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How to make CMake target executed whether specified file was changed?
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Closed 1 year ago.
I'm using a custom target in a CMake file of mine, which looks like this:
add_custom_target(generated_bar
COMMAND ${CMAKE_COMMAND} -DOUT=bar -P generate-bar.cmake
BYPRODUCTS bar
COMMENT "Generating bar from foo"
SOURCES foo)
This works fine for me, and bar gets generated. However, if I make generated_bar again - bar gets generated again, even though the source file foo has not changed.
Why is this happening?
Note: This question is related.
A custom target is always considered to be out of date, so its command always runs. However, that does not extend to its dependencies:
add_custom_command(
OUTPUT bar
COMMAND ${CMAKE_COMMAND} -DOUT=bar -P generate-bar.cmake
DEPENDS "${CMAKE_CURRENT_BINARY_DIR}/generate-bar.cmake" foo
COMMENT "Generating bar from foo"
)
add_custom_target(
generate_bar
DEPENDS "${CMAKE_CURRENT_BINARY_DIR}/bar"
)
You should think of a custom target as like a .PHONY rule in Make... it's there to help you sequence things or to provide special utilities as build rules (that are not "built" as part of ALL)
Related
This is a follow-up to How can I get a target's output-file's name during CMake's configuration phase (not the generation phase)?
I want to achieve something similar to the below:
add_custom_command(
OUTPUT ${CMAKE_BINARY_DIR}/to_zip/$<TARGET_FILE_NAME:Foo>
DEPENDS Foo
COMMAND ${CMAKE_COMMAND} -E copy $<TARGET_FILE:Foo>
${CMAKE_BINARY_DIR}/to_zip/$<TARGET_FILE_NAME:Foo>)
list(APPEND ALL_FILES_IN_TO_ZIP
${CMAKE_BINARY_DIR}/to_zip/$<TARGET_FILE_NAME:Foo>)
add_custom_command(
OUTPUT ${CMAKE_BINARY_DIR}/myzip.zip
DEPENDS ${ALL_FILES_IN_TO_ZIP}
COMMAND <zip everything up in ${CMAKE_BINARY_DIR}/to_zip>)
add_custom_target(create-zip DEPENDS ${CMAKE_BINARY_DIR}/to_zip/myzip.zip)
Basically, when I invoke the create-zip target, I want to copy a lot of files to ${CMAKE_BINARY_DIR}/to_zip, and then zip up everything in it. The issue with the above code is that I am not allowed to use target based generator expression for OUTPUT in add_custom_command, so the above code doesn't work. From the CMake docs:
New in version 3.20: Arguments to OUTPUT may use a restricted set of generator expressions. Target-dependent expressions are not permitted.
Is there a way to workaround this problem to make it work?
I'm pretty sure you don't need to use the name of the target's output file as the OUTPUT of your custom command which does the copy. All you're really using the OUTPUT field for is CMake's dependency mechanisms (where it tracks what things have changed and does things again if anything in DEPENDS has changed (modification time in the filesystem)). You can just create a dummy file that you touch (update the modification time for in the filesystem) whenever the target has changed and once its copy has been made.
set(targets target_foo target_bar target_baz)
foreach(target "${targets}")
set(indicator "${CMAKE_BINARY_DIR}/to_zip/rezip_indicators/${target}")
add_custom_command(
OUTPUT "${rezip_indicator_file}"
DEPENDS "${target}"
COMMAND "${CMAKE_COMMAND}" -E copy $<TARGET_FILE:${target}>
"${CMAKE_BINARY_DIR}/to_zip/$<TARGET_FILE_NAME:${target}>"
COMMAND "${CMAKE_COMMAND}" -E touch "${rezip_indicator_file}"
)
list(APPEND NEEDS_REZIP_INDICATOR_FILES "${rezip_indicator_file}")
endforeach()
add_custom_command(
OUTPUT "${CMAKE_BINARY_DIR}/myzip.zip"
DEPENDS "${NEEDS_REZIP_INDICATOR_FILES}"
COMMAND <zip everything up in ${CMAKE_BINARY_DIR}/to_zip>
)
add_custom_target(create-zip DEPENDS "${CMAKE_BINARY_DIR}/to_zip/myzip.zip")
Or something to that effect.
