java FFI: display a clean error when java module is not imported

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/src/common_ffi/java.nit b/src/common_ffi/java.nit
index 330336f..97d416f 100644 (file)
--- a/src/common_ffi/java.nit
+++ b/src/common_ffi/java.nit
@@ -290,8 +290,10 @@ redef class AExternPropdef
                var sys_class = modelbuilder.try_get_mclass_by_name(self, mmodule, "Sys")
                assert sys_class != null
                var sys_jni_env_meth = modelbuilder.try_get_mproperty_by_name2(self, mmodule, sys_class.mclass_type, "jni_env")
-               assert sys_jni_env_meth != null
-               assert sys_jni_env_meth isa MMethod
+               if sys_jni_env_meth == null or not sys_jni_env_meth isa MMethod then
+                       toolcontext.error(self.location, "Java FFI error: you must import the `java` module when using the FFI with Java")
+                       return
+               end
 
                explicit_call = new MExplicitCall(sys_class.mclass_type, sys_jni_env_meth, mmodule)
                fcc.callbacks.add(explicit_call)