目標的源尚不存在，具體取決於使用 add_custom_command 生成的源的自定義目標

Question

我正在嘗試將介子項目移植到 CMake。 我的主 CMake 文件中有以下子目錄：

add_subdirectory(protos)
add_subdirectory(qtlayershell)
add_subdirectory(demo)

以及protos/CMakeLists.txt中的以下內容：

set(PROTOCOLS
    ${WAYLAND_PROTOCOL_DIR}/stable/xdg-shell/xdg-shell.xml
    wlr-layer-shell-unstable-v1.xml'
)

foreach(XML ${PROTOCOLS})
    get_filename_component(BASENAME ${XML} NAME_WE)
    add_custom_command(
        OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/wayland-${BASENAME}-protocol.c
        COMMAND wayland-scanner private-code ${XML} @OUTPUT@
    )
    add_custom_command(
        OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/wayland-${BASENAME}-protocol.h
        COMMAND wayland-scanner client-header ${XML} @OUTPUT@
    )

    add_custom_command(
        OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/qwayland-${BASENAME}.h
        COMMAND qtwaylandscanner client-header ${XML} @OUTPUT@
    )
    add_custom_command(
        OUTPUT  ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/${BASENAME}-protocol.cpp
        COMMAND qtwaylandscanner client-code ${XML} @OUTPUT@
    )

    list(APPEND PROTOCOL_SRC
        ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/wayland-${BASENAME}-protocol.c
        ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/${BASENAME}-protocol.cpp
    )

    list(APPEND PROTOCOL_HEADERS
        ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/qwayland-${BASENAME}.h
        ${CMAKE_CURRENT_BINARY_DIR}/wayland-protos/wayland-${BASENAME}-protocol.h
    )
endforeach()


set(WAYLAND_PROTOCOL_SRC ${PROTOCOL_SRC} PARENT_SCOPE)
set(WAYLAND_PROTOCOL_HEADERS ${PROTOCOL_HEADERS} PARENT_SCOPE)

add_custom_target(wayland_protocols DEPENDS ${WAYLAND_PROTOCOL_SRC} ${WAYLAND_PROTOCOL_HEADERS})

在qtlayershell/CMakeLists.txt中，目標如下：

add_library(qtlayershell SHARED
    ${QTLAYERSHELL_SRC}
    ${WAYLAND_PROTOCOL_SRC}
    DEPENDS wayland_protocols
)

但是我收到一個錯誤，即somelongbuildpath/protos/wayland-protos/wayland-xdg-shell-protocol.c尚不存在。 這是完整的錯誤：

  Cannot find source file:

    /home/noone/KDE/my/build-qtlayershell-Desktop-Debug/protos/wayland-protos/wayland-xdg-shell-protocol.c

  Tried extensions .c .C .c++ .cc .cpp .cxx .cu .m .M .mm .h .hh .h++ .hm
  .hpp .hxx .in .txx


CMake Error at qtlayershell/CMakeLists.txt:9 (add_library):
  No SOURCES given to target: qtlayershell
CMake Generate step failed.  Build files cannot be regenerated correctly.
CMake process exited with exit code 1.

Answer 1

add_library()命令不接受DEPENDS關鍵字，因此這不是指定目標依賴項的有效方法。 嘗試使用add_dependencies()來指定qtlayershell目標依賴於wayland_protocols自定義目標來生成源：

add_library(qtlayershell SHARED
    ${QTLAYERSHELL_SRC}
    ${WAYLAND_PROTOCOL_SRC}
)
add_dependencies(qtlayershell wayland_protocols)

---

此外， WAYLAND_PROTOCOL_SRC和WAYLAND_PROTOCOL_HEADERS變量設置為PARENT_SCOPE ，因此它們對add_custom_target調用不可用。 相反，您可以嘗試將這些設置為CACHE INTERNAL變量，以便它們在所有范圍內都可用：

set(WAYLAND_PROTOCOL_SRC ${PROTOCOL_SRC} CACHE INTERNAL "Wayland sources" FORCE)
set(WAYLAND_PROTOCOL_HEADERS ${PROTOCOL_HEADERS} CACHE INTERNAL "Wayland headers" FORCE)

add_custom_target(wayland_protocols DEPENDS ${WAYLAND_PROTOCOL_SRC} ${WAYLAND_PROTOCOL_HEADERS})