Add opt-in mull mutation-testing wiring (Linux only)

Author: czhao-dev

CMakeLists.txt

@@ -51,6 +51,19 @@ if(SENTINEL_ENABLE_FUZZING)
   add_link_options(-fsanitize=address)
 endif()
 
+# Off by default, Linux-only: see lib/CMakeLists.txt for what this enables
+# and docs/architecture.md ("Mutation testing") for how to actually run it
+# with mull (https://mull-project.com). MULL_IR_FRONTEND must point at a
+# mull-ir-frontend-N binary whose N matches CMAKE_CXX_COMPILER's own LLVM
+# version exactly -- mull's plugin ABI is not forward/backward compatible
+# even across patch releases built differently (a statically-linked
+# official LLVM release binary vs. a distro's dynamically-linked one), so
+# reproducing this needs an apt-installed clang, not a hand-downloaded
+# LLVM release tarball.
+option(SENTINEL_ENABLE_MUTATION_TESTING
+  "Instrument sentinel-lib for mull mutation testing" OFF)
+set(MULL_IR_FRONTEND "" CACHE FILEPATH "Path to a matching mull-ir-frontend-N")
+
 add_subdirectory(lib)
 add_subdirectory(tools/cpp-sentinel)
 

lib/CMakeLists.txt

@@ -68,3 +68,18 @@ target_compile_definitions(sentinel-lib PRIVATE
   SENTINEL_CLANG_RESOURCE_DIR="${SENTINEL_CLANG_RESOURCE_DIR}"
   SENTINEL_VERSION="${PROJECT_VERSION}"
 )
+
+# Off by default, Linux-only (see docs/architecture.md "Mutation testing"):
+# instruments *only* sentinel-lib (not googletest/yaml-cpp/the test binary
+# itself) with mull's IR-frontend plugin, so mull-runner's mutant search
+# space stays scoped to code this project actually owns. Applying
+# -fpass-plugin globally (e.g. via CMAKE_CXX_FLAGS) instead instruments
+# every dependency too, which is what made an early attempt at this OOM.
+if(SENTINEL_ENABLE_MUTATION_TESTING)
+  if(NOT MULL_IR_FRONTEND)
+    message(FATAL_ERROR
+      "SENTINEL_ENABLE_MUTATION_TESTING requires -DMULL_IR_FRONTEND=/path/to/mull-ir-frontend-N")
+  endif()
+  target_compile_options(sentinel-lib PRIVATE
+    -fpass-plugin=${MULL_IR_FRONTEND} -g -grecord-command-line)
+endif()

mull.yml

@@ -0,0 +1,8 @@
+# Config for mull (https://mull-project.com), only consulted when
+# SENTINEL_ENABLE_MUTATION_TESTING is on -- see docs/architecture.md
+# ("Mutation testing") for how to build and run this. Scopes mutants to
+# this project's own sources; sentinel-lib is also the only CMake target
+# actually compiled with the pass plugin (see lib/CMakeLists.txt), so this
+# is a second, belt-and-suspenders filter on top of that, not the only one.
+includePaths:
+  - ".*/lib/.*\\.cpp$"