[CMake] DEPENDS parameter of add_custom_target

[Craig Scott]

On Mon, Oct 7, 2019 at 9:32 PM Setzer Sebastian (CM-CI2/ECS2) via CMake <
cmake at cmake.org> wrote:

> Dear list,
> The manual says:
> https://cmake.org/cmake/help/latest/command/add_custom_target.html
> Reference files and outputs of custom commands created with
> add_custom_command() command calls in the same directory (CMakeLists.txt
> file). They will be brought up to date when the target is built.
> Use the add_dependencies() command to add dependencies on other targets.
>
> This is different from what the manual of add_custom_command says, and
> would be surprising for all users who only read the manual of
> add_custom_command and then think they know what the parameter means for
> add_custom_target.
>
> But on the other hand, when I test with this:
> --------------------------------------------------
> cmake_minimum_required (VERSION 3.14)
> project(dependency_test LANGUAGES)
>
> add_custom_target(T1
>                   COMMAND echo T1
>                   )
> add_custom_target(T2
>                   COMMAND echo T2
>                   DEPENDS T1
>                   )
>
> # cmake -GNinja -B build .
> # ninja T2
> --------------------------------------------------
> Then T1 and T2 are built, so contrary to what the manual says, it seems to
> work.
>
> Is the manual just outdated (Maybe behavior has changed and only manual
> for add_custom_command has been updated)?
> Should it be the same as for add_custom_command, or are there really some
> differences?
>

As it happens, I just updated the docs for these in the last day or so. You
can find it in the not-yet-merged merge request here:

https://gitlab.kitware.com/cmake/cmake/merge_requests/3891

I wrote an explanation of the specific behavior of the dependencies in the
associated issue here:

https://gitlab.kitware.com/cmake/cmake/issues/19771#note_635547

There is a difference between the two, but it's subtle and specific to the
sort of scenario I mentioned in that issue comment.

-- 
Craig Scott
Melbourne, Australia
https://crascit.com

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