package/qt6: add qmake functionality

The qmake functionality had been missing due to the new host/target
build requirement, to get it working the main parts of the qt5 qmake
has been kept, we're still making our own device spec which we use to
run qmake with along with passing some additional device options for our
flags/cross-compiler.

qt6 has its own cross-compiling qmake wrapper script. However, that
hardcodes the paths to different places than where we have them.

QT6_INSTALL_QT_CONF will be used by the qmake-package infrastructure
later so it is put in qt6.mk, even though currently it's only used by
qt6base.

A big thanks to Angelo Compagnucci for the encouragement and testing.

[dario: fix HostData and add the target install dirs in qt.conf.in,
quote QT_QMAKE_DEVICE_OPTIONS, use TARGET_CFLAGS/TARGET_CXXFLAGS,
change the commit message]

Signed-off-by: Jesse Van Gavere <jesseevg@gmail.com>
Tested-by: Angelo Compagnucci <angelo@amarulasolutions.com>
Tested-by: Richard GENOUD <richard.genoud@bootlin.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>

package/qt6/qt6.mk

@@ -12,3 +12,15 @@ QT6_SITE = https://download.qt.io/archive/qt/$(QT6_VERSION_MAJOR)/$(QT6_VERSION)
 QT6_GIT = git://code.qt.io
 
 include $(sort $(wildcard package/qt6/*/*.mk))
+
+# The file "qt.conf" can be used to override the hard-coded paths that are
+# compiled into the Qt library. We need it to make "qmake" relocatable and
+# tweak the per-package install paths
+define QT6_INSTALL_QT_CONF
+	rm -f $(HOST_DIR)/bin/qt.conf
+	sed -e "s|@@HOST_DIR@@|$(HOST_DIR)|" -e "s|@@STAGING_DIR@@|$(STAGING_DIR)|" \
+		$(QT6BASE_PKGDIR)/qt.conf.in > $(HOST_DIR)/bin/qt.conf
+endef
+
+# Variable for other Qt applications to use
+QT6_QMAKE = $(HOST_DIR)/bin/qmake -spec devices/linux-buildroot-g++

package/qt6/qt6base/qmake.conf

@@ -0,0 +1,34 @@
+# Qt6 has a mechanism to support "device" profiles, so that people can
+# specify the compiler, compiler flags and so on for a specific device.
+
+# We leverage this mechanism in the Buildroot packaging of qt6 to
+# simplify cross-compilation: we have our own "device" definition, which
+# allows us to easily pass the cross-compiler paths and flags from our
+# qt6.mk.
+
+include(../common/linux_device_pre.conf)
+
+# modifications to g++-unix.conf
+QMAKE_CC                = $${CROSS_COMPILE}gcc
+QMAKE_CXX               = $${CROSS_COMPILE}g++
+QMAKE_LINK              = $${CROSS_COMPILE}g++
+
+# modifications to gcc-base.conf
+QMAKE_CFLAGS           += $${BR_COMPILER_CFLAGS}
+QMAKE_CXXFLAGS         += $${BR_COMPILER_CXXFLAGS}
+# Remove all optimisation flags, we really only want our own.
+QMAKE_CFLAGS_OPTIMIZE       =
+QMAKE_CFLAGS_OPTIMIZE_DEBUG =
+QMAKE_CFLAGS_OPTIMIZE_FULL  =
+QMAKE_CFLAGS_OPTIMIZE_SIZE  =
+QMAKE_CFLAGS_DEBUG =
+QMAKE_CXXFLAGS_DEBUG =
+QMAKE_CFLAGS_RELEASE =
+QMAKE_CXXFLAGS_RELEASE =
+CONFIG                 += nostrip
+
+QMAKE_LIBS             += -lrt -lpthread -ldl
+QMAKE_CFLAGS_ISYSTEM   =
+
+include(../common/linux_device_post.conf)
+load(qt_config)

package/qt6/qt6base/qplatformdefs.h

@@ -0,0 +1 @@
+#include "../../linux-g++/qplatformdefs.h"

package/qt6/qt6base/qt.conf.in

@@ -0,0 +1,11 @@
+[Paths]
+Prefix=/usr
+HostPrefix=@@HOST_DIR@@
+HostData=@@STAGING_DIR@@/usr
+Sysroot=@@STAGING_DIR@@
+SysrootifyPrefix=true
+TargetSpec=devices/linux-buildroot-g++
+ArchData=/usr/lib/qt6
+LibraryExecutables=/usr/lib/qt6/libexec
+Plugins=/usr/lib/qt6/plugins
+QmlImports=/usr/lib/qt6/qml

package/qt6/qt6base/qt6base.mk

@@ -436,5 +436,19 @@ define QT6BASE_RM_SBOMS
 endef
 QT6BASE_TARGET_FINALIZE_HOOKS += QT6BASE_RM_SBOMS
 
+define QT6BASE_MAKE_BR_SPEC
+	$(INSTALL) -m 0644 -D $(QT6BASE_PKGDIR)/qmake.conf \
+		$(@D)/mkspecs/devices/linux-buildroot-g++/qmake.conf
+	$(INSTALL) -m 0644 -D $(QT6BASE_PKGDIR)/qplatformdefs.h \
+		$(@D)/mkspecs/devices/linux-buildroot-g++/qplatformdefs.h
+endef
+
+QT6BASE_CONF_OPTS += \
+	-DQT_QMAKE_DEVICE_OPTIONS="CROSS_COMPILE=$(TARGET_CROSS);BR_COMPILER_CFLAGS=$(TARGET_CFLAGS);BR_COMPILER_CXXFLAGS=$(TARGET_CXXFLAGS)"
+
+QT6BASE_PRE_CONFIGURE_HOOKS += QT6BASE_MAKE_BR_SPEC
+
+QT6BASE_POST_INSTALL_STAGING_HOOKS += QT6_INSTALL_QT_CONF
+
 $(eval $(cmake-package))
 $(eval $(host-cmake-package))