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>

28 files changed, 711 insertions, 0 deletions

diff --git a/Tests/InstallMode/CMakeLists.txt b/Tests/InstallMode/CMakeLists.txt
new file mode 100644
index 0000000..96c83a0
--- /dev/null
+++ b/Tests/InstallMode/CMakeLists.txt
@@ -0,0 +1,124 @@
+cmake_minimum_required(VERSION 3.20.0)
+
+project(superpro LANGUAGES NONE)
+
+add_subdirectory(superpro)
+
+include(Subproject.cmake)
+add_subproject(static_lib   DIR subpro_a_static_lib)
+add_subproject(shared_lib   DIR subpro_b_shared_lib)
+add_subproject(nested_lib   DIR subpro_c_nested_lib NO_INSTALL)
+add_subproject(executable   DIR subpro_d_executable
+  DEPENDS
+    static_lib
+    shared_lib
+    nested_lib
+)
+
+include(CTest)
+if(BUILD_TESTING)
+  enable_language(CXX)  # required by GNUInstallDirs
+  include(GNUInstallDirs)
+
+  macro(testme _name _path _symlink)
+    add_test(
+      NAME "${_name}"
+      WORKING_DIRECTORY "${CMAKE_BINARY_DIR}"
+      COMMAND
+        "${CMAKE_COMMAND}"
+        "-DFILE_PATH=${CMAKE_INSTALL_PREFIX}/${_path}"
+        "-DEXPECT_SYMLINK:BOOL=${_symlink}"
+        "-DEXPECT_ABSOLUTE:BOOL=${ARGN}"
+        "-P" "${CMAKE_SOURCE_DIR}/Test.cmake"
+    )
+  endmacro()
+
+  set(_mode $ENV{CMAKE_INSTALL_MODE})
+  if(NOT "${_mode}" OR "${_mode}" STREQUAL "COPY")
+    set(expect_symlink NO)
+  elseif("${_mode}" MATCHES "(REL_)?SYMLINK(_OR_COPY)?")
+    set(expect_symlink YES)
+    set(expect_absolute NO)
+  elseif("${_mode}" MATCHES "ABS_SYMLINK(_OR_COPY)?")
+    set(expect_symlink YES)
+    set(expect_absolute YES)
+  endif()
+
+  # toplevel project should respect CMAKE_INSTALL_MODE
+
+  testme(superproj_file_copy
+    "file_copy.txt" NO)
+  testme(superproj_file_copy_file
+    "file_copy_file.txt" NO)
+  testme(superproj_file_install
+    "file_install.txt"
+    ${expect_symlink}
+    ${expect_absolute})
+  testme(superproj_file_create_link_symbolic
+    "file_create_link_symbolic.txt" YES YES)
+
+  # subprojects should receive and respect CMAKE_INSTALL_MODE too
+
+  testme(subpro_a_static_lib_header
+    "${CMAKE_INSTALL_INCLUDEDIR}/static_lib.h"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+  testme(subpro_a_static_lib_libfile
+    "${CMAKE_INSTALL_LIBDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}the_static_lib${CMAKE_STATIC_LIBRARY_SUFFIX}"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+
+  testme(subpro_b_shared_lib_header
+    "${CMAKE_INSTALL_INCLUDEDIR}/shared_lib.h"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+
+  if(CMAKE_SHARED_LIBRARY_SONAME_CXX_FLAG AND
+      "${CMAKE_CXX_CREATE_SHARED_MODULE}" MATCHES "SONAME_FLAG")
+    # due to semver, this is always a link
+    testme(subpro_b_shared_lib_libfile
+      "${CMAKE_INSTALL_LIBDIR}/${CMAKE_SHARED_LIBRARY_PREFIX}the_shared_lib${CMAKE_SHARED_LIBRARY_SUFFIX}"
+      YES
+      ${expect_absolute}
+    )
+    # this is the actual shared lib, so should follow CMAKE_INSTALL_MODE rules
+    testme(subpro_b_shared_lib_libfile_versuffix
+      "${CMAKE_INSTALL_LIBDIR}/${CMAKE_SHARED_LIBRARY_PREFIX}the_shared_lib${CMAKE_SHARED_LIBRARY_SUFFIX}.2.3.4"
+      ${expect_symlink}
+      ${expect_absolute}
+    )
+  endif()
+
+  testme(subpro_d_executable_exefile
+    "${CMAKE_INSTALL_BINDIR}/the_executable${CMAKE_EXECUTABLE_SUFFIX}"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+
+  # nested subprojects should receive and respect CMAKE_INSTALL_MODE too
+
+  testme(subsubpro_c1_header
+    "${CMAKE_INSTALL_INCLUDEDIR}/c1_lib.h"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+  testme(subsubpro_c1_libfile
+    "${CMAKE_INSTALL_LIBDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}the_c1_lib${CMAKE_STATIC_LIBRARY_SUFFIX}"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+
