Add find_package overrides that also work in CONFIG mode (#498) (#604)

README.md

@@ -214,6 +214,13 @@ In the case that `find_package` requires additional arguments, the parameter `FI
 
 Note that this does not apply to dependencies that have been defined with a truthy `FORCE` parameter. These will be added as defined.
 
+### CPM_DONT_UPDATE_MODULE_PATH
+
+By default, CPM will override any `find_package` commands to use the CPM downloaded version.
+This is equivalent to the `OVERRIDE_FIND_PACKAGE` FetchContent option, which has no effect in CPM.
+To disable this behaviour set the `CPM_DONT_UPDATE_MODULE_PATH` option.
+This will not work for `find_package(CONFIG)` in CMake versions before 3.24.
+
 ### CPM_USE_NAMED_CACHE_DIRECTORIES
 
 If set, CPM use additional directory level in cache to improve readability of packages names in IDEs like CLion. It changes cache structure, so all dependencies are downloaded again. There is no problem to mix both structures in one cache directory but then there may be 2 copies of some dependencies.

cmake/CPM.cmake

@@ -162,7 +162,7 @@ set(CPM_SOURCE_CACHE
     CACHE PATH "Directory to download CPM dependencies"
 )
 
-if(NOT CPM_DONT_UPDATE_MODULE_PATH)
+if(NOT CPM_DONT_UPDATE_MODULE_PATH AND NOT DEFINED CMAKE_FIND_PACKAGE_REDIRECTS_DIR)
   set(CPM_MODULE_PATH
       "${CMAKE_BINARY_DIR}/CPM_modules"
       CACHE INTERNAL ""
@@ -269,11 +269,26 @@ endfunction()
 # finding the system library
 function(cpm_create_module_file Name)
   if(NOT CPM_DONT_UPDATE_MODULE_PATH)
-    # erase any previous modules
+    if(DEFINED CMAKE_FIND_PACKAGE_REDIRECTS_DIR)
+      # Redirect find_package calls to the CPM package. This is what FetchContent does when you set
+      # OVERRIDE_FIND_PACKAGE. The CMAKE_FIND_PACKAGE_REDIRECTS_DIR works for find_package in CONFIG
+      # mode, unlike the Find${Name}.cmake fallback. CMAKE_FIND_PACKAGE_REDIRECTS_DIR is not defined
+      # in script mode, or in CMake < 3.24.
+      # https://cmake.org/cmake/help/latest/module/FetchContent.html#fetchcontent-find-package-integration-examples
+      string(TOLOWER ${Name} NameLower)
+      file(WRITE ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/${NameLower}-config.cmake
+           "include(\"${CMAKE_CURRENT_LIST_DIR}/${NameLower}-extra.cmake\" OPTIONAL)\n"
+           "include(\"${CMAKE_CURRENT_LIST_DIR}/${Name}Extra.cmake\" OPTIONAL)\n"
+      )
+      file(WRITE ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/${NameLower}-version.cmake
+           "set(PACKAGE_VERSION_COMPATIBLE TRUE)\n" "set(PACKAGE_VERSION_EXACT TRUE)\n"
+      )
+    else()
       file(WRITE ${CPM_MODULE_PATH}/Find${Name}.cmake
            "include(\"${CPM_FILE}\")\n${ARGN}\nset(${Name}_FOUND TRUE)"
       )
     endif()
+  endif()
 endfunction()
 
 # Find a package locally or fallback to CPMAddPackage

test/integration/test_basics.rb

@@ -31,8 +31,10 @@ class Basics < IntegrationTest
     assert_same_path File.join(prj.bin_dir, 'cpm-package-lock.cmake'), check_and_get('CPM_PACKAGE_LOCK_FILE')
 
     assert_equal 'OFF', check_and_get('CPM_DONT_UPDATE_MODULE_PATH', 'BOOL')
+    if @cache.entries['CMAKE_FIND_PACKAGE_REDIRECTS_DIR'].nil?
       assert_same_path File.join(prj.bin_dir, 'CPM_modules'), check_and_get('CPM_MODULE_PATH')
     end
+  end
 
