Performance improvement: bypass FetchContent for cached dependencies (#182)

* skip FetchContent for cached dependencies

* set default value for CPM_SKIP_FETCH to avoid conflicts

* add tests to check exported values

cmake/CPM.cmake

@@ -286,6 +286,8 @@ function(CPMAddPackage)
     endif()
   endif()
 
+  set(CPM_SKIP_FETCH FALSE)
+
   if(DEFINED CPM_ARGS_GIT_TAG)
     list(APPEND CPM_ARGS_UNPARSED_ARGUMENTS GIT_TAG ${CPM_ARGS_GIT_TAG})
     # If GIT_SHALLOW is explicitly specified, honor the value.
@@ -374,9 +376,15 @@ function(CPMAddPackage)
     set(download_directory ${CPM_SOURCE_CACHE}/${lower_case_name}/${origin_hash})
     list(APPEND CPM_ARGS_UNPARSED_ARGUMENTS SOURCE_DIR ${download_directory})
     if(EXISTS ${download_directory})
-      # disable the download command to allow offline builds
-      list(APPEND CPM_ARGS_UNPARSED_ARGUMENTS DOWNLOAD_COMMAND "${CMAKE_COMMAND}")
-      set(PACKAGE_INFO "${download_directory}")
+      # avoid FetchContent modules to improve performance
+      set(${CPM_ARGS_NAME}_BINARY_DIR ${CMAKE_BINARY_DIR}/_deps/${lower_case_name}-build)
+      set(${CPM_ARGS_NAME}_ADDED YES)
+      set(${CPM_ARGS_NAME}_SOURCE_DIR ${download_directory})
+      if(NOT CPM_ARGS_DOWNLOAD_ONLY AND EXISTS ${download_directory}/CMakeLists.txt)
+        add_subdirectory(${download_directory} ${${CPM_ARGS_NAME}_BINARY_DIR})
+      endif()
+      set(CPM_SKIP_FETCH TRUE)
+      set(PACKAGE_INFO "${PACKAGE_INFO} at ${download_directory}")
     else()
       # Enable shallow clone when GIT_TAG is not a commit hash. Our guess may not be accurate, but
       # it should guarantee no commit hash get mis-detected.
@@ -389,7 +397,7 @@ function(CPMAddPackage)
 
       # remove timestamps so CMake will re-download the dependency
       file(REMOVE_RECURSE ${CMAKE_BINARY_DIR}/_deps/${lower_case_name}-subbuild)
-      set(PACKAGE_INFO "${PACKAGE_INFO} -> ${download_directory}")
+      set(PACKAGE_INFO "${PACKAGE_INFO} to ${download_directory}")
     endif()
   endif()
 
@@ -405,11 +413,17 @@ function(CPMAddPackage)
     endif()
   endif()
 
-  cpm_declare_fetch(
-    "${CPM_ARGS_NAME}" "${CPM_ARGS_VERSION}" "${PACKAGE_INFO}" "${CPM_ARGS_UNPARSED_ARGUMENTS}"
+  message(
+    STATUS "${CPM_INDENT} adding package ${CPM_ARGS_NAME}@${CPM_ARGS_VERSION} (${PACKAGE_INFO})"
   )
-  cpm_fetch_package("${CPM_ARGS_NAME}" "${DOWNLOAD_ONLY}")
-  cpm_get_fetch_properties("${CPM_ARGS_NAME}")
+
+  if(NOT CPM_SKIP_FETCH)
+    cpm_declare_fetch(
+      "${CPM_ARGS_NAME}" "${CPM_ARGS_VERSION}" "${PACKAGE_INFO}" "${CPM_ARGS_UNPARSED_ARGUMENTS}"
+    )
+    cpm_fetch_package("${CPM_ARGS_NAME}" "${DOWNLOAD_ONLY}")
+    cpm_get_fetch_properties("${CPM_ARGS_NAME}")
+  endif()
 
   set(${CPM_ARGS_NAME}_ADDED YES)
   cpm_export_variables("${CPM_ARGS_NAME}")
@@ -503,8 +517,6 @@ endfunction()
 
