#775: Switch to Qt6 in Linux

With this commit, Linux build starts linking to Qt6.

Here are things needed to use Qt6 in Ubuntu 22.04.

 * Qt6 uses 'libexec' rather than 'bin' to host tools like 'uic'.
 * Qt6 requires 'libgl-dev' in Ubuntu 22.04.
 * Ubuntu 22.04 uses Qt 6.2.4, where you cannot use pkg-config for Qt6
   due to QTBUG-86080 [1]. This commit works around it by injecting
   files like Qt6Core.pc files with 'PKG_CONFIG_PATH' environment
   variable.

 [1]: https://bugreports.qt.io/browse/QTBUG-86080

PiperOrigin-RevId: 558016590

.github/workflows/linux.yaml

@@ -26,12 +26,15 @@ jobs:
       - name: Setup
         run: |
           sudo apt-get update
-          sudo apt-get install -y libibus-1.0-dev qtbase5-dev
+          sudo apt-get install -y libibus-1.0-dev qt6-base-dev libgl-dev
           echo "CC=clang" >> $GITHUB_ENV
           echo "CXX=clang++" >> $GITHUB_ENV
           #
           # Unset the Android NDK setting to skip the unnecessary configuration.
           echo "ANDROID_NDK_HOME=" >> $GITHUB_ENV
+          #
+          # Work around https://bugreports.qt.io/browse/QTBUG-86080 for Ubuntu 22.04
+          echo "PKG_CONFIG_PATH=${PWD}/docker/ubuntu22.04/qt6-core-pkgconfig:${PKG_CONFIG_PATH}" >> $GITHUB_ENV
 
       - name: bazel build
         working-directory: ./src
@@ -59,12 +62,15 @@ jobs:
       - name: Setup
         run: |
           sudo apt-get update
-          sudo apt-get install -y libibus-1.0-dev qtbase5-dev
+          sudo apt-get install -y libibus-1.0-dev qt6-base-dev libgl-dev
           echo "CC=clang" >> $GITHUB_ENV
           echo "CXX=clang++" >> $GITHUB_ENV
           #
           # Unset the Android NDK setting to skip the unnecessary configuration.
           echo "ANDROID_NDK_HOME=" >> $GITHUB_ENV
+          #
+          # Work around https://bugreports.qt.io/browse/QTBUG-86080 for Ubuntu 22.04
+          echo "PKG_CONFIG_PATH=${PWD}/docker/ubuntu22.04/qt6-core-pkgconfig:${PKG_CONFIG_PATH}" >> $GITHUB_ENV
 
       - name: bazel test
         working-directory: ./src

docker/ubuntu22.04/Dockerfile

@@ -40,7 +40,7 @@ RUN apt upgrade -y
 ## Common packages for linux build environment
 RUN apt-get install -y clang libc++-dev libc++abi-dev python3 pkg-config git curl bzip2 unzip make ninja-build
 ## Packages for linux desktop version
-RUN apt-get install -y libibus-1.0-dev libglib2.0-dev qtbase5-dev
+RUN apt-get install -y libibus-1.0-dev libglib2.0-dev qt6-base-dev libgl-dev
 ## Packages for misc tools
 RUN apt-get install -y nano
 
@@ -59,6 +59,8 @@ RUN useradd --create-home --shell /bin/bash --base-dir /home mozc_builder
 USER mozc_builder
 RUN mkdir -p /home/mozc_builder/work
 WORKDIR /home/mozc_builder/work
+## Work around https://bugreports.qt.io/browse/QTBUG-86080 for Ubuntu 22.04
+ENV PKG_CONFIG_PATH="/home/mozc_builder/work/mozc/docker/ubuntu22.04/qt6-core-pkgconfig:${PKG_CONFIG_PATH}"
 
 ## For Android NDK
 RUN curl -LO https://dl.google.com/android/repository/android-ndk-r25c-linux.zip && unzip android-ndk-r25c-linux.zip && rm android-ndk-r25c-linux.zip

docker/ubuntu22.04/qt6-core-pkgconfig/Qt6Core.pc

@@ -0,0 +1,13 @@
+prefix=/usr
+exec_prefix=${prefix}
+bindir=${prefix}/lib/qt6/bin
+libexecdir=${prefix}/lib/qt6/libexec
+libdir=${prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include/x86_64-linux-gnu/qt6
+
+Name: Qt6 Core
+Description: Qt Core module
+Version: 6.2.4
+Libs: -L${libdir} -lQt6Core
+Cflags: -I${includedir}/QtCore -I${includedir} -DQT_CORE_LIB
+Requires: Qt6Platform

docker/ubuntu22.04/qt6-core-pkgconfig/Qt6Gui.pc

@@ -0,0 +1,13 @@
+prefix=/usr
+exec_prefix=${prefix}
+bindir=${prefix}/lib/qt6/bin
+libexecdir=${prefix}/lib/qt6/libexec
+libdir=${prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include/x86_64-linux-gnu/qt6
+
+Name: Qt6 Gui
+Description: Qt Gui module
+Version: 6.2.4
+Libs: -L${libdir} -lQt6Gui
+Cflags: -I${includedir}/QtGui -I${includedir} -DQT_GUI_LIB
+Requires: Qt6Core

docker/ubuntu22.04/qt6-core-pkgconfig/Qt6Platform.pc

@@ -0,0 +1,12 @@
+prefix=/usr
+exec_prefix=${prefix}
+bindir=${prefix}/lib/qt6/bin
+libexecdir=${prefix}/lib/qt6/libexec
+libdir=${prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include/x86_64-linux-gnu/qt6
+mkspecsdir=${prefix}/lib/x86_64-linux-gnu/qt6/mkspecs
+
+Name: Qt6 Platform
+Description: Qt Platform module
+Version: 6.2.4
+Cflags: -I${mkspecsdir}/linux-g++ -I${includedir}

