zend_portability: Remove EMPTY_SWITCH_DEFAULT_CASE() (#20063)

There are several issues with this macro:

- It is incorrectly named: It's not an empty default case. It's an unreachable
  default case.
- It is hiding control flow in its definition, which can be confusing for
  humans and tools (such as Coccinelle) alike, because it looks like it would
  be a statement that belongs to the "current" case rather than opening a new
  one.

Since this macro is exactly as long as explicitly spelling out its definition
(excluding the useless `break;`), it is not even making the code any more
succinct.

Author: TimWolla

UPGRADING.INTERNALS

@@ -86,6 +86,8 @@ PHP 8.6 INTERNALS UPGRADE NOTES
   . The unused ZEND_AST_PARENT_PROPERTY_HOOK_CALL has been removed.
   . ZEND_AST_METHOD_REFERENCE has been renamed to
     ZEND_AST_TRAIT_METHOD_REFERENCE.
+  . The EMPTY_SWITCH_DEFAULT_CASE() macro has been removed. Use
+    default: ZEND_UNREACHABLE(); instead.
 
 ========================
 2. Build system changes

Zend/Optimizer/sccp.c

@@ -1596,7 +1596,7 @@ static void sccp_visit_instr(scdf_ctx *scdf, zend_op *opline, zend_ssa_op *ssa_o
 				case ZEND_SHORT_CIRCUITING_CHAIN_EMPTY:
 					ZVAL_TRUE(&zv);
 					break;
-				EMPTY_SWITCH_DEFAULT_CASE()
+				default: ZEND_UNREACHABLE();
 			}
 			SET_RESULT(result, &zv);
 			break;

Zend/Optimizer/zend_inference.c

@@ -1063,7 +1063,7 @@ static bool zend_inference_calc_binary_op_range(
 		case ZEND_BW_XOR:
 			// TODO
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 	return 0;
 }
@@ -2350,7 +2350,7 @@ static uint32_t binary_op_result_type(
 			/* TODO: +MAY_BE_OBJECT ??? */
 			tmp = MAY_BE_STRING | MAY_BE_RC1 | MAY_BE_RCN;
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 	return tmp;
 }
@@ -3708,7 +3708,7 @@ static zend_always_inline zend_result _zend_update_type_info(
 							case ZEND_FREE:
 								/* This may happen if the using opcode is DCEd.  */
 								break;
-							EMPTY_SWITCH_DEFAULT_CASE()
+							default: ZEND_UNREACHABLE();
 						}
 						j = zend_ssa_next_use(ssa->ops, ssa_op->result_def, j);
 						if (j >= 0) {
@@ -5294,10 +5294,10 @@ ZEND_API bool zend_may_throw_ex(const zend_op *opline, const zend_ssa_op *ssa_op
 					return (t1 & MAY_BE_OBJECT);
 				case IS_OBJECT:
 					return 0;
-				EMPTY_SWITCH_DEFAULT_CASE()
+				default: ZEND_UNREACHABLE();
 			}
 			/* GCC is getting confused here for the Wimplicit-fallthrough warning with
-			 * EMPTY_SWITCH_DEFAULT_CASE() macro */
+			 * default: ZEND_UNREACHABLE(); macro */
 			return 0;
 		case ZEND_ARRAY_KEY_EXISTS:
 			if ((t2 & MAY_BE_ANY) != MAY_BE_ARRAY) {

Zend/zend_API.c

@@ -126,7 +126,7 @@ ZEND_API const char *zend_get_type_by_const(int type) /* {{{ */
 			return "mixed";
 		case _IS_NUMBER:
 			return "int|float";
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -262,7 +262,7 @@ ZEND_API ZEND_COLD void ZEND_FASTCALL zend_wrong_parameter_error(int error_code,
 		case ZPP_ERROR_FAILURE:
 			ZEND_ASSERT(EG(exception) && "Should have produced an error already");
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */

Zend/zend_ast.c

@@ -814,7 +814,7 @@ static zend_result ZEND_FASTCALL zend_ast_evaluate_inner(
 					case IS_OBJECT:
 						zend_cast_zval_to_object(result, &op1, IS_VAR);
 						break;
-					EMPTY_SWITCH_DEFAULT_CASE();
+					default: ZEND_UNREACHABLE();
 				}
 				zval_ptr_dtor_nogc(&op1);
 				if (UNEXPECTED(EG(exception))) {
@@ -1240,7 +1240,7 @@ static zend_result ZEND_FASTCALL zend_ast_evaluate_inner(
 
 					break;
 				}
-				EMPTY_SWITCH_DEFAULT_CASE()
+				default: ZEND_UNREACHABLE();
 			}
 
 			zend_create_fake_closure(result, fptr, fptr->common.scope, called_scope, NULL);
@@ -1961,7 +1961,7 @@ static ZEND_COLD void zend_ast_export_zval(smart_str *str, const zval *zv, int p
 		case IS_CONSTANT_AST:
 			zend_ast_export_ex(str, Z_ASTVAL_P(zv), priority, indent);
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 }
 
