tests/extensions/extensions.proto

syntax = "proto2";

import 'alltypes.proto';

extend AllTypes {
    optional int32 AllTypes_extensionfield1 = 255 [default = 5];
}

message ExtensionMessage {
    extend AllTypes {
        optional ExtensionMessage AllTypes_extensionfield2 = 254;
        // required ExtensionMessage AllTypes_extensionfield3 = 253; // No longer allowed by protobuf 3
        repeated ExtensionMessage AllTypes_extensionfield4 = 252;
    }

    required string test1 = 1;
    required int32 test2 = 2;
}