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Reapply "[lldb/cmake] Plugin layering enforcement mechanism (#144543)" (#145305)
The only difference from the original PR are the added BRIEF and FULL_DOCS arguments to define_property, which are required for cmake<3.23.
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‎lldb/CMakeLists.txt

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@@ -37,6 +37,7 @@ endif()
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include(LLDBConfig)
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include(AddLLDB)
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include(LLDBLayeringCheck)
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set(LLDB_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/include)
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@@ -127,6 +128,8 @@ add_subdirectory(source)
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add_subdirectory(tools)
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add_subdirectory(docs)
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check_lldb_plugin_layering()
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if (LLDB_ENABLE_PYTHON)
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if(LLDB_BUILD_FRAMEWORK)
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set(lldb_python_target_dir "${LLDB_FRAMEWORK_ABSOLUTE_BUILD_DIR}/LLDB.framework/Resources/Python/lldb")

‎lldb/cmake/modules/LLDBLayeringCheck.cmake

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foreach (scope DIRECTORY TARGET)
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define_property(${scope} PROPERTY LLDB_PLUGIN_KIND INHERITED
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BRIEF_DOCS "LLDB plugin kind (Process, SymbolFile, etc.)"
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FULL_DOCS "See lldb/docs/resources/contributing.rst"
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)
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define_property(${scope} PROPERTY LLDB_ACCEPTABLE_PLUGIN_DEPENDENCIES INHERITED
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BRIEF_DOCS "LLDB plugin kinds which the plugin can depend on"
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FULL_DOCS "See lldb/docs/resources/contributing.rst"
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)
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define_property(${scope} PROPERTY LLDB_TOLERATED_PLUGIN_DEPENDENCIES INHERITED
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BRIEF_DOCS "LLDB plugin kinds which are depended on for historic reasons."
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FULL_DOCS "See lldb/docs/resources/contributing.rst"
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)
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endforeach()
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option(LLDB_GENERATE_PLUGIN_DEP_GRAPH OFF)
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function(check_lldb_plugin_layering)
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get_property(plugins GLOBAL PROPERTY LLDB_PLUGINS)
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foreach (plugin ${plugins})
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get_property(plugin_kind TARGET ${plugin} PROPERTY LLDB_PLUGIN_KIND)
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get_property(acceptable_deps TARGET ${plugin}
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PROPERTY LLDB_ACCEPTABLE_PLUGIN_DEPENDENCIES)
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get_property(tolerated_deps TARGET ${plugin}
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PROPERTY LLDB_TOLERATED_PLUGIN_DEPENDENCIES)
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# A plugin is always permitted to depend on its own kind for the purposes
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# subclassing. Ideally the intra-kind dependencies should not form a loop,
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# but we're not checking that here.
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list(APPEND acceptable_deps ${plugin_kind})
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list(APPEND all_plugin_kinds ${plugin_kind})
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get_property(link_libs TARGET ${plugin} PROPERTY LINK_LIBRARIES)
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foreach (link_lib ${link_libs})
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if(link_lib IN_LIST plugins)
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get_property(lib_kind TARGET ${link_lib} PROPERTY LLDB_PLUGIN_KIND)
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if (lib_kind)
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if (lib_kind IN_LIST acceptable_deps)
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set(dep_kind green)
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elseif (lib_kind IN_LIST tolerated_deps)
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set(dep_kind yellow)
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else()
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set(dep_kind red)
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message(SEND_ERROR "Plugin ${plugin} cannot depend on ${lib_kind} "
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"plugin ${link_lib}")
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endif()
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list(APPEND dep_${dep_kind}_${plugin_kind}_${lib_kind} ${plugin})
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endif()
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endif()
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endforeach()
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endforeach()
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if (LLDB_GENERATE_PLUGIN_DEP_GRAPH)
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set(dep_graph "digraph Plugins {\n")
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list(REMOVE_DUPLICATES all_plugin_kinds)
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foreach (from ${all_plugin_kinds})
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foreach (to ${all_plugin_kinds})
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foreach (dep_kind green yellow red)
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if (dep_${dep_kind}_${from}_${to})
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list(REMOVE_DUPLICATES dep_${dep_kind}_${from}_${to})
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string(REGEX REPLACE "lldbPlugin|${from}" "" short_deps
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"${dep_${dep_kind}_${from}_${to}}")
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string(JOIN "\n" plugins ${short_deps})
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string(APPEND dep_graph
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" ${from}->${to}[color=\"${dep_kind}\" label=\"${plugins}\"];\n")
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endif()
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endforeach()
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endforeach()
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endforeach()
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string(APPEND dep_graph "}\n")
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file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/lldb-plugin-deps.dot" "${dep_graph}")
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endif()
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endfunction()

