build: Error if required module explicitly off

Author: real-or-random

CMakeLists.txt

@@ -68,6 +68,9 @@ if(SECP256K1_ENABLE_MODULE_ELLSWIFT)
 endif()
 
 if(SECP256K1_ENABLE_MODULE_SCHNORRSIG)
+  if(DEFINED SECP256K1_ENABLE_MODULE_EXTRAKEYS AND NOT SECP256K1_ENABLE_MODULE_EXTRAKEYS)
+    message(FATAL_ERROR "Module dependency error: You have disabled the extrakeys module explicitly, but it is required by the schnorrsig module.")
+  endif()
   set(SECP256K1_ENABLE_MODULE_EXTRAKEYS ON)
   add_compile_definitions(ENABLE_MODULE_SCHNORRSIG=1)
 endif()

configure.ac

@@ -394,6 +394,9 @@ if test x"$enable_module_ellswift" = x"yes"; then
 fi
 
 if test x"$enable_module_schnorrsig" = x"yes"; then
+  if test x"$enable_module_extrakeys" = x"no"; then
+    AC_MSG_ERROR([Module dependency error: You have disabled the extrakeys module explicitly, but it is required by the schnorrsig module.])
+  fi
   enable_module_extrakeys=yes
   SECP_CONFIG_DEFINES="$SECP_CONFIG_DEFINES -DENABLE_MODULE_SCHNORRSIG=1"
 fi