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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...

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1 回答 1

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您的JOB_POOL 选择服务于用户的选择。您可以创建另一个包含相关参数序列的变量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()

add_custom_command然后在调用中直接使用新变量：

add_custom_command(
  ...
  ${JOB_POOL_PARAMS} # Will expand to additional parameters when needed
)
于 2019-09-11T22:37:54.663 回答