Build fails on macOS if qt6 is installed

[elsiehupp]

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Expected behaviour

Build should succeed if the prerequisites are installed, regardless of whether additional packages are installed.

Actual behaviour

If Qt 6 is installed in addition to Qt 5, the build process will use it instead, leading to a number of compiler errors.

Steps to reproduce

1. Follow the official macOS build instructions (which, incidentally, I personally wrote like a year ago).
2. There will be a bunch of compile errors.

Note that the build will still fail even if Qt 5 is installed alongside Qt 6.

Workaround

I have confirmed that this issue can be mitigated by manually uninstalling Qt 6. First, install Qt 5 with the following command:

brew install qt5

Then uninstall Qt 6 with the following:

brew remove qt6

You may get a warning if Qt 6 is a dependency for another package, and while you can run brew uninstall --ignore-dependencies qt6 to override the warning, it will break the other package until you reinstall Qt 6 (which in turn will break the Nextcloud build process again—yay!).

Note: the build instructions say to install the prerequisites as follows:

% brew install git qt qtkeychain cmake openssl glib cmocka

However, at some point in the past year the qt formula on Homebrew changed from being an alias to qt@5 to being an alias to qt@6. So in addition to the user needing to run brew install qt5 and brew remove qt6 the macOS build instructions should probably be updated so that they no longer install Qt 6 by default.

I got this workaround from gnuradio/gnuradio#4578.

Client configuration

Client version: Git branch master
Operating system: macOS Monterey 12.1 (21C52)

Error output

(Everything above this works.)

