qt5.qtbase: fix cross

pkgs/development/libraries/qt-5/5.15/default.nix

@@ -207,7 +207,8 @@ let
         import ../qtModule.nix
         {
           inherit perl;
-          inherit lib;
+          inherit lib stdenv;
+          inherit buildPackages;
           # Use a variant of mkDerivation that does not include wrapQtApplications
           # to avoid cyclic dependencies between Qt modules.
           mkDerivation =

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

@@ -1,11 +1,13 @@
 if [[ -n "${__nix_qtbase-}" ]]; then
+  if [ -z "${dontWorryAboutQtMismatch-}" ]; then
     # Throw an error if a different version of Qt was already set up.
     if [[ "$__nix_qtbase" != "@dev@" ]]; then
         echo >&2 "Error: detected mismatched Qt dependencies:"
         echo >&2 "    @dev@"
         echo >&2 "    $__nix_qtbase"
         exit 1
     fi
+  fi
 else # Only set up Qt once.
 __nix_qtbase="@dev@"
 

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

@@ -28,10 +28,15 @@
 , developerBuild ? false
 , decryptSslTraffic ? false
 , testers
+, buildPackages
 }:
 
 let
   debugSymbols = debug || developerBuild;
+  qtPlatformCross = plat: with plat;
+    if isLinux
+    then "linux-generic-g++"
+    else throw "Please add a qtPlatformCross entry for ${plat.config}";
 in
 
 stdenv.mkDerivation (finalAttrs: {
@@ -82,6 +87,11 @@ stdenv.mkDerivation (finalAttrs: {
   nativeBuildInputs = [ bison flex gperf lndir perl pkg-config which ]
     ++ lib.optionals stdenv.isDarwin [ xcbuild ];
 
+  # `qtbase` expects to find `cc` (with no prefix) in the
+  # `$PATH`, so the following is needed even if
+  # `stdenv.buildPlatform.canExecute stdenv.hostPlatform`
+  depsBuildBuild = [ buildPackages.stdenv.cc ];
+
   propagatedNativeBuildInputs = [ lndir ];
 
   # libQt5Core links calls CoreFoundation APIs that call into the system ICU. Binaries linked
@@ -161,6 +171,11 @@ stdenv.mkDerivation (finalAttrs: {
     export MAKEFLAGS+=" -j$NIX_BUILD_CORES"
 
     ./bin/syncqt.pl -version $version
+  '' + lib.optionalString (stdenv.buildPlatform != stdenv.hostPlatform) ''
+    # QT's configure script will refuse to use pkg-config unless these two environment variables are set
+    export PKG_CONFIG_SYSROOT_DIR=/
+    export PKG_CONFIG_LIBDIR=${lib.getLib pkg-config}/lib
+    echo 'QMAKE_PKG_CONFIG=''$''${CROSS_COMPILE}pkg-config' >> mkspecs/devices/${qtPlatformCross stdenv.hostPlatform}/qmake.conf
   '';
 
   postConfigure = ''
@@ -208,6 +223,8 @@ stdenv.mkDerivation (finalAttrs: {
   # To prevent these failures, we need to override PostgreSQL detection.
   PSQL_LIBS = lib.optionalString (postgresql != null) "-L${postgresql.lib}/lib -lpq";
 
+  # do not pass --host and --build to configureFlags as QT's configure script doesn't understand them
+  configurePlatforms = [ ];
   # TODO Remove obsolete and useless flags once the build will be totally mastered
   configureFlags = [
     "-plugindir $(out)/$(qtPluginPrefix)"
@@ -234,6 +251,9 @@ stdenv.mkDerivation (finalAttrs: {
     "-L" "${icu.out}/lib"
     "-I" "${icu.dev}/include"
     "-pch"
+  ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    "-device ${qtPlatformCross stdenv.hostPlatform}"
+    "-device-option CROSS_COMPILE=${stdenv.cc.targetPrefix}"
   ]
   ++ lib.optional debugSymbols "-debug"
   ++ lib.optionals developerBuild [

pkgs/development/libraries/qt-5/qtModule.nix

@@ -1,4 +1,8 @@
-{ lib, mkDerivation, perl }:
+{ lib
+, stdenv
+, mkDerivation, perl
+, buildPackages
+}:
 
 let inherit (lib) licenses maintainers platforms; in
 
@@ -17,7 +21,8 @@ mkDerivation (args // {
   patches = (args.patches or []) ++ (patches.${pname} or []);
 
   nativeBuildInputs = (args.nativeBuildInputs or []) ++ [ perl self.qmake ];
-  propagatedBuildInputs = args.qtInputs ++ (args.propagatedBuildInputs or []);
+  propagatedBuildInputs = (args.qtInputs or []) ++ (args.propagatedBuildInputs or []);
+  depsBuildBuild = [ buildPackages.stdenv.cc ];
 
   outputs = args.outputs or [ "out" "dev" ];
   setOutputFlags = args.setOutputFlags or false;
@@ -74,4 +79,7 @@ mkDerivation (args // {
     maintainers = with maintainers; [ qknight ttuegel periklis bkchr ];
     platforms = platforms.unix;
   } // (args.meta or {});
+
+} // lib.optionalAttrs (stdenv.hostPlatform != stdenv.buildPlatform) {
+  dontWorryAboutQtMismatch = true;
 })