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  1. Qt
  2. QTBUG-134683

Deprecated one argument version of qHash still required in qHashMulti

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Details

    • eb1342a3c (dev), db36fea29 (6.9), 1a580ca2a (dev)

    Description

      I was getting a weird compile error:

      FAILED: qtdeclarative/src/qmldom/CMakeFiles/QmlDomPrivate.dir/qqmldomreformatter.cpp.o 
/opt/homebrew/bin/ccache /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -DGL_SILENCE_DEPRECATION -DQMLDOM_LIBRARY -DQT_ASCII_CAST_WARNINGS -DQT_BUILDING_QT -DQT_BUILD_QMLDOM_LIB -DQT_CORE_LIB -DQT_DEPRECATED_WARNINGS -DQT_EXPLICIT_QFILE_CONSTRUCTION_FROM_PATH -DQT_LEAN_HEADERS=1 -DQT_MOC_COMPAT -DQT_NETWORK_LIB -DQT_NO_AS_CONST=1 -DQT_NO_CAST_TO_ASCII -DQT_NO_EXCEPTIONS -DQT_NO_FOREACH -DQT_NO_FOREACH=1 -DQT_NO_JAVA_STYLE_ITERATORS -DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT -DQT_NO_QASCONST -DQT_NO_QEXCHANGE -DQT_NO_QSNPRINTF -DQT_NO_QSNPRINTF=1 -DQT_NO_STD_FORMAT_SUPPORT -DQT_QMLCOMPILER_LIB -DQT_QMLINTEGRATION_LIB -DQT_QMLTOOLINGSETTINGS_LIB -DQT_QML_LIB -DQT_STRICT_QLIST_ITERATORS -DQT_USE_QSTRINGBUILDER -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qmldom/QmlDomPrivate_autogen/include -I/Users/sami/projects/qt-dom-build/qtbase/include -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlDom -I/Users/sami/projects/qt-dom/qtdeclarative/src/qmldom -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qmldom -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlDom/6.10.0 -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlDom/6.10.0/QtQmlDom -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qml -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQml/6.10.0 -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQml/6.10.0/QtQml -I/Users/sami/projects/qt-dom-build/qtbase/src/corelib -I/Users/sami/projects/qt-dom-build/qtbase/include/QtCore/6.10.0 -I/Users/sami/projects/qt-dom-build/qtbase/include/QtCore/6.10.0/QtCore -I/Users/sami/projects/qt-dom-build/qtbase/include/QtCore -I/Users/sami/projects/qt-dom-build/qtbase/lib/QtCore.framework/Headers -I/Users/sami/projects/qt-dom-build/qtbase/mkspecs/macx-clang -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQml -I/Users/sami/projects/qt-dom-build/qtbase/lib/QtQml.framework/Headers -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlIntegration -I/Users/sami/projects/qt-dom/qtdeclarative/src/qmlintegration -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qmlintegration -I/Users/sami/projects/qt-dom-build/qtbase/include/QtNetwork -I/Users/sami/projects/qt-dom-build/qtbase/lib/QtNetwork.framework/Headers -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qmlcompiler -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlCompiler/6.10.0 -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlCompiler/6.10.0/QtQmlCompiler -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlToolingSettings -I/Users/sami/projects/qt-dom-build/qtdeclarative/src/qmltoolingsettings -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlToolingSettings/6.10.0 -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlToolingSettings/6.10.0/QtQmlToolingSettings -I/Users/sami/projects/qt-dom-build/qtbase/include/QtQmlCompiler -I/Users/sami/projects/qt-dom-build/qtbase/lib/QtQmlCompiler.framework/Headers -fsanitize=address -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -std=gnu++17 -arch arm64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.2.sdk -mmacosx-version-min=12 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden -fcolor-diagnostics -F/Users/sami/projects/qt-dom-build/qtbase/lib  -Wall -Wextra -fapplication-extension -ftrivial-auto-var-init=pattern -fstack-protector-strong -fno-exceptions -MD -MT qtdeclarative/src/qmldom/CMakeFiles/QmlDomPrivate.dir/qqmldomreformatter.cpp.o -MF qtdeclarative/src/qmldom/CMakeFiles/QmlDomPrivate.dir/qqmldomreformatter.cpp.o.d -o qtdeclarative/src/qmldom/CMakeFiles/QmlDomPrivate.dir/qqmldomreformatter.cpp.o -c /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomreformatter.cpp
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomreformatter.cpp:4:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomreformatter_p.h:20:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomoutwriter_p.h:20:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomfilelocations_p.h:19:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomitem_p.h:20:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldom_utils_p.h:20:
In file included from /Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomconstants_p.h:20:
In file included from /Users/sami/projects/qt-dom-build/qtbase/include/QtCore/QObject:1:
In file included from /Users/sami/projects/qt-dom-build/qtbase/include/QtCore/qobject.h:1:
In file included from /Users/sami/projects/qt-dom/qtbase/src/corelib/kernel/qobject.h:13:
In file included from /Users/sami/projects/qt-dom-build/qtbase/include/QtCore/qlist.h:1:
In file included from /Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qlist.h:11:
In file included from /Users/sami/projects/qt-dom-build/qtbase/include/QtCore/qhashfunctions.h:1:
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhashfunctions.h:398:12: error: no matching function for call to 'qHashMulti'
  398 |     return qHashMulti(seed, key.first, key.second);
      |            ^~~~~~~~~~
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhash.h:59:16: note: in instantiation of function template specialization 'qHash<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>' requested here
   59 |         return qHash(t, seed);
      |                ^
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhash.h:688:37: note: in instantiation of function template specialization 'QHashPrivate::calculateHash<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>>' requested here
  688 |         size_t hash = QHashPrivate::calculateHash(key, seed);
      |                                     ^
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhash.h:1337:22: note: in instantiation of function template specialization 'QHashPrivate::Data<QHashPrivate::Node<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>, QQmlJS::Dom::CommentedElement>>::findBucket<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>>' requested here
 1337 |         auto it = d->findBucket(key);
      |                      ^
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhash.h:1353:16: note: in instantiation of function template specialization 'QHash<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>, QQmlJS::Dom::CommentedElement>::constFindImpl<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>>' requested here
 1353 |         return constFindImpl(key);
      |                ^
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhash.h:1357:16: note: in instantiation of member function 'QHash<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>, QQmlJS::Dom::CommentedElement>::find' requested here
 1357 |         return find(key);
      |                ^
/Users/sami/projects/qt-dom/qtdeclarative/src/qmldom/qqmldomcomments_p.h:259:45: note: in instantiation of member function 'QHash<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>, QQmlJS::Dom::CommentedElement>::constFind' requested here
  259 |         const auto it = m_commentedElements.constFind(CommentKey{n, location});
      |                                             ^
/Users/sami/projects/qt-dom/qtbase/src/corelib/tools/qhashfunctions.h:352:1: note: candidate template ignored: substitution failure [with T = <QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>]: no matching function for call to 'qHash'
  325 | qHashMulti(size_t seed, const T &... args)
      | ^
1 error generated.

