fix(compiler): 修复类常量继承重写及类型推断

- 正确处理 parent::、self:: 和 static:: 的常量引用与类型解析
- 支持 ::class 魔法常量的编译期求值与字符串类型推断
- 引用其他类常量时继承其实际类型，避免误判为 VAR
- 仅当父类常量有显式声明类型时才校验类型兼容性
- 运行时注册子类常量前先删除父类继承条目以避免重定义冲突

src/Entity/ConstantDef.php

@@ -19,6 +19,8 @@ class ConstantDef
     public string $arrayExpr = '';
     public string $class = '';
     public ?NodeAbstract $valueExpr = null;
+    /** Explicit declared type (e.g. `const int FOO`); null for inferred/untyped constants. */
+    public ?string $declaredType = null;
 
     public function __construct(string $name, int $flags, string $type, string $value)
     {

src/Parser/ClassConstantFetchTrait.php

@@ -31,6 +31,17 @@ trait ClassConstantFetchTrait
                 $self = true;
                 $class = $this->class;
             }
+        } elseif ($class === 'parent') {
+            // `parent::` refers to the parent of the current class. Resolve it to
+            // the real parent class name and treat it like `self` for the purpose
+            // of constant/magic-class resolution.
+            $parentClass = $this->getParentClass($this->class);
+            if ($parentClass !== '' && $this->hasClass($parentClass)) {
+                $class = $this->getClass($parentClass)->name;
+            } else {
+                $class = $parentClass;
+            }
+            $self = true;
         }
 
         $const = $this->escapeString($this->parseIdentifier($expr->name));

src/Preprocessor.php

@@ -757,24 +757,89 @@ class Preprocessor extends CompilerBase
                     'Scalar_String' => Type::STR,
                     default => Type::VAR,
                 };
+                // `::class` is a compile-time magic constant that always yields a string,
+                // so a constant declared as `X = self::class` (or `Foo::class`) must be
+                // typed as a string rather than a generic variant.
+                if ($type === Type::VAR
+                    && $const->value instanceof Node\Expr\ClassConstFetch
+                    && strtolower((string) $const->value->name) === 'class') {
+                    $type = Type::STR;
+                }
+                // A constant whose value references another class constant
+                // (e.g. `X = ParentClass::Y` or `X = self::Y`) must take the referenced
+                // constant's type. This keeps override compatibility checks and the C++
+                // declaration correct, mirroring PHP where overriding an untyped constant
+                // with a value of any (compatible) type is allowed.
+                if ($type === Type::VAR
+                    && $const->value instanceof Node\Expr\ClassConstFetch
+                    && $const->value->class instanceof Node\Name) {
+                    $refType = $this->resolveReferencedConstantType($const->value, $this->getFullClassName());
+                    if ($refType !== null) {
+                        $type = $refType;
+                    }
+                }
             }
             $constName = $this->parseIdentifier($const->name);
             if ($this->classDef->hasConstant($constName)) {
                 $this->fatalError($v, "Duplicate constant `{$constName}`");
             }
-            $constInfo = $this->parseClassLikeConstant($const, $flags, $type, $class);
+            $constInfo = $this->parseClassLikeConstant($const, $flags, $type, $class, $declaredType);
             $constInfo->class = $class;
             $this->classDef->constants[$constInfo->name] = $constInfo;
         }
     }
 
-    private function parseClassLikeConstant(Node\Const_ $const, int $flags, string $type, string $class = ''): ConstantDef
+    /**
+     * Resolve the compile-time type of a class constant whose value is a
+     * `ClassConstFetch` referencing another constant (e.g. `X = ParentClass::Y`
+     * or `X = self::Y`). Returns the referenced constant's type, or null when
+     * the reference cannot be resolved yet (for instance when the referenced
+     * class has not been prepared). `::class` always resolves to a string.
+     */
+    private function resolveReferencedConstantType(Node\Expr\ClassConstFetch $fetch, string $currentClass): ?string
+    {
+        $constName = $fetch->name->toString();
+        if (strcasecmp($constName, 'class') === 0) {
+            return Type::STR;
+        }
+        if (!($fetch->class instanceof Node\Name)) {
+            return null;
+        }
+        $className = $fetch->class->toString();
+        if (strcasecmp($className, 'self') === 0 || strcasecmp($className, 'static') === 0) {
+            $targetClass = $currentClass;
+        } elseif (strcasecmp($className, 'parent') === 0) {
+            $targetClass = $this->getParentClass($currentClass);
+        } else {
+            $targetClass = $this->getNamespacedClassName($className);
+        }
+        if ($targetClass === '' || !$this->hasClass($targetClass)) {
+            return null;
+        }
+        $def = $this->getClass($targetClass);
+        if (!$def->hasConstant($constName)) {
+            return null;
+        }
+        $refConst = $def->getConstant($constName);
+        // Follow the chain in case the referenced constant is itself an
+        // expression that resolves to another constant.
+        if ($refConst->type !== Type::VAR) {
+            return $refConst->type;
+        }
+        if ($refConst->valueExpr instanceof Node\Expr\ClassConstFetch) {
+            return $this->resolveReferencedConstantType($refConst->valueExpr, $targetClass);
+        }
+        return null;
+    }
+
+    private function parseClassLikeConstant(Node\Const_ $const, int $flags, string $type, string $class = '', ?string $declaredType = null): ConstantDef
     {
         $constName = $this->parseIdentifier($const->name);
         $constValue = $this->parseIdentifier($const->value);
 