+  testme(subsubpro_c2_header
+    "${CMAKE_INSTALL_INCLUDEDIR}/c2_lib.h"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+  testme(subsubpro_c2_libfile
+    "${CMAKE_INSTALL_LIBDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}the_c2_lib${CMAKE_STATIC_LIBRARY_SUFFIX}"
+    ${expect_symlink}
+    ${expect_absolute}
+  )
+endif()
diff --git a/Tests/InstallMode/README.txt b/Tests/InstallMode/README.txt
new file mode 100644
index 0000000..a4316eb
--- /dev/null
+++ b/Tests/InstallMode/README.txt
@@ -0,0 +1,43 @@
+This is an example superbuild project to demonstrate the use of the
+CMAKE_INSTALL_MODE environment variable on.
+
+The project hierarchy is like (B = Builds / D = Link Dependency):
+
++---------------------------------------------------------------------+
+|                           Superbuild (Top)                          |
++---------------------------------------------------------------------+
+        |                 |                 |                 |
+        |                 |                 |                 |
+       (B)               (B)               (B)               (B)
+        |                 |                 |                 |
+        v                 v                 v                 v
++---------------+ +---------------+ +---------------+ +---------------+
+| A: Static Lib | | B: Shared Lib | | C: Nested     | | D: Executable |
+|    Project    | |    Project    | |    Superbuild | |    Project    |
++---------------+ +---------------+ +---------------+ +---------------+
+        ^               ^               |       |        |   |   |
+        |               |              (B)     (B)       |   |   |
+        |               |               |       |        |   |   |
+        |               |               v       |        |   |   |
+        |               |  +----------------+   |        |   |   |
+        |               |  | C1: Static Lib |   |        |   |   |
+        |               |  |     Project    |   |       (D) (D) (D)
+        |               |  +----------------+   |        |   |   |
+        |               |       ^               |        |   |   |
+        |               |       |               v        |   |   |
+        |               |      (D) +----------------+    |   |   |
+        |               |       |  | C2: Static Lib |<---+   |   |
+        |               |       +--|     Project    |        |   |
+        |               |          +----------------+        |   |
+        |               |                                    |   |
+        |               +------------------------------------+   |
+        |                                                        |
+        +--------------------------------------------------------+
+
+The superbuild system is built on top of ExternalProject_Add().
+
+NOTE that the subprojects will configure, build and install
+during the build phase ('make') of the top-level project.
+There is no install target in the top-level project!
+The CMAKE_INSTALL_PREFIX is therefore populated during the build
+phase already.
diff --git a/Tests/InstallMode/Subproject.cmake b/Tests/InstallMode/Subproject.cmake
new file mode 100644
index 0000000..e4354d6
--- /dev/null
+++ b/Tests/InstallMode/Subproject.cmake
@@ -0,0 +1,76 @@
+include(ExternalProject)
+
+# add_subproject(<name> [NO_INSTALL] [DIR <dirname>] [DEPENDS [subpro_dep ...]])
+function(add_subproject _name)
+  cmake_parse_arguments(_arg "NO_INSTALL" "DIR" "DEPENDS" ${ARGN})
+
+  if(_arg_UNPARSED_ARGUMENTS)
+    message(FATAL_ERROR "There are unparsed arguments")
+  endif()
+
+  set(_maybe_NO_INSTALL)
+  if(_arg_NO_INSTALL)
+    set(_maybe_NO_INSTALL "INSTALL_COMMAND")
+  else()
+    # This is a trick to get a valid call.
