[jira] [Created] (THRIFT-4560) The logic of CMAKE_DEPENDENT_OPTION seems wrong and can break the build

["Mario Emmenlauer (JIRA)" <ji...@apache.org>]

Mario Emmenlauer created THRIFT-4560:
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             Summary: The logic of CMAKE_DEPENDENT_OPTION seems wrong and can break the build
                 Key: THRIFT-4560
                 URL: https://issues.apache.org/jira/browse/THRIFT-4560
             Project: Thrift
          Issue Type: Bug
          Components: Build Process
    Affects Versions: 1.0
            Reporter: Mario Emmenlauer


The cmake build uses {{CMAKE_DEPENDENT_OPTION}} in several places. But according to my understanding, the resulting logic is wrong and can lead to problems. Consider the following example for building with Qt4 or Qt5 from {{build/cmake/DefineOptions.cmake}}:
{{{
    find_package(Qt5 QUIET COMPONENTS Core Network)
    CMAKE_DEPENDENT_OPTION(WITH_QT5 "Build with Qt5 support" ON
                           "Qt5_FOUND" OFF)
}}}

If a user configures thrift with {{cmake -DWITH_QT5=ON}} but does not have Qt5 installed, they will not get an error. They will just get a warning that the option {{WITH_QT5}} was unused.
Furthermore, if the user must disable Qt5 (i.e. because its broken), then {{cmake -DWITH_QT5=OFF}} will **not** disable the search for Qt5. If the {{find_package(Qt5 QUIET COMPONENTS Core Network)}} fails in error, the build will fail, despite {{cmake -DWITH_QT5=OFF}}.



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