GH-16067: prevent invalid abstract during compilation of methods (GH-16069)

For classes that are not declared `abstract`, produce a compiler error for any
`abstract` methods. For anonymous classes, since they cannot be made abstract,
the error message is slightly different.

Co-authored-by: Ilija Tovilo <ilija.tovilo@me.com>

Author: DanielEScherzer

Zend/tests/abstract_implicit.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Abstract methods not allowed in classes that are not abstract (GH-16067)
+--FILE--
+<?php
+
+// Still allowed via trait
+trait TraitWithAbstract {
+    abstract public function foo();
+}
+class TraitWorks {
+    use TraitWithAbstract;
+}
+
+class NotAbstract {
+    abstract public function bar();
+}
+?>
+--EXPECTF--
+Fatal error: Class NotAbstract declares abstract method bar() and must therefore be declared abstract in %s on line %d

Zend/tests/anon/gh16067.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Compiler prevents explicit `abstract` methods on anonymous classes
+--FILE--
+<?php
+
+$c = new class {
+    abstract public function f();
+}
+?>
+--EXPECTF--
+Fatal error: Anonymous class method f() must not be abstract in %s on line 4

Zend/tests/enum/no-abstract.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Compiler prevents `abstract` methods on enums classes (GH-16067)
+--FILE--
+<?php
+
+enum Example {
+    abstract public function foo();
+}
+
+?>
+--EXPECTF--
+Fatal error: Enum method Example::foo() must not be abstract in %s on line 4

Zend/tests/errmsg/errmsg_018.phpt

@@ -10,4 +10,4 @@ class test {
 echo "Done\n";
 ?>
 --EXPECTF--
-Fatal error: Class test contains 1 abstract method and must therefore be declared abstract or implement the remaining method (test::foo) in %s on line %d
+Fatal error: Class test declares abstract method foo() and must therefore be declared abstract in %s on line %d

Zend/zend_compile.c

@@ -8067,6 +8067,22 @@ static zend_string *zend_begin_method_decl(zend_op_array *op_array, zend_string
 		zend_error(E_COMPILE_WARNING, "Private methods cannot be final as they are never overridden by other classes");
 	}
 
+	if ((fn_flags & ZEND_ACC_ABSTRACT)
+	 && !(ce->ce_flags & (ZEND_ACC_EXPLICIT_ABSTRACT_CLASS|ZEND_ACC_TRAIT))) {
+		// Don't say that the class should be declared abstract if it is
+		// anonymous or an enum and can't be abstract
+		if (ce->ce_flags & ZEND_ACC_ANON_CLASS) {
+			zend_error_noreturn(E_COMPILE_ERROR, "Anonymous class method %s() must not be abstract",
+				ZSTR_VAL(name));
+		} else if (ce->ce_flags & (ZEND_ACC_ENUM|ZEND_ACC_INTERFACE)) {
+			zend_error_noreturn(E_COMPILE_ERROR, "%s method %s::%s() must not be abstract",
+				zend_get_object_type_case(ce, true), ZSTR_VAL(ce->name), ZSTR_VAL(name));
+		} else {
+			zend_error_noreturn(E_COMPILE_ERROR, "Class %s declares abstract method %s() and must therefore be declared abstract",
+				ZSTR_VAL(ce->name), ZSTR_VAL(name));
+		}
+	}
+
 	if (in_interface) {
 		if (!(fn_flags & ZEND_ACC_PUBLIC)) {
 			zend_error_noreturn(E_COMPILE_ERROR, "Access type for interface method "
@@ -8076,10 +8092,6 @@ static zend_string *zend_begin_method_decl(zend_op_array *op_array, zend_string
 			zend_error_noreturn(E_COMPILE_ERROR, "Interface method "
 				"%s::%s() must not be final", ZSTR_VAL(ce->name), ZSTR_VAL(name));
 		}
-		if (fn_flags & ZEND_ACC_ABSTRACT) {
-			zend_error_noreturn(E_COMPILE_ERROR, "Interface method "
-				"%s::%s() must not be abstract", ZSTR_VAL(ce->name), ZSTR_VAL(name));
-		}
 		op_array->fn_flags |= ZEND_ACC_ABSTRACT;
 	}
 

tests/classes/abstract_derived.phpt

@@ -13,4 +13,4 @@ class derived extends base {
 ?>
 ===DONE===
 --EXPECTF--
-Fatal error: Class derived contains 1 abstract method and must therefore be declared abstract or implement the remaining method (derived::show) in %sabstract_derived.php on line %d
+Fatal error: Class derived declares abstract method show() and must therefore be declared abstract in %sabstract_derived.php on line %d

tests/classes/abstract_not_declared.phpt

@@ -10,4 +10,4 @@ class fail {
 echo "Done\n"; // shouldn't be displayed
 ?>
 --EXPECTF--
-Fatal error: Class fail contains 1 abstract method and must therefore be declared abstract or implement the remaining method (fail::show) in %s on line %d
+Fatal error: Class fail declares abstract method show() and must therefore be declared abstract in %s on line %d

tests/classes/abstract_redeclare.phpt

@@ -16,4 +16,4 @@ class fail extends pass {
 echo "Done\n"; // Shouldn't be displayed
 ?>
 --EXPECTF--
-Fatal error: Class fail contains 1 abstract method and must therefore be declared abstract or implement the remaining method (fail::show) in %sabstract_redeclare.php on line %d
+Fatal error: Class fail declares abstract method show() and must therefore be declared abstract in %sabstract_redeclare.php on line %d

tests/classes/abstract_static.phpt

@@ -31,4 +31,4 @@ echo "Done\n"; // shouldn't be displayed
 --EXPECTF--
 Call to function show()
 
-Fatal error: Class fail contains 1 abstract method and must therefore be declared abstract or implement the remaining method (fail::func) in %sabstract_static.php(%d) : eval()'d code on line %d
+Fatal error: Class fail declares abstract method func() and must therefore be declared abstract in %sabstract_static.php(%d) : eval()'d code on line %d

tests/classes/interface_method_private.phpt

@@ -4,7 +4,7 @@ ZE2 An interface method cannot be private
 <?php
 
 interface if_a {
-    abstract private function err();
+    private function err();
 }
 
 ?>