Dereference symbolic links when copying files from ct data folder

When running `rebar3 ct`, `rebar_prv_common_test` copies the data folders
to a different location. If `{name}_SUITE_data` folder contains relative
symbolic links, the symbolic links might stop working since the path
might be different.

A solution is to add the `-L` option to `cp` so it dereferences the
symbolic links and copies the original content in the target file.

This is only done for the data folder but and won't change any code that
previously used `rebar_file_utils:cp_r`.

apps/rebar/src/rebar_file_utils.erl

@@ -33,6 +33,7 @@
          symlink_or_copy/2,
          rm_rf/1,
          cp_r/2,
+         cp_r/3,
          mv/2,
          delete_each/1,
          write_file_if_contents_differ/2,
@@ -207,9 +208,16 @@ rm_rf(Target) ->
     end.
 
 -spec cp_r(list(string()), file:filename()) -> 'ok'.
-cp_r([], _Dest) ->
-    ok;
 cp_r(Sources, Dest) ->
+    cp_r(Sources, Dest, false).
+
+%% @doc Copies files and directories.
+%% If Dereference is true, it follows the Sources symbolic link and copies
+%% the content
+-spec cp_r(list(string()), file:filename(), boolean()) -> 'ok'.
+cp_r([], _Dest, _Dereference) ->
+    ok;
+cp_r(Sources, Dest, Dereference) ->
     case os:type() of
         {unix, Os} ->
             EscSources = [rebar_utils:escape_chars(Src) || Src <- Sources],
@@ -229,8 +237,14 @@ cp_r(Sources, Dest) ->
             {ok, []} = rebar_utils:sh(?FMT("mkdir -p ~ts",
                            [rebar_utils:escape_chars(Dest)]),
                       [{use_stdout, false}, abort_on_error]),
-            {ok, []} = rebar_utils:sh(?FMT("cp -Rp ~ts \"~ts\"",
-                                           [Source, rebar_utils:escape_double_quotes(Dest)]),
+
+            Opt = case Dereference of
+                true -> "-RpL";
+                false -> "-Rp"
+            end,
+
+            {ok, []} = rebar_utils:sh(?FMT("cp ~s ~ts \"~ts\"",
+                                           [Opt, Source, rebar_utils:escape_double_quotes(Dest)]),
                                       [{use_stdout, true}, abort_on_error]),
             ok;
         {win32, _} ->

apps/rebar/src/rebar_prv_common_test.erl

@@ -621,7 +621,7 @@ copy_bare_suites(From, To) ->
     DataDirs = lists:filter(fun filelib:is_dir/1,
                             filelib:wildcard(filename:join([From, "*_SUITE_data"]))),
     ok = rebar_file_utils:cp_r(SrcFiles, To),
-    rebar_file_utils:cp_r(DataDirs, To).
+    rebar_file_utils:cp_r(DataDirs, To, true).
 
 maybe_copy_spec(State, [App|Apps], Spec) ->
     case rebar_file_utils:path_from_ancestor(filename:dirname(Spec), rebar_app_info:dir(App)) of