The indicator file will get its timestamp updated by the touch command in the custom command when the target file has changed. The target file and the needs-rezip indicator file get "synced" when the custom command runs, which will be whenever you run the buildsystem after the target has gotten rebuilt. At least- I'm pretty sure that's how things work.
In the build process, I set directories where I gather the build output of different sub-projects. The directories are set as :
set( CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG "${CMAKE_CURRENT_LIST_DIR}/../build/bin/debug" )
set( CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE "${CMAKE_CURRENT_LIST_DIR}/../build/bin/release" )
Now, I'd like to copy some files (a directory of qt plugins) to that directory dependent on the configuration which it is built for.
I tried:
# copy qt plugins
add_custom_command( TARGET mytarget POST_BUILD
COMMAND ${CMAKE_COMMAND} -E copy_directory
"${QT_DIR}/../../../plugins"
"${$<UPPER_CASE:CMAKE_RUNTIME_OUTPUT_DIRECTORY_$<CONFIG> >}/plugins"
COMMAND_EXPAND_LISTS)
thus, I try to build a string that equals the variable name and then try to expand that as described here: CMake interpret string as variable. In other words: I would like to have a generator expression that evaluates to the content of CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG or CMAKE_RUNTIME_OUTPUT_DIRECTOR_RELEASE dependent on the current build configuration.
However running cmake with the statement above results in an error:
"CMakeLists.txt:112: error: Syntax error in cmake code at [..] when parsing string ${$<UPPER_CASE:CMAKE_RUNTIME_OUTPUT_DIRECTORY_$<CONFIG> >}/plugins Invalid character ('<') in a variable name: '$'
So my question is, how can I use a generator-expression to access the corresponding variable? (Bonus question: is there another/better way to achieve the same goal?)
So my question is, how can I use a generator-expression to access the corresponding variable?
You cannot. There is currently (CMake <=3.23) no way to expand a variable whose name is determined by the value of a generator expression.
Bonus question: is there another/better way to achieve the same goal?
Yes, and you are almost there! You can use $<TARGET_FILE_DIR:...>:
add_custom_command(
TARGET mytarget POST_BUILD
COMMAND
${CMAKE_COMMAND} -E copy_directory
"${QT_DIR}/../../../plugins"
"$<TARGET_FILE_DIR:mytarget>/plugins"
VERBATIM
)
This works because TARGET_FILE_DIR evaluates to the actual directory containing the executable or library file for mytarget, no matter the active configuration, property values, etc.
Docs: https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html#genex:TARGET_FILE_DIR
CMAKE_RUNTIME_OUTPUT_DIRECTORY_<CONFIG> is already relative to the binary directory so you should not try to compute the binary directory in its definition. Also, it supports generator expressions. Thus, the following will be much more robust:
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "bin/$<LOWER_CASE:$<CONFIG>>"
CACHE STRING "Common output directory for runtime artifacts")
This has a bunch of concrete benefits:
No need to set CMAKE_RUNTIME_OUTPUT_DIRECTORY_DEBUG or CMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE
This will work for MinSizeRel and RelWithDebInfo, plus any custom configurations one might add down the line.
Since it's defined as a cache variable, it can be overridden for debugging / working around name clashes, etc.
A bit more context for (3): most CMAKE_* variables are intended to be either read-only or user-configurable (i.e. at the command line, from the GUI, etc.). Overriding their defaults via set(CACHE) is a polite compromise. A notable exception to this rule is the collection of Qt codegen flags (CMAKE_AUTO{MOC,RCC,UIC}). These must typically be set for the build to produce usable binaries.
