Require non-absolute trait method refs to be unambiguous

Currently, when writing something like

class X {
    use T1, T2 {
       func as otherFunc;
    }
    function func() {}
}

where both T1::func() and T2::func() exist, we will simply assume
that func refers to T1::func(). This is surprising, and it doesn't
really make sense that this particular method gets picked.

This commit validates that non-absolute method references are
unambiguous, i.e. refer to exactly one method. If there is
ambiguity, it is required to write T1::func as otherFunc or
similar.

Closes GH-5232.

5 files changed, 88 insertions, 3 deletions

diff --git a/UPGRADING b/UPGRADING
index 41a72c280d..db8e2eb22e 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -149,6 +149,20 @@ PHP 8.0 UPGRADE NOTES
 
         function test($a = [], $b) {}       // Deprecated
         function test(Foo $a = null, $b) {} // Allowed
+  . Non-absolute trait method references in trait alias adaptations are now
+    required to be unambiguous:
+
+        class X {
+            use T1, T2 {
+               func as otherFunc;
+            }
+            function func() {}
+        }
+
+    If both T1::func() and T2::func() exist, this code was previously silently
+    accepted, and func as assumed to refer to T1::func. Now it will generate a
+    fatal error instead, and either T1::func or T2::func needs to be written
+    explicitly.
 
 - COM:
   . Removed the ability to import case-insensitive constants from type
diff --git a/Zend/tests/bug62069.phpt b/Zend/tests/bug62069.phpt
new file mode 100644
index 0000000000..d434e271c6
--- /dev/null
+++ b/Zend/tests/bug62069.phpt
@@ -0,0 +1,32 @@
+--TEST--
+Bug #62069: binding wrong traits if they have same name methods
+--FILE--
+<?php
+
+trait T1 {
+    public function func() {
+        echo "From T1\n";
+    }
+}
+
+trait T2 {
+    public function func() {
+        echo "From T2\n";
+    }
+}
+
+class Bar {
+    public function func() {
+        echo "From Bar\n";
+    }
+    use T1, T2 {
+        func as f1;
+    }
+}
+
+$b = new Bar();
+$b->f2();
+
+?>
+--EXPECTF--
+Fatal error: An alias was defined for method func(), which exists in both T1 and T2. Use T1::func or T2::func to resolve the ambiguity in %s on line %d
diff --git a/Zend/tests/bug62069_2.phpt b/Zend/tests/bug62069_2.phpt
new file mode 100644
index 0000000000..c7c42ba6d1
--- /dev/null
+++ b/Zend/tests/bug62069_2.phpt
@@ -0,0 +1,35 @@
+--TEST--
+Bug #62069: binding wrong traits if they have same name methods (variation 2)
+--FILE--
+<?php
+
+trait T1 {
+    public function func() {
+        echo "From T1\n";
+    }
+}
+
+trait T2 {
+    public function func() {
+        echo "From T2\n";
+    }
+}
+
+class Bar {
+    public function func() {
+        echo "From Bar\n";
+    }
+    use T1 {
+        func as f1;
+    }
+    use T2 {
+        func as f2;
+    }
+}
+
+$b = new Bar();
+$b->f2();
+
+?>
+--EXPECTF--
+Fatal error: An alias was defined for method func(), which exists in both T1 and T2. Use T1::func or T2::func to resolve the ambiguity in %s on line %d
diff --git a/Zend/tests/traits/language011.phpt b/Zend/tests/traits/language011.phpt
index 44de874705..1f5b496308 100644
--- a/Zend/tests/traits/language011.phpt
+++ b/Zend/tests/traits/language011.phpt
@@ -18,7 +18,7 @@ trait World {
 
 
 class MyClass {
-   use Hello, World { sayHello as sayWorld; }
+   use Hello, World { World::sayHello as sayWorld; }
 }
 
 $o = new MyClass();
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index a031207b85..eab275e509 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -1858,8 +1858,12 @@ static void zend_traits_init_trait_structures(zend_class_entry *ce, zend_class_e
 								continue;
 							}
 
-							// TODO: This is ambiguous! The first trait is assumed.
-							break;
+							zend_error_noreturn(E_COMPILE_ERROR,
+								"An alias was defined for method %s(), which exists in both %s and %s. Use %s::%s or %s::%s to resolve the ambiguity",
+								ZSTR_VAL(cur_method_ref->method_name),
+								ZSTR_VAL(trait->name), ZSTR_VAL(traits[j]->name),
+								ZSTR_VAL(trait->name), ZSTR_VAL(cur_method_ref->method_name),
+								ZSTR_VAL(traits[j]->name), ZSTR_VAL(cur_method_ref->method_name));
 						}
 					}
 				}