         $constInfo = new ConstantDef($constName, $flags, $type, $constValue);
         $constInfo->valueExpr = $const->value;
+        $constInfo->declaredType = $declaredType;
 
         if ($this->context->beforeStmtLines) {
             $arrayExpr = '';
@@ -979,7 +1044,7 @@ class Preprocessor extends CompilerBase
                             default => Type::VAR,
                         };
                     }
-                    $constInfo = $this->parseClassLikeConstant($const, $this->parseModifiers($stmt->flags), $type, $class);
+                    $constInfo = $this->parseClassLikeConstant($const, $this->parseModifiers($stmt->flags), $type, $class, $stmt->type ? $type : null);
                     $this->interfaceDef->constants[$constName] = $constInfo;
                 }
                 continue;

src/Resolver/ClassConstantValueTrait.php

@@ -116,6 +116,16 @@ trait ClassConstantValueTrait
             if ($expr instanceof Node\Expr\ClassConstFetch && $expr->class instanceof Node\Name) {
                 $constName = $expr->name->toString();
                 $className = $expr->class->toString();
+                if (strcasecmp($constName, 'class') === 0) {
+                    // `::class` is a compile-time magic constant that resolves to the
+                    // fully qualified class name of the referenced class.
+                    if (strcasecmp($className, 'self') === 0 || strcasecmp($className, 'static') === 0) {
+                        $className = $class;
+                    } elseif (strcasecmp($className, 'parent') === 0) {
+                        $className = $this->getParentClass($class);
+                    }
+                    return ltrim($this->getNamespacedClassName($className, $this->getNamespaceOfClass($class)), '\\');
+                }
                 if (strcasecmp($className, 'self') === 0) {
                     $className = $class;
                 } elseif (strcasecmp($className, 'parent') === 0) {

src/Translator.php

@@ -3477,10 +3477,28 @@ CODE;
                     if ($parentConst->flags & Modifiers::PRIVATE) {
                         continue;
                     }
-                    if ($childConst->type !== $parentConst->type || $childConst->class !== $parentConst->class) {
-                        $this->fatalError($classStmt,
-                            "Declaration of `{$className}::{$name}` must be compatible " .
-                            "with `{$parentClass}::{$name}`");
+                    // PHP only enforces type compatibility when the parent constant
+                    // carries an explicit declared type. Overriding an untyped constant
+                    // with a value of any type is permitted, so the type check is skipped
+                    // in that case. Visibility is always enforced below.
+                    if ($parentConst->declaredType !== null) {
+                        // An untyped child constant whose value is an expression (e.g.
+                        // `X = ParentClass::Y`) is inferred as a variant. Resolve its real
+                        // type from the referenced constant so the compatibility check uses
+                        // the actual value type.
+                        $childType = $childConst->type;
+                        if ($childType === Type::VAR
+                            && $childConst->valueExpr instanceof Node\Expr\ClassConstFetch) {
+                            $resolved = $this->resolveReferencedConstantType($childConst->valueExpr, $this->getFullClassName());
+                            if ($resolved !== null) {
+                                $childType = $resolved;
+                            }
+                        }
+                        if ($childType !== $parentConst->type || $childConst->class !== $parentConst->class) {
+                            $this->fatalError($classStmt,
+                                "Declaration of `{$className}::{$name}` must be compatible " .
+                                "with `{$parentClass}::{$name}`");
+                        }
                     }
                     if ($this->getVisibilityRank($childConst->flags) < $this->getVisibilityRank($parentConst->flags)) {
                         $this->fatalError($classStmt,

