Use backwards compatible term_to_binary (#408)

* Use backwards compatible term_to_binary

So that where we have hashed term_to_binary output in OTP25 or earlier, that has will be matched in OTP 26.

* Test reliability

If all keys are put in order, the max_slots may not be used, as the driver at L0 is penciller cache size, and merge to new files (managed by the parameter) only occurs when there are overlapping files the level below

src/leveled_util.erl

@@ -11,6 +11,7 @@
             integer_now/0,
             integer_time/1,
             magic_hash/1,
+            t2b/1,
             safe_rename/4]).
 
 -define(WRITE_OPS, [binary, raw, read, write]).
@@ -53,7 +54,7 @@ magic_hash({binary, BinaryKey}) ->
     H = 5381,
     hash1(H, BinaryKey) band 16#FFFFFFFF;
 magic_hash(AnyKey) ->
-    BK = term_to_binary(AnyKey),
+    BK = t2b(AnyKey),
     magic_hash({binary, BK}).
 
 hash1(H, <<>>) -> 
@@ -64,6 +65,17 @@ hash1(H, <<B:8/integer, Rest/bytes>>) ->
     hash1(H2, Rest).
 
 
+-spec t2b(term()) -> binary().
+%% @doc
+%% term_to_binary with options necessary to ensure backwards compatability
+%% in the handling of atoms (within OTP 26).
+%% See https://github.com/martinsumner/leveled/issues/407
+%% If the binary() which is outputted is to be hashed for comparison, then
+%% this must be used.
+t2b(Term) ->
+    term_to_binary(Term, [{minor_version, 1}]).
+
+
 -spec safe_rename(string(), string(), binary(), boolean()) -> ok.
 %% @doc
 %% Write a file, sync it and rename it (and for super-safe mode read it back)