How do I get generated files to be built first?

Usage
1

I have a series of files include/openssl/foo.gen that have a custom command to build {build-dir}include/openssl/foo.h. And foo.h is include’d in various source files. How do I ensure that the step runs before compiling bar.c ? I thought it would come for free with dependency building, but that doesn’t seem to be done. Thanks.

2

Add the generated headers with target_sources()
If possible use FILE_SET HEADER

3

Thanks, but what path do I use?
In the top-level CMakeLists I have
foreach (f ${GENHEADERS}) # openssl/crypto.h, etc …
set(in “include/${f}.in”)
set(out “${CMAKE_BINARY_DIR}/include/${f}”)
add_custom_command(COMMENT “Generating ${out}”
OUTPUT “${out}” DEPENDS “${in}” ${mkhdr}
COMMAND ${PERL} ${mkhdr} ${in} ${out}
VERBATIM)
endforeach ()

In ssl/CMakeLists I have
add_executable(openssl)
target_sources(openssl PUBLIC ${APPSOURCE} ${CMAKE_BINARY_DIR}/include/openssl/crypto.h)
target_link_libraries(openssl crypto ssl)

I get the same error:
; mk openssl
[ 0%] Building C object ssl/CMakeFiles/ssl.dir/d1_lib.c.o
In file included from /home/rsalz/git/quictls/quictls/ssl/d1_lib.c:10:
/home/rsalz/git/quictls/quictls/include/internal/e_os.h:17:11: fatal error: openssl/crypto.h: No such file or directory
17 | # include <openssl/crypto.h>

^~~~~~~~~~~~~~~~~~

It’s not picking up the generated file as a dependency nor building it.

4

As I recommended, use FILE_SET HEADER, or set the needed include path yourself:

add_library(crypto)
target_sources(crypto PRIVATE ${CRYPTO_SOURCES} 
    PUBLIC
    FILE_SET public_headers
    TYPE HEADERS
    BASE_DIRS
         ${CMAKE_BINARY_DIR}/include # ....
    FILES
         ${CMAKE_BINARY_DIR}/include/openssl/crypto.h # ...
)

# later 
# ...
target_link_libraries(openssl PUBLIC crypto ssl)
5

I missed the FILE_SET. Thanks for your patience!

6

And it turns out the email I got sent cut off that key line! I’m good to go now, thanks again.

7

A further complication was that “normal” header file foo.h did a #include of generated file crypto.h, so I had to use add_custom_target that depended on all the generated files, and then use add_dependencies on the each target to generate the files. (I’m using 3.21, so couldn’t use FILE_SET)

8

There is no real reason to stay behind the future.

You may always install the newest version with:

pip install cmake
9

I’m using 3.21 because it’s what came on my Ubuntu VM and I since I’m aiming for enterprise users, “step 1: update cmake” isn’t appropriate IMO.

1 Like
10

Ubuntu – Informationen über Paket cmake in noble

11

Thanks for the info. We’re currently on 22.04 LTS, not yet the next LTS release which seems to be in development.