@@ -2396,7 +2396,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case T_PROPERTY_C: APPEND_STR("__PROPERTY__");
 				case T_NS_C:     APPEND_STR("__NAMESPACE__");
 				case T_CLASS_C:  APPEND_STR("__CLASS__");
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_TYPE:
@@ -2405,7 +2405,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case IS_CALLABLE: APPEND_STR("callable");
 				case IS_STATIC:   APPEND_STR("static");
 				case IS_MIXED:    APPEND_STR("mixed");
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_PLACEHOLDER_ARG:
@@ -2439,7 +2439,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case IS_STRING:    PREFIX_OP("(string)", 240, 241);
 				case IS_ARRAY:     PREFIX_OP("(array)",  240, 241);
 				case IS_OBJECT:    PREFIX_OP("(object)", 240, 241);
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_CAST_VOID:
@@ -2473,14 +2473,14 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case ZEND_REQUIRE_ONCE: FUNC_OP("require_once");
 				case ZEND_REQUIRE:      FUNC_OP("require");
 				case ZEND_EVAL:         FUNC_OP("eval");
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_UNARY_OP:
 			switch (ast->attr) {
 				case ZEND_BW_NOT:   PREFIX_OP("~", 240, 241);
 				case ZEND_BOOL_NOT: PREFIX_OP("!", 240, 241);
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_PRE_INC:
@@ -2575,7 +2575,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 					case ZEND_FETCH_CLASS_PARENT:
 						smart_str_append(str, ZSTR_KNOWN(ZEND_STR_PARENT));
 						break;
-					EMPTY_SWITCH_DEFAULT_CASE()
+					default: ZEND_UNREACHABLE();
 				}
 			} else {
 				zend_ast_export_ns_name(str, ast->child[0], 0, indent);
@@ -2598,7 +2598,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case ZEND_BW_AND: BINARY_OP(" &= ",  90, 91, 90);
 				case ZEND_BW_XOR: BINARY_OP(" ^= ",  90, 91, 90);
 				case ZEND_POW:    BINARY_OP(" **= ", 90, 91, 90);
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_ASSIGN_COALESCE: BINARY_OP(" \?\?= ", 90, 91, 90);
@@ -2624,7 +2624,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				case ZEND_POW:                 BINARY_OP(" ** ",  250, 251, 250);
 				case ZEND_BOOL_XOR:            BINARY_OP(" xor ",  40,  40,  41);
 				case ZEND_SPACESHIP:           BINARY_OP(" <=> ", 180, 181, 181);
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 			break;
 		case ZEND_AST_GREATER:                 BINARY_OP(" > ",   180, 181, 181);
@@ -2976,7 +2976,7 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 			zend_ast_export_indent(str, indent);
 			smart_str_appendc(str, '}');
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 	return;
 
@@ -3073,7 +3073,7 @@ zend_ast * ZEND_FASTCALL zend_ast_with_attributes(zend_ast *ast, zend_ast *attr)
 		 * zend_compile_const_decl() checks the kind of the list elements. */
 		ast = zend_ast_list_add(ast, attr);
 		break;
-	EMPTY_SWITCH_DEFAULT_CASE()
+	default: ZEND_UNREACHABLE();
 	}
 
 	return ast;

Zend/zend_compile.c

@@ -891,7 +891,7 @@ static const char *zend_modifier_token_to_string(uint32_t token)
 			return "protected(set)";
 		case T_PRIVATE_SET:
 			return "private(set)";
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 
@@ -1834,7 +1834,7 @@ static bool zend_try_compile_const_expr_resolve_class_name(zval *zv, zend_ast *c
 		case ZEND_FETCH_CLASS_DEFAULT:
 			ZVAL_STR(zv, zend_resolve_class_name_ast(class_ast));
 			return 1;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -2281,7 +2281,7 @@ static void zend_adjust_for_fetch_type(zend_op *opline, znode *result, uint32_t
 		case BP_VAR_UNSET:
 			opline->opcode += 5 * factor;
 			return;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -2444,7 +2444,7 @@ static inline void zend_update_jump_target(uint32_t opnum_jump, uint32_t opnum_t
 		case ZEND_JMP_FRAMELESS:
 			opline->op2.opline_num = opnum_target;
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -3594,7 +3594,7 @@ static void zend_compile_assign(znode *result, zend_ast *ast, bool stmt, uint32_
 				result->op_type = IS_UNUSED;
 			}
 			return;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -3750,7 +3750,7 @@ static void zend_compile_compound_assign(znode *result, zend_ast *ast) /* {{{ */
 			opline = zend_emit_op_data(&expr_node);
 			opline->extended_value = cache_slot;
 			return;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -5012,7 +5012,7 @@ static zend_result zend_compile_func_sprintf(znode *result, zend_ast_list *args)
 				case 'd':
 					zend_emit_op_tmp(&elements[placeholder_count], ZEND_CAST, &elements[placeholder_count], NULL)->extended_value = IS_LONG;
 					break;
-				EMPTY_SWITCH_DEFAULT_CASE();
+				default: ZEND_UNREACHABLE();
 			}
 
