使用组件和可编辑包

可以在 layout() 方法中定义组件，以支持 editable 包的情况。也就是说，如果我们将一个包置于 editable 模式，并且该包定义了 components，那么就需要在 layout() 方法中正确定义组件布局。让我们通过一个实际示例来看看。

请首先克隆源代码以重新创建此项目。您可以在 GitHub 的 examples2 仓库中找到它们。

$ git clone https://github.com/conan-io/examples2.git
$ cd examples2/examples/conanfile/layout/editable_components

在那里我们发现了一个名为 greetings 的子文件夹和包，其中包含两个库：hello 库和 bye 库。每个库都在包食谱中被建模为一个 component

greetings/conanfile.py

class GreetingsConan(ConanFile):
    name = "greetings"
    version = "0.1"
    settings = "os", "compiler", "build_type", "arch"
    generators = "CMakeDeps", "CMakeToolchain"
    exports_sources = "src/*"

    def build(self):
        cmake = CMake(self)
        cmake.configure()
        cmake.build()

    def layout(self):
        cmake_layout(self, src_folder="src")
        # This "includedirs" starts in the source folder, which is "src"
        # So the components include dirs is the "src" folder (includes are
        # intended to be included as ``#include "hello/hello.h"``)
        self.cpp.source.components["hello"].includedirs = ["."]
        self.cpp.source.components["bye"].includedirs = ["."]
        # compiled libraries "libdirs" will be inside the "build" folder, depending
        # on the platform they will be in "build/Release" or directly in "build" folder
        bt = "." if self.settings.os != "Windows" else str(self.settings.build_type)
        self.cpp.build.components["hello"].libdirs = [bt]
        self.cpp.build.components["bye"].libdirs = [bt]

    def package(self):
        copy(self, "*.h", src=self.source_folder,
             dst=join(self.package_folder, "include"))
        copy(self, "*.lib", src=self.build_folder,
             dst=join(self.package_folder, "lib"), keep_path=False)
        copy(self, "*.a", src=self.build_folder,
             dst=join(self.package_folder, "lib"), keep_path=False)

    def package_info(self):
        self.cpp_info.components["hello"].libs = ["hello"]
        self.cpp_info.components["bye"].libs = ["bye"]

        self.cpp_info.set_property("cmake_file_name", "MYG")
        self.cpp_info.set_property("cmake_target_name", "MyGreetings::MyGreetings")
        self.cpp_info.components["hello"].set_property("cmake_target_name", "MyGreetings::MyHello")
        self.cpp_info.components["bye"].set_property("cmake_target_name", "MyGreetings::MyBye")

虽然最终包中 hello 和 bye 库的位置在最终的 lib 文件夹中，因此除了组件的定义之外，package_info() 方法中不需要任何特殊操作。在这种情况下，CMake 生成的文件名和目标的自定义也已包含在内，但对于本示例而言并非必需。

重要的部分是 layout() 定义。除了常见的 cmake_layout 之外，还需要定义组件头文件的位置（self.cpp.source，因为它们是源代码）以及本地构建库的位置。由于库的位置取决于平台，因此最终的 self.cpp.build.components["component"].libdirs 也取决于平台。

通过此食谱，我们可以将包置于可编辑模式并本地构建它

$ conan editable add greetings
$ conan build greetings
# we might want to also build the debug config

在 app 文件夹中，我们有一个包食谱，用于构建两个可执行文件，它们链接到 greeting 包组件。app/conanfile.py 食谱很简单，其 build() 方法构建并运行了使用 CMakeLists.txt 构建的 example 和 example2 两个可执行文件。

# Note the MYG file name, not matching the package name,
# because the recipe defined "cmake_file_name"
find_package(MYG)

add_executable(example example.cpp)
# Note the MyGreetings::MyGreetings target name, not matching the package name,
# because the recipe defined "cmake_target_name"
# "example" is linking with the whole package, both "hello" and "bye" components
target_link_libraries(example MyGreetings::MyGreetings)

add_executable(example2 example2.cpp)
# "example2" is only using and linking "hello" component, but not "bye"
target_link_libraries(example2 MyGreetings::MyHello)

$ conan build app
hello: Release!
bye: Release!

如果您现在打开 bye.cpp 源文件并修改输出消息，然后本地构建 greetings 和 app，则“bye”组件库的最终输出消息应该会改变

$ conan build greetings
$ conan build app
hello: Release!
adios: Release!