D23551: CMake config files: use as min dep version the Qt version we built against

[Friedrich W. H. Kossebau]

kossebau created this revision.
kossebau added reviewers: Frameworks, aacid.
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REVISION SUMMARY
  Some developers have multiple versions of Qt installed on their system.
  And source code often has some version-dependent code paths, e.g. using
  newer API if found available. In that case the resulting build has an
  effective dependency on the Qt version built against.
  
  To properly reflect that, the Qt version set as minimally required version
  of the listed dependencies in the generated CMake config files should use
  that version instead.
  More, KXmlGui uses private API with Qt5::CorePrivate, so also future
  versions of Qt5::Core might not be compatible.
  
  While the current code of KXmlGui does not have such version dependent
  code variants, they are added now and then, so using the Qt version built
  against as minimally required dependency is a good default, and should not
  change anything for all the users with just one Qt version, and improve
  things for those with, catching bad mixes early in the build time.
  And given the use of private Qt::Core API, requiring exactly the same
  version by using "find_dependency(Qt5Core @USED_QT_VERSION@ EXACT)"
  should be more safe, even if the private API might be stable in reality
  for a set of versions.

TEST PLAN
  Generated CMake config files now uses with the find_dependency(Qt5) calls
  the version of the Qt KXmlGui was built against.

REPOSITORY
  R263 KXmlGui

BRANCH
  setusetqtversionasmindep

REVISION DETAIL
  https://phabricator.kde.org/D23551

AFFECTED FILES
  CMakeLists.txt
  KF5XmlGuiConfig.cmake.in

To: kossebau, #frameworks, aacid
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns
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