For users that are using cmake 3.15 or later and are also using Ninja as a generator, I want to set the new JOB_POOL argument to some large add_custom_command() blocks. For other users, I want to keep my add_custom_command() the same (no JOB_POOL).
In earlier steps, I check the version and the generator and set ${JOB_POOLS} and I also set a variable such that users who should use a pool will see (something like):
For historical reasons, I leave this here, although #Tsyvarev
points out that this is the source of my problem!
The double-quotes are NOT wanted here!
set(USE_POOL "JOB_POOL pool_A")
Users that are not using a pool will not have that variable set.
Now how to leverage that variable in my custom command...?
1.) Generator expressions don't work, just including the text with the previous line...
add_custom_command(
...
$<USE_POOL>
)
2.) I can't seem to simply place the variable in the command, again just including the variable contents on the previous line. For example, when ${JOB_POOL} is set to the string "JOB_POOL pool_A", this code...
For historical reasons, I leave this here, although #Tsyvarev
points out that this is the source of my problem!
Don't use a STRING! No double-quotes!
add_custom_command(
OUTPUT foo
DEPENDS bar
# Comment line here...
${USE_POOL}
COMMAND
${CMAKE_COMMAND} -E ...
)
gives this error...
ninja: error: '../path/to/src/dir/JOB_POOL pool_A', needed by 'path/to/src/dir/foo', missing and no known rule to make it
It simply considers the ${JOB_POOL} string to be another dependency!
3.) I can't use the "APPEND" feature of add_custom_command(). It's just ignored...
if (${USE_POOL})
add_custom_command(
...
APPEND
JOB_POOL pool_A
)
endif()
The only thing that seems to work is to put an "if" around my
entire command, which offends my sensibility since I don't like to duplicate so much code...
if(${USE_POOL})
add_custom_command(
...many lines...
JOB_POOL pool_A
)
else()
add_custom_command(
...many lines...
)
endif()
Do you have a better idea...?
Here's a standalone example for #tsyvarev:
cmake_minimum_required(VERSION 3.15)
project foo
set_property(GLOBAL PROPERTY JOB_POOLS pool_A=2)
# For historical reasons, I leave this here, although #Tsyvarev
# points out that this is the source of my problem!
# Don't use a STRING! No double-quotes!
set(USE_POOL "JOB_POOL pool_A")
add_custom_command(
OUTPUT foo.out
DEPENDS foo.in
${USE_POOL}
COMMAND
${CMAKE_COMMAND} -E copy foo.in foo.out
COMMENT "Converting foo.in -> foo.out"
VERBATIM
)
add_custom_target(foo-out
DEPENDS foo.out
)
% cmake -GNinja .
% ninja foo-out
ninja: error: 'JOB_POOL pool_A', needed by 'foo.out', missing and no known rule to make it
It considers the string to be a dependency... If I move the USE_POOL to after the comment, it considers it part of the comment... If I move it to after the command, it considers it part of the command...
Your JOB_POOL option serves for the user's choice. You may create another variable which contains sequence of related parameters for add_custom_command:
if(JOB_POOL)
set(JOB_POOL_PARAMS JOB_POOL pool_A) # Will add 'JOB_POOL pool_A' sequence of params
else()
set(JOB_POOL_PARAMS) # Will add nothing
endif()
Then use new variable directly in add_custom_command call:
add_custom_command(
...
${JOB_POOL_PARAMS} # Will expand to additional parameters when needed
)
I am trying to generate file that depends on a set of files that can
change throughout different make invocations.
To understand it better, let's show you the code:
cmake_minimum_required(VERSION 2.8)
project(demo-one C)
add_custom_command(
OUTPUT
"${CMAKE_BINARY_DIR}/generated.c"
COMMAND
generate -o "${CMAKE_BINARY_DIR}/generated.c"
DEPENDS
"$(shell generate-dependencies-list)"
COMMENT
"Generating generated.c"
)
add_executable(main main.c "${CMAKE_BINARY_DIR}/generated.c")
So, I want to generate the file generated.c with the generate
command and this files needs to be regenerated when the files
specified by generated-dependencies-list command changes. As you may
notice, generated-dependencies-list can generate different set of
files throughout make invocations, so is not feasible to get
the result of generated-dependencies-list at configure time to then
pass the result to add_custom_command.
