Yes, changing the file ID will change the IDs of all types declared within,
unless they have explicitly declared their own IDs.
This only really matters if you are using RPC. Type IDs of interfaces are
part of the wire protocol. Type IDs of structs and enums are not really
used for anything, unless your application itself is using them. So it's
usually fine to change the type IDs of structs and enums.
So if you are only using serialization, not RPC, just go ahead and change
one of the file IDs. If you are using RPC, you will need to manually
override the IDs of the interface types in the file to keep them consistent
with what they were originally, and then you can change the file ID.
Of course, if both files happened to declare an interface with the same
name, those interfaces will have the same ID. In this case you have big
problems. You will have to make a breaking change to one of those two
interfaces.
-Kenton
On Tue, Aug 1, 2023 at 3:02 PM 'Ian Wilson' via Cap'n Proto <
capnproto@googlegroups.com> wrote:
> Hi all, apologies for jumping on this thread a few years later.
>
> I have a similar question: suppose I have 2 different capnp files with the
> same file ID.
>
> # file foo.capnp
> 0xabbeabbeabbeabbe;
>
> struct Foo {
> val @0 : UInt32;
> };
>
> # file bar.capnp
> 0xabbeabbeabbeabbe;
>
> struct Bar {
> val @1 : UInt32;
> };
>
> In my project, someone copy/pasted a file leading to two different schemas
> with the same file ID, 0xabbeabbeabbeabbe.
> I find a use case where I want to import both of these capnp files and
> their types into a new one - of course this runs into a compilation error
> with the duplicate IDs.
>
> I'd like to generate a new file ID to replace one of these, but I'm not
> sure if this would impact the autogenerated type IDs and break other
> systems.
>
> Would merely changing the file ID affect the types that already exist in
> these files?
>
> On Friday, November 27, 2020 at 7:27:09 AM UTC-8 ken...@cloudflare.com
> wrote:
>
>> On Wed, Nov 25, 2020 at 3:43 PM Matt Stern <mjst...@gmail.com> wrote:
>>
>>> When I try to run capnp compile, I get the following:
>>>
>>> error: Import failed: /capnp/java.capnp
>>>
>>
>> You will need to specify the same -I flags (import path) that you
>> normally specify to `capnp compile` when running the Java code generator.
>>
>> If I comment out the Java bits and just compile in C++ (which works for
>>> me), will this have any effect on the unique IDs for the structs in my
>>> schema file?
>>>
>>
>> No, the auto-generated IDs do not in any way depend on the contents of
>> other files. Auto-generated IDs are constructed by concatenating the parent
>> scope ID and the type name, and then taking a hash of that.
>>
>> -Kenton
>>
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