Set default for BUILD_TESTS to OFF.

CMake/TestError.cmake

@@ -0,0 +1,3 @@
+# A very simple script to issue an error if the mlpack_test target is not
+# defined.
+message(FATAL_ERROR "To build the mlpack_test target, reconfigure CMake with the BUILD_TESTS option set to ON!  (i.e. `cmake -DBUILD_TESTS=ON ../`)")

CMakeLists.txt

@@ -13,7 +13,7 @@ option(DEBUG "Compile with debugging information." OFF)
 option(PROFILE "Compile with profiling information." OFF)
 option(ARMA_EXTRA_DEBUG "Compile with extra Armadillo debugging symbols." OFF)
 option(TEST_VERBOSE "Run test cases with verbose output." OFF)
-option(BUILD_TESTS "Build tests." ON)
+option(BUILD_TESTS "Build tests." OFF)
 option(BUILD_CLI_EXECUTABLES "Build command-line executables." ON)
 option(DOWNLOAD_DEPENDENCIES "Automatically download dependencies if not available." OFF)
 option(BUILD_GO_SHLIB "Build Go shared library." OFF)

HISTORY.md

@@ -2,6 +2,10 @@
 ###### ????-??-??
   * Fix mapping of categorical data for Julia bindings (#3305).
 
+  * Set `BUILD_TESTS` to `OFF` by default.  If you want to build tests, like
+    `mlpack_test`, manually set `BUILD_TESTS` to `ON` in your CMake
+    configuration step (#3316).
+
 ### mlpack 4.0.0
 ###### 2022-10-23
   * Bump C++ standard requirement to C++14 (#3233).

src/mlpack/CMakeLists.txt

@@ -6,6 +6,11 @@ add_subdirectory(methods)
 # If necessary, configure the tests.
 if (BUILD_TESTS)
   add_subdirectory(tests)
+else ()
+  # Add convenience target to tell the user they need BUILD_TESTS if they try to
+  # build mlpack_test.
+  add_custom_target(mlpack_test
+      ${CMAKE_COMMAND} -P ${CMAKE_SOURCE_DIR}/CMake/TestError.cmake)
 endif ()
 
 # At install time, we simply install the src/ directory to include/ (though we

src/mlpack/tests/CMakeLists.txt

@@ -2,7 +2,6 @@ include(CTest)
 
 # mlpack test executable.
 add_executable(mlpack_test
-  EXCLUDE_FROM_ALL
   ${MLPACK_TEST_SRCS}
 
   # Tests for neural network code (and reinforcement learning code).