[CMake] Problem with circular dependencies

[Dmytro Ovdiienko]

Hello Tyler,

Please find my comments below.

2009/5/28 Tyler Roscoe <tyler at cryptio.net>

> On Thu, May 28, 2009 at 08:56:04PM +0300, Dmytro Ovdiienko wrote:
> > 1. We have two projects A and B.
> > 2. Project A is stored to <root>/A
> > 3. Project B is stored to <root>/B
> > 4. Project A depends on B.
> > 5. Project B depends on A. (please don't ask me why:) )
> > 6. There is CMakeLists.txt in the <root>
>
> If A and B really depend on each other, I don't know how you would ever
> expect to build them, nor how you would expect CMake to handle this
> case.
>

That was just a sample. CMake  can build it correctly, if you specify full
path to the include directlry.

If you root CMakeLists.txt declares ROOT_PRJ you can write following in the
A project.

INCLUDE_DIRECTORIES(
  ${ROOT_PRJ_SOURCE_DIR}/B
 )

And following in the B project

INCLUDE_DIRECTORIES(
  ${ROOT_PRJ_SOURCE_DIR}/A
 )


>
> But from your Lists below it appears that they don't really depend on
> one another, in a "target A must be built before target B" sense, but
> simply that they use headers from each other's source directories?
>

A and B are static libraries. The order static libraries building has no
mater.



> > #####################################
> > # Project A
> > #####################################
> > SET (PROJECT_NAME A )
> > PROJECT (${PROJECT_NAME})
> >
> > INCLUDE_DIRECTORIES(
> >   ${B_SOURCE_DIR}
> > )
> >
> > FILE (GLOB ${PROJECT_NAME}_SOURCE_LIST
> >     *.cpp
> > )
> >
> > ADD_LIBRARY (${PROJECT_NAME} ${${PROJECT_NAME}_SOURCE_LIST})
> >
> > #####################################
> > # Project B
> > #####################################
> > SET (PROJECT_NAME B )
> > PROJECT (${PROJECT_NAME})
> >
> > INCLUDE_DIRECTORIES(
> >   ${A_SOURCE_DIR}
> > )
> >
> > FILE (GLOB ${PROJECT_NAME}_SOURCE_LIST
> >     *.cpp
> > )
> >
> > ADD_LIBRARY (${PROJECT_NAME} ${${PROJECT_NAME}_SOURCE_LIST})
> >
> >
> > And now we generate the project files and check Additional Includes
> > Directories of the A project.
> >
> > Expected it is equal to <root>/B.
> > But in fact it is empty.
>
> Is ${B_SOURCE_DIR} defined in the CMakeLists for project A?
>

It is defined if B folder is processed before A folder. But then
A_SOURCE_DIR is not defined in the B project (circular dependency)


>
> > The other side of this problem is you have to write ADD_SUBDIRECTORY
> > commands in specific order. IMHO it is inconvenient.
>
> CMakeLists are essentially a scripting language, so of course order
> matters. What would you propose instead?
>

But... why does TARGET_LINK_LIBRARIES work correctly? You can pass not
loaded-yet project name to TARGET_LINK_LIBRARIES.


>
> tyler
>
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