValue()->no(), so not affected
• VoidType: Reports isConstantValue()->no(), so not affected
• Explicit type path (array_key_exists): Uses TypeStringResolver to resolve user-specified type strings — not affected
• Native type path ($nativeType): Returns the declared native type (PHP 8.3+) — not affected

Root cause

NullType::generalize() returns $this because null is a singleton type with no broader family. Similarly, ConstantArrayType::generalize() returns $this for empty arrays. When dynamicConstantNames called generalize() on these types, the result was unchanged, so the constant was still treated as having its literal value. The fix detects this case by checking whether the generalized type is still a constant value and falls back to mixed.

Test

• Added assertType('mixed', DynamicConstantClass::DYNAMIC_NULL_CONSTANT) — null-valued class constant
• Added assertType('mixed', GLOBAL_DYNAMIC_NULL_CONSTANT) — null-valued global constant
• Added assertType('mixed', DynamicConstantClass::DYNAMIC_EMPTY_ARRAY_CONSTANT) — empty-array class constant
• Added assertType('bool', DynamicConstantClass::DYNAMIC_TRUE_CONSTANT) and assertType('bool', DynamicConstantClass::DYNAMIC_FALSE_CONSTANT) — confirm boolean constants still generalize correctly

Fixes phpstan/phpstan#9218