Fix #141: skip leak sanitizer on Apple platforms

LeakSanitizer is unsupported on macOS (clang rejects -fsanitize=leak on
arm64-apple-darwin and other Apple targets); leak detection there is
provided by AddressSanitizer with ASAN_OPTIONS=detect_leaks=1. When
myproject_ENABLE_SANITIZER_LEAK is requested on an Apple host,
myproject_enable_sanitizers now warns and drops it from the sanitizer
list instead of producing an unsupported -fsanitize=leak compile flag.
Adds two CMake-script regression tests that stub target_*_options to
verify leak is filtered out on Apple and still propagated elsewhere.

Author: leftibot

cmake/Sanitizers.cmake

@@ -15,7 +15,14 @@ function(
     endif()
 
     if(${ENABLE_SANITIZER_LEAK})
-      list(APPEND SANITIZERS "leak")
+      # LeakSanitizer is unsupported on Apple platforms (the linker rejects
+      # -fsanitize=leak on macOS, including arm64). On Apple, leak detection
+      # is provided by AddressSanitizer with ASAN_OPTIONS=detect_leaks=1.
+      if(APPLE)
+        message(WARNING "Leak sanitizer is not supported on Apple platforms; ignoring myproject_ENABLE_SANITIZER_LEAK")
+      else()
+        list(APPEND SANITIZERS "leak")
+      endif()
     endif()
 
     if(${ENABLE_SANITIZER_UNDEFINED_BEHAVIOR})

test/CMakeLists.txt

@@ -24,6 +24,16 @@ include(${Catch2_SOURCE_DIR}/extras/Catch.cmake)
 # Provide a simple smoke test to make sure that the CLI works and can display a --help message
 add_test(NAME cli.has_help COMMAND intro --help)
 
+# CMake-script regression tests for cmake/Sanitizers.cmake (issue #141).
+add_test(
+  NAME cmake.sanitizers.apple_excludes_leak
+  COMMAND ${CMAKE_COMMAND} -P
+          ${CMAKE_CURRENT_SOURCE_DIR}/cmake/test_sanitizers_apple_excludes_leak.cmake)
+add_test(
+  NAME cmake.sanitizers.non_apple_includes_leak
+  COMMAND ${CMAKE_COMMAND} -P
+          ${CMAKE_CURRENT_SOURCE_DIR}/cmake/test_sanitizers_non_apple_includes_leak.cmake)
+
 # Provide a test to verify that the version being reported from the application
 # matches the version given to CMake. This will be important once you package
 # your program. Real world shows that this is the kind of simple mistake that is easy

test/cmake/test_sanitizers_apple_excludes_leak.cmake

@@ -0,0 +1,62 @@
+# Regression test for #141: macOS ARM doesn't support leak sanitizer.
+#
+# Simulates an Apple toolchain by setting APPLE=TRUE before including
+# Sanitizers.cmake, stubs the target_*_options commands so that the flags
+# requested by myproject_enable_sanitizers can be inspected, then asserts
+# that "leak" is not propagated to the compiler/linker even when the user
+# enables the leak sanitizer option.
+
+cmake_minimum_required(VERSION 3.21)
+
+set(APPLE TRUE)
+set(MSVC FALSE)
+set(CMAKE_CXX_COMPILER_ID "Clang")
+
+set_property(GLOBAL PROPERTY captured_compile_options "")
+set_property(GLOBAL PROPERTY captured_link_options "")
+
+function(target_compile_options)
+  set_property(GLOBAL PROPERTY captured_compile_options "${ARGN}")
+endfunction()
+
+function(target_link_options)
+  set_property(GLOBAL PROPERTY captured_link_options "${ARGN}")
+endfunction()
+
+include("${CMAKE_CURRENT_LIST_DIR}/../../cmake/Sanitizers.cmake")
+
+myproject_enable_sanitizers(
+  test_target
+  ON  # ENABLE_SANITIZER_ADDRESS
+  ON  # ENABLE_SANITIZER_LEAK (should be filtered out on Apple)
+  OFF # ENABLE_SANITIZER_UNDEFINED_BEHAVIOR
+  OFF # ENABLE_SANITIZER_THREAD
+  OFF # ENABLE_SANITIZER_MEMORY
+)
+
+get_property(compile_options GLOBAL PROPERTY captured_compile_options)
+get_property(link_options GLOBAL PROPERTY captured_link_options)
+
+message(STATUS "Captured compile options: ${compile_options}")
+message(STATUS "Captured link options:    ${link_options}")
+
+if(compile_options MATCHES "leak")
+  message(
+    FATAL_ERROR
+    "Leak sanitizer must not be enabled on Apple platforms (#141), "
+    "but compile options contain 'leak': ${compile_options}")
+endif()
+
+if(link_options MATCHES "leak")
+  message(
+    FATAL_ERROR
+    "Leak sanitizer must not be enabled on Apple platforms (#141), "
+    "but link options contain 'leak': ${link_options}")
+endif()
+
+if(NOT compile_options MATCHES "address")
+  message(
+    FATAL_ERROR
+    "Address sanitizer should still be enabled when leak is filtered out, "
+    "but compile options were: ${compile_options}")
+endif()

test/cmake/test_sanitizers_non_apple_includes_leak.cmake

@@ -0,0 +1,52 @@
+# Companion to test_sanitizers_apple_excludes_leak.cmake (#141).
+# Verifies that on non-Apple platforms the leak sanitizer is still
+# propagated to the compiler/linker, so the Apple-specific guard does
+# not silently disable leak detection elsewhere.
+
+cmake_minimum_required(VERSION 3.21)
+
+set(APPLE FALSE)
+set(MSVC FALSE)
+set(CMAKE_CXX_COMPILER_ID "Clang")
+
+set_property(GLOBAL PROPERTY captured_compile_options "")
+set_property(GLOBAL PROPERTY captured_link_options "")
+
+function(target_compile_options)
+  set_property(GLOBAL PROPERTY captured_compile_options "${ARGN}")
+endfunction()
+
+function(target_link_options)
+  set_property(GLOBAL PROPERTY captured_link_options "${ARGN}")
+endfunction()
+
+include("${CMAKE_CURRENT_LIST_DIR}/../../cmake/Sanitizers.cmake")
+
+myproject_enable_sanitizers(
+  test_target
+  OFF # ENABLE_SANITIZER_ADDRESS
+  ON  # ENABLE_SANITIZER_LEAK
+  OFF # ENABLE_SANITIZER_UNDEFINED_BEHAVIOR
+  OFF # ENABLE_SANITIZER_THREAD
+  OFF # ENABLE_SANITIZER_MEMORY
+)
+
+get_property(compile_options GLOBAL PROPERTY captured_compile_options)
+get_property(link_options GLOBAL PROPERTY captured_link_options)
+
+message(STATUS "Captured compile options: ${compile_options}")
+message(STATUS "Captured link options:    ${link_options}")
+
+if(NOT compile_options MATCHES "leak")
+  message(
+    FATAL_ERROR
+    "Leak sanitizer must still be enabled on non-Apple platforms, "
+    "but compile options were: ${compile_options}")
+endif()
+
+if(NOT link_options MATCHES "leak")
+  message(
+    FATAL_ERROR
+    "Leak sanitizer must still be enabled on non-Apple platforms, "
+    "but link options were: ${link_options}")
+endif()