[CMake] Trouble with conditional generator expression inside target_link_libraries

[Björn Blissing]

Hello,

I am having trouble with a conditional generator expression inside target link libraries, which seems to expand incorrectly (or at least not the way I expect).

In short, I have a list of libraries that is found by a CMake module. The list is composed of a number of elements each preceded by "optimized" or "debug", depending on if there are built for release or debug. These libraries should only be included if a boolean is set to true. I have tried to write a generator expression which only includes the list of libraries if this variable is set. But it seems that this expression gets expanded wrong.

If I try to condense the problem to a minimum example, it would be something like this:

LIST(APPEND MYLIB_LIBRARIES optimized foo)
LIST(APPEND MYLIB_LIBRARIES debug foo_d)

TARGET_LINK_LIBRARIES(target_name
    PUBLIC
        $<$<BOOL:TRUE>:${MYLIB_LIBRARIES}>
)

This generator expression makes my target depend of the following libraries for the release build:
foo.lib & optimized.lib

And for the debug build:
foo_d.lib, foo.lib & optimized.lib

Which is obviously incorrect.

Replacing the generator expression with an IF-statement instead works. But I would like to stick to generator expressions if possible to keep my CMake code consistent.

How should I rewrite my generator expression to get the correct expansion?

Regards,
Björn

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