[CMake] Complex problem : recursive dependency configurations

[Robert Dailey]

As you know, in target_link_libraries(), you can specify "debug",
"optimized", or "general" to specify which configurations a library will be
applied to.

I have developed a system to allow dependencies to recursively add their
own dependencies. Suppose we have 3 targets:

A:
  libx
  liby
  libz

B:
  foo
  bar
  A

C:
  A
  B


Above, I list each target (A, B, C). The items under it are the targets it
depends on. So, target A depends on targets named libx, liby, and libz.
Similarly, target B depends on targets foo, bar, and A.

When I flatten out all of the dependencies for target C, it looks like so:

A
B
libx
liby
libz
foo
bar

This is pretty simple, but each dependency listed can also have a "debug",
"release", or "general" next to it. So let's use the same example as last
time, but introduce some of these prefixes:

A:
  libx
  liby
  libz

B:
  foo
  bar
  A

C:
  debug B

Above, since "B" is listed as "debug", library B and all of its
dependencies should only build in the debug configuration. So when we
flatten this out, you will see the following. Note that this flattened list
is what is sent to target_link_libraries()

debug B
debug foo
debug bar
debug A
debug libx
debug liby
debug libz

Now where this REALLY gets confusing, is when we have a mixture of
"conflicts", where the same target is specified as a dependency twice, but
with different configuration prefixes:


A:
  libx
  liby
  libz

B:
  foo
  bar
  A

C:
  optimized A
  debug B

In this case, A's dependencies are specified as optimized, but B's are
specified as debug, but B also depends on A, so A's dependencies would be
debug as well.

I need to implement a system that can handle such conflicts and resolve
them appropriately. For example, the way A's dependencies would be resolved
is by specifying them as "general" or no prefix at all, since the flattened
list includes them both in debug and optimized. So the final, flattened
list would look like:

A
debug B
libx
liby
libz
debug foo
debug bar

This is VERY complex and due to the way lists work and stuff, I can't think
of how to do this. Any tips?

---------
Robert Dailey
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