Actually the above code somewhat works, but it looks like a hack that
will only work for Makefile backend, also the make rule doesn't look
as what I'm expecting, after all, it's a hack:
generated.c: ../$(shell\ generate-dependencies-list)
Basically, I want this rule or something to get the same result:
generated.c: $(shell generate-dependencies-list)
Has CMake any feature to achieve this?
when the files specified by generated-dependencies-list command changes
If the output of the command generated-dependencies-list depends only on this script and script's parameters then you can just add this script to DEPENDS sub-option:
add_custom_command(
OUTPUT
"${CMAKE_BINARY_DIR}/generated.c"
COMMAND
"${CMAKE_CURRENT_LIST_DIR}/generate-dependencies-list"
COMMAND
generate -o "${CMAKE_BINARY_DIR}/generated.c"
DEPENDS
"${CMAKE_CURRENT_LIST_DIR}/generate-dependencies-list"
COMMENT
"Generating generated.c"
)
I have a CMake project with many subprojects.
Each of them can use a function I provide to generate a small text file with some certain information (by calling add_custom_command).
At the final step I'd like to combine all those files into one big text file.
I've created a custom command which searches for created files (all in one place) and merges them.
The problem is that I'd like to make this final step dependend on all of small steps being made in subprojects while I don't actually know how many files will be provided.
My final command looks like:
add_custom_command(OUTPUT combination.txt
COMMAND create combination.txt from all files from /path/)
and my create-small-text-file-for-each-subproject command looks like:
add_custom_command(OUTPUT /path/${sub_project_name}.txt
COMMAND create /path/${sub_project_name}.txt)
And when I create those small files I'd like to do something like to make "combination.txt" depend on /path/${sub_project_name}.txt
So I wish I could:
add_dependency(combination.txt /path/${sub_project_name}.txt)
However this only works for targets.
I've also tried to use set_source_files_properties with OBJECT_DEPENDS, but it seems to doesn't work (maybe its intend to be used with add_target's cpp files ?)
The last way to get it work I see is to use a cache variable which would accumulate all those small files paths and then use it like this:
add_custom_command(OUTPUT combination.txt
COMMAND create combination.txt from all files from /path/
DEPENDS ${all_small_files_list})
but this is the last thing I want to do.
Instead of using add_custom_command you could use add_custom_target with a correct dependency-definition (so that is it not built every time).
add_custom_target(project
COMMAND touch project.txt)
add_custom_target(project2
COMMAND touch project2.txt)
add_custom_target(combination
COMMAND cat project.txt project2.txt > combination.txt)
add_dependencies(combination project2)
add_dependencies(combination project)
add_executable(t t.c)
add_dependencies(t combination.txt)
Again: make sure you're using the DEPENDS argument of add_custom_target to create a real dependency chain so that a project-target and thus the combination-target gets out of date.
UPDATE: I was too premature. In fact cmake (at least up to 2.8.9) works as follows for dependencies: with a call to add_dependencies you cannot add a dependency which is the OUTPUT of a custom command IOW a (generated) file. With add_dependencies you can only add target as created by add_custom_target. However in a add_custom_target you can depend on an output of add_custom_command by using the DEPENDS-directive. That said this makes it work:
add_custom_command(OUTPUT project.txt
COMMAND uptime >> project.txt MAIN_DEPENDENCY t2.c)
add_custom_target(project DEPENDS project.txt)
add_custom_target(combination
COMMAND cat project.txt project2.txt > combination.txt)
add_dependencies(combination project)
This will make the combination target always be regenerated as it has no MAIN_DEPENDENCY or DEPENDS, but the usage of add_dependencies is allowed.