Fix basho/rebar#388

If the syntax error is in a .hrl file, then the reported error message
is not as useful because it's not clear which .erl file was being
compiled. We can fix that easily by first printing what source file was
being processed. We don't change the actual error message, so this will
still work with your editor of choice for jumping to the right line.

Before
------

Success:
Compiled src/foo.erl

Failure:
include/foo.hrl:10: syntax error [...]

After
-----

Success:
Compiled src/foo.erl

Failure:
Compiling src/foo.erl failed:
include/foo.hrl:10: syntax error [...]

src/rebar_base_compiler.erl

@@ -49,7 +49,7 @@ run(Config, FirstFiles, RestFiles, CompileFn) ->
             Jobs = rebar:get_jobs(Config),
             ?DEBUG("Starting ~B compile worker(s)~n", [Jobs]),
             Pids = [spawn_monitor(F) || _I <- lists:seq(1,Jobs)],
-            compile_queue(Pids, RestFiles)
+            compile_queue(Config, Pids, RestFiles)
     end.
 
 run(Config, FirstFiles, SourceDir, SourceExt, TargetDir, TargetExt,
@@ -139,27 +139,31 @@ compile_each([Source | Rest], Config, CompileFn) ->
         skipped ->
             ?INFO("Skipped ~s\n", [Source]);
         Error ->
+            ?CONSOLE("Compiling ~s failed:\n",
+                     [maybe_absname(Config, Source)]),
             maybe_report(Error),
             ?DEBUG("Compilation failed: ~p\n", [Error]),
             ?FAIL
     end,
     compile_each(Rest, Config, CompileFn).
 
-compile_queue([], []) ->
+compile_queue(_Config, [], []) ->
     ok;
-compile_queue(Pids, Targets) ->
+compile_queue(Config, Pids, Targets) ->
     receive
         {next, Worker} ->
             case Targets of
                 [] ->
                     Worker ! empty,
-                    compile_queue(Pids, Targets);
+                    compile_queue(Config, Pids, Targets);
                 [Source | Rest] ->
                     Worker ! {compile, Source},
-                    compile_queue(Pids, Rest)
+                    compile_queue(Config, Pids, Rest)
             end;
 
-        {fail, Error} ->
+        {fail, [_, {source, Source}}=Error] ->
+            ?CONSOLE("Compiling ~s failed:\n",
+                     [maybe_absname(Config, Source)]),
             maybe_report(Error),
             ?DEBUG("Worker compilation failed: ~p\n", [Error]),
             ?FAIL;
@@ -167,20 +171,20 @@ compile_queue(Pids, Targets) ->
         {compiled, Source, Warnings} ->
             report(Warnings),
             ?CONSOLE("Compiled ~s\n", [Source]),
-            compile_queue(Pids, Targets);
+            compile_queue(Config, Pids, Targets);
 
         {compiled, Source} ->
             ?CONSOLE("Compiled ~s\n", [Source]),
-            compile_queue(Pids, Targets);
+            compile_queue(Config, Pids, Targets);
 
         {skipped, Source} ->
             ?INFO("Skipped ~s\n", [Source]),
-            compile_queue(Pids, Targets);
+            compile_queue(Config, Pids, Targets);
 
         {'DOWN', Mref, _, Pid, normal} ->
             ?DEBUG("Worker exited cleanly\n", []),
             Pids2 = lists:delete({Pid, Mref}, Pids),
-            compile_queue(Pids2, Targets);
+            compile_queue(Config, Pids2, Targets);
 
         {'DOWN', _Mref, _, _Pid, Info} ->
             ?DEBUG("Worker failed: ~p\n", [Info]),
@@ -239,12 +243,7 @@ report(Messages) ->
 
 format_errors(Config, _MainSource, Extra, Errors) ->
     [begin
-         AbsSource = case rebar_utils:processing_base_dir(Config) of
-                         true ->
-                             Source;
-                         false ->
-                             filename:absname(Source)
-                     end,
+         AbsSource = maybe_absname(Config, Source),
          [format_error(AbsSource, Extra, Desc) || Desc <- Descs]
      end
      || {Source, Descs} <- Errors].
@@ -258,3 +257,11 @@ format_error(AbsSource, Extra, {Line, Mod, Desc}) ->
 format_error(AbsSource, Extra, {Mod, Desc}) ->
     ErrorDesc = Mod:format_error(Desc),
     ?FMT("~s: ~s~s~n", [AbsSource, Extra, ErrorDesc]).
+
+maybe_absname(Config, Filename) ->
+    case rebar_utils:processing_base_dir(Config) of
+        true ->
+            Filename;
+        false ->
+            filename:absname(Filename)
+    end.