CMake config: version 8 is compatible with version 7

[dg0yt]

AFAIU curl version 8.0.0 does bring any breaking API changes. However, the change of the major version has the effect that the CMake config is not considered compatible for find_package(CURL 7.123 CONFIG), breaking downstream usage, e.g.
azure-core-cpp

CMake Error at D:/installed/x64-windows-static/share/curl/vcpkg-cmake-wrapper.cmake:11 (_find_package):
  Could not find a configuration file for package "CURL" that is compatible
  with requested version "7.44".

  The following configuration files were considered but not accepted:

    D:/installed/x64-windows-static/share/curl/CURLConfig.cmake, version: 8.0.0-DEV

kubernetes:

CMake Error at D:/installed/x64-windows-static/share/curl/vcpkg-cmake-wrapper.cmake:11 (_find_package):
  Could not find a configuration file for package "CURL" that is compatible
  with requested version "7.58.0".

  The following configuration files were considered but not accepted:

    D:/installed/x64-windows-static/share/curl/CURLConfig.cmake, version: 8.0.0-DEV

This PR changes the default version check to accept version 8 as a compatible major version if version 7 is requested.

[bagder]

Someone needs to help me with this. I don't understand the description nor the patch.

[jzakrzewski]

I understand the problematic but don't yet know, if this is how one should go about the fix.

Basically CMake has a concept of "compatible version". By default it's "same major version". Since curls' major changed, when looking for version like "7.44", "8.x.x" is deemed incompatible when using standard version-file.

[dg0yt]

Doc is there: https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-version-selection

For CMake config, it is up to the package to define what is a compatible version, through script code in the version cmake file. Based on the requested version from the find_package call, CMake sets some input variables for the version file, and it is up to the version file to decide.

CURL uses a CMake function to generate a version file with the "same major version" policy, i.e. any newer version is accepted if it is the same major version. e.g. 8.0.1 would satisfy the request for version 8.0.0 because 8.0.1 is newer and the major version is 8. But it wouldn't satisfy the request for 7.44 because it is a different major version.

This PR adds code before the actual version check which turns a request for 7.44 into a request for 8 by inspecting and modifying the version interface variables before passing control to the generated version check.

[dg0yt]

Alternatively one could generate the version checking code with the AnyNewerVersion policy, but this would change behaviour for find_package(CURL 6.12.3 CONFIG).

[jzakrzewski]

Yeah, AnyNewerVersion is not the way to go as it may have unintended consequences.
I think this change make sense as it is.

[bagder]

Thanks, both!