VSCode CMake Extension rebuild all project each time - c++

Question

I'm working on a project in C++ configured using CMake.
Each time I build the project, all files are recompiled, which is unbearable considering the time it takes.
With Visual Studio Code
I'm trying to use VSCode and the CMake Extension.
The CMake:Configure command works well and so does the CMake:Build command. It takes a lot of time to compile because I use highly templatized header-only libraries like Eigen3, Boost and CGAL, so I need to build a pre-compiled header. It build some librairies too. But it is normal that it takes time for a first compilation.
However, if I build the target again (without modifying anything in the code) the compilation is completely redone ! I just want the modified source files or librairies to be re-compiled. Or if a header in the list of pre-compiled headers is modified, only then should the pre-compiled headers be recompiled.
With Visual Studio 2019
I thought that VSCode didn't work with a concept of "project", and therefore had to reconfigure and recompile the whole project every time it was launched.
So I decided to generate a Visual Studio Solution with the CMake-GUI program and use Visual Studio 2019 instead of VSCode.
Now when I build a second time my project, nothing is recompiled and the program is directly lauched. Visual Studio say :
========== Build: 0 succeeded, 0 failed, 5 up-to-date, 0 skipped ==========
Wonderful!
Unfortunately not..., because if I modify a file, Visual Studio keeps telling me that everything is up-to-date and my modifications are not taken into account. I need to "Rebuild" the project so that everything will be recompiled, which does not solve my problem as it takes a lot of time.
Question
How to recompile only modified source files, librairies or pre-compiled headers (with VS Code, Visual Studio or both) ?
Plaform : Windows 10
Edit 15.04.21
I did some more methodical testing today to find out what the problem might be.
I used a very simple project to do the tests.
CMakeList.txt
cmake_minimum_required (VERSION 3.8)
project ("HelloCMake")
add_executable (HelloCMake "HelloCMake.cpp")
HelloCMake.cpp
#include <iostream>
int main() {
std::cout << "Hello CMake !" << std::endl;
return 0;
}
1. With VSCode and CMake Tools Extension
With the CMake Tools Extension, VSCode can configure and build a CMake project. It generate a Visual Studio Solution (.sln).
Build the target with CMake Tools Extension which makes VSCode to run the command :
cmake --build <PROJECT_DIR>/build --config Release --target HelloCMake --
/maxcpucount:14
The entire target is compiled
I build it again (without changes)
The target is completely recompiled again
The problem is that the target is completely recompiled, every time. I asked the question directly to the CMake Tools developers. GitHub Issue
2. .sln project generated by CMake (Visual Studio 2019)
I generated a Visual Studio Solution with CMake and open it.
I build my project HelloCMake
I do some modifications in source file
I build the project again, but Visual Studio never takes my modifications into account. The builds are always "up-to-date".
The problem is that Visual Studio does not take my changes into account. I have to rebuild the project, which takes too much time.
3. Directly open CMake project with Visual Studio 2019 (Ninja)
If you open a CMakeList.txt with Visual Studio 2019, it is not a Visual Studio Solution that is generated but a Ninja one.
It seems that this way the compilation works correctly !
According to this research, it is the CMake Tools Extension for VSCode as well as the Visual Studio Solution that cause problems.
I can't figure out why such a simple project doesn't compile properly with a Visual Studio Solution generated by CMake.