+    # Since we set UPDATE_COMMAND to ""
+    # explicitly below, this won't harm.
+    set(_maybe_NO_INSTALL "UPDATE_COMMAND")
+  endif()
+
+  if(CMAKE_GENERATOR MATCHES "Ninja Multi-Config")
+    # Replace list separator before passing on to ExternalProject_Add
+    string(REPLACE ";" "|" _CONFIGURATION_TYPES "${CMAKE_CONFIGURATION_TYPES}")
+    string(REPLACE ";" "|" _CROSS_CONFIGS "${CMAKE_CROSS_CONFIGS}")
+    string(REPLACE ";" "|" _DEFAULT_CONFIGS "${CMAKE_DEFAULT_CONFIGS}")
+
+    set(_maybe_NINJA_MULTICONFIG_ARGS
+      "-DCMAKE_CONFIGURATION_TYPES:STRINGS=${_CONFIGURATION_TYPES}"
+      "-DCMAKE_CROSS_CONFIGS:STRINGS=${_CROSS_CONFIGS}"
+      "-DCMAKE_DEFAULT_BUILD_TYPE:STRING=${CMAKE_DEFAULT_BUILD_TYPE}"
+      "-DCMAKE_DEFAULT_CONFIGS:STRINGS=${_DEFAULT_CONFIGS}"
+    )
+  endif()
+
+  ExternalProject_Add("${_name}"
+    DOWNLOAD_COMMAND      ""
+    UPDATE_COMMAND        ""
+    ${_maybe_NO_INSTALL}  ""
+
+    BUILD_ALWAYS          ON
+
+    LOG_DOWNLOAD          OFF
+    LOG_UPDATE            OFF
+    LOG_PATCH             OFF
+    LOG_CONFIGURE         OFF
+    LOG_BUILD             OFF
+    LOG_INSTALL           OFF
+
+    SOURCE_DIR            "${PROJECT_SOURCE_DIR}/${_arg_DIR}"
+
+    # Private build directory per subproject
+    BINARY_DIR            "${PROJECT_BINARY_DIR}/subproject/${_arg_DIR}"
+
+    # Common install directory, populated immediately
+    # during build (during build - not install - of superproject)
+    INSTALL_DIR           "${CMAKE_INSTALL_PREFIX}"
+
+    DEPENDS
+      ${_arg_DEPENDS}
+
+    LIST_SEPARATOR "|"
+    CMAKE_ARGS
+      "-DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>"
+
+      # We can rely on ExternalProject to pick the right
+      # generator (and architecture/toolset where applicable),
+      # however, we need to explicitly inherit other parent
+      # project's build settings.
+      "-DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}"
+      ${_maybe_NINJA_MULTICONFIG_ARGS}
+
+      # Subproject progress reports clutter up the output, disable
+      "-DCMAKE_TARGET_MESSAGES:BOOL=OFF"
+      "-DCMAKE_RULE_MESSAGES:BOOL=OFF"
+  )
+endfunction()
diff --git a/Tests/InstallMode/Test.cmake b/Tests/InstallMode/Test.cmake
new file mode 100644
index 0000000..46c8fa1
--- /dev/null
+++ b/Tests/InstallMode/Test.cmake
@@ -0,0 +1,38 @@
+message("Testing...")
