From a2fe8d48b13df62d3363d448b3d0e2752b10daf9 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Fri, 5 Nov 2021 17:05:55 +0100
Subject: [PATCH] Partially address bug #78647

Produce a sensible error message for the case where inheritance
should fail. There is still a remaining issue that we sometimes
fail inheritance while we should not.
---
 .../variance/class_order_autoload_error7.phpt | 24 +++++++++++++++++++
 Zend/zend_inheritance.c                       |  3 ++-
 2 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 Zend/tests/type_declarations/variance/class_order_autoload_error7.phpt

diff --git a/Zend/tests/type_declarations/variance/class_order_autoload_error7.phpt b/Zend/tests/type_declarations/variance/class_order_autoload_error7.phpt
new file mode 100644
index 00000000000..c4b4cc05ee7
--- /dev/null
+++ b/Zend/tests/type_declarations/variance/class_order_autoload_error7.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Bug #78647: Outstanding dependency obligation
+--FILE--
+<?php
+
+spl_autoload_register(function ($class) {
+    if ($class == 'A') {
+        class A {
+            function m(): B {}
+        }
+    } elseif ($class == 'B') {
+        class B extends A {
+            function m(): X {}
+        }
+    } else {
+        class C extends B {}
+    }
+});
+
+new B;
+
+?>
+--EXPECTF--
+Fatal error: Could not check compatibility between B::m(): X and A::m(): B, because class X is not available in %s on line %d
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index b30bb523d36..57314d78448 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -2548,7 +2548,8 @@ static void report_variance_errors(zend_class_entry *ce) {
 		} else if (obligation->type == OBLIGATION_PROPERTY_COMPATIBILITY) {
 			emit_incompatible_property_error(obligation->child_prop, obligation->parent_prop);
 		} else {
-			zend_error_noreturn(E_CORE_ERROR, "Bug #78647");
+			/* Report variance errors of the dependency, which prevent it from being linked. */
+			report_variance_errors(obligation->dependency_ce);
 		}
 	} ZEND_HASH_FOREACH_END();