xdiff: move xdiff to 'deps'

xdiff is a dependency (from git core) and more properly belongs in the
'deps' directory. Move it there, and add a stub for cmake to resolve
xdiff from the system location in the future. (At present, bundled xdiff
remains hardcoded.)

Author: Edward Thomson

CMakeLists.txt

@@ -36,6 +36,7 @@ option(USE_SHA1                "Enable SHA1. Can be set to CollisionDetection(ON
 option(USE_SHA256              "Enable SHA256. Can be set to HTTPS/Builtin" ON)
 option(USE_GSSAPI              "Link with libgssapi for SPNEGO auth"      OFF)
    set(USE_HTTP_PARSER         "" CACHE STRING "Specifies the HTTP Parser implementation; either system or builtin.")
+#  set(USE_XDIFF               "" CACHE STRING "Specifies the xdiff implementation; either system or builtin.")
    set(REGEX_BACKEND           "" CACHE STRING "Regular expression implementation. One of regcomp_l, pcre2, pcre, regcomp, or builtin.")
 option(USE_BUNDLED_ZLIB        "Use the bundled version of zlib. Can be set to one of Bundled(ON)/Chromium. The Chromium option requires a x86_64 processor with SSE4.2 and CLMUL" OFF)
 

cmake/SelectXdiff.cmake

@@ -0,0 +1,9 @@
+# Optional external dependency: xdiff
+if(USE_XDIFF STREQUAL "system")
+	message(FATAL_ERROR "external/system xdiff is not yet supported")
+else()
+	add_subdirectory("${PROJECT_SOURCE_DIR}/deps/xdiff" "${PROJECT_BINARY_DIR}/deps/xdiff")
+	list(APPEND LIBGIT2_DEPENDENCY_INCLUDES "${PROJECT_SOURCE_DIR}/deps/xdiff")
+	list(APPEND LIBGIT2_DEPENDENCY_OBJECTS "$<TARGET_OBJECTS:xdiff>")
+	add_feature_info(xdiff ON "xdiff support (bundled)")
+endif()

deps/xdiff/CMakeLists.txt

@@ -0,0 +1,28 @@
+
+file(GLOB SRC_XDIFF "*.c" "*.h")
+list(SORT SRC_XDIFF)
+
+add_library(xdiff OBJECT ${SRC_XDIFF})
+target_include_directories(xdiff SYSTEM PRIVATE
+	"${PROJECT_SOURCE_DIR}/include"
+	"${PROJECT_SOURCE_DIR}/src/util"
+	"${PROJECT_BINARY_DIR}/src/util"
+	${LIBGIT2_SYSTEM_INCLUDES}
+	${LIBGIT2_DEPENDENCY_INCLUDES})
+
+# the xdiff dependency is not (yet) warning-free, disable warnings
+# as errors for the xdiff sources until we've sorted them out
+if(MSVC)
+        set_source_files_properties(xdiffi.c PROPERTIES COMPILE_FLAGS -WX-)
+        set_source_files_properties(xemit.c PROPERTIES COMPILE_FLAGS -WX-)
+        set_source_files_properties(xhistogram.c PROPERTIES COMPILE_FLAGS -WX-)
+        set_source_files_properties(xmerge.c PROPERTIES COMPILE_FLAGS -WX-)
+        set_source_files_properties(xutils.c PROPERTIES COMPILE_FLAGS -WX-)
+        set_source_files_properties(xpatience.c PROPERTIES COMPILE_FLAGS -WX-)
+else()
+        set_source_files_properties(xdiffi.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare -Wno-unused-parameter")
+        set_source_files_properties(xemit.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare -Wno-unused-parameter")
+        set_source_files_properties(xhistogram.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
+        set_source_files_properties(xutils.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
+        set_source_files_properties(xpatience.c PROPERTIES COMPILE_FLAGS "-Wno-sign-compare")
+endif()