refactor: Install headers into repo-equivalent directories.

[iphydf]

This allows code to be built from an un-installed toxcore repo the same way it's built from an installed toxcore. I.e. all #include directives will work the same inside the toxcore repo and on a system which has toxcore installed.

Previously, "toxcore/tox.h" was installed as "tox/tox.h", making make install a requirement for building any client code. Now, clients can be built directly from the repo source, which is especially nice for simple clients like echobots.

Output:

-- Installing: /usr/local/include/tox/tox.h
-- Installing: /usr/local/include/toxcore/tox.h
-- Installing: /usr/local/include/toxcore/tox_events.h
-- Installing: /usr/local/include/toxcore/tox_dispatch.h
-- Installing: /usr/local/include/toxcore/tox_private.h
-- Installing: /usr/local/include/tox/toxav.h
-- Installing: /usr/local/include/toxav/toxav.h
-- Installing: /usr/local/include/tox/toxencryptsave.h
-- Installing: /usr/local/include/toxencryptsave/toxencryptsave.h

---

This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.13%. Comparing base (ed2b60c) to head (1a98760).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2599      +/-   ##
==========================================
+ Coverage   73.06%   73.13%   +0.07%     
==========================================
  Files         149      149              
  Lines       30517    30517              
==========================================
+ Hits        22297    22319      +22     
+ Misses       8220     8198      -22     

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[nurupo]

Previously, "toxcore/tox.h" was installed as "tox/tox.h", making make install a requirement for building any client code. Now, clients can be built directly from the repo source, which is especially nice for simple clients like echobots.

1. Why exactly do we want to avoid calling make install on toxcore to build clients? Is it that troublesome to have toxcore installed before building a client?
   1. Even simple clients like echobot would still require that libsodium is installed, no? (or can libsodium be included as source too?)
2. Do we really want to commit to supporting clients building directly off the toxcore source code in addition to the installed prefix (binaries + include files)?
   1. Doesn't that restrict us from adding some logic to our build system that modifies the code at build time, for example template substitution?
3. Isn't it better to change the repository's file structure around instead of changing the /usr/local/include structure, which will affect (break) all downstream projects?
   1. I see that in this PR you have created tox/{tox.h, toxav.h, toxencryptsave.h} in the repository, which contain just the #include {toxcore/tox.h, toxav/toxav.h, toxencryptsave/toxencryptsave.h} line -- isn't that already enough for what you are trying to achieve, without having to change the /usr/local/include structure?
   2. Some projects, e.g. VLC, have include/ in their repository for files that define the public API. This is just one of the possible ways to re-arrange the files within the repository, but what do you think about it?

Feels a bit weird that a single libtoxcore library / the c-toxcore project, uses three separate /usr/local/include/{toxcore,toxav,toxencryptsave} namespaces, instead of using just one and subdirectoring it. This doesn't seem to be a common thing to do. Are there some precedents of other projects doing this?

[nurupo]

Sorry, misclicked, didn't mean to close.

[iphydf]

Previously, "toxcore/tox.h" was installed as "tox/tox.h", making make install a requirement for building any client code. Now, clients can be built directly from the repo source, which is especially nice for simple clients like echobots.

1. Why exactly do we want to avoid calling make install on toxcore to build clients? Is it that troublesome to have toxcore installed before building a client?

Yes, it's quite troublesome when developing toxcore together with a client. Iterating on both client and toxcore development is slowed down quite a bit by having to make install each time. I don't suffer from this myself, because I develop mostly using bazel.

1. Even simple clients like echobot would still require that libsodium is installed, no? (or can libsodium be included as source too?)

libsodium isn't co-developed with clients, so the above is less of an issue. libsodium also generally changes less, so installing it once is less overhead than installing toxcore many times as it's in active development.

2. Do we really want to commit to supporting clients building directly off the toxcore source code in addition to the installed prefix (binaries + include files)?

Yes. Until it's too much of a burden.

1. Doesn't that restrict us from adding some logic to our build system that modifies the code at build time, for example template substitution?

Yes, and that's quite intentional. We should stay away from build system integrated codegen as much as possible. Generating files and committing them to git is ok, we already do that for events, and we may do more of that as part of semfmt, but we should always in principle own all our code.

3. Isn't it better to change the repository's file structure around instead of changing the /usr/local/include structure, which will affect (break) all downstream projects?

Why is it better? This PR does not break any downstream projects.

1. I see that in this PR you have created tox/{tox.h, toxav.h, toxencryptsave.h} in the repository, which contain just the #include {toxcore/tox.h, toxav/toxav.h, toxencryptsave/toxencryptsave.h} line -- isn't that already enough for what you are trying to achieve, without having to change the /usr/local/include structure?

It's not quite enough, because one other things that this change enables is that toxav could include "../toxcore/tox.h" instead of re-declaring struct Tox with the ifndef thing around it (which is trouble for many reasons, not the least C++ modules and apigen).

2. Some projects, e.g. VLC, have include/ in their repository for files that define the public API. This is just one of the possible ways to re-arrange the files within the repository, but what do you think about it?

That's possible, but right now you can simply do tcc my_code.c $(find tox* -name "*.c") third_party/cmp/cmp.c) and have a working binary. That's really quite nice, and something that @irungentoo has always been doing and has made quite sure to always continue supporting (this is also why we committed apidsl outputs instead of build-system-ing them).

Feels a bit weird that a single libtoxcore library / the c-toxcore project, uses three separate /usr/local/include/{toxcore,toxav,toxencryptsave} namespaces, instead of using just one and subdirectoring it.

The 3 libraries are really quite separate libraries and should become even more separate. We're building a single .so for convenience (used to build multiple), but I can see a future in which toxav is maintained in a separate repo, build, install, etc (not necessarily in practice, but we should make it theoretically possible, so design decisions should move us towards that being possible).

This doesn't seem to be a common thing to do. Are there some precedents of other projects doing this?

Probably. I can't think of any right now, but I'm also not very interested in following precedents, and rather make logical decisions based on goals and requirements.

[zoff99]

@iphydf i think the autotools config was not updated to reflect the changes

[iphydf]

@iphydf i think the autotools config was not updated to reflect the changes

Yes that was intentional. Do you use the autotools build? I was keeping it around for unmaintained clients, so I didn't update it so there are fewer changes to those builds.