Download and install Cygwin : https://www.cygwin.com/setup-x86_64.exe Install it and and install the following packages : flex bison curl git unzip
Download and install last stable release of CMake : https://cmake.org/download/
I think we don't need to install git with Windows installer because we already have it with cygwin but I failed to clone https repo and I don't know which cygwin package a need to install.
Download Visual Studio 2019 Community : https://my.visualstudio.com/Downloads?q=visual%20studio%202019&wt.mc_id=o~msft~vscom~older-downloads Install the workload C++ Desktop development
Download and install OSGeo4w v2 : http://download.osgeo.org/osgeo4w/v2/osgeo4w-setup.exe
From a new cygwin console:
git clone https://github.com/jef-n/OSGeo4W.git
cd OSGeo4W/src/qgis-dev/osgeo4w
export OSGEO4W_REP=/cygdrive/C/OSGeo4W
# In order to set VCSDK correctly, take a look of the folder name in C:\Program Files (x86)\Windows Kits\10\Lib
export VCSDK=10.0.19041.0
# Comment line 112 to 116 of the package.sh file, associated to grass (I imagine there is something more to be done to make this lines work)
./package.shto start the program, you then need to copy the directory C:\cygwin64\home\Julien\OSGeo4W\src\qgis-dev\osgeo4w to C:\cygwin64\home\Julien\OSGeo4W\src\qgis-dev\osgeo4w\osgeo4w and modify qgis-dev.bat script in bon dir to change the start line with this
start "QGIS" /B "%OSGEO4W_ROOT%\apps\qgis-dev\bin\qgis.exe" %*
In package.sh, replace Ninja with Visual Studio 16 2019 in the CMake command call and add "exit 0" just after, then call package.sh script.
Then from a new cmd interface
cd C:\cygwin64\home\Julien\OSGeo4W\src\qgis-dev\osgeo4w\build
call ../osgeo4w/bin/o4w_env.bat
"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\devenv.exe" qgis.slnYou can now build your QGIS target inside Visual Studio 2019
Thanks you a lot @troopa81!
Building QGIS on Windows is definitively lacking of a good and shared documentation! Your notes are enlightening a dark box!