Regression: Broken configure.ac in zbar 0.23.93 release (Qt5 related)

[hosiet]

zbar/configure.ac

Lines 664 to 683 in 6ea7392

	AS_IF([test "x$with_qt" != "xno"],
	[AS_IF([test "x$with_qt6" != "xno"],
	PKG_CHECK_MODULES([QT],
	[Qt6],
	[MOC=`pkg-config Qt6 --variable=moc`
	QT_VERSION=`$PKG_CONFIG Qt6 --modversion`
	QT6_HEADERS=`pkg-config Qt6 --variable=headerdir`
	CPPFLAGS="$CPPFLAGS -I$QT6_HEADERS -I$QT6_HEADERS/QtWidgets -I$QT6_HEADERS/QtCore -I$QT6_HEADERS/QtGui"
	qt_pkgconfig_file="zbar-qt5.pc"
	],
	[with_qt6="no"]))
	AS_IF([test "x$with_qt6" = "xno"],
	PKG_CHECK_MODULES([QT],
	[Qt5Core >= 5 Qt5Gui >= 5 Qt5Widgets >= 5.0 Qt5X11Extras >= 5.0],
	[MOC=`pkg-config Qt5 --variable=moc`
	QT_VERSION=`$PKG_CONFIG Qt5 --modversion`
	qt_pkgconfig_file="zbar-qt5.pc"
	],
	[with_qt="no"]))
	])

The following issues (actually regressions) exist in this code block:

1. Hardcoded pkg-config reappears. We should use $PKG_CONFIG whenever possible, as seen in zbar <= 0.23.92.
2. The AS_IF() macro needs the [ and ] guarding for each of its parameter. In this code, the second parameter of AS_IF() has missing [] around the PKG_CHECK_MODULES() invocation.
3. The Qt5 detection logic is now broken, compared with zbar 0.23.92. The configure result would be like this:

checking for Qt5Core >= 5 Qt5Gui >= 5 Qt5Widgets >= 5.0 Qt5X11Extras >= 5.0... yes
Package Qt5 was not found in the pkg-config search path.
Perhaps you should add the directory containing `Qt5.pc'
to the PKG_CONFIG_PATH environment variable
Package 'Qt5', required by 'virtual:world', not found
configure: using Qt version 
configure: using moc from 
checking for javac... no
checking for jikes... no

This is due to Qt5 (at least in Linux distributions) never shipped a Qt5.pc anywhere. As a result, the invocation of $PKG_CONFIG Qt5 will never succeed. Please revert to the old logic of detection $MOC and $QT_VERSION or seek other methods that correctly uses Qt5 pkg-config files.

[jubalh]

It appears you have already patches ready at https://salsa.debian.org/debian/zbar/-/tree/master/debian/patches
Would you mind creating a PR?

[mchehab]

This is due to Qt5 (at least in Linux distributions) never shipped a Qt5.pc anywhere. As a result, the invocation of $PKG_CONFIG Qt5 will never succeed. Please revert to the old logic of detection $MOC and $QT_VERSION or seek other methods that correctly uses Qt5 pkg-config files.

On Fedora, we have:

• a Qt5 pkg-config file is at /usr/lib64/pkgconfig/Qt5.pc (see qt5-qtbase-devel-5.15.11-7.fc39.x86_64);
• a Qt6 pkg-config file is at /usr/lib64/pkgconfig/Qt6.pc (see qt6-qtbase-devel-6.6.0-6.fc39.x86_64).

Perhaps the logic needs to be changed to try first Qt5.pc, then Qt.pc. If not found, fail back to the old way.

[mchehab]

The upstream changes are there to better cope with installs were both Qt5 and Qt6 devel libs are installed. So, a simple solution like https://salsa.debian.org/debian/zbar/-/blob/master/debian/patches/0003-configure.ac-Use-old-way-to-detect-Qt5.patch may not be doing the right thing.

[mchehab]

Ok, tested applying both patches from Debian: no breakages on Fedora. I'll apply them both.