Clean up serialization build code (#8369)

packaging/CMakeLists.txt

@@ -37,7 +37,7 @@ if (TARGET Halide_Adams2019)
 endif ()
 
 # Halide_LLVM
-foreach (dep IN ITEMS Halide_LLVM Halide_wabt Halide_flatbuffers)
+foreach (dep IN ITEMS Halide_LLVM Halide_wabt)
     if (TARGET ${dep})
         install(TARGETS ${dep} EXPORT Halide_Targets)
     endif ()

src/CMakeLists.txt

@@ -442,68 +442,46 @@ add_library(Halide
 
 # Build serialization, enabled by default
 option(WITH_SERIALIZATION "Include experimental Serialization/Deserialization code" ON)
-
-# flatbuffers is small and compiles quickly, but if you want/need to use
-# a local version (via find_package), configure with FLATBUFFERS_USE_FETCHCONTENT=OFF
-option(FLATBUFFERS_USE_FETCHCONTENT "Enable to download the Flatbuffers library via FetchContent" ON)
-set(FLATBUFFERS_VER 23.5.26 CACHE STRING "The Flatbuffers version to use (or download)")
-
 if (WITH_SERIALIZATION)
+    # flatbuffers is small and compiles quickly, but if you want/need to use
+    # a local version (via find_package), configure with FLATBUFFERS_USE_FETCHCONTENT=OFF
+    option(FLATBUFFERS_USE_FETCHCONTENT "Enable to download the Flatbuffers library via FetchContent" ON)
+    set(FLATBUFFERS_VER 23.5.26 CACHE STRING "The Flatbuffers version to use (or download) ")
+
     if (FLATBUFFERS_USE_FETCHCONTENT)
         include(FetchContent)
-        message(STATUS "Fetching flatbuffers ${FLATBUFFERS_VER}...")
         FetchContent_Declare(
             flatbuffers
             GIT_REPOSITORY https://github.com/google/flatbuffers.git
             GIT_TAG v${FLATBUFFERS_VER}
             GIT_SHALLOW TRUE
+            SYSTEM
         )
         # configuration for flatbuffers
         set(FLATBUFFERS_BUILD_TESTS OFF)
         set(FLATBUFFERS_INSTALL OFF)
         FetchContent_MakeAvailable(flatbuffers)
         set_target_properties(flatbuffers PROPERTIES POSITION_INDEPENDENT_CODE ON)
 
-        add_library(Halide_flatbuffers INTERFACE)
-        target_sources(Halide_flatbuffers INTERFACE $<BUILD_INTERFACE:$<TARGET_OBJECTS:flatbuffers>>)
-        target_include_directories(Halide_flatbuffers
-                                   SYSTEM # Use -isystem instead of -I; this is a trick so that clang-tidy won't analyze these includes
-                                   INTERFACE
-                                   $<BUILD_INTERFACE:${flatbuffers_SOURCE_DIR}>/include
-                                   $<BUILD_INTERFACE:${flatbuffers_BINARY_DIR}>/include)
-        set_target_properties(Halide_flatbuffers PROPERTIES EXPORT_NAME flatbuffers)
-
+        add_library(flatbuffers::flatbuffers ALIAS flatbuffers)
         add_executable(flatbuffers::flatc ALIAS flatc)
+
         message(STATUS "Using fetched-and-built flatbuffers, version ${FLATBUFFERS_VER}")
+        set(flatbuffers_target "$<BUILD_LOCAL_INTERFACE:flatbuffers::flatbuffers>")
     else ()
-        # Sadly, there seem to be at least three variations of the Flatbuffer package
-        # in terms of the case of the relevant CMake files; if we guess wrong, we
-        # fail on case-sensitive file systems. We'll try this as a hack workaround:
-        # just try all three. (Note that the internal CMake library name appears to be
-        # `flatbuffers` in all cases.)
-        set(FB_NAME "")
-        foreach (N IN ITEMS flatbuffers Flatbuffers FlatBuffers)
-            # TODO: should we check the version here?
-            find_package(${N} QUIET)
-            if (${N}_FOUND)
-                set(FB_NAME ${N})
-                message(STATUS "Using installed flatbuffers, version ${${N}_VERSION}")
-                break()
-            endif ()
-        endforeach ()
-
-        if (NOT FB_NAME)
-            message(FATAL_ERROR "WITH_SERIALIZATION is ON and FLATBUFFERS_USE_FETCHCONTENT is OFF, "
-                                "but could not find flatbuffers installed locally. "
-                                "Either install flatbuffers or build with WITH_SERIALIZATION=OFF.")
-        endif ()
-
-        add_library(Halide_flatbuffers ALIAS flatbuffers::flatbuffers)
+        # Sadly, there seem to be at least three variations of the Flatbuffer
+        # package in terms of the case of the relevant CMake files. Fortunately,
+        # the IMPORTED targets appear to be consistently named `flatbuffers`.
+        find_package(
+            flatbuffers ${FLATBUFFERS_VER}
+            NAMES flatbuffers Flatbuffers FlatBuffers
+            REQUIRED
+        )
+        set(flatbuffers_target flatbuffers::flatbuffers)
     endif ()
 
-    set(fb_dir "${Halide_BINARY_DIR}/flatc/include")
-
     set(fb_def "${CMAKE_CURRENT_SOURCE_DIR}/halide_ir.fbs")
+    set(fb_dir "${Halide_BINARY_DIR}/include/flatc")
     set(fb_header "${fb_dir}/halide_ir.fbs.h")
     add_custom_command(
         OUTPUT "${fb_header}"
@@ -512,21 +490,21 @@ if (WITH_SERIALIZATION)
         VERBATIM
     )
     add_custom_target(generate_fb_header DEPENDS "${fb_header}")
-    set_source_files_properties("${fb_header}" PROPERTIES GENERATED TRUE)
 
     add_dependencies(Halide generate_fb_header)
     target_include_directories(Halide PRIVATE "$<BUILD_INTERFACE:${fb_dir}>")
-    target_link_libraries(Halide PRIVATE Halide_flatbuffers)
+    target_link_libraries(Halide PRIVATE ${flatbuffers_target})
     target_compile_definitions(Halide PRIVATE WITH_SERIALIZATION)
 endif ()
 
 # Enable serialization testing by intercepting JIT compilation with a serialization roundtrip;
 # This is used only for special builds made specifically for testing, and must be disabled by default.
-option(WITH_SERIALIZATION_JIT_ROUNDTRIP_TESTING "Intercepting JIT compilation with a serialization roundtrip, for test only" OFF)
+cmake_dependent_option(
+    WITH_SERIALIZATION_JIT_ROUNDTRIP_TESTING "Intercepting JIT compilation with a serialization roundtrip, for test only" OFF
+    "WITH_SERIALIZATION" OFF
+)
 if (WITH_SERIALIZATION_JIT_ROUNDTRIP_TESTING)
-    if (WITH_SERIALIZATION)
-        target_compile_definitions(Halide PRIVATE WITH_SERIALIZATION_JIT_ROUNDTRIP_TESTING)
-    endif ()
+    target_compile_definitions(Halide PRIVATE WITH_SERIALIZATION_JIT_ROUNDTRIP_TESTING)
 endif ()
 
 add_library(Halide::Halide ALIAS Halide)