adds llvm-project to //third_party

Rather than depending on the system's LLVM and Clang, we move Subspace
to pull a specific version of llvm-project instead. Due to more modern
versions of LLVM being incompatible with Subdoc, we conservatively pin
the tag at LLVM 17.0.6, which is the version used by CI.

Author: Christopher Di Bella

subdoc/CMakeLists.txt

@@ -83,16 +83,23 @@ add_executable(subdoc
 # subdoc_lib
 subspace_default_compile_options(subdoc_lib)
 
-find_package(LLVM REQUIRED)
-find_package(Clang REQUIRED)
 llvm_config(subdoc_lib)
-target_include_directories(subdoc_lib PUBLIC ${LLVM_INCLUDE_DIRS})
-target_link_directories(subdoc_lib PUBLIC ${LLVM_LIBRARY_DIRS})
+include(FetchContent)
+FetchContent_GetProperties(llvm-project)
+target_include_directories(subdoc_lib PUBLIC
+    "${llvm-project_SOURCE_DIR}/clang/include"
+    "${llvm-project_SOURCE_DIR}/llvm/include"
+    "${llvm-project_BINARY_DIR}/include"
+    "${llvm-project_BINARY_DIR}/tools/clang/include"
+)
+target_link_directories(subdoc_lib PUBLIC
+    "${llvm-project_BINARY_DIR}/clang/lib"
+)
 
-target_link_libraries(subdoc_lib
-    subspace::lib
-    md4c
-    md4c-html
+set(SUBDOC_LLVM_DEPS
+    Support
+)
+set(SUBDOC_CLANG_DEPS
     clangAnalysis
     clangAnalysisFlowSensitive
     clangAnalysisFlowSensitiveModels
@@ -136,6 +143,14 @@ target_link_libraries(subdoc_lib
     clangToolingSyntax
     clangTransformer
 )
+llvm_map_components_to_libnames(llvm_libs "${SUBDOC_LLVM_DEPS};${SUBDOC_CLANG_DEPS}")
+
+target_link_libraries(subdoc_lib
+    subspace::lib
+    md4c
+    md4c-html
+    ${llvm_libs}
+)
 
 # subdoc binary
 subspace_binary_default_compile_options(subdoc)

third_party/CMakeLists.txt

@@ -1,5 +1,8 @@
 include(FetchContent)
 
+# Thirds-party projects should be built with warnings disabled to limit noise and build breaks.
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -w -Wno-error")
+
 # This directory handles third-party dependency package management.
 #
 # Packages that use CMake are handled using `FetchContent`. `FetchContent` is split into two

third_party/FetchContent_Declare.cmake

@@ -3,3 +3,4 @@ add_subdirectory(fmt)
 add_subdirectory(googletest)
 add_subdirectory(md4c)
 add_subdirectory(nanobench)
+add_subdirectory(llvm-project)

third_party/FetchContent_MakeAvailable.cmake

@@ -13,3 +13,5 @@ if(SUBSPACE_BUILD_BENCHMARKS)
   FetchContent_MakeAvailable(nanobench)
   set_property(TARGET nanobench PROPERTY CXX_STANDARD 20)
 endif()
+
+FetchContent_MakeAvailable(llvm-project)

third_party/llvm-project/CMakeLists.txt

@@ -0,0 +1,17 @@
+set(LLVM_BUILD_TOOLS               No      CACHE BOOL "")
+set(LLVM_ENABLE_PROJECTS          "llvm;clang" CACHE BOOL "")
+set(LLVM_ENABLE_WARNINGS           No      CACHE BOOL "")
+set(LLVM_INSTALL_BINUTILS_SYMLINKS No      CACHE BOOL "")
+set(LLVM_INSTALL_CCTOOLS_SYMLINKS  No      CACHE BOOL "")
+set(LLVM_TARGETS_TO_BUILD         "Native" CACHE BOOL "")
+set(LLVM_TOOLS_INSTALL_DIR        "bin"    CACHE STRING "")
+
+FetchContent_Declare(
+  llvm-project
+  GIT_REPOSITORY https://github.com/llvm/llvm-project.git
+  GIT_TAG        llvmorg-17.0.6
+  GIT_SHALLOW    Yes
+  SOURCE_SUBDIR  llvm
+  SYSTEM
+  OVERRIDE_FIND_PACKAGE
+)