Abort if erl_first_files is not a list of strings

 - resolves #1645

3 files changed, 27 insertions, 3 deletions

diff --git a/src/rebar_erlc_compiler.erl b/src/rebar_erlc_compiler.erl
index c588a25..ebdd9dd 100644
--- a/src/rebar_erlc_compiler.erl
+++ b/src/rebar_erlc_compiler.erl
@@ -285,6 +285,7 @@ gather_src(Opts, BaseDirParts, [Dir|Rest], Srcs, CompileOpts) ->
 %% files, so that yet to be compiled parse transformations are excluded from it.
 erl_first_files(Opts, ErlOpts, Dir, NeededErlFiles) ->
     ErlFirstFilesConf = rebar_opts:get(Opts, erl_first_files, []),
+    valid_erl_first_conf(ErlFirstFilesConf),
     NeededSrcDirs = lists:usort(lists:map(fun filename:dirname/1, NeededErlFiles)),
     %% NOTE: order of files here is important!
     ErlFirstFiles =
@@ -796,3 +797,10 @@ dir_recursive(Opts, Dir, CompileOpts) when is_list(CompileOpts) ->
         undefined -> rebar_dir:recursive(Opts, Dir);
         Recursive -> Recursive
     end.
+
+valid_erl_first_conf(FileList) ->
+    case rebar_utils:is_list_of_strings(FileList) of
+        true -> true;
+        false -> ?ABORT("An invalid file list (~p) was provided as part of your erl_files_first directive",
+                        [FileList])
+    end.
diff --git a/src/rebar_utils.erl b/src/rebar_utils.erl
index 604abb8..2ded481 100644
--- a/src/rebar_utils.erl
+++ b/src/rebar_utils.erl
@@ -73,7 +73,8 @@
          list_dir/1,
          user_agent/0,
          reread_config/1,
-         get_proxy_auth/0]).
+         get_proxy_auth/0,
+         is_list_of_strings/1]).
 
 
 %% for internal use only
@@ -919,3 +920,11 @@ get_proxy_auth() ->
         undefined -> [];
         {ok, ProxyAuth} -> ProxyAuth
     end.
+
+-spec rebar_utils:is_list_of_strings(term()) -> boolean().
+is_list_of_strings(List) when not is_list(hd(List)) ->
+    false;
+is_list_of_strings(List) when is_list(hd(List)) ->
+    true;
+is_list_of_strings(List) when is_list(List) ->
+    true.
diff --git a/test/rebar_utils_SUITE.erl b/test/rebar_utils_SUITE.erl
index e4a5bd3..233fcff 100644
--- a/test/rebar_utils_SUITE.erl
+++ b/test/rebar_utils_SUITE.erl
@@ -32,7 +32,8 @@
          blacklisted_otp_version/1,
          sh_does_not_miss_messages/1,
          tup_merge/1,
-         proxy_auth/1]).
+         proxy_auth/1,
+        is_list_of_strings/1]).
 
 -include_lib("common_test/include/ct.hrl").
 -include_lib("eunit/include/eunit.hrl").
@@ -48,7 +49,7 @@ all() ->
     [{group, args_to_tasks},
      sh_does_not_miss_messages,
      tup_merge,
-     proxy_auth].
+     proxy_auth, is_list_of_strings].
 
 groups() ->
     [{args_to_tasks, [], [empty_arglist,
@@ -312,3 +313,9 @@ restore_proxy_env(ProxyEnvKey, false) ->
     os:putenv(ProxyEnvKey, "");
 restore_proxy_env(ProxyEnvKey, ProxySpec) ->
     os:putenv(ProxyEnvKey, ProxySpec).
+
+is_list_of_strings(_Config) ->
+    ?assert(rebar_utils:is_list_of_strings(["foo"])),
+    ?assert(rebar_utils:is_list_of_strings([])),
+    ?assert(rebar_utils:is_list_of_strings("")),
+    ?assert(rebar_utils:is_list_of_strings("foo") == false).