[CMake] DEPENDS parameter of add_custom_target

[Setzer Sebastian (CM-CI2/ECS2)]

Hi Craig,

On Mon, 7. Oct 2019 12:56 Craig Scott wrote:
> As it happens, I just updated the docs for these in the last day or so.

You mean you updated the docs of the two commands, but you did not update the docs of the DEPENDS parameter, right?

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

So the manual for the DEPENDS parameter of add_custom_target is outdated, but fixing it is not as easy as copying it from add_custom_command.

Regards,
Sebastian
 

From: Craig Scott <craig.scott at crascit.com> 
Sent: Montag, 7. Oktober 2019 12:56
To: Setzer Sebastian (CM-CI2/ECS2) <Sebastian.Setzer at de.bosch.com>
Cc: cmake at cmake.org
Subject: Re: [CMake] DEPENDS parameter of add_custom_target



On Mon, Oct 7, 2019 at 9:32 PM Setzer Sebastian (CM-CI2/ECS2) via CMake <mailto: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Is the manual just outdated (Maybe behavior has changed and only manual for add_custom_command has been updated)?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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