QNetworkInterface: replace CMake check for ifr_index with SFINAE

Detecting if a member exists is very easy and saves us from running the
test at CMake time. Saves about 350 ms.

Change-Id: I2b24e1d3cad44897906efffd178007fdcdd18e37
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 14 insertions, 36 deletions

diff --git a/src/network/configure.cmake b/src/network/configure.cmake
index 8a9ad6b614..b11a1ec8c8 100644
--- a/src/network/configure.cmake
+++ b/src/network/configure.cmake
@@ -37,22 +37,6 @@ freeifaddrs(list);
 "# FIXME: use: unmapped library: network
 )
 
-# ifr_index
-qt_config_compile_test(ifr_index
-    LABEL "ifr_index"
-    CODE
-"#include <net/if.h>
-
-int main(void)
-{
-    /* BEGIN TEST: */
-struct ifreq req;
-req.ifr_index = 0;
-    /* END TEST: */
-    return 0;
-}
-")
-
 # ipv6ifname
 qt_config_compile_test(ipv6ifname
     LABEL "IPv6 ifname"
@@ -212,10 +196,6 @@ qt_feature("getifaddrs" PUBLIC
     CONDITION UNIX AND NOT QT_FEATURE_linux_netlink AND TEST_getifaddrs
 )
 qt_feature_definition("getifaddrs" "QT_NO_GETIFADDRS" NEGATE VALUE "1")
-qt_feature("ifr_index" PRIVATE
-    LABEL "ifr_index"
-    CONDITION UNIX AND NOT QT_FEATURE_linux_netlink AND TEST_ifr_index
-)
 qt_feature("ipv6ifname" PUBLIC
     LABEL "IPv6 ifname"
     CONDITION UNIX AND NOT QT_FEATURE_linux_netlink AND TEST_ipv6ifname
diff --git a/src/network/kernel/qnetworkinterface_unix.cpp b/src/network/kernel/qnetworkinterface_unix.cpp
index fc508e7095..116e7d0ff5 100644
--- a/src/network/kernel/qnetworkinterface_unix.cpp
+++ b/src/network/kernel/qnetworkinterface_unix.cpp
@@ -52,7 +52,18 @@ static QHostAddress addressFromSockaddr(sockaddr *sa, int ifindex = 0, const QSt
         }
     }
     return address;
+}
 
+template <typename Req> [[maybe_unused]]
+static auto &ifreq_index(Req &req, std::enable_if_t<sizeof(std::declval<Req>().ifr_index) != 0, int> = 0)
+{
+    return req.ifr_index;
+}
+
+template <typename Req> [[maybe_unused]]
+static auto &ifreq_index(Req &req, std::enable_if_t<sizeof(std::declval<Req>().ifr_ifindex) != 0, int> = 0)
+{
+    return req.ifr_ifindex;
 }
 
 uint QNetworkInterfaceManager::interfaceIndexFromName(const QString &name)
@@ -71,11 +82,7 @@ uint QNetworkInterfaceManager::interfaceIndexFromName(const QString &name)
 
     uint id = 0;
     if (qt_safe_ioctl(socket, SIOCGIFINDEX, &req) >= 0)
-#  if QT_CONFIG(ifr_index)
-        id = req.ifr_index;
-#  else
-        id = req.ifr_ifindex;
-#  endif
+        id = ifreq_index(req);
     qt_safe_close(socket);
     return id;
 #else
@@ -95,12 +102,7 @@ QString QNetworkInterfaceManager::interfaceNameFromIndex(uint index)
     int socket = qt_safe_socket(AF_INET, SOCK_STREAM, 0);
     if (socket >= 0) {
         memset(&req, 0, sizeof(ifreq));
-#  if QT_CONFIG(ifr_index)
-        req.ifr_index = index;
-#  else
-        req.ifr_ifindex = index;
-#  endif
-
+        ifreq_index(req) = index;
         if (qt_safe_ioctl(socket, SIOCGIFNAME, &req) >= 0) {
             qt_safe_close(socket);
             return QString::fromLatin1(req.ifr_name);
@@ -185,11 +187,7 @@ static QNetworkInterfacePrivate *findInterface(int socket, QList<QNetworkInterfa
     // Get the interface index
 #  ifdef SIOCGIFINDEX
     if (qt_safe_ioctl(socket, SIOCGIFINDEX, &req) >= 0)
-#    if QT_CONFIG(ifr_index)
-        ifindex = req.ifr_index;
-#    else
-        ifindex = req.ifr_ifindex;
-#    endif
+        ifindex = ifreq_index(req);
 #  else
     ifindex = if_nametoindex(req.ifr_name);
 #  endif