cmake: refactor zlib selection

Move zlib selection into its own cmake module.

cmake/SelectZlib.cmake

+# Optional external dependency: zlib
+include(SanitizeBool)
+
+SanitizeBool(USE_BUNDLED_ZLIB)
+if(USE_BUNDLED_ZLIB STREQUAL ON)
+	set(USE_BUNDLED_ZLIB "Bundled")
+endif()
+
+if(USE_BUNDLED_ZLIB STREQUAL "OFF")
+	find_package(ZLIB)
+	if(ZLIB_FOUND)
+		list(APPEND LIBGIT2_SYSTEM_INCLUDES ${ZLIB_INCLUDE_DIRS})
+		list(APPEND LIBGIT2_LIBS ${ZLIB_LIBRARIES})
+		if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
+			list(APPEND LIBGIT2_PC_LIBS "-lz")
+		else()
+			list(APPEND LIBGIT2_PC_REQUIRES "zlib")
+		endif()
+		add_feature_info(zlib ON "using system zlib")
+	else()
+		message(STATUS "zlib was not found; using bundled 3rd-party sources." )
+	endif()
+endif()
+if(USE_BUNDLED_ZLIB STREQUAL "Chromium")
+	add_subdirectory("${libgit2_SOURCE_DIR}/deps/chromium-zlib" "${libgit2_BINARY_DIR}/deps/chromium-zlib")
+	list(APPEND LIBGIT2_INCLUDES "${libgit2_SOURCE_DIR}/deps/chromium-zlib")
+	list(APPEND LIBGIT2_OBJECTS $<TARGET_OBJECTS:chromium_zlib>)
+	add_feature_info(zlib ON "using (Chromium) bundled zlib")
+elseif(USE_BUNDLED_ZLIB OR NOT ZLIB_FOUND)
+	add_subdirectory("${libgit2_SOURCE_DIR}/deps/zlib" "${libgit2_BINARY_DIR}/deps/zlib")
+	list(APPEND LIBGIT2_INCLUDES "${libgit2_SOURCE_DIR}/deps/zlib")
+	list(APPEND LIBGIT2_OBJECTS $<TARGET_OBJECTS:zlib>)
+	add_feature_info(zlib ON "using bundled zlib")
+endif()

src/CMakeLists.txt

@@ -99,42 +99,10 @@ include(SelectHTTPParser)
 include(SelectRegex)
 include(SelectSSH)
 include(SelectWinHTTP)
+include(SelectZlib)
 
 target_sources(git2internal PRIVATE ${SRC_SHA1})
 
-# Optional external dependency: zlib
-SanitizeBool(USE_BUNDLED_ZLIB)
-if(USE_BUNDLED_ZLIB STREQUAL ON)
-	set(USE_BUNDLED_ZLIB "Bundled")
-endif()
-
-if(USE_BUNDLED_ZLIB STREQUAL "OFF")
-	find_package(ZLIB)
-	if(ZLIB_FOUND)
-		list(APPEND LIBGIT2_SYSTEM_INCLUDES ${ZLIB_INCLUDE_DIRS})
-		list(APPEND LIBGIT2_LIBS ${ZLIB_LIBRARIES})
-		if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
-			list(APPEND LIBGIT2_PC_LIBS "-lz")
-		else()
-			list(APPEND LIBGIT2_PC_REQUIRES "zlib")
-		endif()
-		add_feature_info(zlib ON "using system zlib")
-	else()
-		message(STATUS "zlib was not found; using bundled 3rd-party sources." )
-	endif()
-endif()
-if(USE_BUNDLED_ZLIB STREQUAL "Chromium")
-	add_subdirectory("${libgit2_SOURCE_DIR}/deps/chromium-zlib" "${libgit2_BINARY_DIR}/deps/chromium-zlib")
-	list(APPEND LIBGIT2_INCLUDES "${libgit2_SOURCE_DIR}/deps/chromium-zlib")
-	list(APPEND LIBGIT2_OBJECTS $<TARGET_OBJECTS:chromium_zlib>)
-	add_feature_info(zlib ON "using (Chromium) bundled zlib")
-elseif(USE_BUNDLED_ZLIB OR NOT ZLIB_FOUND)
-	add_subdirectory("${libgit2_SOURCE_DIR}/deps/zlib" "${libgit2_BINARY_DIR}/deps/zlib")
-	list(APPEND LIBGIT2_INCLUDES "${libgit2_SOURCE_DIR}/deps/zlib")
-	list(APPEND LIBGIT2_OBJECTS $<TARGET_OBJECTS:zlib>)
-	add_feature_info(zlib ON "using bundled zlib")
-endif()
-
 # Optional external dependency: ntlmclient
 if(USE_NTLMCLIENT)
 	set(GIT_NTLM 1)