Add pid to the list of attributes automatically captured for tracing

README.org

@@ -159,7 +159,7 @@
 
 * Tracing
   Lager supports basic support for redirecting log messages based on log message
-  attributes. Lager automatically captures the module, function and line at the
+  attributes. Lager automatically captures the pid, module, function and line at the
   log message callsite. However, you can add any additional attributes you wish:
 
 #+BEGIN_EXAMPLE
@@ -207,3 +207,10 @@
   ...
   lager:stop_trace(Trace)
 #+END_EXAMPLE
+
+  Tracing to a pid is somewhat of a special case, since a pid is not a
+  data-type that serializes well. To trace by pid, use the pid as a string:
+
+#+BEGIN_EXAMPLE
+  lager:trace_console([{pid, "<0.410.0>"}])
+#+END_EXAMPLE

src/lager_transform.erl

@@ -65,9 +65,14 @@ transform_statement({call, Line, {remote, Line1, {atom, Line2, lager},
                         {atom, Line, module}, {atom, Line, get(module)}]},
                     {cons, Line, {tuple, Line, [
                                 {atom, Line, function}, {atom, Line, get(function)}]},
-                    {cons, Line, {tuple, Line, [{atom, Line, line}, {integer,
-                                    Line, Line}]},
-                        {nil, Line}}}},
+                        {cons, Line, {tuple, Line, [
+                                    {atom, Line, line},
+                                    {integer, Line, Line}]},
+                        {cons, Line, {tuple, Line, [
+                                    {atom, Line, pid},
+                                    {call, Line, {atom, Line, pid_to_list}, [
+                                            {call, Line, {atom, Line ,self}, []}]}]},
+                            {nil, Line}}}}},
             {Traces, Arguments} = case Arguments0 of
                 [Format] ->
                     {DefaultAttrs, [Format, {nil, Line}]};