WIP: Loads qt plugin paths as registered...

This adds the list of Qt plugin paths into builds using `qtbase`.

The plugins list will be added to the Qt plugin path through the
additional patch.

This ensures that no special environment is required to get the desired
plugin path for Qt software.

This should fix all issues where Qt is unable to load its platform
plugin.

This may fix the issue where Qt tries to load a mismatched version of a
plugin.

pkgs/development/libraries/qt-5/5.11/default.nix

@@ -39,6 +39,7 @@ let
   patches = {
     qtbase = [
       ./qtbase.patch
+      ./qtbase-additional.patch
       ./qtbase-darwin.patch
       ./qtbase-revert-no-macos10.10.patch
     ];

pkgs/development/libraries/qt-5/5.11/qtbase-additional.patch

@@ -0,0 +1,32 @@
+diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
+index 5ae3fd62e5..ec3fccfc76 100644
+--- a/src/corelib/kernel/qcoreapplication.cpp
++++ b/src/corelib/kernel/qcoreapplication.cpp
+@@ -2533,6 +2533,27 @@ QStringList QCoreApplication::libraryPaths()
+         QStringList *app_libpaths = new QStringList;
+         coreappdata()->app_libpaths.reset(app_libpaths);
+
++		{
++			// Start at the binary; this allows us to *always* start by stripping the last part.
++			QStringList components = applicationFilePath().split(QDir::separator());
++
++			// We don't care about /nix/store/nix-support, only /nix/store/*/nix-support
++			// This is why we're checking for more than 3 parts. It will bail out once /nix/xtore/*/nix-support/qt-plugin-paths has been tested.
++			while (components.length() > 4) {
++				components.removeLast();
++				const QString support_plugin_paths = QDir::cleanPath(QDir::separator() + components.join(QDir::separator()) + QStringLiteral("/nix-support/qt-plugin-paths"));
++				if (QFile::exists(support_plugin_paths)) {
++					QFile file(support_plugin_paths);
++					if (file.open(QIODevice::ReadOnly | QIODevice::Text)) {
++						QTextStream in(&file);
++						while (!in.atEnd()) {
++							app_libpaths->append(in.readLine());
++						}
++					}
++				}
++			}
++		}
++
+         // Add library paths derived from PATH
+         const QStringList paths = QFile::decodeName(qgetenv("PATH")).split(':');
+         const QString plugindir = QStringLiteral("../" NIXPKGS_QT_PLUGIN_PREFIX);

pkgs/development/libraries/qt-5/5.9/default.nix

@@ -37,7 +37,7 @@ let
   srcs = import ./srcs.nix { inherit fetchurl; inherit mirror; };
 
   patches = {
-    qtbase = [ ./qtbase.patch ] ++ optional stdenv.isDarwin ./qtbase-darwin.patch;
+    qtbase = [ ./qtbase.patch ./qtbase-additional.patch ] ++ optional stdenv.isDarwin ./qtbase-darwin.patch;
     qtdeclarative = [ ./qtdeclarative.patch ];
     qtscript = [ ./qtscript.patch ];
     qtserialport = [ ./qtserialport.patch ];

pkgs/development/libraries/qt-5/5.9/qtbase-additional.patch

@@ -0,0 +1,32 @@
+diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
+index 5ae3fd62e5..ec3fccfc76 100644
+--- a/src/corelib/kernel/qcoreapplication.cpp
++++ b/src/corelib/kernel/qcoreapplication.cpp
+@@ -2533,6 +2533,27 @@ QStringList QCoreApplication::libraryPaths()
+         QStringList *app_libpaths = new QStringList;
+         coreappdata()->app_libpaths.reset(app_libpaths);
+
++		{
++			// Start at the binary; this allows us to *always* start by stripping the last part.
++			QStringList components = applicationFilePath().split(QDir::separator());
++
++			// We don't care about /nix/store/nix-support, only /nix/store/*/nix-support
++			// This is why we're checking for more than 3 parts. It will bail out once /nix/xtore/*/nix-support/qt-plugin-paths has been tested.
++			while (components.length() > 4) {
++				components.removeLast();
++				const QString support_plugin_paths = QDir::cleanPath(QDir::separator() + components.join(QDir::separator()) + QStringLiteral("/nix-support/qt-plugin-paths"));
++				if (QFile::exists(support_plugin_paths)) {
++					QFile file(support_plugin_paths);
++					if (file.open(QIODevice::ReadOnly | QIODevice::Text)) {
++						QTextStream in(&file);
++						while (!in.atEnd()) {
++							app_libpaths->append(in.readLine());
++						}
++					}
++				}
++			}
++		}
++
+         // Add library paths derived from PATH
+         const QStringList paths = QFile::decodeName(qgetenv("PATH")).split(':');
+         const QString plugindir = QStringLiteral("../" NIXPKGS_QT_PLUGIN_PREFIX);

pkgs/development/libraries/qt-5/hooks/qtbase-setup-hook.sh

@@ -62,3 +62,59 @@ postPatchMkspecs() {
 if [ -z "$dontPatchMkspecs" ]; then
     postPhases="${postPhases}${postPhases:+ }postPatchMkspecs"
 fi
+
+_Qt_sortless_uniq() {
+	# `uniq`, but keeps initial order.
+	# This is to remove risks of combinatorial explosion of plugin paths.
+	cat -n | sort -uk2 | sort -nk1 | cut -f2-
+}
+
+_QtGetPluginPaths() {
+	# Lists all plugin paths for current Qt for given buildInputs and propagatedBuildInputs
+	local i
+	local _i
+	local o
+	local inputs
+
+	# FIXME : this causes output path cycles...
+	# I am unsure if it is even needed, though.
+	## Outputs self's plugins paths
+	#for o in $outputs; do
+	#	o="${!o}/@qtPluginPrefix@"
+	#	if [ -e "$o" ]; then
+	#		echo "$o"
+	#	fi
+	#done
+
+	inputs="$(
+		for i in $buildInputs $propagatedBuildInputs; do
+			echo "$i"
+		done | uniq
+	)"
+
+	for i in $inputs; do
+		_i="$i/@qtPluginPrefix@"
+		if [ -e "$_i" ]; then
+			echo "$_i"
+		fi
+		_i="$i/nix-support/qt-plugin-paths"
+		if [ -e "$_i" ]; then
+			cat "$_i"
+		fi
+	done
+}
+
+postAddPluginPaths() {
+	# Dumps all plugins paths to a nix-support file inside all outputs.
+	local o
+
+	for o in $outputs; do
+		o="${!o}/nix-support"
+		mkdir -p "$o"
+		_QtGetPluginPaths | _Qt_sortless_uniq > $o/qt-plugin-paths
+	done
+}
+
+if [ -z "$dontAddPluginPaths" ]; then
+    postPhases="${postPhases}${postPhases:+ }postAddPluginPaths"
+fi

pkgs/development/libraries/qt-5/modules/qtbase.nix

@@ -382,7 +382,13 @@ stdenv.mkDerivation {
           sed -i "$dev/lib/pkgconfig/Qt5Core.pc" \
               -e "/^host_bins=/ c host_bins=$dev/bin"
         ''
-    );
+      )
+    + ''
+        # Adds `qtbase-bin` as a basic dependency to *all* qtbase builds.
+        mkdir -p $dev/nix-support
+        echo "$bin/$qtPluginPrefix" >> $dev/nix-support/qt-plugin-paths
+      ''
+   ;
 
   setupHook = ../hooks/qtbase-setup-hook.sh;