src/gen_stub.php

@@ -2354,18 +2354,29 @@ class EvaluatedValue
                 }
 
                 if ($expr instanceof Expr\ClassConstFetch) {
+                    $constName = $expr->name->__toString();
+                    if (strcasecmp($constName, 'class') === 0) {
+                        // `::class` is a compile-time magic constant that resolves to the
+                        // fully qualified class name of the referenced class.
+                        $className = getClassConstFetchClassName($expr);
+                        if (strcasecmp($className, 'self') === 0 || strcasecmp($className, 'static') === 0) {
+                            return ClassInfo::$currentClass;
+                        }
+                        if (strcasecmp($className, 'parent') === 0) {
+                            return getTranslator()->getParentClass(ClassInfo::$currentClass);
+                        }
+                        return ltrim($className, '\\');
+                    }
                     $class = getClassConstFetchClassName($expr);
                     if ($class === 'self') {
-                        $constName = ClassInfo::$currentClass . "::" . $expr->name->__toString();
+                        $constName = ClassInfo::$currentClass . "::" . $constName;
                         if (isset($allConstInfos[$constName])) {
                             return formatConstValue($allConstInfos[$constName]->getValue($allConstInfos)->value);
                         } else {
-                            return formatConstValue(getTranslator()->getClassConstValue($expr, ClassInfo::$currentClass, $expr->name->toString()));
+                            return formatConstValue(getTranslator()->getClassConstValue($expr, ClassInfo::$currentClass, $constName));
                         }
-                    } elseif ($expr->name->__toString() === 'class') {
-                        return $class;
                     } else {
-                        return formatConstValue(getTranslator()->getClassConstValue($expr, $class, $expr->name->__toString(), ClassInfo::$currentClass));
+                        return formatConstValue(getTranslator()->getClassConstValue($expr, $class, $constName, ClassInfo::$currentClass));
                     }
                 } else {
                     $constName = $expr->name->__toString();
@@ -2490,16 +2501,14 @@ class EvaluatedValue
 
         // PHP single-quote to C double-quote string
         if ($this->type->isString()) {
-            if (
-                $this->expr instanceof PhpParser\Node\Expr\ClassConstFetch
-            ) {
-                if ($this->expr->class instanceof PhpParser\Node\Name\FullyQualified and
-                    $this->expr->name instanceof PhpParser\Node\Identifier and
+            if ($this->expr instanceof PhpParser\Node\Expr\ClassConstFetch) {
+                if ($this->expr->name instanceof PhpParser\Node\Identifier and
                     $this->expr->name->__toString() === 'class') {
-                    $expr = '"' . addcslashes($this->expr->class->name, '\\') . '"';
-                } else {
-                    return $this->value;
+                    // `::class` is a compile-time magic constant that resolves to the
+                    // fully qualified class name (already stored in $this->value).
+                    return '"' . addcslashes($this->value, '\\') . '"';
                 }
+                return $this->value;
             } elseif ($this->expr instanceof Expr\ConstFetch) {
                 return getTranslator()->getConstValue($this->expr->name->toString());
             } elseif (!($this->expr instanceof String_)) {
@@ -2899,6 +2908,12 @@ class ConstInfo extends VariableLike
         $code .= "\tzend_string *const_{$constName}_name = zend_string_init_interned(\"$constName\", sizeof(\"$constName\") - 1, true);\n";
         $nameCode = "const_{$constName}_name";
 
+        // A child class may override a constant inherited from its parent. The
+        // runtime copies the parent's constants into the child, so re-declaring
+        // the constant would fail with "Cannot redefine class constant".
+        // Drop any inherited entry first so the child's value replaces it.
+        $code .= "\tzend_hash_del(&class_entry->constants_table, $nameCode);\n";
+
         if ($this->exposedDocComment) {
             $commentCode = "const_{$constName}_comment";
             $escapedCommentInit = $this->exposedDocComment->getInitCode();

tests/compiler/const/class-const-override-variants.phpt

@@ -0,0 +1,51 @@
+--TEST--
+class const override variants (self::class, parent::class, references, multi-level)
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+class Base
+{
+    public const NAME = 'Base';
+    public const GREETING = 'hello';
+    public const VALUE = 42;
+}
+
+class Other
+{
+    public const TAG = 'other';
+}
+
+class Mid extends Base
+{
+    public const NAME = Base::GREETING;       // 'hello'
+    public const SELF_NAME = self::class;     // 'Mid'
+    public const PARENT_NAME = parent::class; // 'Base'
+    public const CROSS = Other::TAG;          // 'other'
+}
+
+class Leaf extends Mid
+{
+    public const VALUE = Mid::NAME;           // 'hello' (overrides Base::VALUE int with a string)
+    public const LEAF_NAME = self::class;     // 'Leaf'
+    public const GREET = Base::GREETING;      // 'hello'
+}
+
+function main()
+{
+    var_dump(Mid::NAME, Mid::SELF_NAME, Mid::PARENT_NAME, Mid::CROSS);
+    var_dump(Leaf::VALUE, Leaf::LEAF_NAME, Leaf::GREET);
+    var_dump(Base::VALUE, Leaf::VALUE);
+}
+?>
+--EXPECT--
+string(5) "hello"
+string(3) "Mid"
+string(4) "Base"
+string(5) "other"
+string(5) "hello"
+string(4) "Leaf"
+string(5) "hello"
+int(42)
+string(5) "hello"

tests/compiler/const/class-const-override.phpt

@@ -0,0 +1,30 @@
+--TEST--
+class const override referencing another constant
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+abstract class ParentClass
+{
+    public const A = 'A';
+    public const B = 'B';
+}
+
+class TestClass extends ParentClass
+{
+    public const A = ParentClass::B;
+    public const B = 'bbb';
+}
+
+function main()
+{
+    var_dump(ParentClass::A, ParentClass::B);
+    var_dump(TestClass::A, TestClass::B);
+}
+?>
+--EXPECT--
+string(1) "A"
+string(1) "B"
+string(1) "B"
+string(3) "bbb"