docker/ubuntu22.04/qt6-core-pkgconfig/Qt6Widgets.pc

@@ -0,0 +1,13 @@
+prefix=/usr
+exec_prefix=${prefix}
+bindir=${prefix}/lib/qt6/bin
+libexecdir=${prefix}/lib/qt6/libexec
+libdir=${prefix}/lib/x86_64-linux-gnu
+includedir=${prefix}/include/x86_64-linux-gnu/qt6
+
+Name: Qt6 Widgets
+Description: Qt Widgets module
+Version: 6.2.4
+Libs: -L${libdir} -lQt6Widgets
+Cflags: -I${includedir}/QtWidgets -I${includedir} -DQT_WIDGETS_LIB
+Requires: Qt6Core Qt6Gui

docs/build_mozc_in_docker.md

@@ -143,8 +143,9 @@ Note: This section is not about our officially supported build process.
 
 * Python: 3.7 or later
 * Ibus: 1.5.4 or later
-* Qt5: 5.12 or later
-* libglib
+  * libglib
+* Qt6: 6.2.5 or later, or Qt 6.2.x with working around [QTBUG-86080](https://bugreports.qt.io/browse/QTBUG-86080) by yourself
+  * libgl
 
 You may also need other libraries.
 See the configurations of

src/WORKSPACE.bazel

@@ -118,7 +118,7 @@ new_local_repository(
 # Qt for Linux
 pkg_config_repository(
   name = "qt_linux",
-  packages = ["Qt5Core", "Qt5Gui", "Qt5Widgets"],
+  packages = ["Qt6Core", "Qt6Gui", "Qt6Widgets"],
 )
 
 # Qt for macOS

src/bazel/pkg_config_repository.bzl

@@ -75,7 +75,7 @@ cc_library(
 """
 
 EXPORTS_FILES_TEMPLATE = """
-exports_files(glob(["bin/*"]))
+exports_files(glob(["libexec/*"]))
 """
 
 def _exec_pkg_config(repo_ctx, flag):
@@ -107,10 +107,9 @@ def _pkg_config_repository_impl(repo_ctx):
     }
     build_file_data = BUILD_TEMPLATE.format(**data)
 
-    # host_bins
-    host_bins = _exec_pkg_config(repo_ctx, "--variable=host_bins")
-    if len(host_bins) == 1:
-        repo_ctx.symlink(host_bins[0], "bin")
+    libexecdir = _exec_pkg_config(repo_ctx, "--variable=libexecdir")
+    if len(libexecdir) == 1:
+        repo_ctx.symlink(libexecdir[0], "libexec")
         build_file_data += EXPORTS_FILES_TEMPLATE
 
     repo_ctx.file("BUILD.bazel", build_file_data)

src/bazel/qt.bzl

@@ -82,12 +82,12 @@ def mozc_qt_moc(name, srcs, outs):
         outs = outs,
         cmd = mozc_select(
             default = "$(location //third_party/qt:moc) -p $$(dirname $<) -o $@ $(SRCS)",
-            oss_linux = "$(location @qt_linux//:bin/moc) -p $$(dirname $<) -o $@ $(SRCS)",
+            oss_linux = "$(location @qt_linux//:libexec/moc) -p $$(dirname $<) -o $@ $(SRCS)",
             oss_macos = "$(location @qt_mac//:bin/moc) -p $$(dirname $<) -o $@ $(SRCS)",
         ),
         tools = mozc_select(
             default = ["//third_party/qt:moc"],
-            oss_linux = ["@qt_linux//:bin/moc"],
+            oss_linux = ["@qt_linux//:libexec/moc"],
             oss_macos = ["@qt_mac//:bin/moc"],
         ),
     )
@@ -99,12 +99,12 @@ def mozc_qt_uic(name, srcs, outs):
         outs = outs,
         cmd = mozc_select(
             default = "$(location //third_party/qt:uic) -o $@ $(SRCS)",
-            oss_linux = "$(location @qt_linux//:bin/uic) -o $@ $(SRCS)",
+            oss_linux = "$(location @qt_linux//:libexec/uic) -o $@ $(SRCS)",
             oss_macos = "$(location @qt_mac//:bin/uic) -o $@ $(SRCS)",
         ),
         tools = mozc_select(
             default = ["//third_party/qt:uic"],
-            oss_linux = ["@qt_linux//:bin/uic"],
+            oss_linux = ["@qt_linux//:libexec/uic"],
             oss_macos = ["@qt_mac//:bin/uic"],
         ),
     )
@@ -116,12 +116,12 @@ def mozc_qt_rcc(name, qrc_name, qrc_file, srcs, outs):
         outs = outs,
         cmd = mozc_select(
             default = "$(location //third_party/qt:rcc) -o $@ -name " + qrc_name + " " + qrc_file,
-            oss_linux = "$(location @qt_linux//:bin/rcc) -o $@ -name " + qrc_name + " $(location " + qrc_file + ")",
+            oss_linux = "$(location @qt_linux//:libexec/rcc) -o $@ -name " + qrc_name + " $(location " + qrc_file + ")",
             oss_macos = "$(location @qt_mac//:bin/rcc) -o $@ -name " + qrc_name + " $(location " + qrc_file + ")",
         ),
         tools = mozc_select(
             default = ["//third_party/qt:rcc"],
-            oss_linux = ["@qt_linux//:bin/rcc"],
+            oss_linux = ["@qt_linux//:libexec/rcc"],
             oss_macos = ["@qt_mac//:bin/rcc"],
         ),
     )