add reverse_pretty_stacktrace env var, default true

src/lager.erl

@@ -597,18 +597,32 @@ is_record_known(Record, Module) ->
 
 %% @doc Print stacktrace in human readable form
 pr_stacktrace(Stacktrace) ->
+    Stacktrace1 = case application:get_env(lager, reverse_pretty_stacktrace, true) of
+                      true ->
+                          lists:reverse(Stacktrace);
+                      _ ->
+                          Stacktrace
+                  end,
+    pr_stacktrace_(Stacktrace1).
+
+pr_stacktrace_(Stacktrace) ->
     Indent = "\n    ",
     lists:foldl(
         fun(Entry, Acc) ->
             Acc ++ Indent ++ error_logger_lager_h:format_mfa(Entry)
         end,
         [],
-        lists:reverse(Stacktrace)).
+        Stacktrace).
 
 pr_stacktrace(Stacktrace, {Class, Reason}) ->
-    lists:flatten(
-        pr_stacktrace(Stacktrace) ++ "\n" ++ io_lib:format("~s:~p", [Class, Reason])).
-    
+    case application:get_env(lager, reverse_pretty_stacktrace, true) of
+        true ->
+            lists:flatten(
+              pr_stacktrace_(lists:reverse(Stacktrace)) ++ "\n" ++ io_lib:format("~s:~p", [Class, Reason]));
+        _ ->
+            lists:flatten(
+              io_lib:format("~s:~p", [Class, Reason]) ++ pr_stacktrace_(Stacktrace))
+    end.
 
 %% R15 compatibility only
 filtermap(Fun, List1) ->

test/pr_stacktrace_test.erl

@@ -52,4 +52,18 @@ ExpectedPart = "
     pr_stacktrace_test:pr_stacktrace_bad_arity_test/0 line 46
     lists:concat([], [])
 error:undef",
-    ?assertNotEqual(0, string:str(Result, ExpectedPart)).
+    ?assertNotEqual(0, string:str(Result, ExpectedPart)).
+
+pr_stacktrace_no_reverse_test() ->
+    application:set_env(lager, reverse_pretty_stacktrace, false),
+    Result = try
+        bad_arity()
+    catch
+        Class:Reason ->
+            lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})
+    end,
+ExpectedPart = "error:undef
+    lists:concat([], [])
+    pr_stacktrace_test:pr_stacktrace_bad_arity_test/0 line 60",
+
+    ?assertEqual(0, string:str(Result, ExpectedPart)).