cmake: Add docs and checks to AddTargetMacros module

Author: hebasto

cmake/module/AddTargetMacros.cmake

@@ -4,7 +4,14 @@
 
 include_guard(GLOBAL)
 
+# Functions in this module are drop-in replacements for CMake's add_library
+# and add_executable functions. They are mandatory for use in the Bitcoin
+# Core project, except for imported and interface libraries.
+
 function(subtree_add_library name)
+  if(NOT name MATCHES "^crc32c.*|^leveldb.*|^minisketch.*|^secp256k1.*")
+    message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION}() was called to add a non-subtree target \"${name}\".")
+  endif()
   cmake_parse_arguments(PARSE_ARGV 1 FWD "" "" "")
   add_library("${name}" ${FWD_UNPARSED_ARGUMENTS})
   target_link_libraries("${name}" PRIVATE core_base_interface)
@@ -17,6 +24,9 @@ function(subtree_add_library name)
 endfunction()
 
 function(bitcoincore_add_library name)
+  if(name MATCHES "^crc32c.*|^leveldb.*|^minisketch.*|^secp256k1.*")
+    message(FATAL_ERROR "${CMAKE_CURRENT_FUNCTION}() was called to add a subtree target \"${name}\".")
+  endif()
   cmake_parse_arguments(PARSE_ARGV 1 FWD "" "" "")
   add_library("${name}" ${FWD_UNPARSED_ARGUMENTS})
   target_link_libraries("${name}" PRIVATE core_interface)