CMake中的return命令用于从文件、目录或函数返回，其格式如下：

return([PROPAGATE <var-name>...])

      当在包含文件中(in an included file)遇到此命令时(通过include或find_package命令)，它会导致当前文件的处理停止并将控制权返回给包含文件(including file)。如果在另一个文件不包含的文件中遇到它，例如CMakeLists.txt，调用由cmake_language(DEFER)安排的延迟调用，如果有的话，则控制权返回到父目录。
      如果在function中调用return，则将控制权返回给function的调用者。注意：与function不同，macro是在原地(in place)展开的,因此无法处理return.

      Policy CMP0140控制return命令参数的行为。除非该策略设置为NEW，否则所有参数都将被忽略。
      PROPAGATE：3.25版本中引入。此选项用于父目录或function调用者范围中set或unset指定的变量。这相当于set(PARENT_SCOPE)或unset(PARENT_SCOPE)命令。

function(func1 addr)
    set(${addr} "https://blog.csdn.net/fengbingchun" PARENT_SCOPE)
endfunction()

function(func2 addr)
    return()
    set(${addr} "https://blog.csdn.net/fengbingchun" PARENT_SCOPE)
endfunction()

set(addr "csdn:")
func1(addr)
message("addr: ${addr}") # addr: https://blog.csdn.net/fengbingchun

set(addr "csdn:")
func2(addr)
message("addr: ${addr}") # addr: csdn:

      执行上述测试代码需要3个文件：build.sh, CMakeLists.txt, test_return.cmake

      build.sh内容如下：

#! /bin/bash

# supported input parameters(cmake commands)
params=(function macro cmake_parse_arguments \
		find_library find_path find_file find_program find_package \
		cmake_policy cmake_minimum_required project include \
		string list set foreach message option if while return \
		math file)

usage()
{
	echo "Error: $0 needs to have an input parameter"

	echo "supported input parameters:"
	for param in ${params[@]}; do
		echo "  $0 ${param}"
	done

	exit -1
}

if [ $# != 1 ]; then
	usage
fi

flag=0
for param in ${params[@]}; do
	if [ $1 == ${param} ]; then
		flag=1
		break
	fi
done

if [ ${flag} == 0 ]; then
	echo "Error: parameter \"$1\" is not supported"
	usage
	exit -1
fi

if [[ ! -d "build" ]]; then
	mkdir build
	cd build
else
	cd build
fi

echo "==== test $1 ===="

# test_set.cmake: cmake -DTEST_CMAKE_FEATURE=$1 --log-level=verbose ..
# test_option.cmake: cmake -DTEST_CMAKE_FEATURE=$1 -DBUILD_PYTORCH=ON ..
cmake -DTEST_CMAKE_FEATURE=$1 ..
# It can be executed directly on the terminal, no need to execute build.sh, for example: cmake -P test_set.cmake

      CMakeLists.txt内容如下：

cmake_minimum_required(VERSION 3.22)
project(cmake_feature_usage)

message("#### current cmake version: ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}.${CMAKE_PATCH_VERSION}")
include(test_${TEST_CMAKE_FEATURE}.cmake)
message("==== test finish ====")

      test_return.cmake:为上面的所有示例代码

      可能的执行结果如下图所示:

      GitHub: https://github.com/fengbingchun/Linux_Code_Test