[CMake] Circular dependencies with Ninja, not with Unix Makefiles

[Robert Maynard]

Hi,

This is caused by doing an in source build and thereby causing the issue.
The custom command is outputting a file called 'foo', which is also the
chosen name of a target in the ninja file. All of this results in ninja
conflating the two and causing a circular dependency.

Your options are to not to in source builds, or to choose a different name
for your custom target.

On Thu, May 4, 2017 at 3:55 AM, Ignacio Fernández Galván via CMake <
cmake at cmake.org> wrote:

> Hello,
>
> I have a project where circular dependencies are generated when I use the
> Ninja generator, but not the default Unix Makefiles. I could create a
> minimal test like this:
>
> $ cat CMakeLists.txt
> add_subdirectory (ext ${PROJECT_BINARY_DIR}/ext)
>
> $ cat ext/CMakeLists.txt
> set (OUT ${CMAKE_CURRENT_LIST_DIR})
>
> add_custom_command (OUTPUT ${OUT}/foo
>     COMMAND touch ${OUT}/foo
>     )
>
> add_custom_target (foo ALL
>     DEPENDS ${OUT}/foo
>     )
>
> add_custom_command (TARGET foo
>     POST_BUILD
>     COMMAND cp ${OUT}/foo ${CMAKE_BINARY_DIR}/foo
>     )
>
> $ touch ext/bar
>
> $ cmake -G Ninja .
> [...]
>
> $ ninja
> ninja: warning: multiple rules generate ext/foo. builds involving this
> target will not be correct; continuing anyway [-w dupbuild=warn]
> ninja: error: dependency cycle: ext/foo -> ext/CMakeFiles/foo.util ->
> ext/CMakeFiles/foo -> ext/foo
>
> I used a freshly compiled CMake 3.8 and the latest binary ninja from
> https://github.com/Kitware/ninja/releases.
>
> Ignacio
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