cmake: Include headers from every target_capnp_sources call in TARGET_headers #372

pull ryanofsky wants to merge 1 commits into bitcoin-core:master from ryanofsky:pr/capnphdrs changing 1 files +8 −0

ryanofsky commented at 3:36 AM on October 2, 2026: collaborator

target_capnp_sources creates a TARGET_headers custom target that other targets can depend on to make sure generated headers exist, but it only creates it on the first call for a target. Headers from later calls for the same target, for example optional schemas or schemas added with a different include prefix, are left out, so building TARGET_headers does not generate them.

Bitcoin Core runs into this in bitcoin/bitcoin#10102, which adds wallet.capnp to bitcoin_ipc with a second target_capnp_sources call (it is only built with the wallet enabled). The CI iwyu job only builds the *_headers targets before running IWYU, so wallet.capnp.h and wallet.capnp.proxy.h were never generated and files including them failed to compile, which fails the job since bitcoin/bitcoin#36235.

This PR makes later calls add a helper target for their headers and makes TARGET_headers depend on it, since dependencies cannot be added to an existing custom target.

cmake: Include headers from every target_capnp_sources call in TARGET_headers

target_capnp_sources creates a TARGET_headers custom target that other
targets can depend on to make sure generated headers exist, but it only did
this on the first call for a target. Headers from later calls for the same
target, for example optional schemas or schemas added with a different
include prefix, were left out, so building TARGET_headers did not generate
them.

Bitcoin Core hit this when its multiprocess PR added wallet.capnp to
bitcoin_ipc with a second call: the CI iwyu job only builds the *_headers
targets, so wallet.capnp.h and wallet.capnp.proxy.h were never generated and
files including them failed to compile.

On later calls, add a helper target for that call's headers and make
TARGET_headers depend on it, since dependencies cannot be added to an
existing custom target.

This change was written with Claude Opus 5.5 (1M context).

cdd4fdcc0a

DrahtBot commented at 3:36 AM on October 2, 2026: none



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in cmake/TargetCapnpSources.cmake:131 in cdd4fdcc0a

 126 | +    # for example to add optional schemas or schemas with a different include
 127 | +    # prefix. Dependencies can't be added to an existing custom target, so add
 128 | +    # these headers through a helper target that ${target}_headers depends on.
 129 | +    string(MD5 headers_hash "${CMAKE_CURRENT_SOURCE_DIR};${generated_headers}")
 130 | +    add_custom_target("${target}_headers_${headers_hash}" DEPENDS ${generated_headers})
 131 | +    add_dependencies("${target}_headers" "${target}_headers_${headers_hash}")

hebasto commented at 5:21 PM on October 3, 2026:

style nit: Quoting here seems unnecessary.

hebasto commented at 5:42 PM on October 3, 2026: member

Concept ACK.

For https://github.com/bitcoin/bitcoin/pull/10102, which requires CMake >=3.22, the following single line would work:

    target_sources(${target}_headers PRIVATE ${generated_headers})

For CMake <3.20, the following should work:

  if(NOT TARGET ${target}_headers)
    add_custom_target(${target}_headers)
  endif()
  set_property(TARGET ${target}_headers APPEND PROPERTY SOURCES ${generated_headers})

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hebasto

cmake: Include headers from every target_capnp_sources call in TARGET_headers #372

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