Alternative symlink-creating mode for file(INSTALL ...)

An new environment variable 'CMAKE_INSTALL_MODE' is introduced,
which can be used to ask CMake to create symbolic links
instead of copying files during a file(INSTALL ...).

The operation is at the file level only, directory trees are
still created using actual directories, not links.

Signed-off-by: Felix Lelchuk <felix.lelchuk@gmx.de>

4 files changed, 87 insertions, 0 deletions

diff --git a/Tests/InstallMode/subpro_b_shared_lib/CMakeLists.txt b/Tests/InstallMode/subpro_b_shared_lib/CMakeLists.txt
new file mode 100644
index 0000000..eb118c9
--- /dev/null
+++ b/Tests/InstallMode/subpro_b_shared_lib/CMakeLists.txt
@@ -0,0 +1,66 @@
+# This CMakeLists.txt is part of the subproject B (ExternalProject_Add).
+
+cmake_minimum_required(VERSION 3.20)
+project(shared_lib_project VERSION 2.3.4 LANGUAGES CXX)
+
+include(GNUInstallDirs)
+
+add_library(the_shared_lib SHARED
+  "include/shared_lib.h"
+  "src/shared_lib.cpp"
+)
+
+set_target_properties(the_shared_lib
+  PROPERTIES
+    VERSION   "${PROJECT_VERSION}"
+    SOVERSION "${PROJECT_VERSION}"
+)
+
+target_include_directories(the_shared_lib PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)
+
+install(
+  DIRECTORY   "${CMAKE_CURRENT_SOURCE_DIR}/include/"
+  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
+)
+
+install(
+  TARGETS
+    the_shared_lib
+  EXPORT main
+  ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+  LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+)
+
+set(INSTALL_CMAKE_DIR "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}")
+
+include(CMakePackageConfigHelpers)
+
+configure_package_config_file(
+  "cmake/PackageConfig.cmake.in"
+  "${PROJECT_NAME}Config.cmake"
+  INSTALL_DESTINATION "${INSTALL_CMAKE_DIR}"
+  PATH_VARS
+    CMAKE_INSTALL_INCLUDEDIR
+    CMAKE_INSTALL_LIBDIR
+)
+
+write_basic_package_version_file("${PROJECT_NAME}Version.cmake"
+  VERSION       "${PROJECT_VERSION}"
+  COMPATIBILITY SameMajorVersion
+)
+
+install(
+  EXPORT      main
+  FILE        "${PROJECT_NAME}Targets.cmake"
+  DESTINATION "${INSTALL_CMAKE_DIR}"
+)
+
+install(
+  FILES
+    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Version.cmake"
+  DESTINATION "${INSTALL_CMAKE_DIR}"
+)
diff --git a/Tests/InstallMode/subpro_b_shared_lib/cmake/PackageConfig.cmake.in b/Tests/InstallMode/subpro_b_shared_lib/cmake/PackageConfig.cmake.in
new file mode 100644
index 0000000..0fe72c9
--- /dev/null
+++ b/Tests/InstallMode/subpro_b_shared_lib/cmake/PackageConfig.cmake.in
@@ -0,0 +1,8 @@
+set(@PROJECT_NAME@_VERSION @PROJECT_VERSION@)
+
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
+
+set_and_check(@PROJECT_NAME@_INCLUDE_DIR  "@PACKAGE_CMAKE_INSTALL_INCLUDEDIR@")
+set_and_check(@PROJECT_NAME@_LIB_DIR      "@PACKAGE_CMAKE_INSTALL_LIBDIR@")
diff --git a/Tests/InstallMode/subpro_b_shared_lib/include/shared_lib.h b/Tests/InstallMode/subpro_b_shared_lib/include/shared_lib.h
new file mode 100644
index 0000000..fd960db
--- /dev/null
+++ b/Tests/InstallMode/subpro_b_shared_lib/include/shared_lib.h
@@ -0,0 +1,3 @@
+#pragma once
+
+void shared_hello();
diff --git a/Tests/InstallMode/subpro_b_shared_lib/src/shared_lib.cpp b/Tests/InstallMode/subpro_b_shared_lib/src/shared_lib.cpp
new file mode 100644
index 0000000..2820d5d
--- /dev/null
+++ b/Tests/InstallMode/subpro_b_shared_lib/src/shared_lib.cpp
@@ -0,0 +1,10 @@
+#include <iostream>
+
+#include <shared_lib.h>
+
+using namespace std;
+
+void shared_hello()
+{
+  cout << "Hello from shared_lib" << endl;
+}