 			if (rope_elements == 0) {
@@ -5329,7 +5329,7 @@ static const char *zend_get_cstring_from_property_hook_kind(zend_property_hook_k
 			return "get";
 		case ZEND_PROPERTY_HOOK_SET:
 			return "set";
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 
@@ -5879,7 +5879,7 @@ static void zend_compile_unset(const zend_ast *ast) /* {{{ */
 			opline = zend_compile_static_prop(NULL, var_ast, BP_VAR_UNSET, false, false);
 			opline->opcode = ZEND_UNSET_STATIC_PROP;
 			return;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 /* }}} */
@@ -9465,7 +9465,7 @@ static void zend_compile_use_trait(const zend_ast *ast) /* {{{ */
 			case ZEND_AST_TRAIT_ALIAS:
 				zend_compile_trait_alias(adaptation_ast);
 				break;
-			EMPTY_SWITCH_DEFAULT_CASE()
+			default: ZEND_UNREACHABLE();
 		}
 	}
 }
@@ -9837,7 +9837,7 @@ static HashTable *zend_get_import_ht(uint32_t type) /* {{{ */
 				zend_hash_init(FC(imports_const), 8, NULL, str_dtor, 0);
 			}
 			return FC(imports_const);
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 
 	return NULL;
@@ -9853,7 +9853,7 @@ static char *zend_get_use_type_str(uint32_t type) /* {{{ */
 			return " function";
 		case ZEND_SYMBOL_CONST:
 			return " const";
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 
 	return " unknown";
@@ -10219,7 +10219,7 @@ static bool zend_try_ct_eval_magic_const(zval *zv, const zend_ast *ast) /* {{{ *
 				ZVAL_EMPTY_STRING(zv);
 			}
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 
 	return 1;
@@ -10961,7 +10961,7 @@ static void zend_compile_assign_coalesce(znode *result, zend_ast *ast) /* {{{ */
 			zend_emit_op_data(&default_node);
 			assign_node = var_node_w;
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 
 	opline = zend_emit_op_tmp(NULL, ZEND_QM_ASSIGN, &assign_node, NULL);
@@ -11181,7 +11181,7 @@ static void zend_compile_isset_or_empty(znode *result, const zend_ast *ast) /* {
 			opline = zend_compile_static_prop(result, var_ast, BP_VAR_IS, false, false);
 			opline->opcode = ZEND_ISSET_ISEMPTY_STATIC_PROP;
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 
 	result->op_type = opline->result_type = IS_TMP_VAR;
@@ -11697,7 +11697,7 @@ static void zend_compile_const_expr_class_name(zend_ast **ast_ptr) /* {{{ */
 		case ZEND_FETCH_CLASS_STATIC:
 			zend_error_noreturn(E_COMPILE_ERROR,
 				"static::class cannot be used for compile-time class name resolution");
-		EMPTY_SWITCH_DEFAULT_CASE()
+		default: ZEND_UNREACHABLE();
 	}
 }
 
@@ -11805,7 +11805,7 @@ static void zend_compile_const_expr_fcc(zend_ast **ast_ptr)
 		case ZEND_AST_STATIC_CALL:
 			args_ast = &(*ast_ptr)->child[2];
 			break;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 	if ((*args_ast)->kind != ZEND_AST_CALLABLE_CONVERT) {
 		zend_error_noreturn(E_COMPILE_ERROR, "Constant expression contains invalid operations");
@@ -11843,7 +11843,7 @@ static void zend_compile_const_expr_fcc(zend_ast **ast_ptr)
 			}
 			break;
 		}
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 }
 

Zend/zend_compile.h

@@ -430,7 +430,7 @@ static zend_always_inline uint32_t zend_visibility_to_set_visibility(uint32_t vi
 			return ZEND_ACC_PROTECTED_SET;
 		case ZEND_ACC_PRIVATE:
 			return ZEND_ACC_PRIVATE_SET;
-		EMPTY_SWITCH_DEFAULT_CASE();
+		default: ZEND_UNREACHABLE();
 	}
 }