cmake: add ONLY_CAPNP target_capnp_sources option #230

1. 
   ryanofsky commented at 8:25 am on October 22, 2025: collaborator

   Make target_capnp_sources function take ONLY_CAPNP option to only add cap’n proto-generated files to the target library and not add libmultiprocess-generated ones.

   This is needed in https://github.com/bitcoin/bitcoin/pull/10102 to support building with ENABLE_IPC=ON and ENABLE_WALLET=OFF because libmultiprocess-generated wallet files wallet.capnp.proxy*.c++ can’t be built without causing link errors, while the wallet.capnp.c++ file is still necessary to build because it is referenced by init.capnp and node.capnp there.

2. cmake: add ONLY_CAPNP target_capnp_sources option

   Make `target_capnp_sources` function take `ONLY_CAPNP` option to only add cap'n
   proto-generated files to the target library and not add
   libmultiprocess-generated ones.
   
   This is needed in https://github.com/bitcoin/bitcoin/pull/10102 to support
   building with ENABLE_IPC=ON and ENABLE_WALLET=OFF because libmultiprocess-generated
   wallet files `wallet.capnp.proxy*.c++` can't be built without causing link
   errors, while the `wallet.capnp.c++` file is still necessary to build because
   it is referenced by `init.capnp` and `node.capnp` there.

   81c652687b
3. 
   DrahtBot commented at 8:25 am on October 22, 2025: none

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4. in cmake/TargetCapnpSources.cmake:119 in 81c652687b

   113@@ -111,5 +114,7 @@ function(target_capnp_sources target include_prefix)
   114   # dependencies explicitly because while cmake detect dependencies of non
   115   # generated files on generated headers, it does not reliably detect
   116   # dependencies of generated headers on other generated headers.
   117-  add_custom_target("${target}_headers" DEPENDS ${generated_headers})
   118+  if(NOT TARGET "${target}_headers")
   119+    add_custom_target("${target}_headers" DEPENDS ${generated_headers})
   120+  endif()
   

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   hebasto commented at 4:30 pm on November 4, 2025:

   These changes are reasonable on their own. Maybe split them into a separate commit?

   nit: I don’t think quoting is needed here.

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   ryanofsky commented at 1:44 pm on November 6, 2025:

   These changes are reasonable on their own. Maybe split them into a separate commit?

   nit: I don’t think quoting is needed here.

   These are good suggestions. Just to save effort I will leave this as-is for now but would welcome a followup to make quoting more consistent. I am a little confused by quoting rules in cmake, and am not sure if for example maybe quotes would be added around generated_headers if generated filenames could contain spaces.

5. hebasto approved
6. 
   hebasto commented at 4:31 pm on November 4, 2025: member

   ACK 81c652687b8dd60bc83d71a7381d16db1d746474, I have reviewed the code and it looks OK.
7. ryanofsky merged this on Nov 6, 2025
8. ryanofsky closed this on Nov 6, 2025

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Contributors
ryanofsky DrahtBot hebasto