Make sure that abstract private is implemented in same class

Normally it's enough to mark the class as "abstract" if an abstract
method was not implemented. However, if there are abstract private
methods, then even they really must be implemented, or it must
be forwarded to a method with higher visibility.

Author: nikic

Zend/tests/traits/abstract_method_6.phpt

@@ -0,0 +1,20 @@
+--TEST--
+Abstract private trait method not implemented
+--FILE--
+<?php
+
+trait T {
+    abstract private function method(int $a, string $b);
+}
+
+abstract class C {
+    use T;
+}
+
+class D extends C {
+    private function method(int $a, string $b) {}
+}
+
+?>
+--EXPECTF--
+Fatal error: Class C must implement 1 abstract private method (C::method) in %s on line %d

Zend/tests/traits/abstract_method_7.phpt

@@ -0,0 +1,23 @@
+--TEST--
+Abstract private trait method forwarded as abstract protected method
+--FILE--
+<?php
+
+trait T {
+    abstract private function method(int $a, string $b);
+}
+
+abstract class C {
+    use T;
+
+    abstract protected function method(int $a, string $b);
+}
+
+class D extends C {
+    protected function method(int $a, string $b) {}
+}
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/zend_inheritance.c

@@ -2128,20 +2128,18 @@ typedef struct _zend_abstract_info {
 
 static void zend_verify_abstract_class_function(zend_function *fn, zend_abstract_info *ai) /* {{{ */
 {
-	if (fn->common.fn_flags & ZEND_ACC_ABSTRACT) {
-		if (ai->cnt < MAX_ABSTRACT_INFO_CNT) {
-			ai->afn[ai->cnt] = fn;
-		}
-		if (fn->common.fn_flags & ZEND_ACC_CTOR) {
-			if (!ai->ctor) {
-				ai->cnt++;
-				ai->ctor = 1;
-			} else {
-				ai->afn[ai->cnt] = NULL;
-			}
-		} else {
+	if (ai->cnt < MAX_ABSTRACT_INFO_CNT) {
+		ai->afn[ai->cnt] = fn;
+	}
+	if (fn->common.fn_flags & ZEND_ACC_CTOR) {
+		if (!ai->ctor) {
 			ai->cnt++;
+			ai->ctor = 1;
+		} else {
+			ai->afn[ai->cnt] = NULL;
 		}
+	} else {
+		ai->cnt++;
 	}
 }
 /* }}} */
@@ -2150,16 +2148,23 @@ void zend_verify_abstract_class(zend_class_entry *ce) /* {{{ */
 {
 	zend_function *func;
 	zend_abstract_info ai;
-
-	ZEND_ASSERT((ce->ce_flags & (ZEND_ACC_IMPLICIT_ABSTRACT_CLASS|ZEND_ACC_INTERFACE|ZEND_ACC_TRAIT|ZEND_ACC_EXPLICIT_ABSTRACT_CLASS)) == ZEND_ACC_IMPLICIT_ABSTRACT_CLASS);
+	zend_bool is_explicit_abstract = (ce->ce_flags & ZEND_ACC_EXPLICIT_ABSTRACT_CLASS) != 0;
 	memset(&ai, 0, sizeof(ai));
 
 	ZEND_HASH_FOREACH_PTR(&ce->function_table, func) {
-		zend_verify_abstract_class_function(func, &ai);
+		if (func->common.fn_flags & ZEND_ACC_ABSTRACT) {
+			/* If the class is explicitly abstract, we only check private abstract methods,
+			 * because only they must be declared in the same class. */
+			if (!is_explicit_abstract || (func->common.fn_flags & ZEND_ACC_PRIVATE)) {
+				zend_verify_abstract_class_function(func, &ai);
+			}
+		}
 	} ZEND_HASH_FOREACH_END();
 
 	if (ai.cnt) {
-		zend_error_noreturn(E_ERROR, "Class %s contains %d abstract method%s and must therefore be declared abstract or implement the remaining methods (" MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT ")",
+		zend_error_noreturn(E_ERROR, !is_explicit_abstract
+			? "Class %s contains %d abstract method%s and must therefore be declared abstract or implement the remaining methods (" MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT ")"
+			: "Class %s must implement %d abstract private method%s (" MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT MAX_ABSTRACT_INFO_FMT ")",
 			ZSTR_VAL(ce->name), ai.cnt,
 			ai.cnt > 1 ? "s" : "",
 			DISPLAY_ABSTRACT_FN(0),
@@ -2438,7 +2443,9 @@ ZEND_API int zend_do_link_class(zend_class_entry *ce, zend_string *lc_parent_nam
 	if (interfaces) {
 		zend_do_implement_interfaces(ce, interfaces);
 	}
-	if ((ce->ce_flags & (ZEND_ACC_IMPLICIT_ABSTRACT_CLASS|ZEND_ACC_INTERFACE|ZEND_ACC_TRAIT|ZEND_ACC_EXPLICIT_ABSTRACT_CLASS)) == ZEND_ACC_IMPLICIT_ABSTRACT_CLASS) {
+	if (!(ce->ce_flags & (ZEND_ACC_INTERFACE|ZEND_ACC_TRAIT))
+		&& (ce->ce_flags & (ZEND_ACC_IMPLICIT_ABSTRACT_CLASS|ZEND_ACC_EXPLICIT_ABSTRACT_CLASS))
+	) {
 		zend_verify_abstract_class(ce);
 	}