From 31c232d3b7297cbc288815297c75968d5c80ac18 Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date: Mon, 3 Aug 2020 16:42:30 +0200
Subject: QList: properly declare operator== for MSVC

The operators were declared as friend function templates (so, free
functions in the Qt namespace). Unfortunately, the template argument
of the operators was also defaulted -- causing MSVC trying to
instantiate those functions at all times, causing interesting
recursive template instantiation errors (C2968). It's extremely
likely that we're facing a MSVC bug, but work around it by not
defaulting the template argument. This in turn requires to move
the function definition outside QList's definition, otherwise
an extern template definition (like the ones we have for QList<QPoint>)
would cause a template redefinition error...

Change-Id: If03477ac1fa0a72aa252bb9e08e2a19c2b517b1b
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/tools/qlist.h | 38 ++++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 443789b411..35dc286191 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -162,22 +162,10 @@ public:
 
     void swap(QList<T> &other) noexcept { qSwap(d, other.d); }
 
-    template <typename U = T>
-    friend QTypeTraits::compare_eq_result<U> operator==(const QList &l, const QList &r)
-    {
-        if (l.size() != r.size())
-            return false;
-        if (l.begin() == r.begin())
-            return true;
-
-        // do element-by-element comparison
-        return l.d->compare(l.begin(), r.begin(), l.size());
-    }
-    template <typename U = T>
-    friend QTypeTraits::compare_eq_result<U> operator!=(const QList &l, const QList &r)
-    {
-        return !(l == r);
-    }
+    template <typename U>
+    friend QTypeTraits::compare_eq_result<U> operator==(const QList<U> &l, const QList<U> &r);
+    template <typename U>
+    friend QTypeTraits::compare_eq_result<U> operator!=(const QList<U> &l, const QList<U> &r);
 
     qsizetype size() const noexcept { return d->size; }
     qsizetype count() const noexcept { return size(); }
@@ -792,6 +780,24 @@ size_t qHash(const QList<T> &key, size_t seed = 0)
     return qHashRange(key.cbegin(), key.cend(), seed);
 }
 
+template <typename U>
+QTypeTraits::compare_eq_result<U> operator==(const QList<U> &l, const QList<U> &r)
+{
+    if (l.size() != r.size())
+        return false;
+    if (l.begin() == r.begin())
+        return true;
+
+    // do element-by-element comparison
+    return l.d->compare(l.begin(), r.begin(), l.size());
+}
+
+template <typename U>
+QTypeTraits::compare_eq_result<U> operator!=(const QList<U> &l, const QList<U> &r)
+{
+    return !(l == r);
+}
+
 template <typename T>
 auto operator<(const QList<T> &lhs, const QList<T> &rhs)
     noexcept(noexcept(std::lexicographical_compare(lhs.begin(), lhs.end(),
-- 
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