      when trying to implement qHash() on one of my classes:

      // inside a private header
struct CommentAnchor
{
    qsizetype location = -1;
    friend bool comparesEqual(const CommentAnchor &a, const CommentAnchor &b) noexcept
    {
        return a.location == b.location;
    }
    Q_DECLARE_EQUALITY_COMPARABLE(CommentAnchor)
};

size_t qHash(const CommentAnchor &key, size_t seed) noexcept
{
    return qHashMulti(seed, key.location);
}

      Then, using QHash<std::pair<QQmlJS::AST::Node *, QQmlJS::Dom::CommentAnchor>, QQmlJS::Dom::CommentedElement> would lead to a compilation error. Using QHash<CommentAnchor, int> on the other hand compiles fine.
      It turned that out that QHashCombine is used by qMultiHash and uses the one argument versions of qHash. Adding a default argument to size_t qHash(const CommentAnchor &key, size_t seed = 0) noexcept made the compilation work again.

      Should the documentation at https://doc.qt.io/qt-6/qhash.html#the-hashing-function be fixed to mention the default argument, or should QHashCombine work with both one and two argument versions of qHash()?

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          resulted in

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-134690 qHashMulti and qHashMultiCommutative use the slower seed==0 algorithms for strings

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Open
          For Gerrit Dashboard: QTBUG-134683
          # Subject Branch Project Status CR V
          631512,10 qHashMulti: switch to passing the seed to the qHash() function in 7.0 dev qt/qtbase Status: NEW 0 0
          631472,3 QHash/Doc: be explicit that we need single-arg calls for qHashMulti() dev qt/qtbase Status: ABANDONED 0 0
          631509,3 qHash: break up the long line and add constexpr to the 1-arg catch-all dev qt/qtbase Status: MERGED +2 0
          631510,6 qHashMulti*: use the seed argument in the template and noexcept traits dev qt/qtbase Status: MERGED +2 0
          631511,2 qHashMultiCommutative: explicitly pass a zero seed dev qt/qtbase Status: ABANDONED 0 0
          631645,2 qHash: break up the long line and add constexpr to the 1-arg catch-all 6.9 qt/qtbase Status: MERGED +2 0
          632053,1 qHash: break up the long line and add constexpr to the 1-arg catch-all 6.9.0 qt/qtbase Status: ABANDONED +2 0

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              thiago Thiago Macieira
              sami.shalayel Sami Shalayel
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                Created:
                Updated:
                Resolved: