CMake V2 + Cpp20 + (Almost) Header only

[BDoignies]

PR Description

A proposal for new CMake :

• New CMake minimum standard to 3.20 (at least 3.18 is recommended for FindPython)
• Installation mostly managed by CMake
• Move dependency management files to deps/folder
• Build target per folder (instead of globbing everything into the library)
• Removed unnecessary files

Header only changes:

• Previous .cpp files are copied to corresponding .ih files
• Global variables are now inline (requires C++17)
• Board was with its .cpp files; but it would probably be a good idea to use [email protected]:c-koi/libboard.git instead
• StdDefs are left in .cpp files for now, until their benefits for faster compilation are tested.

Standard to C++20, which has the following side effects on the code:

• Plain old enums are now inline constexpr : C++20 depreciates addition between enums + their namespace was not used
• Allocator for MPolynomial uses std::allocator_traits (C++20 removes most Alloc::* types...)

TODO :

• Update documentation (if necessary) for the new CMake (at least for linking with DGtal::DGtal)
• Validate CMake (my tests may have been too shallow, @dcoeurjo there was a problem with eigen if I am right)
• Test Python binding to see if building still works
• Test github actions

Sorry for the big PR, there was a bit too much cascading from what I thought were simple changes...

Checklist

• Unit-test of your feature with Catch.
• Doxygen documentation of the code completed (classes, methods, types, members...)
• Documentation module page added or updated.
• New entry in the ChangeLog.md added.
• No warning raised in Debug mode.
• All continuous integration tests pass (Github Actions)

[dcoeurjo]

Thanks for the edits

[dcoeurjo]

Before I can merge, can you please enhanced a bit the changelog?

[dcoeurjo]

• documentation ? At least the "building" module page

[BDoignies]

I enhanced a bit the changelog, is it sufficient ?

I made minor edits to moduleBuildDGtal.dox. But I do not know if anything more is needed... Everything is backward compatible; cmake commands, variable as well as C++ modules are the same.
The very few things that changed in the C++ code are:

• The allocators, and this is compatible with C++17 which was the previous minimal standard
• Warning fixes for examples and tests
• Removal of .cpp files (that are not included by any code anyway)

[BDoignies]

Btw : Shall I also clean the Codacy Static Code analysis?

[BDoignies]

Note: do not merge yet, there is no test / examples built by the PR. Wait a bit until I fixed DGTalTools / DGTal compilation with the new build system.

[BDoignies]

Hey @dcoeurjo

I fixed the compilation with DGTalTools.

Can you check that the new GH action suits you ? It checks compilation against the PR main2.0 of DGTalTools. The last commits also changes the Install.cmake and the CheckDependancies files (there was an issue with ITK including non-existent paths...).

[dcoeurjo]

All good thx!

[dcoeurjo]

I will merge this one to the main2.0 branch, thx @BDoignies

[dcoeurjo]

all good, merging, thx