[  9%] Building CXX object src/libsync/CMakeFiles/nextcloudsync.dir/nextcloudsync_autogen/mocs_compilation.cpp.o
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/mocs_compilation.cpp:2:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/moc_abstractnetworkjob.cpp:10:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/../../../../../src/libsync/abstractnetworkjob.h:19:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/QObject:1:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/qobject.h:46:
In file included from /usr/local/include/QtCore/qobjectdefs.h:48:
In file included from /usr/local/include/QtCore/qnamespace.h:44:
/usr/local/include/QtCore/qglobal.h:96:6: error: "Qt requires a C++17 compiler"
#    error "Qt requires a C++17 compiler"
     ^
/usr/local/include/QtCore/qglobal.h:773:43: error: no template named 'is_arithmetic_v' in namespace 'std'; did you mean 'is_arithmetic'?
         typename = std::enable_if_t<std::is_arithmetic_v<T> && std::is_arithmetic_v<U> &&
                                     ~~~~~^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/type_traits:1117:50: note: 'is_arithmetic' declared here
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_arithmetic
                                                 ^
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/mocs_compilation.cpp:2:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/moc_abstractnetworkjob.cpp:10:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/../../../../../src/libsync/abstractnetworkjob.h:19:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/QObject:1:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/qobject.h:46:
In file included from /usr/local/include/QtCore/qobjectdefs.h:48:
In file included from /usr/local/include/QtCore/qnamespace.h:44:
/usr/local/include/QtCore/qglobal.h:773:70: error: no template named 'is_arithmetic_v' in namespace 'std'; did you mean 'is_arithmetic'?
         typename = std::enable_if_t<std::is_arithmetic_v<T> && std::is_arithmetic_v<U> &&
                                                                ~~~~~^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk/usr/include/c++/v1/type_traits:1117:50: note: 'is_arithmetic' declared here
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_arithmetic
                                                 ^
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/mocs_compilation.cpp:2:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/moc_abstractnetworkjob.cpp:10:
In file included from /Users/elsiehupp/Repositories/nextcloud-desktop/build/src/libsync/nextcloudsync_autogen/EWIEGA46WW/../../../../../src/libsync/abstractnetworkjob.h:19:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/QObject:1:
In file included from /usr/local/opt/qt@5/lib/QtCore.framework/Headers/qobject.h:46:
In file included from /usr/local/include/QtCore/qobjectdefs.h:48:
In file included from /usr/local/include/QtCore/qnamespace.h:44:
/usr/local/include/QtCore/qglobal.h:773:87: error: expected '>'
         typename = std::enable_if_t<std::is_arithmetic_v<T> && std::is_arithmetic_v<U> &&
                                                                                      ^
/usr/local/include/QtCore/qglobal.h:773:37: note: to match this '<'
         typename = std::enable_if_t<std::is_arithmetic_v<T> && std::is_arithmetic_v<U> &&
                                    ^
/usr/local/include/QtCore/qglobal.h:773:65: error: expected ',' or '>' in template-parameter-list
         typename = std::enable_if_t<std::is_arithmetic_v<T> && std::is_arithmetic_v<U> &&
                                                                ^
/usr/local/include/QtCore/qglobal.h:774:66: error: expected unqualified-id
                                     std::is_floating_point_v<T> == std::is_floating_point_v<U> &&
                                                                 ^
/usr/local/include/QtCore/qglobal.h:785:35: error: no type named 'Promoted' in namespace 'QTypeTraits::detail'
using Promoted = typename detail::Promoted<T, U>::type;
                 ~~~~~~~~~~~~~~~~~^~~~~~~~
/usr/local/include/QtCore/qglobal.h:785:43: error: expected ';' after alias declaration
using Promoted = typename detail::Promoted<T, U>::type;
                                          ^
/usr/local/include/QtCore/qglobal.h:797:31: error: no template named 'Promoted' in namespace 'QTypeTraits'
constexpr inline QTypeTraits::Promoted<T, U> qMin(const T &a, const U &b)
                 ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:799:28: error: no template named 'Promoted' in namespace 'QTypeTraits'
    using P = QTypeTraits::Promoted<T, U>;
              ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:800:5: error: unknown type name 'P'
    P _a = a;
    ^
/usr/local/include/QtCore/qglobal.h:801:5: error: unknown type name 'P'
    P _b = b;
    ^
/usr/local/include/QtCore/qglobal.h:805:31: error: no template named 'Promoted' in namespace 'QTypeTraits'
constexpr inline QTypeTraits::Promoted<T, U> qMax(const T &a, const U &b)
                 ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:807:28: error: no template named 'Promoted' in namespace 'QTypeTraits'
    using P = QTypeTraits::Promoted<T, U>;
              ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:808:5: error: unknown type name 'P'
    P _a = a;
    ^
/usr/local/include/QtCore/qglobal.h:809:5: error: unknown type name 'P'
    P _b = b;
    ^
/usr/local/include/QtCore/qglobal.h:813:31: error: no template named 'Promoted' in namespace 'QTypeTraits'
constexpr inline QTypeTraits::Promoted<T, U> qBound(const T &min, const U &val, const T &max)
                 ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:816:31: error: no template named 'Promoted' in namespace 'QTypeTraits'
constexpr inline QTypeTraits::Promoted<T, U> qBound(const T &min, const T &val, const U &max)
                 ~~~~~~~~~~~~~^
/usr/local/include/QtCore/qglobal.h:819:31: error: no template named 'Promoted' in namespace 'QTypeTraits'
constexpr inline QTypeTraits::Promoted<T, U> qBound(const U &min, const T &val, const T &max)
                 ~~~~~~~~~~~~~^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
make[2]: *** [src/libsync/CMakeFiles/nextcloudsync.dir/nextcloudsync_autogen/mocs_compilation.cpp.o] Error 1
make[1]: *** [src/libsync/CMakeFiles/nextcloudsync.dir/all] Error 2
make: *** [all] Error 2

(After this the build process exits back to the command prompt.)

[github-actions]

This bug report did not receive an update in the last 4 weeks. Please take a look again and update the issue with new details, otherwise the issue will be automatically closed in 2 weeks. Thank you!

[github-actions]

This bug report is getting automatically closed due to no answer since the issue has been staled. Thank you!

[github-actions]

This bug report is getting automatically closed due to no answer since the issue has been staled. Thank you!

[github-actions]

This bug report did not receive an update in the last 4 weeks. Please take a look again and update the issue with new details, otherwise the issue will be automatically closed in 2 weeks. Thank you!

[elsiehupp]

Still waiting...

[camilasan]

Still waiting...

We still need to make changes so we can use Qt6.

I will close this one in favor of #4461.