‎lldb/docs/resources/contributing.rst

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@@ -56,6 +56,56 @@ subset of LLDB tests (the API tests) use a different system. Refer to the
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`lldb/test <https://github.com/llvm/llvm-project/tree/main/lldb/test>`_ folder
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for examples.
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LLDB plugins and their dependencies
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-----------------------------------
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LLDB has a concept of *plugins*, which are used to provide abstraction
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boundaries over functionality that is specific to a certain architecture,
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operating system, programming language, etc. A plugin implements an abstract
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base class (rarely, a set of related base classes), which is a part of LLDB
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core. This setup allows the LLDB core to remain generic while making it possible
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to support for new architectures, languages, and so on. For this to work, all
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code needs to obey certain rules.
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The principal rule is that LLDB core (defined as: everything under lldb/source
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*minus* lldb/source/Plugins) must not depend on any specific plugin. The only
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way it can interact with them is through the abstract interface. Explicit
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dependencies such as casting the base class to the plugin type are not permitted
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and neither are more subtle dependencies like checking the name plugin or or
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other situations where some code in LLDB core is tightly coupled to the
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implementation details of a specific plugin.
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The rule for interaction between different plugins is more nuanced. We recognize
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that some cross-plugin dependencies are unavoidable or even desirable. For
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example, a plugin may want to extend a plugin of the same kind to
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add/override/refine some functionality (e.g., Android is a "kind of" Linux, but
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it handles some things differently). Alternatively, a plugin of one kind may
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want to build on the functionality offered by a specific plugin of another kind
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(ELFCore Process plugin uses ELF ObjectFile plugin to create a process out of an
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ELF core file).
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In cases such as these, direct dependencies are acceptable. However, to keep the
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dependency graph manageable, we still have some rules to govern these
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relationships:
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* All dependencies between plugins of the same kind must flow in the same
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direction (if plugin `A1` depends on plugin `B1`, then `B2` must not depend on
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`A2`)
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* Dependency graph of plugin kinds must not contain loops (dependencies like
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`A1->B1`, `B2->C2` and `C3->A3` are forbidden because they induce a cycle in
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the plugin kind graph even though the plugins themselves are acyclical)
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The first of these rules is checked via CMake scripts (using the
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`LLDB_ACCEPTABLE_PLUGIN_DEPENDENCIES` property). Dependencies in this category
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are expected and permitted (subject to other constraints such as that dependency
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making sense for the particular pair of plugins). Unfortunately, due to historic
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reasons, not all plugin dependencies follow this rule, which is why we have
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another category called `LLDB_TOLERATED_PLUGIN_DEPENDENCIES`. New dependencies
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are forbidden (even though they are accepted by CMake) and existing ones should
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be removed whereever possible.
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.. _Error handling:
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Error handling and use of assertions in LLDB

‎lldb/source/Plugins/ABI/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND ABI)
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set_property(DIRECTORY PROPERTY LLDB_TOLERATED_PLUGIN_DEPENDENCIES
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ProcessUtility
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TypeSystem
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)
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foreach(target AArch64 ARM ARC Hexagon LoongArch Mips MSP430 PowerPC RISCV SystemZ X86)
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if (${target} IN_LIST LLVM_TARGETS_TO_BUILD)
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add_subdirectory(${target})

‎lldb/source/Plugins/Architecture/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND Architecture)
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add_subdirectory(Arm)
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add_subdirectory(Mips)
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add_subdirectory(PPC64)

‎lldb/source/Plugins/Disassembler/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND Disassembler)
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add_subdirectory(LLVMC)

‎lldb/source/Plugins/DynamicLoader/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND DynamicLoader)
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set_property(DIRECTORY PROPERTY LLDB_ACCEPTABLE_PLUGIN_DEPENDENCIES ObjectFile)
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set_property(DIRECTORY PROPERTY LLDB_TOLERATED_PLUGIN_DEPENDENCIES
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Process # part of a loop (Process<->DynamicLoader).
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TypeSystem
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)
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add_subdirectory(Darwin-Kernel)
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add_subdirectory(FreeBSD-Kernel)
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add_subdirectory(MacOSX-DYLD)

‎lldb/source/Plugins/ExpressionParser/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND ExpressionParser)
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add_subdirectory(Clang)

‎lldb/source/Plugins/Instruction/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND Instruction)
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add_subdirectory(ARM)
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add_subdirectory(ARM64)
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add_subdirectory(LoongArch)

‎lldb/source/Plugins/InstrumentationRuntime/CMakeLists.txt

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set_property(DIRECTORY PROPERTY LLDB_PLUGIN_KIND InstrumentationRuntime)
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add_subdirectory(ASan)
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add_subdirectory(ASanLibsanitizers)
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add_subdirectory(MainThreadChecker)

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