[Development] Qt 6 buildsystem support requirements

[Alexander Neundorf]

On 2018 M07 21, Sat 18:24:23 CEST Giuseppe D'Angelo via Development wrote:
> Il 21/07/2018 17:42, Jean-Michaël Celerier ha scritto:
> > Besides... why would it matter that they are implemented in C++ instead
> > of cmake-lang ? If anything, CMake's automoc is in my experience much
> > faster to process the whole repo.
> 
> Playing devil's advocate, please bear with me:
> 
> 
> Because it makes people worry that cmake-lang is too limited, and if you
> need to do certain things (*), you need to resort to patch the tool itself.
> 
> Which opens other sets of problems, such as:
> 
> * what are the things that I can do in cmake-lang and the things I can't
> do?

you can do almost everything in cmake-lang ;-)
By now, in 2018, most build-related challenges should have been taken care of 
in CMake.
I think the biggest issues are:
- IDE integration: cmake server mode is still relatively new and and I don't 
know exactly how powerful it currently is
- better documentation/tutorial especially for old vs. new-style cmake
- new technology that appaers with new operating system features etc. often 
needs a new cmake release

> * Does all of this imply having changes landing in CMake itself, or can
> one have some sort of plugin system so that a project can ship the CMake
> C++ plugins to build it?

there is intentionally no plugin system/public API in CMake, to keep changing 
the internals of cmake itself easy.
But really a lot can be done via cmake scripts.

> * If the former, what happens if my users are running a "slightly older"
> CMake that doesn't have my patches in it yet?

The older cmake will error out saying that the project requires a newer 
version of CMake.

Alex