ccls version: tag: 0.20201219

compile_commands.json

[
{
  "directory": "/home/tj/test/aaa/build",
  "command": "/usr/bin/c++ -DQT_CORE_LIB -DQT_DBUS_LIB -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_NO_DEBUG -DQT_SQL_LIB -DQT_WIDGETS_LIB -isystem /usr/include/x86_64-linux-gnu/qt5 -isystem /usr/include/x86_64-linux-gnu/qt5/QtCore -isystem /usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++ -isystem /usr/include/x86_64-linux-gnu/qt5/QtWidgets -isystem /usr/include/x86_64-linux-gnu/qt5/QtGui -isystem /usr/include/x86_64-linux-gnu/qt5/QtNetwork -isystem /usr/include/x86_64-linux-gnu/qt5/QtDBus -isystem /usr/include/x86_64-linux-gnu/qt5/QtSql -fPIC -o CMakeFiles/aaa.dir/src/main.cpp.o -c /home/tj/test/aaa/src/main.cpp",
  "file": "/home/tj/test/aaa/src/main.cpp"
}
]

put compile_commands.json to the project root path directly, it can not work.
create .ccls, fill with %compile_commands.json, it can not work.
create .ccls, fill with below, it can work.

clang++

-DQT_CORE_LIB
-DQT_DBUS_LIB
-DQT_GUI_LIB
-DQT_NETWORK_LIB
-DQT_NO_DEBUG
-DQT_SQL_LIB
-DQT_WIDGETS_LIB
-isystem
/usr/include/x86_64-linux-gnu/qt5
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtCore
-isystem
/usr/lib/x86_64-linux-gnu/qt5/mkspecs/linux-g++
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtWidgets
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtGui
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtNetwork
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtDBus
-isystem
/usr/include/x86_64-linux-gnu/qt5/QtSql