Vcpkg: Using VS2015 when VS2017 is available

[chrullrich]

I have both VS2015 and VS2017 installed and would like to have one vcpkg environment for each toolset. Is there a way to get vcpkg to use the older one? I have tried running it in a VS2015 developer command prompt; it still uses the newer compilers.

[ras0219-msft]

We don't currently have an easy, supported way to opt out of VS2017. We'd like to do better in the future, but for now the closest options are:

1. Set the VCPKG_PLATFORM_TOOLSET variable in a triplet. You can make a new triplet for this purpose by copying one of the existing ones (inside triplets\) and adding the line:

set(VCPKG_PLATFORM_TOOLSET "v140")

This will work for CMake-based ports that don't use Ninja and possibly others. Notably, this will _not_ change boost.

2. In your "VS2015" vcpkg enlistment, modify scripts\findVisualStudioInstallationInstances.ps1 to immediately return an empty string. This will "properly" hijack _all_ uses of VS2017, including the initial bootstrap of vcpkg.exe itself.

In the future, we would like to make option 1 above the official, supported way (and make it work for all portfiles).

[jacobblock]

Hi, is this still the case? I don't see any flexibility in picking a toolset during the bootstrap process. v140 is only searched if v141 isn't found in scripts\findVisualStudioInstallationInstances.ps1.

Thanks!

[ras0219-msft]

We don't currently have a way to opt-out from using v141 during the _bootstrap_ process, since it doesn't affect any of the produced libraries and we want the tool to be as fast as possible with the latest toolset 😄.

Could you detail a bit more about the issues you're having with using VS2017 while boostrapping vcpkg.exe?

[jacobblock]

Ah well then perhaps I have some other issue. I was basically setting VCPKG_PLATFORM_TOOLSET to v140 in my triplet file and getting an immediate build error with zlib. The build was still trying to be performed with VS2017 (and works if I don't specify the VCPKG_PLATFORM_TOOLSET). Forcing the bootstrap to find VS2015 instead of VS2017 fixed the error; perhaps I needed to do some more investigation if the bootstrap shouldn't impact the build process.

[traversaro]

Small note: given that backward compatibility of libraries generated with v141 with executable compiled with v140 is not guaranteed (see https://docs.microsoft.com/en-us/cpp/porting/binary-compat-2015-2017?view=vs-2017) this feature may be important to anyone that wants to build and distribute libraries that could be consumable by both VS2015 and VS2017.

[tnie]

@jacobblock

Ah well then perhaps I have some other issue. I was basically setting VCPKG_PLATFORM_TOOLSET to v140 in my triplet file and getting an immediate build error with zlib. The build was still trying to be performed with VS2017 (and works if I don't specify the VCPKG_PLATFORM_TOOLSET).

vcpkg install zlib:xxx using ninja.

About setting VCPKG_PLATFORM_TOOLSET

This will work for CMake-based ports that don't use Ninja and possibly others. Notably, this will _not_ change boost.