[vcpkg-tool] Allow overriding FETCHCONTENT_FULLY_DISCONNECTED

[Thomas1664]

Describe the pull request

• What does your PR fix?

  Fixes Forcing FETCHCONTENT_FULLY_DISCONNECTED is inappropriate and breaks projects using private registries #28386
  Alternative to [vcpkg_configure_cmake] Partially revert #26959 #28483

We can't simply remove FETCHCONTENT_FULLY_DISCONNECTED because this would lead to bugs for users that want to build on isolated machines. Therefore, we have to set this variable in vcpkg_configure_cmake() as well. Since using vcpkg_configure_cmake() is deprecated, it shouldn't break ports in private registries. If a user still needs FETCHCONTENT_FULLY_DISCONNECTED set to OFF, they can override it via OPTIONS.

[ras0219-msft]

While vcpkg_configure_cmake() is deprecated, that does not mean we can break existing ports. We must take #28483, which reverts the change only for vcpkg_configure_cmake().

However, we absolutely should support the override for vcpkg_cmake_configure() as you've done in this PR. I think @dg0yt's suggested improvement is best -- we need to move the vcpkg "preset" options above the user's supplied OPTIONS.

[Neumann-A]

VCPKG_CMAKE_CONFIGURE_OPTIONS is designed to override all settings. So I don't get why this is even needed.

[dg0yt]

VCPKG_CMAKE_CONFIGURE_OPTIONS is designed to override all settings. So I don't get why this is even needed.

IMO it is generally bad to override anything which is already passed explicitly in OPTIONS. Because this is the primary interface for this purpose.
VCPKG_CMAKE_CONFIGURE_OPTIONS is nice to have for use in triplet files.

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[Thomas1664]

We must take #28483, which reverts the change only for vcpkg_configure_cmake().

Why do we have to take #28483 before merging this PR? This would introduce a bug (see PR description above) until this PR gets merged.

[Cheney-W]

@Thomas1664 Could you please handle the conflicts?

[BillyONeal]

Thanks for your fix :). I merged Robert's change which had only baseline issues, merged that with this, and committed (as this has a green run).

[Thomas1664]

Thanks for your fix :). I merged Robert's change which had only baseline issues, merged that with this, and committed (as this has a green run).

@BillyONeal Now FETCHCONTENT_FULLY_DISCONNECTED is not enabled in vcpkg_configure_cmake. What's wrong with setting it on this one as well? one can override it just like with vcpkg_cmake_configure.

[BillyONeal]

What's wrong with setting it on this one as well?

It breaks backwards compatibility with old port versions.