Merge pull request #298 from habibutsu/master

Function for printing stacktrace in human readable form

README.md

@@ -392,6 +392,20 @@ Lager 2.0 changed the backend API, there are various 3rd party backends for
 lager available, but they may not have been updated to the new API. As they
 are updated, links to them can be re-added here.
 
+Exception Pretty Printing
+----------------------
+
+```erlang
+try
+    foo()
+catch
+    Class:Reason ->
+        lager:error(
+            "~nStacktrace:~s",
+            [lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})])
+end.
+```
+
 Record Pretty Printing
 ----------------------
 Lager's parse transform will keep track of any record definitions it encounters

src/error_logger_lager_h.erl

@@ -31,7 +31,7 @@
 -export([init/1, handle_call/2, handle_event/2, handle_info/2, terminate/2,
         code_change/3]).
 
--export([format_reason/1]).
+-export([format_reason/1, format_mfa/1, format_args/3]).
 
 -record(state, { 
         shaper :: lager_shaper(),

src/lager.erl

@@ -33,7 +33,7 @@
         get_loglevel/1, get_loglevel/2, set_loglevel/2, set_loglevel/3, set_loglevel/4, get_loglevels/1,
         update_loglevel_config/1, posix_error/1, set_loghwm/2, set_loghwm/3, set_loghwm/4,
         safe_format/3, safe_format_chop/3, unsafe_format/2, dispatch_log/5, dispatch_log/7, dispatch_log/9,
-        do_log/9, do_log/10, do_log_unsafe/10, pr/2, pr/3]).
+        do_log/9, do_log/10, do_log_unsafe/10, pr/2, pr/3, pr_stacktrace/1, pr_stacktrace/2]).
 
 -type log_level() :: debug | info | notice | warning | error | critical | alert | emergency.
 -type log_level_number() :: 0..7.
@@ -580,3 +580,17 @@ is_record_known(Record, Module) ->
             end
     end.
 
+
+%% @doc Print stacktrace in human readable form
+pr_stacktrace(Stacktrace) ->
+    Indent = "\n    ",
+    lists:foldl(
+        fun(Entry, Acc) ->
+            Acc ++ Indent ++ error_logger_lager_h:format_mfa(Entry)
+        end,
+        [],
+        lists:reverse(Stacktrace)).
+
+pr_stacktrace(Stacktrace, {Class, Reason}) ->
+    lists:flatten(
+        pr_stacktrace(Stacktrace) ++ "\n" ++ io_lib:format("~s:~p", [Class, Reason])).

test/pr_stacktrace_test.erl

@@ -0,0 +1,55 @@
+-module(pr_stacktrace_test).
+
+-compile([{parse_transform, lager_transform}]).
+
+-include_lib("eunit/include/eunit.hrl").
+
+make_throw() ->
+    throw({test, exception}).
+
+bad_arity() ->
+    lists:concat([], []).
+
+bad_arg() ->
+    integer_to_list(1.0).
+
+pr_stacktrace_throw_test() ->
+    Result = try
+        make_throw()
+    catch
+        Class:Reason ->
+            lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})
+    end,
+ExpectedPart = "
+    pr_stacktrace_test:pr_stacktrace_throw_test/0 line 18
+    pr_stacktrace_test:make_throw/0 line 8
+throw:{test,exception}",
+    ?assertNotEqual(0, string:str(Result, ExpectedPart)).
+
+
+pr_stacktrace_bad_arg_test() ->
+    Result = try
+        bad_arg()
+    catch
+        Class:Reason ->
+            lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})
+    end,
+ExpectedPart = "
+    pr_stacktrace_test:pr_stacktrace_bad_arg_test/0 line 32
+    pr_stacktrace_test:bad_arg/0 line 14
+error:badarg",
+    ?assertNotEqual(0, string:str(Result, ExpectedPart)).
+
+
+pr_stacktrace_bad_arity_test() ->
+    Result = try
+        bad_arity()
+    catch
+        Class:Reason ->
+            lager:pr_stacktrace(erlang:get_stacktrace(), {Class, Reason})
+    end,
+ExpectedPart = "
+    pr_stacktrace_test:pr_stacktrace_bad_arity_test/0 line 46
+    lists:concat([], [])
+error:undef",
+    ?assertNotEqual(0, string:str(Result, ExpectedPart)).