+message("FILE_PATH =       ${FILE_PATH}")
+message("EXPECT_SYMLINK =  ${EXPECT_SYMLINK}")
+message("EXPECT_ABSOLUTE = ${EXPECT_ABSOLUTE}")
+
+if(NOT DEFINED FILE_PATH)
+  message(FATAL_ERROR "FILE_PATH variable must be defined")
+endif()
+
+if(NOT EXISTS "${FILE_PATH}")
+  message(FATAL_ERROR "File ${FILE_PATH} does not exist")
+endif()
+
+if(NOT DEFINED EXPECT_SYMLINK)
+  message(FATAL_ERROR "EXPECT_SYMLINK must be defined")
+endif()
+
+if(EXPECT_SYMLINK)
+  if(NOT DEFINED EXPECT_ABSOLUTE)
+    message(FATAL_ERROR "EXPECT_ABSOLUTE variable must be defined")
+  endif()
+
+  if(NOT IS_SYMLINK "${FILE_PATH}")
+    message(FATAL_ERROR "${FILE_PATH} must be a symlink")
+  endif()
+
+  file(READ_SYMLINK "${FILE_PATH}" TARGET_PATH)
+
+  if(EXPECT_ABSOLUTE AND NOT IS_ABSOLUTE "${TARGET_PATH}")
+    message(FATAL_ERROR "${FILE_PATH} must be an absolute symlink")
+  elseif(NOT EXPECT_ABSOLUTE AND IS_ABSOLUTE "${TARGET_PATH}")
+    message(FATAL_ERROR "${FILE_PATH} must be a relative symlink")
+  endif()
+else()
+  if(IS_SYMLINK "${FILE_PATH}")
+    message(FATAL_ERROR "${FILE_PATH} must NOT be a symlink")
+  endif()
+endif()
diff --git a/Tests/InstallMode/subpro_a_static_lib/CMakeLists.txt b/Tests/InstallMode/subpro_a_static_lib/CMakeLists.txt
new file mode 100644
index 0000000..7cd32cc
--- /dev/null
+++ b/Tests/InstallMode/subpro_a_static_lib/CMakeLists.txt
@@ -0,0 +1,60 @@
+# This CMakeLists.txt is part of the subproject A (ExternalProject_Add).
+
+cmake_minimum_required(VERSION 3.20)
+project(static_lib_project VERSION 1.2.3 LANGUAGES CXX)
+
+include(GNUInstallDirs)
+
+add_library(the_static_lib STATIC
+  "include/static_lib.h"
+  "src/static_lib.cpp"
+)
+
+target_include_directories(the_static_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_static_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 "${INSTALL_CMAKE_DIR}"
+)
diff --git a/Tests/InstallMode/subpro_a_static_lib/cmake/PackageConfig.cmake.in b/Tests/InstallMode/subpro_a_static_lib/cmake/PackageConfig.cmake.in
new file mode 100644
index 0000000..0fe72c9
--- /dev/null
+++ b/Tests/InstallMode/subpro_a_static_lib/cmake/PackageConfig.cmake.in
@@ -0,0 +1,8 @@
+set(@PROJECT_NAME@_VERSION @PROJECT_VERSION@)
+
+@PACKAGE_INIT@
+
+include("${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_a_static_lib/include/static_lib.h b/Tests/InstallMode/subpro_a_static_lib/include/static_lib.h
new file mode 100644
index 0000000..bd82d2e
--- /dev/null
+++ b/Tests/InstallMode/subpro_a_static_lib/include/static_lib.h
@@ -0,0 +1,3 @@
+#pragma once
+
+void static_hello();
diff --git a/Tests/InstallMode/subpro_a_static_lib/src/static_lib.cpp b/Tests/InstallMode/subpro_a_static_lib/src/static_lib.cpp
new file mode 100644
index 0000000..fe1cd85
--- /dev/null
+++ b/Tests/InstallMode/subpro_a_static_lib/src/static_lib.cpp
@@ -0,0 +1,10 @@
+#include <iostream>
+
+#include <static_lib.h>
+
+using namespace std;
+
+void static_hello()
+{
+  cout << "Hello from static_lib" << endl;
+}
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;
+}
diff --git a/Tests/InstallMode/subpro_c_nested_lib/CMakeLists.txt b/Tests/InstallMode/subpro_c_nested_lib/CMakeLists.txt
new file mode 100644
index 0000000..e397c02
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/CMakeLists.txt
@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.20.0)
+
+project(subpro_c_nested_lib LANGUAGES NONE)
+
+include(../Subproject.cmake)
+add_subproject(c1_lib   DIR subsubpro_c1_lib)
+add_subproject(c2_lib   DIR subsubpro_c2_lib
+  DEPENDS
+    c1_lib
+)
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/CMakeLists.txt b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/CMakeLists.txt
new file mode 100644
index 0000000..89f3755
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/CMakeLists.txt
@@ -0,0 +1,61 @@
+# This CMakeLists.txt is a nested subproject of the
+# subproject C (ExternalProject_Add).