   # Test when env CPM_SOURCE_CACHE is set
   def test_env_cpm_source_cache

test/unit/local_dependency/ModuleCMakeLists.txt.in

@@ -8,6 +8,10 @@ option(ENABLE_TEST_COVERAGE "Enable test coverage" OFF)
 
 # ---- Dependencies ----
 
+if (@TEST_FORCE_MODULE_MODE@)
+  unset(CMAKE_FIND_PACKAGE_REDIRECTS_DIR CACHE)
+endif()
+
 include(@CPM_PATH@/CPM.cmake)
 
 CPMAddPackage(
@@ -15,21 +19,23 @@ CPMAddPackage(
   SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR}/dependency
 )
 
-# ---- check if generated modules override find_package ----
-
-if (@test_check_find_package@)
-  find_package(@TEST_DEPENDENCY_NAME@ REQUIRED)
-endif()
-
 # ---- Call dependency method to validate correct addition of directory ----
 
 dependency_function()
 
-# ---- Check parameters ----
-
+# ---- Check newly added ----
 include(@CPM_PATH@/testing.cmake)
-
 ASSERT_TRUTHY(@TEST_DEPENDENCY_NAME@_ADDED)
+
+# ---- Check if generated modules override find_package ----
+
+if (@TEST_FIND_PACKAGE@)
+  find_package(@TEST_DEPENDENCY_NAME@ @TEST_FIND_PACKAGE_CONFIG@ REQUIRED)
+  find_package(@TEST_CANT_FIND_PACKAGE_NAME@ @TEST_FIND_PACKAGE_CONFIG@ QUIET)
+  ASSERT_FALSY(@TEST_CANT_FIND_PACKAGE_NAME@_FOUND)
+endif()
+
+# ---- Check parameters ----
 ASSERT_DEFINED(@TEST_DEPENDENCY_NAME@_SOURCE_DIR)
 ASSERT_DEFINED(@TEST_DEPENDENCY_NAME@_BINARY_DIR)
 ASSERT_EQUAL("${CPM_LAST_PACKAGE_NAME}" "@TEST_DEPENDENCY_NAME@")

test/unit/modules.cmake

@@ -3,7 +3,8 @@ include(${CPM_PATH}/testing.cmake)
 
 set(TEST_BUILD_DIR ${CMAKE_CURRENT_BINARY_DIR}/modules)
 
-function(init_project_with_dependency TEST_DEPENDENCY_NAME)
+function(init_project_with_dependency TEST_DEPENDENCY_NAME TEST_CANT_FIND_PACKAGE_NAME)
+  set(TEST_FIND_PACKAGE ON)
   configure_package_config_file(
     "${CMAKE_CURRENT_LIST_DIR}/local_dependency/ModuleCMakeLists.txt.in"
     "${CMAKE_CURRENT_LIST_DIR}/local_dependency/CMakeLists.txt"
@@ -18,11 +19,17 @@ function(init_project_with_dependency TEST_DEPENDENCY_NAME)
   assert_equal(${ret} "0")
 endfunction()
 
-init_project_with_dependency(A)
-assert_exists(${TEST_BUILD_DIR}/CPM_modules)
-assert_exists(${TEST_BUILD_DIR}/CPM_modules/FindA.cmake)
-assert_not_exists(${TEST_BUILD_DIR}/CPM_modules/FindB.cmake)
+init_project_with_dependency(A B)
+init_project_with_dependency(B A)
 
-init_project_with_dependency(B)
-assert_not_exists(${TEST_BUILD_DIR}/CPM_modules/FindA.cmake)
-assert_exists(${TEST_BUILD_DIR}/CPM_modules/FindB.cmake)
+if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.24.0")
+  set(TEST_FIND_PACKAGE_CONFIG CONFIG)
+  init_project_with_dependency(A B)
+  init_project_with_dependency(B A)
+
+  # Test the fallback path for CMake <3.24 works
+  set(TEST_FIND_PACKAGE_CONFIG)
+  set(TEST_FORCE_MODULE_MODE ON)
+  init_project_with_dependency(A B)
+  init_project_with_dependency(B A)
+endif()