cmake: Bump minimum required CMake version to 3.22

Ubuntu 20.04 LTS has reached the end of standard support. There no
longer appear to be compelling reasons to maintain compatibility with
CMake 3.16.
The new suggested minimum, CMake 3.22, is shipped with Ubuntu 22.04 LTS,
which is supported until April 2027.

This change also introduces new CMake policies, from CMP0098 to CMP0128.

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.16)
+cmake_minimum_required(VERSION 3.22)
 
 #=============================
 # Project / Package metadata
@@ -15,17 +15,6 @@ project(libsecp256k1
 enable_testing()
 list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake)
 
-if(CMAKE_VERSION VERSION_LESS 3.21)
-  # Emulates CMake 3.21+ behavior.
-  if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-    set(PROJECT_IS_TOP_LEVEL ON)
-    set(${PROJECT_NAME}_IS_TOP_LEVEL ON)
-  else()
-    set(PROJECT_IS_TOP_LEVEL OFF)
-    set(${PROJECT_NAME}_IS_TOP_LEVEL OFF)
-  endif()
-endif()
-
 # The library version is based on libtool versioning of the ABI. The set of
 # rules for updating the version can be found here:
 # https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html

CMakePresets.json

@@ -1,5 +1,4 @@
 {
-  "cmakeMinimumRequired": {"major": 3, "minor": 21, "patch": 0}, 
   "version": 3,
   "configurePresets": [
     {

src/CMakeLists.txt

@@ -48,20 +48,12 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     VERSION ${${PROJECT_NAME}_soversion}.${${PROJECT_NAME}_LIB_VERSION_AGE}.${${PROJECT_NAME}_LIB_VERSION_REVISION}
   )
 elseif(APPLE)
-  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.17)
-    math(EXPR ${PROJECT_NAME}_compatibility_version "${${PROJECT_NAME}_LIB_VERSION_CURRENT} + 1")
-    set_target_properties(secp256k1 PROPERTIES
-      MACHO_COMPATIBILITY_VERSION ${${PROJECT_NAME}_compatibility_version}
-      MACHO_CURRENT_VERSION ${${PROJECT_NAME}_compatibility_version}.${${PROJECT_NAME}_LIB_VERSION_REVISION}
-    )
-    unset(${PROJECT_NAME}_compatibility_version)
-  elseif(BUILD_SHARED_LIBS)
-    message(WARNING
-      "The 'compatibility version' and 'current version' values of the DYLIB "
-      "will diverge from the values set by the GNU Libtool. To ensure "
-      "compatibility, it is recommended to upgrade CMake to at least version 3.17."
-    )
-  endif()
+  math(EXPR ${PROJECT_NAME}_compatibility_version "${${PROJECT_NAME}_LIB_VERSION_CURRENT} + 1")
+  set_target_properties(secp256k1 PROPERTIES
+    MACHO_COMPATIBILITY_VERSION ${${PROJECT_NAME}_compatibility_version}
+    MACHO_CURRENT_VERSION ${${PROJECT_NAME}_compatibility_version}.${${PROJECT_NAME}_LIB_VERSION_REVISION}
+  )
+  unset(${PROJECT_NAME}_compatibility_version)
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
   set(${PROJECT_NAME}_windows "secp256k1")
   if(MSVC)