+
+cmake_minimum_required(VERSION 3.20)
+project(c1_lib_project VERSION 1.2.3 LANGUAGES CXX)
+
+include(GNUInstallDirs)
+
+add_library(the_c1_lib STATIC
+  "include/c1_lib.h"
+  "src/c1_lib.cpp"
+)
+
+target_include_directories(the_c1_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_c1_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 "${INSTALL_CMAKE_DIR}"
+)
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/cmake/PackageConfig.cmake.in b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/cmake/PackageConfig.cmake.in
new file mode 100644
index 0000000..0fe72c9
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/cmake/PackageConfig.cmake.in
@@ -0,0 +1,8 @@
+set(@PROJECT_NAME@_VERSION @PROJECT_VERSION@)
+
+@PACKAGE_INIT@
+
+include("${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_c_nested_lib/subsubpro_c1_lib/include/c1_lib.h b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/include/c1_lib.h
new file mode 100644
index 0000000..245f9d4
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/include/c1_lib.h
@@ -0,0 +1,3 @@
+#pragma once
+
+void c1_hello();
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/src/c1_lib.cpp b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/src/c1_lib.cpp
new file mode 100644
index 0000000..c405056
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c1_lib/src/c1_lib.cpp
@@ -0,0 +1,10 @@
+#include <iostream>
+
+#include <c1_lib.h>
+
+using namespace std;
+
+void c1_hello()
+{
+  cout << "Hello from c1_lib" << endl;
+}
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/CMakeLists.txt b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/CMakeLists.txt
new file mode 100644
index 0000000..e139446
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/CMakeLists.txt
@@ -0,0 +1,68 @@
+# This CMakeLists.txt is a nested subproject of the
+# subproject C (ExternalProject_Add).
+
+cmake_minimum_required(VERSION 3.20)
+project(c2_lib_project VERSION 1.2.3 LANGUAGES CXX)
+
+find_package(c1_lib_project REQUIRED)
+
+include(GNUInstallDirs)
+
+add_library(the_c2_lib STATIC
+  "include/c2_lib.h"
+  "src/c2_lib.cpp"
+)
+
+target_link_libraries(the_c2_lib
+  PUBLIC
+    the_c1_lib
+)
+
+target_include_directories(the_c2_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_c2_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 "${INSTALL_CMAKE_DIR}"
+)
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/cmake/PackageConfig.cmake.in b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/cmake/PackageConfig.cmake.in
new file mode 100644
index 0000000..45a177a
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/cmake/PackageConfig.cmake.in
@@ -0,0 +1,11 @@
+set(@PROJECT_NAME@_VERSION @PROJECT_VERSION@)
+
+@PACKAGE_INIT@
+
+include("${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@")
+
+include(CMakeFindDependencyMacro)
+find_dependency(c1_lib_project REQUIRED)
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/include/c2_lib.h b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/include/c2_lib.h
new file mode 100644
index 0000000..5056814
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/include/c2_lib.h
@@ -0,0 +1,3 @@
+#pragma once
+
+void c2_hello();
diff --git a/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/src/c2_lib.cpp b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/src/c2_lib.cpp
new file mode 100644
index 0000000..cd2c932
--- /dev/null
+++ b/Tests/InstallMode/subpro_c_nested_lib/subsubpro_c2_lib/src/c2_lib.cpp
@@ -0,0 +1,12 @@
+#include <iostream>
+
+#include <c1_lib.h>
+#include <c2_lib.h>
+
+using namespace std;
+
+void c2_hello()
+{
+  cout << "Hello from c2_lib and also..." << endl;
+  c1_hello();
+}
diff --git a/Tests/InstallMode/subpro_d_executable/CMakeLists.txt b/Tests/InstallMode/subpro_d_executable/CMakeLists.txt
new file mode 100644
index 0000000..9847227
--- /dev/null
+++ b/Tests/InstallMode/subpro_d_executable/CMakeLists.txt
@@ -0,0 +1,24 @@
+# This CMakeLists.txt is part of the subproject B (ExternalProject_Add).