 # declares a package in FetchContent_Declare
 function(cpm_declare_fetch PACKAGE VERSION INFO)
-  message(STATUS "${CPM_INDENT} adding package ${PACKAGE}@${VERSION} (${INFO})")
-
   if(${CPM_DRY_RUN})
     message(STATUS "${CPM_INDENT} package not declared (dry run)")
     return()

cmake/testing.cmake

@@ -16,18 +16,38 @@ function(ASSERT_EMPTY)
   endif()
 endfunction()
 
+function(ASSERT_DEFINED KEY)
+  if(DEFINED ${KEY})
+    message(STATUS "test passed: '${KEY}' is defined")
+  else()
+    message(FATAL_ERROR "assertion failed: '${KEY}' is not defiend")
+  endif()
+endfunction()
+
+function(ASSERT_TRUTHY KEY)
+  if(${${KEY}})
+    message(STATUS "test passed: '${KEY}' is set truthy")
+  else()
+    message(FATAL_ERROR "assertion failed: value of '${KEY}' is not true (${${KEY}})")
+  endif()
+endfunction()
+
 function(ASSERTION_FAILED)
   message(FATAL_ERROR "assertion failed: ${ARGN}")
 endfunction()
 
 function(ASSERT_EXISTS file)
-  if(NOT EXISTS ${file})
+  if(EXISTS ${file})
+    message(STATUS "test passed: '${file}' exists")
+  else()
     message(FATAL_ERROR "assertion failed: file ${file} does not exist")
   endif()
 endfunction()
 
 function(ASSERT_NOT_EXISTS file)
-  if(EXISTS ${file})
+  if(NOT EXISTS ${file})
+    message(STATUS "test passed: '${file}' does not exist")
+  else()
     message(FATAL_ERROR "assertion failed: file ${file} exists")
   endif()
 endfunction()

test/unit/local_dependency/ModuleCMakeLists.txt.in

@@ -24,3 +24,11 @@ endif()
 # ---- Call dependency method to validate correct addition of directory ----
 
 dependency_function()
+
+# ---- Check parameters ----
+
+include(@CPM_PATH@/testing.cmake)
+
+ASSERT_TRUTHY(@TEST_DEPENDENCY_NAME@_ADDED)
+ASSERT_DEFINED(@TEST_DEPENDENCY_NAME@_SOURCE_DIR)
+ASSERT_DEFINED(@TEST_DEPENDENCY_NAME@_BINARY_DIR)

test/unit/local_dependency/OverrideCMakeLists.txt.in

@@ -17,3 +17,11 @@ CPMAddPackage(
 # ---- Call dependency method to validate correct addition of directory ----
 
 dependency_function()
+
+# ---- Check parameters ----
+
+include(@CPM_PATH@/testing.cmake)
+
+ASSERT_TRUTHY(Dependency_ADDED)
+ASSERT_DEFINED(Dependency_SOURCE_DIR)
+ASSERT_DEFINED(Dependency_BINARY_DIR)

test/unit/remote_dependency/CMakeLists.txt.in

@@ -22,3 +22,11 @@ CPMAddPackage(
 add_executable(CPMExampleCatch2 main.cpp)
 target_link_libraries(CPMExampleCatch2 fibonacci)
 set_target_properties(CPMExampleCatch2 PROPERTIES CXX_STANDARD 17 COMPILE_FLAGS "-Wall -pedantic -Wextra -Werror")
+
+# ---- Check parameters ----
+
+include(@CPM_PATH@/testing.cmake)
+
+ASSERT_TRUTHY(fibonacci_ADDED)
+ASSERT_DEFINED(fibonacci_SOURCE_DIR)
+ASSERT_DEFINED(fibonacci_BINARY_DIR)