Re: [PATCH 08/10] cmake (Windows): initialize vcpkg/build dependencies automatically

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Sibi,

On Wed, 30 Sep 2020, Sibi Siddharthan wrote:

> On Fri, Sep 25, 2020 at 7:58 PM Johannes Schindelin via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> >
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > The idea of having CMake support in Git's source tree is to enable
> > contributors on Windows to start contributing with little effort. To
> > that end, we just added some sensible defaults that will let users open
> > the worktree in Visual Studio and start building.
> >
> > This expects the dependencies (such as zlib) to be available already,
> > though. If they are not available, we expect the user to run
> > `compat/vcbuild/vcpkg_install.bat`.
> >
> > Rather than requiring this step to be manual, detect the situation and
> > run it as part of the CMake configuration step.
> >
> > This concludes our journey to make it as effortless as possible to start
> > developing Git in Visual Studio: all the developer needs to do is to
> > clone Git's repository, open the worktree via `File>Open>Folder...` and
> > wait for CMake to finish configuring.
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  contrib/buildsystems/CMakeLists.txt | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
> > index d21849b730..1eaeb8b8e0 100644
> > --- a/contrib/buildsystems/CMakeLists.txt
> > +++ b/contrib/buildsystems/CMakeLists.txt
> > @@ -42,6 +42,10 @@ cmake_minimum_required(VERSION 3.14)
> >  set(CMAKE_SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR}/../..)
> >  if(WIN32)
> >         set(VCPKG_DIR "${CMAKE_SOURCE_DIR}/compat/vcbuild/vcpkg")
> > +       if(NOT EXISTS ${VCPKG_DIR})
> > +               message("Initializinge vcpkg and building the Git's dependencies (this will take a while...)")
> > +               execute_process(COMMAND ${CMAKE_SOURCE_DIR}/compat/vcbuild/vcpkg_install.bat)
> > +       endif()
> >         list(APPEND CMAKE_PREFIX_PATH "${VCPKG_DIR}/installed/x64-windows")
> >
> >         # In the vcpkg edition, we need this to be able to link to libcurl
> > --
> > gitgitgadget
> >
>
> After reading the patch series I seem to get to feeling that people on
> Windows are being nudged to use Visual Studio and vcpkg.
> Although they are great tools, when I want to specify my own libraries
> I don't see an option here.
> I think we need to define a variable, which this conditional block
> uses, which is set to true if we are using a Visual Studio Generator.
> We also need a way to override this option if needed.
> If this variable(explained above) is not set or false or OFF, we defer
> building vcpkg libraries. This can also save time in the case
> when we already have the dependencies(libraries) and just want to
> point to them instead of building with vcpkg.
> I also see that people who use gcc(MinGW) are left out. I think we
> also need to set the supported compiler(s) here before executing
> vcpkg_install.bat. People who use gcc would need to point to their own
> libraries with CMAKE_PREFIX_PATH.

Good points, even if our current CMake push really tries to cater only to
Visual Studio (or at least, MS Visual C) users.

I added a further guard to the conditional: `MSVC` needs to be true. This
makes sense, as our current support for MSVC/Visual Studio hinges on
having vcpkg build the dependencies, we simply do not support anything
else. (And it would be easy enough for a proficient Visual Studio user to
_still_ override the vcpkg system with their own libraries, if they
really want to make that work.)

Thanks,
Dscho