+
+cmake_minimum_required(VERSION 3.20)
+project(subpro_d_executable LANGUAGES CXX)
+
+find_package(static_lib_project REQUIRED)
+find_package(shared_lib_project REQUIRED)
+find_package(c2_lib_project REQUIRED)
+
+add_executable(the_executable
+  "src/main.cpp"
+)
+
+target_link_libraries(the_executable PRIVATE
+  the_static_lib
+  the_shared_lib
+  the_c2_lib
+)
+
+install(
+  TARGETS
+    the_executable
+  RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
+)
diff --git a/Tests/InstallMode/subpro_d_executable/src/main.cpp b/Tests/InstallMode/subpro_d_executable/src/main.cpp
new file mode 100644
index 0000000..ec12004
--- /dev/null
+++ b/Tests/InstallMode/subpro_d_executable/src/main.cpp
@@ -0,0 +1,13 @@
+#include <cstdlib>
+
+#include <c2_lib.h>
+#include <shared_lib.h>
+#include <static_lib.h>
+
+int main()
+{
+  static_hello();
+  shared_hello();
+  c2_hello();
+  return EXIT_SUCCESS;
+}
diff --git a/Tests/InstallMode/superpro/CMakeLists.txt b/Tests/InstallMode/superpro/CMakeLists.txt
new file mode 100644
index 0000000..ae4d25c
--- /dev/null
+++ b/Tests/InstallMode/superpro/CMakeLists.txt
@@ -0,0 +1,29 @@
+# This CMakeLists.txt is part of the superproject (add_subdirectory).
+
+# Below file transfers are executed at configuration time!
+
+file(
+  COPY
+    "file_copy.txt"
+  DESTINATION
+    "${CMAKE_INSTALL_PREFIX}"
+)
+
+file(COPY_FILE
+  "${CMAKE_CURRENT_SOURCE_DIR}/file_copy_file.txt"
+  "${CMAKE_INSTALL_PREFIX}/file_copy_file.txt"
+)
+
+file(
+  INSTALL
+    "file_install.txt"
+  DESTINATION
+    "${CMAKE_INSTALL_PREFIX}"
+)
+
+file(
+  CREATE_LINK
+    "${CMAKE_CURRENT_SOURCE_DIR}/file_create_link_symbolic.txt"
+    "${CMAKE_INSTALL_PREFIX}/file_create_link_symbolic.txt"
+  SYMBOLIC
+)
diff --git a/Tests/InstallMode/superpro/file_copy.txt b/Tests/InstallMode/superpro/file_copy.txt
new file mode 100644
index 0000000..aacbb96
--- /dev/null
+++ b/Tests/InstallMode/superpro/file_copy.txt
@@ -0,0 +1 @@
+This file should always be copied into CMAKE_INSTALL_PREFIX.
diff --git a/Tests/InstallMode/superpro/file_copy_file.txt b/Tests/InstallMode/superpro/file_copy_file.txt
new file mode 100644
index 0000000..aacbb96
--- /dev/null
+++ b/Tests/InstallMode/superpro/file_copy_file.txt
@@ -0,0 +1 @@
+This file should always be copied into CMAKE_INSTALL_PREFIX.
diff --git a/Tests/InstallMode/superpro/file_create_link_symbolic.txt b/Tests/InstallMode/superpro/file_create_link_symbolic.txt
new file mode 100644
index 0000000..16a481b
--- /dev/null
+++ b/Tests/InstallMode/superpro/file_create_link_symbolic.txt
@@ -0,0 +1,2 @@
+This file should always be installed into CMAKE_INSTALL_PREFIX
+as a symbolic link to the original file.
diff --git a/Tests/InstallMode/superpro/file_install.txt b/Tests/InstallMode/superpro/file_install.txt
new file mode 100644
index 0000000..eac9782
--- /dev/null
+++ b/Tests/InstallMode/superpro/file_install.txt
@@ -0,0 +1,6 @@
+This file should be placed in CMAKE_INSTALL_PREFIX
+as a copy if the CMAKE_INSTALL_MODE environment variable
+is unset or equals "COPY".
+If the variable's value is "SYMLINK" or "SYMLINK_OR_COPY",
+the CMAKE_INSTALL_PREFIX should rather receive a symbolic
+link to this file.