问覆盖超级构建CMakeLists.txt中的缓存变量

EN

# This is a super build project
cmake_minimum_required(VERSION 3.0)

project(SuperBuild VERSION 1.0 LANGUAGES CXX)

# Trying to override the FOO option of "third party" foo
set(FOO OFF)
# Trying to override the BAR cache variable of "third party" foo
set(BAR "foo")

# Incorporate the Foo third party project.
# Should be done using FetchContent(GIT_REPOSITORY .../foo.git) but, here
# I used add_subdirectory(foo) to keep it simple...
add_subdirectory(foo)

cmake_minimum_required(VERSION 3.0)

# option() honors normal variables.
# without this policy, cmake will "clear" the super build variable value
# and will use the option defualt value -_-
# see: https://cmake.org/cmake/help/git-stage/policy/CMP0077.html
if(POLICY CMP0077)
  cmake_policy(SET CMP0077 NEW)
endif()

# An option ON by default
option(FOO "My FOO option" ON)
message(WARNING "FOO: ${FOO}")

# A string variable cached with default "bar"
# we can override it on command line using for example -DBAR:STRING="foo"
# but here since we are in a super build we want to override it in the super
# build CMakeLists.txt directly
set(BAR "bar" CACHE STRING "My cache entry with default 'bar'")
message(WARNING "BAR: ${BAR}")

echo "First run"
cmake -S. -Bbuild
echo "Second run"
cmake -S. -Bbuild

First run

-- The CXX compiler identification is GNU 10.1.0
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ - works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Warning at foo/CMakeLists.txt:13 (message):
  FOO: OFF
CMake Warning at foo/CMakeLists.txt:20 (message):
  BAR: bar
-- Configuring done
-- Generating done
-- Build files have been written to: build

Second run

CMake Warning at foo/CMakeLists.txt:13 (message):
  FOO: OFF
CMake Warning at foo/CMakeLists.txt:20 (message):
  BAR: foo
-- Configuring done
-- Generating done
-- Build files have been written to: build

rm -rf build
cmake -S. -Bbuild -DBAR:STRING=plop
CMake Warning at foo/CMakeLists.txt:13 (message):
  FOO: OFF
CMake Warning at foo/CMakeLists.txt:20 (message):
  BAR: plop
-- Configuring done
-- Generating done
-- Build files have been written to: build

cmake -S. -Bbuild -DBAR:STRING=plop
CMake Warning at foo/CMakeLists.txt:13 (message):
  FOO: OFF
CMake Warning at foo/CMakeLists.txt:20 (message):
  BAR: plop
-- Configuring done
-- Generating done
-- Build files have been written to: build